Hi Tim,

I don't know how easy it would be to attach a sleeve on my Emco C8. As far as I can understand from your post my C8 is different from the Myfords – see photo

 I would have to make a new nut for adjusting the axial play. I just use a copper hammer to knock any MT tooling out of the mandrel.

Thor

Edited By Thor on 17/01/2016 15:10:52

To be honest, Tim, I don't think there is a reasonably practicable way of providing a self-extracting drawbar on the ML7 [which may be why Myford devised those special MT2 collets] … But it's a very good question, and I hope someone proves me wrong.

My best wacky alternative, so far, is to make a giant 'valve spring compressor' that picks up on the spindle nose and operates a pusher-bar. … But that would be very big & very clumsy,

MichaelG

First, don't over tighten the drawbar in the first place! I believe the morse taper is designed to use quite small axial force to lock. For example, you don't have a drawbar for the tailstock. And I believe the main reason for the Myford pattern collet with extractor groove is so you can pass longer items into the headstock bore. I don't often use taper tooling in the Super 7 headstock, but I've never had to give it more than a gentle tap to remove, nor have I had problems of it not locking. The tailstock is a different matter….

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I agree 100%, John … But it's good to be prepared for the unforeseen; and 'lock hard' is what a Morse Taper can do.

Addressing Tim's question is a nice exercise for a cold Sunday afternoon.

MichaelG.

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P.S. I'm sure you are correct regarding the Myford special collets.

I don't see the problem. If a collet or what ever has a locking taper unscrew draw bar a bit and tap the end of it. It can take a pretty hefty tap.

I did think of making a screw extractor for my dore westbury but it's not worth the effort. It doesn't cause any problems because the very end that I "tap" isn't threaded and the draw bar is located well in the spindle so can't flex much or anything like that. It should be easy to arrange for the same thing to happen in a lathe spindle. Assuming that the draw bar is much smaller than the bore of the spindle make a "nut" with an extension on it that is a nice fit into the spindle and say 1 bore diameter or more long. The thread on the draw bar itself could always remain in the "nut" so no worry about bending it or damaging it.

That sort of arrangement could be turned into a screwed extractor. It needs a fixed part that engages with a shoulder and pushes in the right direction when the "nut" is unscrewed. As there is usually no or little spare space on the end of a lathe spindle the fixed part could be a suitably sized clearance slot in a plate fastened to the headstock.

All a lot of effort compared with an arrangement that can be given a bit of a whack.

A "nut" that engages into the bore of the spindle isn't a bad idea when a draw bar is used to pull work back onto a face plate. It will help keep the draw bar central and on axis. If the draw bar is at an angle it can centralise it's self while turning the part and as a result woirk loose.

John

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Edited By Ajohnw on 17/01/2016 17:36:46

Edited By Ajohnw on 17/01/2016 17:37:09

I don't know what sort of I.D. your spindle is, but is there any chance of tapping it, if it's near the tapping size of any appropriate thread, assuming also it's not thru' hardened?

Easy then to make an extractor bar.

Drawbar then easily made using a flanged bush in the end of the spindle.

A useful technique for locking and releasing tapers using a single coaxial drawbar is to use an internal thread in spindle and having a threaded bar that matches it and the thread in the collet. As long as the two threads are different pitch then the difference per rev will either draw the collet in or eject it. This takes a little thinking about but it works really well. You would obviously need some sort of threaded insert in the back end of the spindle but you could easily put a hand wheel on the end as you don't need much torque to get it all tight. I might do this on my milling machines to save all the beating they get! I had thought of getting a pre-set torque bar and using it to tighten/release the thing instead of a spanner and hammer……

Mark

EGA, yes, it is a system I have used a number of times on industrial stuff and the undoing is normally much harder than the doing up!

Have attached a diagram to explain the idea a bit for those that have never seen it.

Mark

EGA, that looks like the threads are about the same size but obviously the free end must pass through the spindle thread. In my sketch I emphasised the difference so it was obvious but as you say, as long as there is a pitch difference it will work. You can even have the thread the same size if you can find a way of putting it together (screw into the spindle first and then attache hand wheel etc. For practical applications there usually ends up being a decent diameter difference! You would also need to make the bar thick enough to prevent it buckling when pushing the collet out.

Mark

Mark C:

The diameters are respectively 7/16" and 3/8", the former chosen because the existing spindle hole was a suitable size for tapping the necessary thread. Good point about the need for adequate draw bar thickness. A thicker bar would have been impractical in my own case and for that reason I regret the trend towards 3MT tooling being threaded M12 or 1/2". I'm guessing that a thin draw bar would be even more undesirable when it is being bashed!

Talking about being "thick", I agree that the idea "takes a little thinking about" and I am still a bit puzzled by the third thread; fortunately, the thing works whether or not it is understood by the user!

Ega,

Yes, the diameters looked close in the picture.

I missed the third thread? I just sketched a separate insert piece with the larger thread on as my lathes have a large bore in the end and it would be hard to thread the spindle directly so needs bushing down. The bush would need to be fixed to the spindle to locate it and ensure it did not turn. This was why I sketched the arrangement the way I did.

For anyone thinking about this, you often have to wind the screw the wrong way to tighten up but it depends on the arrangement.

Mark

I think the OP said it was for beginners and unthreaded Myford spindle. How many beginners are going to take a cutting tool of any sort to their pride and joy.

The answer, though ungainly, might be a large G clamp modified to have a splayed fixed end to go around the end of the collet but bear on the front end of the spindle while the screw end pushes on the end of the drawbar. Myford headstocks are pretty small so the length of the arms is not too great. BIt more difficult on a Colchester.