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View Full Version : Rant. This is a very frustrating hobby



loose nut
06-12-2010, 04:37 PM
Being an amateur at this and always will be, I find that trying to cram the equivalent of a lifetime of a "real" machinist's machining experience into a couple of hours a week of fumbling about the workshop turning etc. to be very much like beating oneself on the head, with a hammer, over and over.

Set up's that seem simple in the mind aren't, setting the cross feed the last couple of thou. to get the diam. right on the money always gets you two thou. under sized and best of all, being very careful to get everything set up just right so that the job comes out parallel will always turn a taper.

At work we have some very talented machinist, I'm not one of them, just a lowly welder (pipe and pressure vessel)/pipefitter/boilermaker/tinsmith/gasket cutter (asbestos naturally) and general dogs body/maintenance man. If they don't do it it comes to me, alone, by myself, no help at all. Oh, woe is me, Sorry just basking in a little self pity.

They are really good at sharing techniques with me, if I ask them a how-to question, so it is very annoying when I pick up a tip from them on how to do an operation which seems easy enough when they do it and it turns into a complete hash up when I try it at home.

Sometimes I feel like giving up and taking up fishing but I hate fish and fishing and cleaning fish and taking care of a fishing boat and anything else with the word fish in it and..........:rolleyes:

Liger Zero
06-12-2010, 04:41 PM
Practice practice practice.

My first "home" lathe was a yellow Clarke POS-86. I practiced on PVC pipe which is cheap enough.

That's all I can suggest... practice on cheap material over and over and over until you get a feel for your machine. Soon it becomes second-nature.

John Stevenson
06-12-2010, 04:52 PM
If I have a demanding diameter to do like a bearing fit I never try to turn to size.
I always go a couple of thou up and polish to size, trying to creep up to size with fine cuts is a recipe for disaster because even if you do you are measuring on the crests of the tooling marks, push a bearing on and it's then undersize.

Black_Moons
06-12-2010, 04:55 PM
taper and diamiter errors can often be a result of spring in the work or tooling.
Before the final pass, Try taking 2 or 3 passes without incressing the tool depth, untill swaff stops appearing (On materials that do NOT work harden of course!), then measure and adjust for the final pass, and the final pass may require a few more passes at the same tool depth to achive the correct diamiter.

For materials that do work harden, you basicly have to take successive passes at the same depth so that tool/work loading is the same for your final pass as it is for the pass that produced your last diamiter messurement

overshooting diamiters due to spring is because on your lighter final pass, there is less force bending the tool/work, so your actualy cutting deeper then what you incressed the dials by.

And taper is also caused by this because the work bends more at the unsupported tip (or center if using tailstock) then at the supported end(s)
Multiple 'spring passes' at the same diamiter are a good way to help fix the problem

loose nut
06-12-2010, 04:58 PM
I usually take a few spring passes before I beat my self senseless, I mean try turning to size.

Why is it that when you mic a diam. say 2 thou to big, set 1 thou on the cross feed, take a cut and it is still 2 thou to big. Repeat this two or three times more because there isn't an apparent change on the diam. and then miraculously it's is 2 thou under sized.

Where the hell is that hammer.

Have I mentioned fishing.

jkilroy
06-12-2010, 05:02 PM
I, like Sir John, almost never try to turn to size on a picky fit. If specs aren't a problem I will cut to size but I make sure and leave a good amount so I can take a real CUT at it. Keep your tools sharp, as in OUCH. If you favor inserts, don't rough on an insert for two hours and then expect to take that last fine finish cut with it. Swap inserts with two cuts left if you fear it is worn.

loose nut
06-12-2010, 05:04 PM
Got to go now, I have to clamp my head to the milling machine table and mill my brains out. Still better then fishing.

Paul Alciatore
06-12-2010, 05:16 PM
Boy, what John said! Yes, do consider the surface roughness. If you want a polished finish, you must turn at least two thousanths oversized. On a diameter, two thousanths is only one thousanth on each side. If you start polishing with 100 grit paper, then that thousanth will disappear really fast and you need to be careful not to wind up undersized. Oh, and when using abrasive paper/cloth like this, do wet it with oil or cutting fluid. It will keep the dust down and also improve the finish. And clean and measure frequently.

As for just two or three hours a week, that may not be the real problem. You should look at and consider the equipment you have vs. what the pros have at work. A hobby mill or lathe is going to be more of a challenge than a $10K to $100K machine you may see in a professional enviroment. In reality, you may actually need better skills than the pros have to produce the same results.

Turning tapers: This can be addressed by properly mounting and leveling (actually straightening) your lathe. Have you done so? The mount, the table MUST be solid and MUST be solidly tied down to a SOLID floor. Believe me, I know as my lathe is presently in a trailer and is almost impossible to level. If you haven't properly mounted and set up your lathe, then you will have to stick to short parts or go to extra measures to eliminate the taper.

rkepler
06-12-2010, 05:24 PM
The hardest thing to learn is this: if you're not making mistakes you're probably not making anything at all.

KiddZimaHater
06-12-2010, 06:00 PM
I've found that trying to 'creep' up on a diameter by .001 or .002 usually bites me in the arse, whereas when I do a final pass at .030 deep, the diameter is usually right on the money.
I'm funny that way. :confused:

airsmith282
06-12-2010, 06:08 PM
if i need a really percise Diameter to turn to i use my Micrometer, not my calipers, also i will alway go about 6 passes per cut when iam with in 5 thou this way i know all the metal that can come off does, also when your that close i also hardely allow the cross feed to turn in very micro turns and when iam with in that very last 1 thou i take the pass then i check it then if its good them ok if not then i leave the setting alone and just take several finishing passes till i can not see any thing else cutting off then i cheack again andif iam good then iam done if not then onemore micro turn like when iam talking micro i mean micro .. anyhow thats how i do it and it never usualy fails me,

but ya lots of pratice pratic pratice if you dont put in the time you will have a hard time advanceing your skill level,

Al Messer
06-12-2010, 06:21 PM
I usually take a few spring passes before I beat my self senseless, I mean try turning to size.

Why is it that when you mic a diam. say 2 thou to big, set 1 thou on the cross feed, take a cut and it is still 2 thou to big. Repeat this two or three times more because there isn't an apparent change on the diam. and then miraculously it's is 2 thou under sized.

Where the hell is that hammer.

Have I mentioned fishing.


Mia Culpa---if I can get within a couple of thous. of the finished size, I grab the big file, not the big hammer.

John Stevenson
06-12-2010, 06:27 PM
I don't know if I should tell you this, it took me years to find out :rolleyes:

Turning taper and with a centre for support, if it smaller at the chuck end, slack the tailstock off, pull towards you on the centre whilst tightening the tailstock back again.

If opposite push the centre.
I know they are on guided ways be we are looking for a gnats cock of a micron here to correct it.

lynnl
06-12-2010, 06:35 PM
If I have a demanding diameter to do like a bearing fit I never try to turn to size.
I always go a couple of thou up and polish to size, trying to creep up to size with fine cuts is a recipe for disaster because even if you do you are measuring on the crests of the tooling marks, push a bearing on and it's then undersize.

