work slipping while threading …

[BASS 666Participant @bass666]

myford ml7 with 3 jaw chuck …

i'm having bother threading mild steel with a tailstock die holder and the stock being held in the chuck ..

i turned a bar down yesterday to 9.5mm for a 3/8×24 die and it was in the chuck but when i try to thread it using the die holder the work just slips no matter how much i tighten the chuck ..

it will make the first small part of thread then just slip even with a good chamfer …

yes i can take it out and finish in the vice but i would rather do it on the lathe .. is there a way to make the chuck grip tighter ?

the only thing i can think of is maybe a soft collar using two halfs ??

any input guys ? thanks ..

[BASS 666Participant @bass666]

[Jeff DaymanParticipant @jeffdayman43397]

Piece of ordinary paper between work and jaws can make a big difference in grip. Same for work held in a mill vise or clamped to a machine table.

[EmgeeParticipant @emgee]

If the chuck is well used perhaps the jaws have become bell mouthed, this drastically reduces the gripping area.

Emgee

[BASS 666Participant @bass666]

the chuck is worn a fair bit i think because i needed a 12mm hole through 6 penny washers so i put them in the chuck to bore through them with a drill and the washers closest to the outer edge of the chuck fell out when i tightened it ..

i done them 3 at a time ..

[Ady1Participant @ady1]

You need to cut a deeper start thread on the lathe, your die is doing too much work

do most of the threading work on the lathe, the die finishes off, 10mm is medium-big work

Edited By Ady1 on 17/04/2022 00:43:34

[BASS 666Participant @bass666]

Posted by Ady1 on 17/04/2022 00:34:52:

You need to cut a deeper start thread on the lathe, your die is doing too much work

do most of the threading work on the lathe, the die finishes off, 10mm is medium-big work

Edited By Ady1 on 17/04/2022 00:43:34

i can't cut threads on a lathe yet and the die works perfect in the vice …

[HopperParticipant @hopper]

You have a bellmouthed chuck as your washers proved. It needs regrinding or replacing.

Meanwhile you can make life easier by reducing the diameter of your steel bar by 5 thou or more. Die goes on much easier and thread is just as strong.

And try wrapping a piece of emery paper around the job where the jaws grip.

[CalumParticipant @calumgalleitch87969]

Assuming you are not peeling off tenths with your turning tools, you're applying as much force with a cutting tool as you are with a die, or thereabouts.

The two obvious things to me, besides checking the chuck is in good order, are (a) is it definitely mild steel and (b) is it definitely a 3/8" die and it hasn't been cranked up tight by the Incredible Hulk?

[Ady1Participant @ady1]

Your die will survive a lot longer if you do most of the work on the lathe

All you're doing is stressing out your 3 jaw and die

You can make a roundbar holder or split collet for the vice which won't mark the stock so much

10-12mm is too much for a die without some precut

[BASS 666Participant @bass666]

i will take this all on board and try the things mentioned .. might have a go at grinding the chuck jaws as well …

[Ady1Participant @ady1]

Everything takes forever to start with, until you get organised and get experience

It's a steep curve at the start but well worth the effort

[oldveloParticipant @oldvelo]

An old mentor of mine back in time used to say. "To Tighten a three jaw chuck use the key in all of four holes".

It will be so tight you may need an extension on the chuck key handle to loosen it.

Never use an extension to tighten the chuck.

[Martin ConnellyParticipant @martinconnelly55370]

Slightly off topic but I once had an apprentice complain about drills slipping in a pillar drill chuck, I told him to use the chuck key in all three positions on the chuck to tighten it. He was surprised how much the second tightening in the second position moved the jaws.

The point is that with any self centring chuck, lathe or drill, unless everything involved in tightening it is glass smooth and lubricated there will be some mechanical effort wasted due to leverage and friction. The easiest way to overcome the low leverage on the far side of each key position is to move around each position and tighten until loaded movement of the key stops.

Martin C

[jimmy bParticipant @jimmyb]

Holding in a collet would be the most secure.

Threading with a die is much more pressure than a turning tool!

Jim

[HopperParticipant @hopper]

Posted by oldvelo on 17/04/2022 03:40:42:

An old mentor of mine back in time used to say. "To Tighten a three jaw chuck use the key in all of four holes".

It will be so tight you may need an extension on the chuck key handle to loosen it.

I do this as a matter of course on the old chuck on my Myford and it works well. But I have never had to use an extension to get it undone. Although, a good bump with the heel of the hand on the chuck key handle is often necessary.

[Martin KyteParticipant @martinkyte99762]

Stick it in the 4 Jaw

regards Martin

[SillyOldDufferModerator @sillyoldduffer]

Washers falling out strongly suggest the chuck jaws are worn, and it's not getting a good grip on the blank rod. Regrinding them is an option, how to do it is worth starting another thread.

