PDA

View Full Version : Power feed when parting off, yes or no??



Malc-Y
03-01-2008, 03:49 PM
When parting off in the lathe should the tool be fed into the work by hand or can the power cross feed be used? What speeds and feed rates should be used on steel?

Malc. :cool:

IOWOLF
03-01-2008, 04:13 PM
It really depends on your experience, among other things.

What it boils down to is Do You feel comfortable using the power?

b2u44
03-01-2008, 04:24 PM
I typically feed by hand so I can constantly adjust the feed to maintain a reasonable chip-load and smooth cutting action. If I have a lot of parts to cut, I will take the time to find (usually by trial and error) a good feed-rate, working my way up until the chips come off smoothly. If you do use the power-feed, make sure to start gently and gradually increase the feed. Otherwise you could take an overly large bite and stall the lathe, damage the chuck, break the parting tool, etc...

As far as speed goes: I go slowly, with lots of oil. Parting steel with HSS tools can get hairy in a hurry, so slower is better. Keep a hand on the power-feed lever to disengage it quickly if things start to bog down.

motorworks
03-01-2008, 04:24 PM
It depends on a number of things:
What type of set up
How rigid your lathe is
CArbide or HSS
etc

Your speeds and feeds depend on the tool
If the piece is large and heavy I find it better to
take over by hand for the last .100" or so and to have
a way to catch the part. (rod held in the tailstock pushed through the work)

I use flood coolant to 'flush out' the chips

John Stevenson
03-01-2008, 04:27 PM
Don't be frightened to use the tailstock for support.
It makes a hell of a difference and contary to popular opinion the part doesn't jam up in the cut but just tilts to one side and stops rotating.

.

tattoomike68
03-01-2008, 04:55 PM
Most of the parting I have done ay work was stuff like cutting through weld to remove drive line yokes so it was done by hand feeding.

A cnc parts a bit fast but a multi spindle screw machine parts off at full speed and high rate of feed, it also has 100psi of cutting oil blasting on the part and tool though.

Most of the problem people have parting is from too little oil and too far away from the chuck or collet.

.RC.
03-01-2008, 05:16 PM
Don't be frightened to use the tailstock for support.
It makes a hell of a difference and contary to popular opinion the part doesn't jam up in the cut but just tilts to one side and stops rotating.

.

I never use the tailstock for support as it does jam up the part at the end of the cut..

I also use a carbide insert parting off tool and and always use power feed..

Here is a short video I made years ago --->>> http://users.beagle.com.au/lathefan/20901395331%5b1%5d.wmv

John Stevenson
03-01-2008, 05:28 PM
I never use the tailstock for support as it does jam up the part at the end of the cut..



I would be interested to hear other peoples remarks on this one - genuinely.

I make gears for Myfords that Gert used to sell on Ebay.
They are sold in pairs and I can cut 10 gears at a time on the Stevo E-Lec-tronic hobber.
I normally make about 40 to 60 blanks one night after tea and cut them the following night.

It actually takes longer to make the blanks than cut the gears.

I take a piece of 30mm mild steel and drill it both end to just under 5/8", then ream it.
I can then part off 8 gears from each end before running out of reamed bore.
These are parted off on the CVA as it runs on neat oil and always followed up with the centre as additional support.

Run out isn't a problem as the OD of all 10 are skimmed on the same mandrel that fits the hobber.

Broke tools before but never had one jam because of the tailstock.
Most problems are caused by me rushing the job.

Also do worm wheels out of 3" brass and these are parted off the same but in brass it's not as much a problem as mild steel.

.

Alistair Hosie
03-01-2008, 05:40 PM
I always part off by hand and have(touch wood) never had a problem at the college club we were always told to use the tailstock as it was safer try making sure you are not using too much pressure on the tailstock or it could be a potential problem otherwise go ahead and watch your speed.Alistair

Frank Ford
03-01-2008, 05:58 PM
I've not had a problem with the part binding when parting off with a tailstock supporting the work, but I don't do it with anything over about an inch in diameter. I've always assumed the risk went up greatly with larger diameters. For those, I part almost all the way through, then retract the tailstock to finish the last bit.

IOWOLF
03-01-2008, 05:59 PM
As far as using the tail stock It would depend on the application, and the length of piece cut off, Wouldn't it?
I have done both and I have used a rod in the tail chuck for washer type stuff.

torker
03-01-2008, 06:01 PM
I always use powerfeed.
I could do it by hand but I'm too lazy, tired, dog ate my homework etc. :D
I sorta figured that's what that lever that makes the cross slide move was for.