Yep. Fortunately for me, I learned that early on, while taking a few evening machining courses at the local tech school. One of the projects was a tap handle, about 10", like the straight Starrett type. By leaving the sliding part enough oversize, I polished that sucker down just right to get a sliding fit that would hold a suction. That remains one of my proudest moments! :D

MotorradMike
06-12-2010, 06:53 PM
Are you guys serious? 1/1000 of an inch?
Impossible. Not even the guys who built the pyramids tried for that.

Work to the nearest 1/16 and everybody will be a lot happier.

oldtiffie
06-12-2010, 06:56 PM
If I have a demanding diameter to do like a bearing fit I never try to turn to size.
I always go a couple of thou up and polish to size, trying to creep up to size with fine cuts is a recipe for disaster because even if you do you are measuring on the crests of the tooling marks, push a bearing on and it's then undersize.

I am glad you said that John - very.

Some here seem to think that "its not "manly"" to use a file and/or "emery paper" - I use "wet and dry" to get that last bit to size and to finish.

I've done it all my life where needed.

It sorts out any "bumps" or small tapers that need attention as well.

As you say, a less than very good finish (which looks like a fine pitch screw-cut) will soon have the crests cropped or rolled to convert a light press or push fit into a sliding fit.

"Getting it done on a lathe" includes filing and papering - always has - and done correctly can almost turn a lathe into a pretty fair cylindrical grinder - always has.

I don't get as "hung up" as some seem to do about getting my lathe to turn a taper 6" long and to keep it within 0.001" or less. I can work around that if needs be. My lathe is pretty good.

I "know" my machines and tools pretty well and can anticipate whether the job will be easy or difficult and I can take measures to work around it.

I don't always get it right - but I usually do. Its not too often that a job is irrecoverable - but it happens occasionally.

I try to plan my work by breaking it down into its component parts and with regards to the tools I need and the sequences of the processes and it smooths the job no end.

My work only gets what it needs - if a rough finish is all thats needed, that's all it gets. If a size has a large tolerance - I use it.

If fine finishes or tight tolerances are needed - it gets it.

"Practice" and "feel" are essential and it takes a lot of practice to get them and not much less to keep them.

A "poor" machine is not always the cause of a poor job as its a poor operator as often as not. A good operator will anticipate the problem and work with the machine to get around the problem. Doesn't always work - but it mostly does. A good machine or tool can quite often make it easier and better too - but not always.

I am amazed that so many seem to need a machine or a "guide" to sharpen drills and lathe tools as I've always regarded them as "off-hand" jobs for the pedestal grinder.

wierdscience
06-12-2010, 07:03 PM
I do the same as John,but if the diameter needs much reduction unless you flood coolant on it there will be heat envolved.

So my method is to make the finish pass within .006" or so,feel the part.If it's over room temps I go off and work on something else for awhile while it cools off.Then I come back and make my finish pass and polish off the last .0015-.002"

J Tiers
06-12-2010, 08:59 PM
John's advice is right-on...

And, if you have to not only get it on-size, but get it on-size over a significant length, leave MORE. Hand methods may take a bit more practise to get parallelism correct.

Between polishing, AND getting it parallel, you may need more allowance.... I suggest getting it parallel first, and then on-size.......

RobbieKnobbie
06-12-2010, 09:38 PM
Learning to manipulate spring cuts is pretty straightforward - once you know you're dealing with it and not just random mystery movements from your cross slide.

If you're getting tapers, look at the twist of the bed and the offset of the tailstock (as mentioned above)

Liger Zero
06-12-2010, 10:12 PM
Once was a man named Robbie
Who made metal-working his hobby
He said with a frown
As his machine it broke down
"All I did was turn the knobby!"

Carld
06-12-2010, 10:44 PM
loose nut, learn how to file to size and how to use emery cloth. As others have said, trying it machine to exact size is not the best way.

A sure fire method to get real close it to use a dial indicator and mag base with the indicator rod against a solid part of the cross slide. Unless the cross screw and nut have no wear .001" on the dial will not move the cross feed .001" and only a dial indicator will tell you exactly how much it moved. Always leave about .005" to file off because a good looking finish may have a lot of low spots hiding on it.

I used a dial indicator on any lathe I wanted to be exact on the DOC. and even then many issues can cause it to still cut under or over.

Buy some lathe files and learn to use them.

As to taper on a shaft if you center drill an indicated shaft in a lathe there is no guarantee the center is really in the center. If I need it as close as possible I chuck the shaft very close to the jaws and indicate it in and center drill it then I single point the center with a special ground cutter. That's about as close as you'll get.

You always start with an oversize shaft and turn down to size so cut the shaft long enough for the length you need plus 1". Now with the shaft chucked with 1/2" in the jaws and indicated in and the live center in the end start turning and when you have about .050" left to take off take a pass at .002" DOC. Then mic the shaft at each end and if there is taper use a dial indicator against the side of tail stock with the mag base on the ways. Adjust the tail stock half of the difference in the mic readings. That is, if there is .004" difference end to end move the tail stock .002" toward or away from you to remove the taper. If it's small on the live center end move the tail stock away from you. Do this until the ends are the same. You have to slightly loosen the clamp plate holding the tail stock while you adjust the screws to move the tail stock. DON'T loosen it to much, just enough so you can move the screws. Back one screw off and adjust the other and be careful to get exactly what you want it to move.

Is it easy, no, is it fast, no but it works.

EDIT: of course after you center the tail stock with light cuts you can then finish out the work with reasonable cuts but don't expect to turn to exact size.

Tony Ennis
06-12-2010, 11:12 PM
As a perma-n00b, I know where you're coming from. Until you skill up some, can you select projects that don't need precision to .001?

My first 'big' lathe project won't require more than .01" precision in most places.

Mcgyver
06-12-2010, 11:23 PM
imo the secret is read read read. collect books then get some more. take advantage of the author's 50,000 hours of experience he's so carefully put down for you. of course you need practical experience but as hobbyists there are only so many practical hours available... but peeking in on others recorded experience accelerates the curve....I find it astounding the number of people trying to be HSM's who clearly (from their Q's) have never cracked even a basic book on the subject....I see it more on cnc zone than here,...it reminds of that biblical quote something about he who helps himself.....

You will never get the hours of a commercial machinist, but with the right attitude and quest for knowledge you will surpass him in ability. The guys I know in the trade who's work i respect bitch all the time about what hacks they have to work with - i'm talking about you surpassing the commercial hack who thinks not about metal after 5 and could care less about learning anything more than what he needs to to avoid a firing. Now the commercial machinist who also has the right attitude and thirst for knowledge, well he is what you call a professional and its best just to listen.

J. Randall
06-12-2010, 11:31 PM
I usually rough down until I am about .060 to .080 over final dimension and then divide what is left into 1/3's, then try to take them all 3 equally , if the first one is off a little, fine tune it, same with the second. By the time I get to the third cut I am usually right on, and that is leaving a thou or so over for polishing. Works a lot better for me than trying to sneak up a thou at a time.
James

oldtiffie
06-13-2010, 12:24 AM
As a perma-n00b, I know where you're coming from. Until you skill up some, can you select projects that don't need precision to .001?

