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spinrow
05-12-2006, 11:58 PM
In the current edition of the HSM there is an interesting article on threading in the lathe. One problem I have had with threading especially on projects with a fine thread is starting each successive pass at the same starting point. I was thinking of placing a mechanical stop on the lathe so I could go back to same spot each time. Has anyone ever tried this or is there a better way? Thanks Paul

J Tiers
05-13-2006, 12:04 AM
Not sure what you mean....... thread dials normally work fine.....

If the machine is sloppy enough, I can see where fine threads could be a problem.

TECHSHOP
05-13-2006, 12:22 AM
If I remember correctly spinrow has a old (pre 1900) or a 9in SB without the "optional" threading dial. Why that sticks in my head, I can't explain, because he is a "quite" poster.

I am interested in the same thing as my lathe doesn't have a treading dial, yet (project number 15,843 on my list, I think).

JCHannum
05-13-2006, 09:10 AM
If the threads are not picking up on subsequent passes, backlash may be a problem. Make sure there is enough room before the cut starts for the lathe to make several revolutions.

If the problem is the lack of a thread dial, starting with the carriage in the same position will not always pick up the thread. The carriage and the lead screw must be in the same postion for it to pick up.

Lacking a thread dial, do not release the half nuts, but stop the lathe and reverse to return to the starting point. The advice about removing backlash applies here as well.

If you plan on doing a lot of threading, moving the threading dial project up your priority list is recommended.

Moxiedad2001
05-13-2006, 09:43 AM
A mechanical stop on the lathe will not work because you must engage the half nuts at the same position with respect to the rotating lead screw, not the same position with respect to the lathe bed. There is a mistake in that article. The author states that the half nuts must be engaged at the exact same mark on the thread dial for each pass. This is not the case. For example, an even-numbered thread can be picked up at ANY mark on the dial, not just the one used for the initial pass. K. Steiner

Tin Falcon
05-13-2006, 12:58 PM
here are the rules guys:
1) Even # threads engage at any division.
2) odd # engage at any main division ie 1,2,3,4
3) 1/2 pitch every other main division 1&3 , 2&4 11 1/2 pipe for example
4)other fractional pich same division each time
5) Any multiple of the lead screw no dial needed
so if the lead screw is a 8 pitch you can cut a 8,16.24,32,40, or48 pitch thread with no thread dial.
Tin

Leigh
05-13-2006, 01:19 PM
Hi Falcon,

Good info. Does it apply to all lathes (specifically the Monarch 10ee)? TIA

Tin Falcon
05-13-2006, 02:01 PM
Leigh:
Yes this is general info for all lathes. The key to threading without the dial is lead scew pitch this will vary from lathe to lathe. So you need to know the pitch of the lead screw on you particular lathe. you still need to be able to set your gears or gear box to the needed pitch.
Here is a plug gage and back plate I just did in 1" -16 with no thread dial.
http://i78.photobucket.com/albums/j108/Tin_Falcon/Back_plate.jpg


Tin Falcon

Fasttrack
05-13-2006, 02:39 PM
Alright - newbie question here:
What is a thread dial?

IOWOLF
05-13-2006, 04:27 PM
No thread dial? no half nuts? Are you sure you are not useing a wood lathe? :)

Tin Falcon
05-13-2006, 04:38 PM
Fasttrack: the thread dial is the thingy on the side of the apron that goes round and round when the lead screw turns.
tin

Tin Falcon
05-13-2006, 04:58 PM
Fasttrack :
sorry for the wiseguy response your lathe may not have a thread dial the original on my south bend was missing when i got the machine. this link will show photo as well as other usefull info also info on turning tapers.
www.etec.wwu.edu/faculty/McKell/Tapering&Threading.pdf

Tin Falcon

Fasttrack
05-14-2006, 01:54 AM
Haha - yeah no thread dial for me. I on a Smithy machine - the cheapest one as a matter of fact. Theres not a whole lot of luxuries included with this package! I've seen thread dials before on a "real" lathe but my little one doesnt have one. Threading has been an interesting expierence! :)

IOWOLF
05-14-2006, 08:34 AM
There is an old saying..."You get what you pay for" I guess in this case it fits.