Mark McGrath
03-01-2008, 07:11 PM
To answer J S`s question.
I never use the tailstock to support the work while parting off as that`s what I was taught forty odd years ago.but I do use the power feed.But,machines and tools have moved on and I know a guy who always uses the tailstock and has never had a jam and he`s usually parting 3"-4" stainless with the power feed,in a Colchester which is not the best of lathes to part off in.I find there is more chance of chatter hand feeding than power feeding.It depends a lot on the machine but most people are frightened of parting off and run the work too slow and don`t feed heavy enough.I usually run the work at not much less than for normal turning.In an auto where I don`t have a choice it`s the same speed.Another thing that does not help is holding the job in a three jaw chuck,when the jaws are opened out for bigger diameters the work can lift between them and it`s curtains for the tool.Better in a four jaw or a collet.
Mark.

JRouche
03-01-2008, 08:31 PM
I use the tail and a bullnose for pipe, keeps the chatter down. JRouche

J Tiers
03-01-2008, 08:36 PM
I like SOMETHING At the end for long parts. But just a "finger" type deal sticking into a hole, or a ring around.

An actual center seems to be no particular help, and maybe a bit of a jam-up, depending.

JCHannum
03-01-2008, 09:20 PM
I try to do my cutting off close to the chuck, but I do use the tailstock on long parts, and would use it when baloney slicing like John does for his gears. I usually back off just before it breaks through. The trick is not to put too much pressure on the tailstock.

I just recently aquired a carbide insert cutoff holder, and have only used it to play with, normally I use HSS and the thinner, the better.

I almost always use power feed, and once I got the hang of it, I found that I, and I think most newbies go too slow. When it starts to chatter, don't be afraid to speed up the feed or RPMs. All this assumes sharp cutter, ground properly, rigid lathe and toolpost and coolant. I use dark sulfur cutting oil.

fasto
03-01-2008, 10:50 PM
And I do use the tailstock.
http://www.psinteg.net/files/partoff1.JPG
http://www.psinteg.net/files/partoff2.JPG

4.5" CPVC rod there ($10 per INCH), making blanks for one of my products. The trusty "Hardinge Brothers" live center in the tailstock holds the outboard end. I'm going at 130 RPM & as fast as the power crossfeed will go, 0.020/rev IIRC. Lathe is a 13" Colchester. Using the Aloris HSS parting tool holder & whatever HSS parting blade McMaster provided. I don't part it all the way through on the first pass.
In the picture it looks like I've bungled the furthest left cut, the one underway, but I only turned the outside diameter to just beyond where the cut line is.
http://www.psinteg.net/files/partoff3.JPG
A considerable amount of stickout of the parting blade, but no troubles in cutting.
Mind, it IS plastic, after all.

Allan Waterfall
03-01-2008, 11:56 PM
From my limited experience...if you try to part off at too slow a speed when hand feeding,the tendency is that you end up using to much depth of cut and the work jams. A fast speed seems to prevent this.It also helps to keep a firm infeed on.

I use a VFD and increase the speed as I get further in,usually ending up at a fast speed approaching normal turning speeds.I've got a rear mounted toolpost in a drawer somewhere and it never gets used because I don't really have any problems using the normal one.

My lathe is a Myford.
When I originally went to buy my lathe the chap demonstrated a rear mounted tool post and power feed...the tool jammed.:D

Allan

Carld
03-02-2008, 12:13 AM
I have parted off up to 6" dia using the tailstock with a bullnose and never had parts jam. It depends on what I am doing whether I use power feed or manual feed. I have found a higher speed most times works best. You have to take into consideration the diameter of the work for the rpm you select. you'll know if it's to fast.

If parting away from the chuck jaws it will chatter and you need tailstock support. I have parted DOM steel tube like fasto shows and used a tailstock for support. I have also used a steady rest with the tailstock.

radish1us
03-02-2008, 02:16 AM
When parting off, try to have the parting off tool as close to the jaws as you possibly can, this keeps the job steady and it does stop quite a bit of chatter. The further away from the jaws, the bigger the risk of chattering starting and once it's started, you got it till it's parted of.
HSS tools should be run so that the chip coming of is hot, but not turning blue, or the sharp cutting edge will vanish very quickly, if possible use a cutting fluid/misting spray/anything at all to keep the HSS cool and it sure helps the cutting.
For indexable tips used in parting of, get the revs up around 5 hundred, see what happens and adjust the speed up or down and if you want to, kick in the power feed, cutting fluid recommended again, to keep everything cool.
Now if the bit that is being parted of is any longer than a couple of inches long, then bloody well use the tailstock to support it. If it's a heavy bit, use it again, unless you despise your lathe.
Ever seen what a piece of 3 to 6 inch long x 1 inch bar can do to you, the longer it is, the worse the whipping will be, as it's nearly parted of?
The workpiece being parted of WILL NOT jamb up, as has been suggested, it will just flop down and rub a bit until the lathe stops, big deal.
I use a tailstock at work, or at home, for just about everything, even down to tiny bits on my Unimat 3. I've made the mistake before of not supporting the work and boy, do they flap around and fly.
Don't be afraid to crank it up when parting of, just support it and it's no longer a chore to do.