My first 'big' lathe project won't require more than .01" precision in most places.

Tony,

you may be surprised at just how many of those jobs there really are. Not all - or even most - jobs are to or better than 0.001" (a thou).

My advice is to get a good grip of limits and tolerances as regards sizes and surface finishes and you will be well on your way.

Most fits on shafts or holes have limits (that you have to work between) of 0.001" to a lot more. If you have that range to work within - use it - and don't buggerise around chasing "tenths" needlessly.

All too often "spring" or too fine a cuts only rub - the more so with blunt (or not sharp enough tools) which can cause a varying range of localised work-hardening which only dulls the tool and makes it "dig in". That is time to stop the tool and use the file and the "emery cloth".

An example of tolerancing and limits:

If say a shaft had a tolerance of 2.000" + 0.000/- 0.002" it has limits of 2.000/1.998".

If the bore it is to suit has a tolerance of say 2.000 +0.001"/+0.003" it has limits of 2.001/2.003"

The "fit" limits are:

maximum: largest hole - smallest shaft = 2.003 - 1.998 = 0.005"

minimum: smallest hole - largest shaft = 2.001 - 2.000 = 0.001"

Now if this was a "one off" job where one part was to fit another without regard to anything else your clearance limits for the correct fit are 0.005 - 0.001 = 0.004"

If you were to bore the hole to get that fit on an existing 0.199" diameter shaft that needed no further work, the bore tolerance = shaft size + 0.005/0.001" = 1.999 +0.001/0.005" = bore limits of 2.000/2.004"

So you now have limits for the bore that are 0.004" apart to get the right fit.

I prefer to leave the "finer" sizes for the shaft as it is easier to measure sizes accurately whereas accurate measuring of a shaft can be a lot harder to do.

Most of the work in a HSM shop is making one part to suit an existing other part. I just "soak up" the available limits on the existing part and add them to to part I am working on.

The same principles apply for all classes and types of fit.

Surface finishes are pretty well the same.

A lot of what good experienced operators know and do is a personal skill, but a lot of that is pure common-sense and should be all too obvious to a less experienced operator as soon as they see it or have it explained to them.

Many of these skills are used "alone" and many are used in combination. The permutations and combinations numbers can be mind-boggling but if you can put aside panic, or loss of self-confidence and just take your time and use bit of logic, you will find a way.

Just don't get over-awed and/or give up/on - just ask if needs be - there will be others who will try to help.

Just ignore the snipers and the smart-ar$es.

Get on and enjoy it.

KIMFAB
06-13-2010, 12:44 AM
I consider myself a total hack but I have found that down to about .003" I can do easily, if it needs to be tighter than that it takes a whole different outlook.
In other words cutting to .003 is a science, cutting to .001 is an art.

I have to approach the close tolerance stuff with a totally different mindset, kinda like welding you got to get into the "zone".

Fasttrack
06-13-2010, 12:50 AM
Why is it that when you mic a diam. say 2 thou to big, set 1 thou on the cross feed, take a cut and it is still 2 thou to big. Repeat this two or three times more because there isn't an apparent change on the diam. and then miraculously it's is 2 thou under sized.



Don't worry, loose nut. We've all been where you are (or at least most of us has). I still have bad days where I feel like I've no idea what I'm doing and everything I touch is just going to get screwed up. But in a relatively short amount of time, you'll have the process mastered.

What's happening there is that spring action everyone has been talking about. Most lathes aren't stiff enough to take 0.001 DOC if the tooling isn't razor sharp. Just a slightly dull tool will cause the compound/toolpost to flex out of the cut, resulting in the tool just gliding across the surface. This continues for a couple of passes until finally you have enough "spring tension" built up in your tool post that actually starts cutting. Now all bets are off as to how much it will actually take.

The trick is to take a healthy sized bite and do it with sharp tooling. I've rarely had a problem hitting a diameter spot on with my Pacemakers. I have reliably taken 0.001" DOC passes. On my Smithy, there is no chance of doing that. I usually have to take a minimum of 0.006" to get it to cut and when I dial 0.006", I know I actually get slightly over 0.006" with the geometry of the cutters I use and the fact that they tend to be slightly below center - this means that when they "grab" and start cutting, the tool post is pulled forward into the cut slightly.

Also, as John pointed out, the surface finish becomes important when you're talking about 0.002 or so. I don't bother to try to get that accuracy on hot rolled because it takes so much trouble to get a good surface finish with a tool. Much easier to do John's method. The only time I "cut to size" is with materials that I can reliably get a good finish on - SS, aluminum, brass, cast iron, 4140, 4130 etc.

EDIT: And as OT mentions, turning to 0.001 or "tenths" is often a purely aesthetic pursuit for HSM guys. Rarely is that level of accuracy actually needed, but I understand the desire to achieve it just for bragging rights ;)

Black Forest
06-13-2010, 01:14 AM
I don't know why you all have trouble working to a tenth. It is not difficult at all. Let's face it, a tenth of an inch is easy to just eyeball!

oldtiffie
06-13-2010, 01:18 AM
A tenth of a metre is marginally less difficult - but difficult never the less - "down here" in OZ as we are standing on our heads as far as you lucky lot in the Northern Hemisphere are concerned.

Its tough!!

bobw53
06-13-2010, 01:43 AM
I've found that trying to 'creep' up on a diameter by .001 or .002 usually bites me in the arse, whereas when I do a final pass at .030 deep, the diameter is usually right on the money.
I'm funny that way. :confused:

I agree.

I haven't read the rest of the thread yet, BUT, that whole "sneaking up" on a diameter is just a recipe for total disaster.

The trick is to repeat EXACTLY what you just did. Say you want to get to 1" with a .010 doc finish pass. So, rough down to 1.040, then take your "test" finish pass. Measure, hopefully you're close to 1.020. Dial in .020 on diameter the difference. And you'll be right there. All you are doing is repeating, as close as possible(speed, feed, depth of cut, diameter), what you just did, and making a slight adjustment if needed.

Also skip the little itty bitty cuts, they seldom work out the way you want them too. That's why they make "shop rolls" and handheld belt sanders.

Hang in there, you'll get it.

MuellerNick
06-13-2010, 05:47 AM
There are only two "secrets" to know how to work to size.
1.) Know your inserts (or you HSS). Carbide inserts simply don't work when they have no material to cut. Try to cut 0.02mm and you'll fail. They need above 0.1mm DOC or even more. Depends on the insert.
2.) You need to aproach the final size with (almost) constant DOCs. If you change the DOC, you won't cut as much (or more) as you intended. So after roughing, you need about 4 passes finish-cutting. Start with about 0.5mm over size and work your way down always adjusting to get to say 10.40mm 10.20mm.