Sorry for your problems,

Fasttrack
05-14-2006, 11:15 AM
There is an old saying..."You get what you pay for" I guess in this case it fits.

Sorry for your problems,


Too true - but then i didn't expect to get any more than i paid for. I just didn't have money or room to buy anything bigger or better, so, for under a thousand dollars, and considering i'm student in highschool and living with my parents, i'm happy with it.

John Stevenson
05-14-2006, 11:31 AM
Good for you, keep plugging away.
Remember, now you have a lathe you can make many parts on it that you need.
You can often improve on what is commercially available at far less cost given that your time doesn't come into it.

Two of my lathes don't have thread dials but it doesn't stop me threading on them.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/hidden/TOS2.jpg

Doesn't show all the saddle but you can see from the fixed guard there is no way to run a threading dial.

Timleech
05-14-2006, 12:27 PM
The way we were taught at school, with no threading dials & no reverse, was to put a chalk mark on the chuck or the work, and another on the leadscrew. With the carriage always starting from the same spot, wait for the two marks to come round to their original points, then engage the half nuts
That's what I remember, it was 40 years ago though.

Tim

brettjones
05-14-2006, 01:23 PM
I have a logan chucker (7515) with a dc variable speed motor that runs the carrage and cross feed. The feed screw is not threaded (so I guess it's not a screw). Has anyone cut threads on a unit like this. I've not had the time to even power the lathe up yet and I didn't plan on using it for cutting threads, mostly because I assumed it could not do the job. This thread lead me to wonder if it's possible and since I'm a very green to machine work, I figured I'd ask.

gundog
05-14-2006, 02:29 PM
Tin Falcon,
Thanks I have printed this and it goes on the wall by my lathe.

1) Even # threads engage at any division.
2) odd # engage at any main division ie 1,2,3,4
3) 1/2 pitch every other main division 1&3 , 2&4 11 1/2 pipe for example
4)other fractional pich same division each time

IOWOLF
05-14-2006, 08:13 PM
So John, across the pond do you have to cut metric threads the way we have to with a SAE lead screw,IE without disengageing the 1/2 nuts?

lane
05-14-2006, 08:57 PM
16in South Bend Lathes have a6 pitch screw that Rule does not work for them . Just play like you are cutting metric threads Dont disengage the half nuts . crank out an reverse the lathe back to the end stop crank in start lathe go again.

J Tiers
05-14-2006, 09:55 PM
Actually, it is the relation of the leadscrew pitch to tooth count on the gear, plus markings on the dial that determine whether that system works.

some dials cannot be used with quarter threads,, Logan OEM dial for one, so you have to not disengage for those threads on that type.

But a SB dial, 32 teeth and 8 marks, works for 1/4 threads on a Logan.

Leigh
05-14-2006, 11:01 PM
Here is a plug gage and back plate I just did in 1" -16 with no thread dial.
Hi Falcon,

Thanks very much for the info. Nice work.

I'm supposed to know how to run a lathe. I did a lot of lathe work during my apprenticeship, but that was 40 years ago. I'm a Bridgeport miller, and I can do almost anything on that machine that you can do on a lathe (I said almost :D).

Just got the 10ee, and haven't even taken delivery yet, so I'm trying to brush up on my lathe skills.

