ER Colletts - will they hold my plug?

Frances ...

Pardon me for trying to help !!

There was clearly a misunderstanding by Jim regarding "the Frances method", so I simply pointed him to your most recent post.

MichaelG.

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Edit: I presume that Jim is capable of reading back through the thread, to appreciate your previous contributions.

Edited By Michael Gilligan on 02/09/2016 18:18:36

The grip length of an ER40 collet is too long really for holding 4mm x 25mm accurately. It's the main problem with this style of collet.

If I had a lot to do I suspect I would make something to hold them first. That could simply be a recess in something that was a snug fit using grub screw to hold them in place but you may have to avoid marking them so the screws would need some thought. Soft solder ends maybe. Or some steel plate on a surface plate. Drill a hole through it, slit into the hole from one edge, drill and tap a hole through the edge to clamp it up. Mount on the lathe face plate with the clamp screw tightened a touch and then machine the recess for the screw heads.

Soft jaws are another option and maybe normal a normal 3 jaw chuck with the jaws reversed. That way you will have a square on face to press the head up against. If you rotate the work by hand just as the jaws close on it things generally will run as accurately as the chuck does. There is a bit of a knack to doing that though. A small chuck will do this sort of thing easily. Big ones too if the part is big enough. It may be feasible to machine up a split ring if that's the case. You may find that you can't get the part out if you do that though.

Rotagrip stock soft jaws but be prepared to spend a while fitting them to the chuck by hand with a file. I think they are deliberately made a touch over size. Getting them to a really good fit usually takes me 1/2 hr or so being very careful to find out what aspect needs relieving. They only need thou's removing as well.

John

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It is a a standard 1.5. The problem I'm having is griping the 4mm head of the plug and getting it to turn true.

Forgive terminology I'm new to all this!!!

That's because you're addressing the wrong problem.

As Frances says you need to make a jig to clamp on the thread. Either use a nut or make a threaded bush. Ideally the nut/bush would be split so when you tighten the chuck or collet the thread is gripped firmly. I can't imagine that it is critical that the recess is exactly centred; a few thou out isn't going to matter.

Andrew

Edited By Frances IoM on 05/09/2016 11:17:55

Edited By Frances IoM on 05/09/2016 11:19:00

Hi Jim,

I'm at the inexperienced end of the spectrum so I'll be interested to see what the experts make of this.

I'd use a bar across the body of the chuck to provide a flat surface against which the top of your plug can be pressed to get it at a right angle to the ways.

Then press the plug against the flat provided by the bar near the tip of the chuck and tighten the jaws.

I tap the bar out because of the trouble it will cause if it comes loose with the lathe turning!

Probably not the best way of doing the job but it might be 'good enough'.

I used two parallels as the bar only because they happened to be the right size to suit the bolt used as my example. Anything that provides a flat face to locate the work whilst allowing the jaws to be tightened on the job will do.

Cheers,

Dave

I have moved the lively debate about ER collets holding properties to here

Dave, I quite often use the same method myself when faced with this problem, you just need to provide something that is square to the lathe for the back of the plug to rest against. Only proviso is as I mentioned before the head needs to be concentric with the thread which if the head was forged may not be the case.

If faces with a bolt like you have shown rather than s stummpy plug it is easy to hold the thread of teh bolt in the tailstock 3-jaw while the main 3-jaw is tightened. This could be done with teh plug if the OP already has ER32 and a holder that fits the tailstock.

Edited By JasonB on 05/09/2016 12:55:44

Tailstock 3-jaw??? I think the OP may be slightly less well provisioned than you otherwise he would be sufficiently experienced not to need to ask this question in the first place.

As the threaded part is 15mm dia I think you might be able to find a bit of copper plumbing pipe, cut some bits to length, slit lengthways, and use more than one layer to give you enough thickness to enable the thread to be gripped in your chuck without the head fouling.

Bad use of words, I meant a drill chuck which would hold a small dia like Daves example.

Thanks Jason for confirming that the method I suggested isn't barking mad!

I also appreciate your useful tailstock 3-jaw suggestion. It could be done with a drill chuck in the diameters I most often hit this problem with and should be less of a fiddle.

Thanks also to the other contributors to the thread: lots of interesting suggestions for me to profit from.

Cheers,

Dave

PS Post crossed with Jason correcting tailstock chuck to drill chuck!  He got there first.

Edited By SillyOldDuffer on 05/09/2016 16:06:07

As will just reversing the chuck jaws if they will close up on the head diameter. At 25mm dia a small chuck will.

John

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The split bush is probably the easiers option as Andrews says. I think a plain bore would give enough grip for what you want to do if you use a soft metal such as aluminium.

Assuming your plug looks a bit like the cap on the left then find an odd bar end that is just over the dia or A/F of the head, bore it out until the plug just slips in and face off to length of plug or a bit less. Take it out of the lathe and put a saw cut lengthways.

Now slip the plug into the bush

And you now have a longer length to hold the plug by which should help keep it from being held crooked and it will also be concentric to the thread regardless of head shape. Also minimum sticking out of the chuck so it won't get snagged by the tool.

Jason, this is what I was advocating a couple of days ago. It may be that I had not described my method properly, but what you have described is exactly what I meant. It is a simple but effective method. Why make something complicated when this method will do the trick.

Lots of ways to approach this problem. Thanks for all the advice guys.

With ER collets. I have made a collet fixture, I use at work. it goes into a dedicated set of softjaws. It has on the back a plate that is used as a stop. This is for ER40 collets. I have a set of spacers and also spacers that have the diameter of the work piece that locates into the last 5mm or so of the ER40 collet, with the front of the stop being used as a true face for the part to sit against. The area between the part and the 5mm engaged with the collet diameter is relieved a little, I make it smaller by 0.2mm in diameter. This allows me to hold onto parts sometimes only 2mm length to hold. Of course you only take cuts according to the ability to hold the part.

This effectively makes the ER collet like a fixed length collet chuck, which is great for repetition of parts. I also make my own ER collets for specific tasks and only takes parts to a tight limit, Exact size or smaller by 0.02mm max. The collets I make , I only slit them from the front and leave the back as a single ring. The slits only go to about 5mm from the back of the collet. I drill a hole for the end point of the slots. If the parts need to all be the same length, then I make a stop block to suit. The stop blocks are held by a M8 capscrew. But a smaller similar system could be made fro ER30 or any other ER collet size.

I can take some pics if anyone is interested and then add them tomorrow.

Neil

If Jim were to start with a blank long enough to include the part plus a generous amount to chuck on he could eliminate the need for collets.

Clamp the blank in the 3 jar and do all the machining on the threaded end.

Part off leaving a little material for a finish cut.

Chuck on the threads. Use a split bush or pad the jaws with copper or aluminum.

Finish the big end.

If Jim is looking for an excuse to buy a collet setup, ignore what I wrote.

If using an ER collet be sure to make a plug to fit the back of the collet. With a short length in the collet it may be difficult to get the part to run true. Use a ball bearing mounted to a shank to push the outer end to run true and re tighten the collet. With a short length held in the collet it will be necessary to take very light cuts to prevent throwing the work out of the collet.