Practice that for half a day and you'll find out that you can work to +/- 0.01mm. If a file is daily practice, go back to apprenticeship or consider being a farmer.


Nick

Black Forest
06-13-2010, 06:26 AM
Practice that for half a day and you'll find out that you can work to +/- 0.01mm. If a file is daily practice, go back to apprenticeship or consider being a farmer.


Nick, You should quit hammering on us farmers! Couldn't you change that to garbage collector?

Weston Bye
06-13-2010, 06:30 AM
I find that even after years of experience (well, attempts) I find myself performing machine-assisted metal sculpture rather than actual machining.

John Stevenson
06-13-2010, 06:41 AM
Practice that for half a day and you'll find out that you can work to +/- 0.01mm. If a file is daily practice, go back to apprenticeship or consider being a farmer.


Nick

But some of us are only human, not all have God like status.

If half a day is all you need why did you do a 5 year apprentice ship ?

oldtiffie
06-13-2010, 07:31 AM
There are only two "secrets" to know how to work to size.
1.) Know your inserts (or you HSS). Carbide inserts simply don't work when they have no material to cut. Try to cut 0.02mm and you'll fail. They need above 0.1mm DOC or even more. Depends on the insert.
2.) You need to aproach the final size with (almost) constant DOCs. If you change the DOC, you won't cut as much (or more) as you intended. So after roughing, you need about 4 passes finish-cutting. Start with about 0.5mm over size and work your way down always adjusting to get to say 10.40mm 10.20mm.

Practice that for half a day and you'll find out that you can work to +/- 0.01mm. If a file is daily practice, go back to apprenticeship or consider being a farmer.


Nick

Nick.

I don't see that the "hairy-chested" superior approach was needed. It "came accross to me like that. I'd like to think that it wasn't meant that way.

I'd agree in most part of what you say - but not all.

You are right as regards the tools - HSS and TC etc. - but it is the geometry of the tool to suit the job and the machine that counts.

I, like John S, did a 5-year indentured apprenticeship - age 15>21 - in accordance with the Brit Board of Trade standards which was adopted by our Apprenticeship Commissions here in OZ.

A mandatory pre-requisite was a minimum of three with a preferred four year pre-Apprentice ship Technical School pass and Certificates before we were even allowed to be considered for an apprenticeship with an approved employer.

During that pre-apprenticeship schooling we had to - amongst other things - master hand-ground tools first on small basic lathes to bigger ones. We soon found out what made a good tool what it should be - and what didn't - and why. So we were pretty well prepared for more of same as Apprentices.

I have seen some excellent tradesmen at age 18 - while still Apprentices - that could keep up with a lot of more experienced tradesmen - machinists, fitters, tool makers etc. They just had to hone what skills they had and to learn more of them before finishing their apprenticeships. It was a big deal to be classified as a First Class Fitter and Turner/machinist - at age 21 - when I finished my apprenticeship which required a minimum of three years - I did five - of compulsory further schooling at Trade School both on "day release" of one full day-time and two evening classes every week. They were "full on".

We had some who were very good, others who were mediocre and others that were all but useless but "got through". A lot just "fell by the wayside".

My point here is that we were teen-agers (11>15) and had pretty well mastered the basics before we were apprentices.

There is no reason that I can see why others here can't do it without being apprentices either and then move on to better things and skills.

For the information of some who may have missed it, the +/- 0.01mm that Nick refers to is ~ +/- 0.0004" which is pretty close to +/- 0.0005" (half a thou) where the size limits are 0.0008" (for +/- 0.01mm) or +/- 0.0005" for "inch". Many metric tools are graduated in 0.01mm increments which is a metric "preferred value" and is no big deal - either way.

Many, if not most, of the newer or older USA and UK and European - and Chinese - lathes (and other machines - and tools) that I see here CAN do that well even if it takes a bit more effort, skill and time - so stop fretting.

There is NOTHING wrong with using a file or emery paper etc. - as long as it does the job.

I can't recall a drawing or a job-sheet/card that said "No filing or emery paper to be used".

Just do the best you can with what you have - you may well very pleasantly surprise yourself and give your self esteem a boost as well. It should impress some other that matter to you too.

Its not only worth trying, but its very much about doing it well.

Keep at it - and "stuff" the "knockers".

Your Old Dog
06-13-2010, 07:41 AM
I do the same as John,but if the diameter needs much reduction unless you flood coolant on it there will be heat envolved.

So my method is to make the finish pass within .006" or so,feel the part.If it's over room temps I go off and work on something else for awhile while it cools off.Then I come back and make my finish pass and polish off the last .0015-.002"

I work a lot of aluminum for antenna parts and find Wierd's temperature suggestion a huge problem. When I let the aluminum stabilize with the room temperature then I usually have no trouble getting the fit I want. Final passes on really hot stock is making life rough on yourself and that BFH could actually hurt you :D

This has been a valuable thread for me, thanks for raising it.

Richard-TX
06-13-2010, 08:07 AM
I usually take a few spring passes before I beat my self senseless, I mean try turning to size.

Why is it that when you mic a diam. say 2 thou to big, set 1 thou on the cross feed, take a cut and it is still 2 thou to big. Repeat this two or three times more because there isn't an apparent change on the diam. and then miraculously it's is 2 thou under sized.



Sounds like a typical stiction issue to me. I used to have that problem when I first got the lathe. Now I don't have that problem. In my case the answer was actually two things wrong.

1 - ways too tight
2 - not using way oil.

Once I loosened the ways and started using way oil, all of that nonsense stopped.

A.K. Boomer
06-13-2010, 09:03 AM
Getting a close fit is one of the most troublesome parts of machining,

the shop motto is "sneak up on it like a blind paraplegic"


the machine, the cutter, the material, the speeds and feeds, coolant?

they all play a role, my friend gets things consistently to the money within a couple tenths with no tooling marks on say something like 416ss because he knows what the hell he's doing, a tiny little radius on a super sharp tool bit will keep the tool cutting even with the mildest of interference and yield a mirror polish with zero tool marks on the part,

Iv gotten close on his machine (with his assistance) but generally I use the SJ approach when in my shop and there's nothing wrong with that,
The proof is in the pudding and the bottom line is the end result - if its a snug fit bearing race surface and your seating it on "peaks" due to having tooling marks in the valley's then operating vibrations alone can loosen up the fit over time --- I get close and then double up some 400 grit to bring it in - if parallel is in question I get the appropriate size parallel and use it as a backing for the paper on the last touch up, some times i finish it off with some scotch brite just to make it look pretty.

I believe the big argument about being able to let the machine do the work for you has not much to do with the home shop machinist -- it has everything to do with production, if you have to kick out 100+ parts its a great time saver to be able to dial in your machine instead of having to hand finish each and every part to size...