Thanks again.

jstinem
05-14-2006, 11:02 PM
My Shoptask 3 in 1 doesn't have half nuts or a thread dial and I make any threads I want. The Shoptask just has a lever to start the leadscrew and the sadle nut is solid and always engaged. I put a stop on the ways out past the start of the thread and mark the chuck so I can bring it back the same place to start each pass. At the end of each pass I disengage the leadscrew, disengage the spindle clutch, Backout the crosslide, and wind everthing back to starting point. When the sadle is against the stop and chuck is aligned with the mark I engage the leadscrew and then the spindle clutch to go again. I never had a lathe with half nuts but I would be surprised of the very much easier that this to use.
Joe

IOWOLF
05-15-2006, 04:38 AM
I always knew there were reasons I never wanted a 3 in 1 machine,Your stories have Cemented this.

Tin Falcon
05-15-2006, 07:52 AM
Guys I am supprised the number of newer lathes that are shipped without a thread dial. I know with some of the older south bends parts and accessories sell for a premium things disapear or the uscrupulous may partialy strip and sell parts seperate. I also know that some lathes like the haringe(SP) do not have lead screw change gears etc. Nor do the sherlines etc. and cnc do not need them . But even my little grizzly 7x1O and the craftsman dunlaps have thread dials. And these are by no means full featured tool room lathes. I guess I am a bit suprised.
Tin

J Tiers
05-15-2006, 10:24 AM
Sherline doesn't have a dial because it isn't a threading lathe. You CAN do it, but not the way you would on a S-B.

Hardinge and some others don't have them because they thread a different way.

Some machines DO work with a simple disconnect thread feed and move carriage system because of the way the disconnecting clutch works.... it automatically re-establishes the correct alinement with the spindle just as if you had reversed the feed.

the 3 in 1 and some other small cheap chinese machines don't have them because in general for cheaper ones at least, there are no halfnuts, the carriage is permanently linked to the lead screw.

And some don't (like the Companion/Craftsman/Dunlap AA) because they were an option and the buyer didn't buy that option.

Millman
05-15-2006, 11:03 AM
Sounds like you guys are making this more complicated than it needs to be. I try to tell everyone that a machine tool; no matter what type , has it's own "personality", It's funny to see how many people will try to come up with the solutions for an actual machine tool that they have never seen or touched. Hell, I could sit here for hours telling you what I Think may be your problem..... but that would take all the fun out of DISCOVERING what your own machine tool is capable of. That would take all the fun out of seeing what YOUR tool can do. If you want to be the best at what you do....You have to experiment to see what YOUR tool or tooling limitations are. AS always; Play safe! If you don't know what the safety parameters are.....Don't fire up the machine.

IOWOLF
05-15-2006, 11:06 AM
Well said, Millman.

Millman
05-15-2006, 11:13 AM
Thanks, IOWULF, I try to deal in common sense, MOST of the time, unless I get all fired up over some remark that is totally out in "Left Field".

IOWOLF
05-15-2006, 11:14 AM
Hmmmmmmm,I know someone else like that.

Great minds think alike.

mklotz
05-15-2006, 01:55 PM
J. Tiers remarks about it all depending on leadscrew pitch, thread dial gear
and thread dial marks are spot on.

For the benefit of the newbies and/or folks who may have non-standard thread
dial setups, the following procedure may be useful. Note that it assumes that
one is cutting Imperial threads on a lathe with an Imperial leadscrew.
(Thread dials on metric lathes are a different ballgame.)

With the lathe off and the half-nuts disengaged, the TD engaged, use a DI to
measure the carriage movement. Establish what TD mark interval correlates with
carriage movements of the following amounts. (For a concrete example I've
indicated in parens what it would be for the more-or-less standard 8 tpi
leadscrew, 32 tooth TD gear marked 1-4 with 'half' lines between each numbered
line.)

a. 1/2 inch movement (any line to adjacent line)
b. 1 inch movement (numbered line to numbered line)
c. 2 inch movement (numbered line to opposite numbered line, e.g. 1-3, 2-4)

Now, if cutting an even-numbered pitch (e.g. 32, 40 tpi), the threading tool
will perfectly reengage the thread if I move the tool a distance of 1/2 inch.
So using whatever you discovered for your lathe under option 'a' above will
work when cutting an even-numbered thread.