Otherwise:

• It's usual for screws to be cut on a smaller diameter than nominal, up to 1% less, so 9.43mm rather than 9.525.
• Cutting fluid is essential,
• Dies tend to push metal as well as cut it, so threading can cause a pile up especially in softish metals. Ordinary mild steel is a bit smeary and the effect is much worse if the die is blunt, or a split die is over tightened. Never assume a second-hand die is sharp, and not all new ones are trustworthy!
• Some dies without a split are intended to tidy up existing threads rather than cut new ones. They work, but can't be tweaked to cut tight or loose like a split die, and are more likely to get into trouble cutting a new thread.
• 10mm is about the maximum I'd cut in a lathe without using the lathe to single-point a starter thread. Cutting a three-quarter deep thread with the lathe creates an accurate spiral for a die to follow and much reduces the work it has to do. Best of both worlds – the lathe does the grunt work and provides an accurate spiral, while the die shapes the thread's valley, flank, and crest to the correct form. The tendency of a die to squeeze rather than cut metal is reduced too. On the other hand, completely die cut threads are usually plenty good enough, and cutting a starter thread with a lathe might be considered a waste of time.

Dave

[HopperParticipant @hopper]

Has been threads on here before and article(s) in MEW on regrinding chuck jaws. It just needs a clover leaf plate, or three small bits of flat bar to push the outer ends of the jaws OUTWARDS while regrinding with a Dremel held in the toolpost.

[BASS 666Participant @bass666]

thanks for all the advice guys …

[Mark RandParticipant @markrand96270]

In the meantime:-

1. Have you got a drive dog that you could clamp around the part to give a bit of extra torque?
2. Could you file three flats on the part to give the jaws a better grip?
3. Could you drill a radial hole into the part and insert a pin to give a drive against a chuck jaw?

And last, but not least. Is the die opened up as far as it will go? Is it the right way around? Are you uing cutting oil with it?

[Howard LewisParticipant @howardlewis46836]

If the work is slipping in the chuck, apart from bell mouthed chuck jaws there are other possibilities.

It is assumed that there is a small lead in chamfer on the end of the work, equal to the depth of the thread to be cut.

Also that the Die is the right way round. The marked end should lead, but I have encountered an odd Die where the marking was on the back of the Die. Inserting the Die the other way round cured the problem.

Might be worth checking that the leading end of the Die is the chamfered end!

If not as the work progresses into the unchamfered section of the Died

1. The Die may be blunt

2. The Die may be overtightend

To set a Die, use a commercial 3/8 UNF bolt or setscrew, and adjust until the bolt / setscrew is slightly stiff to rotate in the Die. It must not cut

3., The Tap or Die should be copiously lubricated. Trefolex, Rocol STD or even bacon fat are good lubricants.for Taps and Dies.

4. Don't be afraid to withdraw, and clear the swarf, regularly..

If the workpiece is rather hard, you can always open up the Dies and take a first cut, tightening it for second or third cuts. The final cut should be with the Dies adjusted to a commercial thread (Which ought to be made to the correct dimensions. )

If the worst comes to the worst, having fully engaged the Die, the work can be removed from the lathe and gripped in the vice, whilst the remainder of the thread is cut using Die Holder. But apply equal force to both handles, or you could finish up with a drunken thread.

As an aside, if you are dealing with Imperial sizes, and you have the correct measuring equipment, why not work in Imperial units. 9.5 mm x 24 UNF threads are not standard, 3/8 are!.

Howard

[David-Clark 1Participant @david-clark1]

Turn the end of the shaft to root diameter if long enough to hold the thread true.

[Nigel McBurney 1Participant @nigelmcburney1]

I use a ER32 hexagon Stevenson collet block in the lathe chuck from Arc Euro Trade,to hold round rod when cutting threads in the lathe,the ER collets when firmly tightened have very good gripping power and do not slip even when cutting coarse whit threads,similarly taps can be held in an ER collet and holder with MT shank. The problem of work slipping in a 3 jaw chuck and taps slipping in jacob chucks went away when I started using ER collets, To my mind if a drill or lathe chuck has to be tightened to such a degree that the key has to be inserted in all the positions then it is putting undue strain on the chuck jaws,,and good three jaw chucks are a lot more expensive than er collets. I have found that ER collets will hold securely a 11/8 inch whit tap when making nuts for a f/size traction engine,though at this size the strain on a tailstock would be far too much,I have made a 4 mt holder which is bolted to the saddle of a 6 1/2in lathe,which also allows the use of 4mt drills .During my apprenticeship I never saw anyone tightening a chuck by multi insertions of a chuck key.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Howard Lewis on 17/04/2022 14:11:40:

…

As an aside, if you are dealing with Imperial sizes, and you have the correct measuring equipment, why not work in Imperial units. 9.5 mm x 24 UNF threads are not standard, 3/8 are!.

My workshop is metric first, and I often mix systems as an operating convenience when forced kicking and screaming back to Imperial. As the dials on my machines are calibrated in millimetres, it's easier to cut in millimetres, even if the target is an Imperial equivalent.

I think the reverse is true of an Imperial first workshop making metric items – to cut an M10 thread with a die, easier to turn a rod to a few thou under 0.394" and apply an M10 die than to do mental gymnastics with two systems.

Dave

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