Mcgyver
06-13-2010, 09:18 AM
If a file is daily practice, go back to apprenticeship or consider being a farmer.
Nick

that's what i was taught in high school, it was a real no-no met with yells and screams and lots of negative attention. Growing up thinking this just wasn't done, i didn't do it ....imo its like grinding hss tools, only difficult if you've convinced yourself of it :D Not that i've never done it, just not SOP...and while haven't been a garbage man i am (or have been) a farmer so no excuses from the Ag community.

speaking of hss and accuracy.....when a dimension has to be dead on, like mounting a bearing or such i do sneak up on the diameter. The trick i've found is to work with hyper sharp hss. if you look at how a chip is formed on the end of a tool bit, its clear that for a certain sized chip, a certain amount of rounding on the edge is fine - the shear plane will still form properly. However you can't take the same rounded edge and take 1/50th of the DOC and and still have it work - the shear plane tries to form on a tangent to that roundness - the smaller the chip and the more roundness, the more the tangent will tend toward parallelism with the direction of cut. That = impossibility.

Put a lapped mirror finish on that hss and you can accurately take a very small amount off.....Anyone who's scraped knows full well it is routine making a .0001 chip - you just need a very good edge.

To turn to tenths (no i don't everyday but can when required) get a peice of hss with a super fine edge on it - not roughly stoned with a 200x stone, done with a 4000 stone or higher or lap so its a mirror. Put the compound at just under 6 degrees - 5.7 is the goal but we cant easily measure that exactly. Now each .001" graduation on the compound dia; moves the toolbit close to .0001" closer to the lathe's axis.

Because there are sources of error such as not be exactly at 5.73 degrees etc, get close, within a couple of thou and advance the tool to take half a thou off each side - 5 divisions. If it reduced the diameter by say 1.1 thou instead of exactly 1, use this information to figure out how how to move the compound for the next and final cut - its taking 110% if what was expected. if there's now 1.4 thou to come off, and we're cutting 110% more than expected, advance the compound just under 6 1/2 graduations (.0014 = .0007 per side, .0007/110% = .000636) and you should be, or very close to, within a tenth of the desired diameter.

people will say it cant be done, horse balls. It needs a very sharp tool and the compound slideways in good shape and well fit with their gib...but that's not the same as impossible :D.

I also always wondered about John's point, when trying to do very accurate work we're measuring across the peaks which get knocked off spoiling our accuracy. A wider radius tip and slow feed helps but its still there. What i do is shoot for a tenth over and then polish with 600 paper thinking i'm knocking off the peaks. the 600 seems to take off about a tenth when starting with a good finish

Richard-TX
06-13-2010, 09:40 AM
One other thing that I learned when turning to high precision is that things like coolant, cutting oil, etc can all affect the DOC depending on the tool's cutting edge quality, it's geometry, and the material being cut.

If you are working with reasonably easy to machine materials and are having issues with DOC, try cutting dry or try a different angle on your HSS tooling.

Like McGyver said, hyper sharp tooling is very important for a good finish cut.

saltmine
06-13-2010, 10:16 AM
Forcing yourself to work to tight tolerances is just another way to abuse yourself. If you're learning, don't try any close tolerance projects, until your confidence is improved.
My biggest problem is overconfidence. I'll be sailing along, get cocky, and next thing I know, I'm making more parts than I wanted to.
Nothing like trying to "sneak up" on a finished size only to find that you've missed it by a zip code or two.

One of my hobbies is to find uses for all of the extra, out of spec parts I make. I already have enough "paperweights" to collapse my desk, so I'll probably have to take up fishing since I have so many sinkers.

What makes this hobby fun is figuring out how to do things, and what to use the rejects for.

Like Martha Stewart once said,"It's all good."

J Tiers
06-13-2010, 10:27 AM
Forcing yourself to work to tight tolerances is just another way to abuse yourself. If you're learning, don't try any close tolerance projects, until your confidence is improved.



Disagree.....

Best thing you can do is even when it does not matter, pick an acceptable dimension within your range and try to hit it dead-on.

if you miss, your part is still good, so no harm done. But you get a lot more experience that way.

If you can do it when it does not matter, you are much more likely to be able to do it when it WILL matter.

MuellerNick
06-13-2010, 11:12 AM
Nick, You should quit hammering on us farmers!

I'm not bashing farmers!
Being a farmer requires different skills. And it also takes a lot of learning and even more experience. That skill maybe is better to obtain for some kind of people.

Farmers do have my full respect, I live among them and I decided to move there because of their distrinct way of living and working. I like the smell of manure, cutting hay, being in the cows' stable etc.


Nick

BobWarfield
06-13-2010, 12:12 PM
Disagree.....

Best thing you can do is even when it does not matter, pick an acceptable dimension within your range and try to hit it dead-on.

if you miss, your part is still good, so no harm done. But you get a lot more experience that way.

If you can do it when it does not matter, you are much more likely to be able to do it when it WILL matter.

For a beginner, this is important. You're not getting much time on the machine, so there is a tendency to be so focused on making the part, you don't think about what you could be learning along the way. There are so many things to be learned. Some is available in books, some online, some by seeing others, and some only by doing it yourself. The more you learn, the more it may slow down the current job, but the faster you'll do future jobs. Err on the side of the latter as a beginner.

The beginner wants to feel like they are in control of the machine (DUH!). And there were a lot of variables floating around that will affecting your work and make you feel like you don't have that control. I started with a few principles:

- If I could measure it, I could (eventually) machine to it. Measurement is very important, so I got used to measuring everything much more often than I really needed to. Cut a pass on the lathe, stop the lathe, take a bunch of measurements just to see what happened. Did it taper? Did it cut the amount I turned on the dial?

- Experiment and try a lot of variation. Measure with the calipers, then measure with the mic. How close are the measurements? How do I get better technique with the calipers? When have I reached the point where I know how acurately I can measure with each tool? Which depths of cut does my machine get right versus which are problematic?

- Write it all down. Best shop tools I had starting out were a box of Sharpies, a box of steno pads, and a calculator. I would write every pass down so I knew what was the final finished dimension I was working to, what was the goal dimension for that pass, how much did I turn the handwheel, what dimension did I wind up with.

It all sounds very tedious, but it's kind of like school, where I always took a lot of notes and didn't refer back to them because the act of taking the notes fixed what was happening in my mind. You will learn quickly making these lists what your machine does versus what you told it to do.

When I got to the point where the machine did what I expected--I wrote down the target dimension, I turned the handwheel the amount I thought would work, and I measured a result that was accurate to my spec (0.001"), I was happy. If I could do that repeatably, I would write down less and less. Eventually it is easy to just walk up to the machine and make the part without writing anything down.

A whole lot of variables have been mentioned here to learn how to be in control of your machine:

- Rigidity of machine, tooling and work leading to the need for spring passes.

- Sharp HSS to creep up on it versus making relatively deeper cuts with carbide that have to get there correctly without creeping up. BTW, this is pretty pronounced on carbide. There's a bunch to learn to be good with HSS and a bunch with carbide, but either will work once you understand the vagaries.

- Machine adjustment leading to stiction and other bad behavior. Nobody has mentioned backlash either, which is an odd beast that not every beginner understands they have to cope with. Just as you need to know your machine, you should be used to adjusting it for best performance. Try some experiments with the gib adjustment to see what impact it has.