For an odd numbered thread (e.g. 11, 13 tpi), the threading tool will only
reengage the thread if I move it a distance of 1 inch. So option 'b' is for
odd-numbered threads.

For 'half' threads (e.g. 11-1/2 tpi), perfect reengagement will only occur if
I move the threading tool 2 inches. So option 'c' is for 'half' threads.


pcarpenter
05-15-2006, 02:17 PM
One thing that maybe ought to come out of this thread...for those who are lathe shopping...is that buying a lathe for which a threading dial is at least available is probably a wise idea.

I owned one of the asian mini-lathes for several years before I was able to afford a full-size lathe and after reading this I have to say that its apparent that there's cheap and then there is *real* cheap. The 7x10,12,14 mini-lathes get a bad rap sometimes, but for the guy with only $400-500 to spend and no access to a good used machine, they may meet a need. The usual assumption that you have to do a lot to them to get them to work just didn't hold in my case. I have modified things for convenience, (longer slide travel, QC toolpost, quick tailstock lock etc), but was fully functional out of the box.

They come with some things that may not be that necessary (like variable speed), but also come with some pretty useful stuff like a traveling steady and faceplate and a *threading dial*. If Smithy is selling a lathe with threading ability and no threading dial, they are not selling a good lathe for a beginner. As someone else said, this is another reason not to get a 3-1 machine. Under $1000 would have bought you a mini-lathe and mini-mill....and you could cut threads without any hassle.

Paul

Millman
05-15-2006, 02:35 PM
Paul, you pretty much summed it up. Threading dials are something that you will need..maybe later on ,depending on your budget. There is no need to degrade someone operating within their personal budget. All boils down to the individual knowing what the limitations are of themselves and any particular machine tool. Amazing things can be done on Cheaper tools if you experiment with them. Burns my Ass when people say there is only one way to set up and perform a certain task. This forum is only opinions, some justified, some not. I have seen alot of that, so I just bite my tongue.....SOMETIMES!

pcarpenter
05-15-2006, 04:16 PM
I just skimmed the article the other night, but I think there was one thing missing:

They recommend (reasonably) that you use the compound for advancing the cutter into the work, and then repeatedly make reference to continuing until you have reached the right depth. However, it appeared to me that there was no discussion of how to determine that. In the absence of being able to try the mating part while in the midst of turning, a brief discussion of how much the compound actually advances each time would let the beginner understand how to use the compound dials accurately. If I am not mistaken, this would be sin(30degrees) or .5 times the actual dial reading meaning it is one half. Then, too, you have to know if the readings on the compound dials are diameter or radius....but then you always need to know that :)

Did I miss this in skimming the article or was the reader left to figure out when to quit cutting deeper, on his own?
Paul

Tin Falcon
05-15-2006, 06:27 PM
Marv: Thanks for the clairification.
PC carpenter also good points. Yes it is a good idea to do the math and know how far the tool advances when using the compound. I aggree that the little asian minis are pretty capable for the size.
I think another lesson to be learned here is when shopping for a machine know your needs and lean the cabability of the machines you are considering for purchase. This will prevent disapointment down the road.
Tin

IOWOLF
05-15-2006, 06:27 PM
In My Humble Opinion......Don't wast your money on a lathe without at least the place for a thread dial. You will be sorry, yes I know you can get the job done without it but "it only costs a few dollars more to go first class".
Who ever sells a new lathe without a thread dial(or as an option for more $) should be neutered with a spoon.
Your Opinion May Differ.

TECHSHOP
05-15-2006, 08:11 PM
Since my homeshop lathe has no threading dial but uses half-nuts, and I have no wish to travel to China, with or without a spoon, and my lead screw is 3/4-10, where do I look to get my thinking straight, on making a useful one. Oh, the screw is covered like Sir Sumpwater's machine.