regards radish

mark61
03-02-2008, 02:35 AM
Using the tail stock helps prevent all the worn in slop from truning to chatter. You can back it off just before parting thru if it worries you. I have more trouble with the tool twisitng and going croocked when power feeding. Even taking all the precaustions trying to prevent it. It depends on the machine. Some are worse than others. Depends how far away from the chuck and the material too.

mark61

J Tiers
03-02-2008, 03:07 AM
If your machine has a QC box, no reason not to power feed, as it will leave your hands free to make sure the cut gets cutting oil in it.

Mine has change gears, so the feed speed for parting would take a long time to set right. Consequently I use hand feed.

As for the jam up, I remembered why....... when the part is cut off, it tends to slide down the cone of the center and back into contact with cutter and spinning stock. That does indeed make it flop around a bit, and can make it fly, especially if it is short and large diameter. If you just use a straight 'finger" in the end hole (if any) or a ring around for a long part, it tends not to do that.

If you part off far enough away from the chuck that the piece will flex from cutting, which is a bad idea, then the center WILL make it close in on the cutter and cause trouble. But you'd have trouble of some sort if you did NOT use the center too.

malbenbut
03-02-2008, 04:40 AM
I've never had a jam when using tailstock for support,my own preference was to use hand feed probably due to the crappy and ancient machines we had to put up with when working in machine shops in the UK. Most amateur machine shops posted on this and other sites have better equipped machine shops that most employers expected you to use.
MBB

Mark McGrath
03-02-2008, 06:30 AM
"I've never had a jam when using tailstock for support,my own preference was to use hand feed probably due to the crappy and ancient machines we had to put up with when working in machine shops in the UK. Most amateur machine shops posted on this and other sites have better equipped machine shops that most employers expected you to use."

What`s that old saying about workman,tools,bad,blame?
Mark

Your Old Dog
03-02-2008, 06:53 AM
I have had jams when using the tailstock but I found out why. I was using a lantern style holder and was not always dead on center and likely going in just above center. With the tool on center there isn't much reason for a crash while using the tailstock. I usually part without the tailstock but then I'm working right up against the chuck or not more then 2 diameters away from it.

As for the power feed, for me it's abit the same as Wolf's take on it. If the mood strikes me I use it, if not, I go it by hand. If I'm doing a large diameter I'm more prone to use it as it frees up one hand for oiling. The other hand is always on the switch in my shop !

malbenbut
03-02-2008, 08:31 AM
Quote-
What`s that old saying about workman,tools,bad,blame?
Mark
I wasn't blaming the tools as you still had to produce good work within tolerances stipulated in the drawings. I just stated a fact that the machines you had to use were not as good as the machines the average home machine shop had. Some of the Uk workshops were very poorly equiped, I worked in one workshop where their wasn't even a mic in the workshop.
(we used to measure with a bit of string and if it was to short we used to measure with a piece of elastic so you could stretch it and make it fit)
MBB

John Stevenson
03-02-2008, 08:39 AM
True story about no invvestment in machine tools.

Norton motor cycles were based in Birmingham and were bought out by the AMC group who made Matchless and AJS.

The whole plant was moved from Bracebridge Street to Plumbstead in East London and setup there, all the Birmingham guys were made redundant.

When the first run of Commando crankcases were run they were off spec to the drawings even though all the work was done on specialised machines and jigs. After much head scratching someone suggested they go see old Bert in Birmingham who ran the job.

So they troop up to Birmingham and knock on old Bill's front door and explain the problem. Bill scratches his head and has a think.

"Did you take the plank with you to London ?
"

"What plank ?"