- Carl mentions a dial indicator. A DRO is nice too, and with cheap scales, even a simple DRO can be rigged up that will tell you a lot of things (not all of them happy!) about what your machine is doing.

Cheers,

BW

darryl
06-13-2010, 09:40 PM
I've kind of adopted a method that encompasses the most important aspects of 'precision turning'. I'll rough turn the part to within about 20 thou oversize, then measure the diameter. I'll pass a file over it, usually I'll reverse the spindle once, pass the file, then back to normal rotation and pass the file again. Measure again. This is how I determine how large the final turning has to be so it can be cleaned up with a file and arrive at the intended diameter. I reverse the spindle rotation once during the filing operation because I feel that it allows more of the burnished-over material to be removed. On the last file pass, I feel that the part gets to the optimum 'leveled' stage, and can be considered the end result.

At this point I often will sharpen the tool. Next cut is made and the diameter measured. Another cut is made and the diameter measured. Now I know exactly how much to dial in to remove the remaining material to get within filing range. Because I'm never removing very much material with the file, I don't get screwed up by making the part out of round or tapered, or rounding over an end, etc.

If this is a repeat operation, I'll then be able to skip some of the steps, because I've already determined the results based on the depth of cuts dialed in. I can go straight from a roughly 20 thou over diameter to a 'file-ready' state, knowing that my last turning pass will leave the diameter very close to what I expect.

Having said all this, I don't always use the file. Most of the time, the results from the last two finishing passes show that I can hit the wanted diameter with the last pass, and the majority of the work I do doesn't require better accuracy than this. I can pretty easily hit a one thou over, or half thou over diameter, then the final is reached by taking a spring pass or two, or by filing or sanding as I see fit.

Obviously, you get into the realm of measuring accuracy when the fit has to be that close. You have inside-outside dimension reading discrepancies, so you also have to characterize that before you go about relying on measurements alone to achieve a parts fit. Sometimes I'll creep up to a precision fit by filing or sanding, and trying the mating part for fit. Once a fit is achieved, I'll measure both parts again and make mental note of the differences in readings. My most used caliper, for instance, shows a two thou difference between inside measurements and outside measurements. If I see that difference being very consistent, I can begin to rely on measurements alone to get to a decent close fit.

Don't get me wrong here- I'm just as apt as anybody to get a diameter too small by cutting corners, being impatient, or not paying enough attention to what I'm doing. I'll get tired, distracted- then I get choked when I find that I've blown the job for lack of one extra minute of care-

If the machine, and/or the skill level of the operator is such than you can't arrive consistently at a 'pre-finish' diameter close enough for a few files passes to 'clean up', then you have to shoot for a larger pre-finish diameter and rely on the sanding or filing to remove more material. The compromise here is the potential to round over, taper, or out-of -round the workpiece. Often though, the required precision is somewhat relaxed, and with care you can hit the target by turning only, and sticking to a proven workable routine such as I've outlined above. Your routine and parameters may be different than mine, but the need is the same- to know how much material is going to come off with your last finishing pass, and how much will come off with a spring pass.

At this level of accuracy, the various plays in the lathes' mechanisms will have become big players. It's mostly a matter of knowing the machine, knowing what your cutters will do in various states of sharpness and geometry, and knowing what your limitations are as the operator. This is the experimental part of the job, and should be an expected part of the process.

The Artful Bodger
06-13-2010, 09:45 PM
I guess I am doing it all wrong as I hardly ever measure anything, I just make each bit to fit the other bit.:cool:

vpt
06-13-2010, 10:55 PM
I always emery cloth my way to size the last couple thou like every one else mentioned when I need a perfect fit.


I love fishing! I just got back from a week long camping/fishing trip and can't wait to go back!

http://img189.imageshack.us/img189/1431/camping007.jpg

oldtiffie
06-14-2010, 12:33 AM
All of the comment - with which I mostly agree - seems to have been focused on turning external diameters - ie "shafts" to the exclusion of the more difficult "holes".

Holes are much more difficult to get right and measure accurately than shafts are. They are not all that easy to "file" or "emery cloth" either.

I use the "most metal left to remove" process when machining.

It involves the understanding of "limits and fits" and tolerancing.

I aim for the largest shaft and the smallest hole as it gives me a lot more lee-way for any further machining and to stay within my limits.

"Sizes" implies that there are limits and "measurement" implies a range of possible errors too.

I use my measuring tools as comparators. That is to say I don't necessarily rely on absolute measurement but on relative measurement. If I have a part that I have to make another to fit, I use the micrometer etc. to measure the "existing" part and then apply my allowance to that micrometer reading so that I can work out what my limits are. I do use my micrometer "sticks" to check at times but as they only work at the limits of the micrometer travel (the ends) I use my slip guages for the zone I am measuring in. If there is an error in the micrometer I don't always re-adjust it, I just allow for the error in setting the limits on.

Digital micrometers really shine there as I can measure a part and zero the micrometer at that setting and can rely on the "+" or "-" feature of the micrometer to tell me how far I have to go. I can't do that with a standard micrometer.

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Gear-measure5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Gear-measure6.jpg

I have a digital inside caliper that is graduated to 0.01mm (~0.0004") that I can set the limits on and it will tell me how far I have to go.

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper1.jpg

I can quite easily "hold" an accuracy of 0.001" with friction inside calipers or telescopic or ball bore guages. I can hold 0.0004" (0.01mm - we are "metric" here in OZ) with a bit more effort.

My point here is that knowing just what the size is on a lathe is not only a matter of how good the lathe and the tool are but how good the measuring device is and how good the user of it is.

loose nut
06-14-2010, 08:23 PM
Forcing yourself to work to tight tolerances is just another way to abuse yourself.



Hey I'm all for self abuse. Oh, you mean in the shop, OK maybe not.

loose nut
06-14-2010, 08:41 PM
Here is another example of my frustration. If you read the thread on steadies you will know I haven't been a fan of them when it comes to setting work up in them. Well, I asked a machinist at work how he does it (this is for a hollow work that can't be centered on the tail stock).

First centre it in the 4 jaw (18" long piece of 1.5" pipe) then move the indicator out to the other end and tap it true in both axis. Go back to the 4 jaw and it is off so you repeat this several times reducing the error at each end until it is right. Carefully apply the steady and off you go.

OK so tonight after supper, out to the shop where I proceeded to use this method with the addition of using an indicator (to set the steady fingers) on the opposite side of the work from the two bottom supports to see when I had the finger touching the work. Took about 30-40 minutes and I had everything within a thou. Easy peasy. Now for the kick in the ass, I still had to have about 4 to 5 inches hanging out from the steady, the bit to be turned and did it chatter, nothing helps.

I have to go bang my head against the wall now. I will bring back my remaining brain cells tomorrow.

Carld
06-14-2010, 08:54 PM
Try stuffing a rag in the pipe to stop the chatter. Experiment with how loose or tight to ram it in.

You can also try using emery cloth between the fingers and the pipe with the emery side toward the fingers and the smooth side toward the pipe. Use some oil on the pipe at the emery cloth. Clamp the ends of the emery where the steady rest is split.