Evan
05-15-2006, 08:20 PM
I have never owned a lathe with a threading dial. I have used one but never got around to making one for my SB. Russ (torker) sent me a gear to make one but it is still sitting in the tooling drawer :) . One of these days I might use it to make a threading dial. I usually thread in back gear as the standard speeds are a bit fast on the SB9. To return on a long thread pass I throw the back gear out of gear and there is just enough drag in the spindle to bull gear to run the lathe and carriage back at high speed.

TECHSHOP
05-15-2006, 08:40 PM
How do I determine the number of teeth on the gear end of the dial to have useful "numbers" on the other "visible" end?

Would 20 teeth be more or less "useful" than 40 teeth? or do I want a number like 35 teeth? (or will 25 teeth give me approx "metric").

Or should I just leave this thing on the round tuit list?

Mike Burdick
05-15-2006, 09:16 PM
Techshop,

Actually, one could get by with a gear that has the same number of teeth as the lead screw on the lathe if the gear can physically be made (min. teeth constraints). For example, if the lead screw was 8 tpi than the gear would have 8 teeth; if the lead screw had 10 tpi than the gear would have 10 teeth. The critical thing here is that the dial is measuring at least one inch of lead screw travel. But...that gear is pretty small and if one was threading 4 tpi then that little dial would be spinning pretty darn fast making it very hard to line up the marks. So if one doubles the teeth (two inches of travel), the dial will be going 1/2 the speed and it will allow two chances for marks to line up - much better odds! ;) Now double that again (4 inches of travel), and the speed is slowed by another 1/2 and it gives you 4 chances on the dial - much, much better odds!

So when one makes the gear, use teeth numbers for either 1, 2, or 4 inches of travel of the lead screw. To be 'practical' though, use at least a gear that will travel 2 inches of the lead screw.

Another benefit, if one uses 4 inches of travel, it is easy to use the thread dial for locating multiple start threads.

J Tiers
05-16-2006, 12:05 AM
How do I determine the number of teeth on the gear end of the dial to have useful "numbers" on the other "visible" end?

Would 20 teeth be more or less "useful" than 40 teeth? or do I want a number like 35 teeth? (or will 25 teeth give me approx "metric").

Or should I just leave this thing on the round tuit list?

You could make it with 20 teeth, and 4 marks, 2 numbered. Then it is

Even, any mark
odd any number
half, same number

or 40 teeth 8 marks 4 numbered resulting in

even any mark
odd any number
half, odd numbers
quarter, same number

You CLOULD make a metric conversion one, but I believe it would need 254 teeth! In amy case, it would have to have one mark at the travel which is the convergence of the two systems..... I figured this out once, but I am just dashing thru and don't have time to re-figure it.

IOWOLF
05-16-2006, 04:55 AM
:(
Since my homeshop lathe has no threading dial but uses half-nuts, and I have no wish to travel to China, with or without a spoon, and my lead screw is 3/4-10, where do I look to get my thinking straight, on making a useful one. Oh, the screw is covered like Sir Sumpwater's machine.

You went all the way to China for that thing? My Thought is you got it from the North west,or was sent to you from there,therefor the salesman is there, Call and ask if there is a way to do this. The one you got may be a striped down model and the next one or two better may have the means to add one.

BTW,One so young that has a Sig. line like yours is just asking for flames.One needs a little experience to be arrogant.
This is not a flame,so don't take it as such,It is my opinion.

Other opinions may vary.

John Stevenson
05-16-2006, 05:01 AM
Since my homeshop lathe has no threading dial but uses half-nuts, and I have no wish to travel to China, with or without a spoon, and my lead screw is 3/4-10, where do I look to get my thinking straight, on making a useful one. Oh, the screw is covered like Sir Sumpwater's machine.