"Well you see the second spindle of the drill runs off so I used to hold this plank against it whist it was drilling to stop it wandering"




.

oil mac
03-02-2008, 09:49 AM
To despite myself, i have absolutely no problems in parting off work, maybe because i tend to use the four paw most prevelantly, as one gets a better hold on the work, also, a good solid lathe helps a lot, my big Holbrook, has extremely ridgid bearings and slides, and i believe the heavy saddle is contributary to good work also, As regards my Myford super 7 No sweat either although smaller work, ( horses for courses!) I tend to prefer to part of from the front, as near the chuck jaws as i can get also, why have a headstock for rigidity and not take the advantage of it by parting off far out, unless some special circumstance dictates, And i tend to also use the tailstock on occasions if possible.
My own preferrence is to feed by hand, and on work, over 2" dia on the big Holbrook, i take a cut in to a depth of say3/8" draw the tool back, move forward (using top slide) approx half width of tool, and start cutting again by making a wide kerf, and cutting in drawing back, and moving over in each succesive side, i find i dont get cutting jam ups and never break a tool
Sometimes i am intrigued by the clangs and bangs from some people, (which i have observed) with the parted off components clouting the lathe bed, An old turner taught me, if you can put a board over the lathe bed and cross slide, keep your bed safe, Do It!
Some years ago, a person i knew purchased a new Harrison M250, and a few days later was on the phone moaning to me that the so& so lathe was only good for breaking parting tools, A man i am sad to say who would never listen to common sense or advice.
When going up to see the problem, i found our genius, was trying to part of 1.500" bar using little 1/16" parting tools and putting on a power feed as well which would on the longitudinal feed be about one thou/inch, so on his cross feed would be about half that from memory, , so in went the poor little tool,work glazed up, bang! combination of light tool and wrong feed rate couldnt convince the stupid man. Plenty of little broken tools in the swarf tray!
Where i was employed at one time, we had a Harrison L5 lathe lousy for parting off, due to the inherent small and weak bearings in the head, and narrow bed not a wonderful design As a machine the modern Harrisons such as the M250 & 500 were a reasonably good machine

Malc-Y
03-02-2008, 10:57 AM
My reason for starting this thread is that in the past when my lathe was a Myford ML7, I never had any luck with parting off, the tool would always dig in causing the tool to break or the work to be ruined. I was always careful to set the tool exactly on centre height and made sure that it was correctly ground and honed to a good edge.
I never had any formal training as an engineer and am entirely self taught in machine work, learning fron reading engineering text books and Model Engineer magazine and by trial and error. I am an amateur in the true sense of the word and have no connection with engineering in my employment ( I drive trains for a living).
Now, back to the parting problems. I have now sold the Myford and bought a Colchester Triumph 2000 (15" in the USA). The Myford did not have a power feed so there was no question of whether or not to use it or hand feed. The Colchester however is a much larger , heavier and more rigid tool altogether and of course has a power cross feed. Yesterday I thought I would have a go at parting off with a short length of 1 1/2"dia steel out of the scrap box and gripped in a 6 jaw chuck. I have not used the Colchester for parting of before and I wondered about using the power feed as everything that I had read about parting had said use a steady hand feed. The finest feed on the Colchester is .00075" per revolution and I thought that this was a lot finer and steadier than I could feed manually. I recently bought 2 new brazed tip parting tools with 1" square shanks on ebay very cheaply. These have a cutting edge about 7mm wide so I decided to use the slowest speed, 25rpm and see what happened. With considerable trepidation I started the cut and was ready the stop the lathe if any thing went wrong, but nothing did! I did not use any coolant as I have recently cleaned out the coolant tank and not refilled it, in fact I don't use the lathe frequently enough to fill it up only to have it go rancid, so I usually use a plastic bottle with a small hole drilled in the cap and squirt the coolant on as required, just ordinary soluble oil, Shell Dromus mixed about 30 to 1 with water. However as the revs and feed were so low coolant wasn't needed.
Although it took some considerable time, the cut was completely successful. I think the revs could have been raised and coolant used, as it was the piece parted off, about 1/4" thick was only just warm when the cut was completed.
I apologise for rambling on a bit but felt that a explanation was required and I welcome any constructive criticism.

Malc. :cool:

Your Old Dog
03-02-2008, 12:58 PM
I apologise for rambling on a bit but felt that a explanation was reqired and I welcome any constructive criticism.

Malc. :cool:

Alright Wolf, you're up. He asked for it so make him bleed ! :D

loose nut
03-02-2008, 06:36 PM
Don't worry about it, if parting under power turns out to be a bad idea you'll know about it real quick.

Tyro 001
03-02-2008, 08:35 PM
Check my post of 11/01/07. A lot of the guys on this board had some good comments. By the way, I got the top casting for the steady rest within 5 days. I'm still waiting for the follow rest. It's apparently on back order until the sun burns out.