BadDog
06-14-2010, 08:56 PM
I sometimes do center mounting similarly on long (but not too long) bars.

I have recently been making a number of spool/rollers starting from 6" dia blanks, 12" long. I start by mounting them in the 4 jaw and rough aligning at the chuck end. Then, with jaws only snugged slightly, I use a smallish mallet to bump the far side (t.s. end) close so that it is near coaxial, but still likely a few thou out. Finally, I use the 4 jaw to get the t.s. end near dead true, and then use the center drill in the t.s. Switch drill for heavy Rohm live center and seat in new center drilled hole, slightly slack and snug the chuck, and then finally align head the stock for minimal run out. Now, when I clean up the OD of the 6" extruded bar, I'm still within (relatively loose) tolerance for final OD, and when I flip it to do the other end I've got true surfaces making everything a lot easier (plus by then I'll have a through hole to support outboard end).

Ideally this would use centers both sides, but this has worked very well on the first several without fussing with working between centers.

Your Old Dog
06-14-2010, 08:57 PM
............................
Nothing like trying to "sneak up" on a finished size only to find that you've missed it by a zip code or two. ...........................................


On this machinist forum I think it's safe to say the quips won't get much better then this. :D

thedieter
06-14-2010, 11:41 PM
I have not been able to read the last couple of pages so maybe it was mentioned. I think that if a lathe fails to remove the amount that is dialed, assuming a good tool edge, it may be because the gibes are not adjusted to snug position.

The finish would have some effect but the finish difference between the two cuts would have to be extreme. That shouldn't be the case if the final cut is only .002 inch.

As far as the frustration of the hobby goes, it should be fun and the learning process is part of the fun.

Years ago, when my family was on a fishing trip to Fish Lake in Utah, we were having dinner at the lodge when an elderly gentleman came in a panic asking if anyone had a camera. He had been spending about four hours catching a Brown Trout that was about 39" long and about 44 pounds by a non certified scale. Did I mention that he was using 10 pound line?

My Son had a camera and he took pictures of it which we later sent to him.

There were no certified scales so he had the fish wrapped up in wet towels and put in the cooler for the night and had it weighed the next day at the nearest town. It turned out to be just a little short of the record and may have lost weight in the cooler.

When I saw the gentleman the next day, I didn't recognize him because he had recovered from the stress of the day before...so much for fishing to get away from stress. I used to enjoy fishing and have been many times but no longer go since my wife and I have been vegetarians for a few years.

Best regards, Jack

darryl
06-15-2010, 01:31 AM
Well, I'm not much of a fisherman, but I sure like the outdoors and relaxation anyway. Just don't hit the road on a long weekend- stress, stress, stress

Oh well. I wanted to add some thoughts on this issue of not being able to make shallow cuts on a lathe. I know there's more than one reason for this, but for the moment I'm thinking about the cutting tool. If it's sharp and has the correct relief angles, it should be possible to dial in a thou and find the workpiece to be exactly two thou smaller- same for any small amount dialled in. If the relief angles are right, the tool should neither repel from the work, or dig into it. I know I'm making a generalization here, but I think it is something a person could reasonably expect from any decent lathe. I'm not saying the problem shouldn't exist, because it does as some have already suggested. I am saying that if you can't skim one thou, or three thou, or a half thou off a typical material by selecting a proper cutting tool, then there are issues with the machinery or the operator which should be addressed. I'd be ill if I couldn't get my lathe to work that well.

Of course you don't expect that performance from a carbide with the cutting edge stoned off, but if you can't get it with a properly formed and sharp HSS tool in any normal material- that's the issue I'm talking about. We can discuss loose spindle bearings, rocking toolposts, sloppy leadscrews, wonky dovetail ways, cutting edge height, etc- all issues which a machine operator should be happy enough to learn about and work with.

John Stevenson
06-15-2010, 03:21 AM
Here is another example of my frustration. If you read the thread on steadies you will know I haven't been a fan of them when it comes to setting work up in them. Well, I asked a machinist at work how he does it (this is for a hollow work that can't be centered on the tail stock).

First centre it in the 4 jaw (18" long piece of 1.5" pipe) then move the indicator out to the other end and tap it true in both axis. Go back to the 4 jaw and it is off so you repeat this several times reducing the error at each end until it is right. Carefully apply the steady and off you go.




Stuff lump of Scrapbinium [ TM ] in 3 jaw with 1 1/2" sticking out.
Turn to finish size of tube.
Put steady next to chuck and adjust to run on lump of Scrapbinium [TM]
Slide steady to other end, fit pipe in 3 jaw or change to 4 jaw and fit pipe.
Adjust chuck end for concentricity if needed with 4 jaw.

Go down pub.

.

jugs
06-15-2010, 04:50 AM
Stuff lump of Scrapbinium [ TM ] in 3 jaw with 1 1/2" sticking out.
Turn to finish size of tube.
Put steady next to chuck and adjust to run on lump of Scrapbinium [TM]
Slide steady to other end, fit pipe in 3 jaw or change to 4 jaw and fit pipe.
Adjust chuck end for concentricity if needed with 4 jaw.

Go down pub.

.

So if you are in the pub who does the turning :confused:

PS love - Scrapbinium [ TM ]
:D

MuellerNick
06-15-2010, 05:35 AM
So if you are in the pub who does the turning

Drink beer until your head is spinning. :-)


Nick

oldtiffie
06-15-2010, 08:12 AM
Good idea Nick.

http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Wannabeer1.jpg

J Tiers
06-15-2010, 08:22 AM
For the hollow tube.....

"pipe center"..... a large diameter cone center....if you do some but not too much of that sort of thing you can make a large cone to fit onto a standard center point as a "poor man's pipe center".... oil the daylights out of it.

With a hollow tube, it may howl and chatter simply because the wall is thin...... ESPECIALLY at the open end, it is like a bell. Stuff with something, or move steady a few times to present the smallest amount possible to work on. Or both

Your 4 or 5 inches is an invitation to chattering and roaring... might have been different if you had only an inch or 2 sticking out.

oldtiffie
06-15-2010, 08:45 AM
I use a variation of John Stevenson's method.

Put the pipe in the 4-jaw chuck and indicate to minimum run-out at the chuck. Tap it true at the tail-stock end (near enough anyway).

Bring the fixed steady up to the face of the chuck. Adjust the lower two pads/rollers to just touch the tube and clamp them. Bring the top pad/roller down top barely touch the pipe and then clamp it. The stead is now set to the head-stock axis. Open the steady, lift the top of it and slide the steady back to where you want it to be. Close the top of the steady and clamp it shut. The pipe is on the head-stock spindle axis.

Now if the lathe tool is "right side up", run the lathe in reverse and cut the tube with the tool on the back of centre. The reaction of of the pipe an gravity will force the pipe down onto the lower two steady pads. Use lots of cutting oil on the steady pads.

You can get the same result by inverting the lathe tool in the tool post and with the lathe in reverse, cut on the front side of centre.