It's Sir John actually, Sumpwater is the name of the family seat where we have the three phase mines ;)

Now I have a confession to make.
After I bought the little TOS lathe new it was only then I realised that it didn't have a dial so I had a spat on with the suppliers and they supplied a dial off another machine but there was still no lace to put it , mounting hole and one piece guard willing.

The mounting hole was easy as when I bought my cordless drill it came with a big box of various sized holes, found one to fit and glued it into the apron.
The guard was reasonably easy as it had the local sheet metal bashers to chop it into three longwise and only fitted the top and bottom section, leaving a slot for the gear to stick thru.

So now we were in business, working thread dial etc. This TOS lathe has a few features I haven't seen on other lathes, one is that the clutched reverse is 1- 1/3 times faster than forward so when you wind back it saves time.

After a couple of times threading using the dial I just fell back into reversing out the cut and not bothering. The dial is still fitted but the gear is out of mesh and has been for about 3 - 4 years.

I use the dial on the CVA as it's a pig to reverse, Tim Leeches two CVA's are later than mine and have electric reversing on them and no clutch.
Mine has the clutch and just hitting reverse before it's stopped make horrible noises.
Later I aim the convert this to VFD drive just for the softstart and reverse facilities.

.

JFitz
05-16-2006, 10:17 AM
In regards to the discussion of Threading on the lathe, does anyone just line up the proper line on their threading dial, by moving the carriage manually and then engage the half nuts, prior to turning on the machine to save on the wear on the half nuts?: In my limited threading experiance it seems that the sudden engagement of the half nuts in the threading process must cause havoc on the leadscrew and half nut threads.

J Tiers
05-16-2006, 10:20 AM
Not really, if you time it correctly they slip right in. No "clashing of gears" needed.

Unskillful previous owners MAY have managed to wear a double groove into the halfnuts, that has been known to happen. Then one is "engaged" with the nuts partly closed, and one with them entirely closed. Annoying if yours is like that.

pcarpenter
05-16-2006, 12:29 PM
with regard to half-nut clashing, I would offer the following:

If you are heaving on the half nut lever, you run the risk of breaking something in the mechanism somwhere anyway--even if they mesh immediately, as the half-nuts themselves may be bronze or cast iron. There is no need to be heavy handed.

Assuming a light touch, if you are off by just a fraction on the engagement, you are just bringing the top of a square (Acme actually) thread to touch on the top of another square thread surface. These two will slide across one another until they mesh. When the lead screw rotates just a bit more, these threads just drop into place. In effect, the threads on the half nuts are either engaged or not, and are not grinding prior to meshing. Again, a gentle touch is all it takes. Sometimes it is easy for our brains to confuse the need for a precisely timed, very positive movement, with the need to move it harshly.

Paul

TECHSHOP
05-16-2006, 09:00 PM
Mike Bur**** and J Tiers:

After I posted my last question, I powered down, and moved on to the "thinking chair." I realized the answer to my question is to use a 40 tooth gear (same ratio as 32 teeth and 8 tpi, right?) if it can physically fit.

As to the metric threading dial I will still end up doing the "power there and back again crank" routine, unless I add a metric lead screw and a "gear cluster" to the threading dial. (Could maybe get by with 127 teeth, J Tiers).

John Stevenson:

Sorry, not up on the Order of Peckers. My elders got the hint about royalty when the Reds shot the tsar and relocated to the States. Also sorry to hear your mines flooded, hope you don't have to drill any new wells.

IOWOLF:

My lathes SWMBO sold, when I wasn't looking after them, had threading dials, but the "replacement" ain't got one, any good kick the a$$ gets you farther down the road...