The chatter should be largely if not entirely eliminated.

Use low revs.

Gravity is your friend.

MuellerNick
06-15-2010, 08:46 AM
Oldtiffie, that picture is so incredibly terrible!
The dress is not authentic, someone abroad invented it with an Japanese tourist in Munich in his mind.
That's not the way to pour a beer (strictly from a geometrical POV).
If this "gag" is their way of selling pee or beer, they better produce American Whiskey (tastes the same like pee with a lot of alcohol, I guess).


Nick, Bavaria, where all political effords failed to forbid to have a beer at noon (at work).

oldtiffie
06-15-2010, 09:02 AM
Thanks Nick.

I thought you'd like it.

For more choice - see here:
http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Take-Ya-pick1.jpg

Here's one for so-called "multi-taskers":
http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Multi-tasking1.gif

It will be interesting to see who "necks" these - and who doesn't:
http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Howtostopmendrinking.jpg

My guess is that some of the egotists with "weeny weenies" are in this lot:
http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Roadwarriors_Cars1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Modern_man1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Funnies/Is_that_all1.jpg

vpt
06-15-2010, 11:08 AM
Why can't the tailstock be used with a cone?


http://www.curttheobald.com/photos/CenteringConeLg.jpg

lakeside53
06-15-2010, 11:13 AM
Sometimes it can, but often you need a steady to face the pipe so it rests squarely on the bullnose.

Richard Wilson
06-15-2010, 12:08 PM
Stuff lump of Scrapbinium [ TM ] in 3 jaw with 1 1/2" sticking out.
Turn to finish size of tube.
Put steady next to chuck and adjust to run on lump of Scrapbinium [TM]
Slide steady to other end, fit pipe in 3 jaw or change to 4 jaw and fit pipe.
Adjust chuck end for concentricity if needed with 4 jaw.

Go down pub.

.
Why not put steady next to 3 jaw chuck, put pipe in chuck and adjust steady to run on pipe, slide steady down to other end, go to pub even sooner?

Richard

A.K. Boomer
06-15-2010, 12:21 PM
Oldtiffie, that picture is so incredibly terrible!


Bad marketing -------- AND

It's totally disgusting - even if your trying to sell beer to just women their not going to buy that!

Now show some coming from one of the "tah-tah's" from that nice looking babe in the background (who's got hair that looks like she just took a roll in the hay) and you will have an incredible line-up esp. from all the poor slobs who never where breast fed...

oldtiffie
06-15-2010, 03:27 PM
Here is another example of my frustration. If you read the thread on steadies you will know I haven't been a fan of them when it comes to setting work up in them. Well, I asked a machinist at work how he does it (this is for a hollow work that can't be centered on the tail stock).

First centre it in the 4 jaw (18" long piece of 1.5" pipe) then move the indicator out to the other end and tap it true in both axis. Go back to the 4 jaw and it is off so you repeat this several times reducing the error at each end until it is right. Carefully apply the steady and off you go.

OK so tonight after supper, out to the shop where I proceeded to use this method with the addition of using an indicator (to set the steady fingers) on the opposite side of the work from the two bottom supports to see when I had the finger touching the work. Took about 30-40 minutes and I had everything within a thou. Easy peasy. Now for the kick in the ass, I still had to have about 4 to 5 inches hanging out from the steady, the bit to be turned and did it chatter, nothing helps.

I have to go bang my head against the wall now. I will bring back my remaining brain cells tomorrow.

The above is the OP in the matter of over-hanging work held in a steady for work that is turned internally and presumably has to be concentric with the outside diameter - so any tail-stock centre support is out. It has to be supported by the steady.

The bore of most tubing - "as supplied" - is not accurately concentric with the outside diameter - which is normally is quite accurate as regards "round" and size.

So, it seems that the work has to be supported by and overhung from the fixed steady (ie is cantilevered) while the job is bored and presumably faced.

Falcon67
06-15-2010, 04:14 PM
I spent many years in manufacturing. In the early days before things went digital, the machines we built had a ton of mechanical items with lots of machined parts. I didn't do any machining, but I spent several years in QA. I got to read a LOT of blueprints, everything from hand drawn stuff on a sheet of copy paper to F size bluelines. I've inspected parts with a C size print with page two being the hole schedule. I kinda got used to seeing tolerances for certain items - +0 / -.005 for shafting running in bushings, ream holes for press fit bushings or bearings sometimes with a secondary operation called, and general machined parts - shafts, collars, brackets, etc, etc. By and large for most parts you were looking at called for +/- .005. Shafting used as guide rails between frames might have a tight location tolerance from zero datum. And over all, those pieces fit together nicely unless there was some gross error in there somewhere. So as I practice at trying to screw up less and less chunks of metal, I remind myself that I used to see plenty of high tech stuff go together just fine with what amounts to a .1 variance available in the mating parts. That can take a little weight off the natural way you tend to think about "It's got to be .360". If it's not .360, its wrong. Well - no, it's most likely OK. Depends on the application, but for most stuff +/- .005 is pretty decent IMHO. If I can hit that, I feel I've done reasonably well.

I will also now feel less of a hack when using emory or a file. ;)

J Tiers
06-15-2010, 06:32 PM
The above is the OP in the matter of over-hanging work held in a steady for work that is turned internally and presumably has to be concentric with the outside diameter - so any tail-stock centre support is out. It has to be supported by the steady.

The bore of most tubing - "as supplied" - is not accurately concentric with the outside diameter - which is normally is quite accurate as regards "round" and size.

So, it seems that the work has to be supported by and overhung from the fixed steady (ie is cantilevered) while the job is bored and presumably faced.

Oh aye...... But of course if you support by the inner, the outer WILL BE concentric when you are done........ if you have the thickness.....;)

Of course, if the OD must be turned, it may not be 'round", in which case it can't be concentric with anything as-delivered..

One way of setting the steady pretty doggone closely is to have a gage that is your center height....(they can be very handy anyhow, good to have). Now mic the part, and set the upper jaw to the gage plus half the mic'd diameter........

toyjeep73
06-16-2010, 10:41 PM
This is a little off topic but:

I read about every post in this thread and do you know what I learned from it (Edit: besides tips on holding a long hollow tube)?

There are two very different types of “noob” machinists.... those that have gone through 1-8 years of apprenticeships and other formal training and are new to their professional job and those that are like me, in their mid 30's with a career that has nothing to do with machining but have the interest. I see the replies from those that are obviously professionals in this field and they can’t seem to understand how the basics slip by others ..... from what I can tell the derogatory posts are mostly from people who make money from machining, not people who do this for hobby. I for one cannot find a formal school of any sort to learn from in my general area, so am stuck with books.

It is refreshing to see the positive remarks to actually help new people understand the finer skills needed to perform work that many, many people go through years of training to achieve. I for one may have 4-6 hours a week to devote to this (I have other hobbies as well) for the next 20-30 years until retirement. I have decided I want to learn this because I like the art and the challenge and think it can entertain me long into retirement, I only hope that I don’t still make only paper weights then.