To all:

Not worried about flames, trained and experiance professional, also qualified in taking verbal and physical abuse daily from others, part of mandatory OJT in my line of work. Have E-stop on computer, not afraid to use it...

lynnl
05-17-2006, 04:27 PM
I just skimmed the article the other night, but I think there was one thing missing:

They recommend (reasonably) that you use the compound for advancing the cutter into the work, and then repeatedly make reference to continuing until you have reached the right depth. However, it appeared to me that there was no discussion of how to determine that. In the absence of being able to try the mating part while in the midst of turning, a brief discussion of how much the compound actually advances each time would let the beginner understand how to use the compound dials accurately. If I am not mistaken, this would be sin(30degrees) or .5 times the actual dial reading meaning it is one half. Then, too, you have to know if the readings on the compound dials are diameter or radius....but then you always need to know that :)

Did I miss this in skimming the article or was the reader left to figure out when to quit cutting deeper, on his own?
Paul

I had not been following this discussion since the first few posts.

But I think the actual depth advance, relative to the compound reading (set at 30deg), would be the product of cosine 30deg (or .866) X compound reading. ...would it not?

Been a long time since trig classes, but I recall sine = opposite/hypotenuse and cosine = adjacent/hyp.

Somebody correct me if I'm wrong.

Fasttrack
05-17-2006, 06:57 PM
Lynnl - i also figured it to be cosine but i guess it also depends on how the thirty is measured. The way i look at it is thirty degrees from a line perpindicular to the work, in which case the depth of cut would be the cosine of thirty (or twenty nine and a half or whatever). I think... :D Either way cosine is adjacent over hypotenuse and sine is opposite of hypotenuse.

mklotz
05-17-2006, 07:15 PM
For 60 degree threads, the depth-of-thread, measured perpendicular to the axis
of the thread, is given by H = P*cos(30), where P=1/tpi is the thread pitch.

To obtain the infeed on the (angled) compound, compute:

cin = H/cos(ca)

where:

cin = compound infeed
ca = compound angle

As a check, note that, if ca=30 deg, the above reduces to cin=P. If you draw a
cross-section view of a thread, you'll see that it's an equilateral triangle
with each side equal to P. At ca=30 deg, we're feeding along the flank of the
thread so we have to feed in an amount equal to the pitch, P. For ca<30, cin
is less than P but not much if ca is close to 30.

There's a program on my page (DOT (Depth of Thread)) that will do the math for
any variation of all the parameters in the problem.

spinrow
05-17-2006, 09:18 PM
Thanks to all for your helpful suggestions. I do have a SB 9 lathe and it does have a thread dial. I will try your recommendations and get back with you. Paul

J Tiers
05-17-2006, 10:59 PM
With all due respect, the thread is right when the gage says it is, or the wires say it is, etc.

The gage may be a nut already made, I am not arguing for precision mil-spec.

But just feeding in a specific amount is probably just going to be "close". Mebbe close and too big, mebbe close and too small. Maybe even right.....

Timleech
05-20-2006, 05:08 AM
It's Sir John actually, Sumpwater is the name of the family seat where we have the three phase mines ;)

I use the dial on the CVA as it's a pig to reverse, Tim Leeches two CVA's are later than mine and have electric reversing on them and no clutch.
Mine has the clutch and just hitting reverse before it's stopped make horrible noises.
Later I aim the convert this to VFD drive just for the softstart and reverse facilities.

.

John

Have you tried just reversing the leadscrew on the CVA? As it's on a single tooth dog clutch it should work OK, maybe not very kind to the mechanisms though. The dog clutches do have a bit of a lead to help with engagement. I've not tried it 'in anger', but just experimentally reversing the screw at threading speeds doesn't feel or sound too horrible!
My K&T CVA has some sort of electric braking, which stops the motor quickly when you switch off, but the later H Cole & sons model has just the basic contactors & can take a while to stop from high speeds. Not that anyone would be threading at 3000 rpm!
They do struggle to get up to top speeds on my phase converter, I'd fancied putting a VFD on one but the money has gone on spindle bearings etc.

Tim

John Stevenson
05-20-2006, 05:37 AM
Not tried that Tim, I'll give it a go next week when I have a couple of short bits to do.
.