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Myford ML7 tailstock bore, and threading the barrel to fit a chuck

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Mike Donnerstag14/07/2019 10:55:31
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I have a Myford Super 7 with the Super 7 tailstock and understand that the ML7 tailstock fits on the Super 7 bed.

I wondered whether anyone can tell me the bore size for an ML7 tailstock as I'm looking into the possibility of gripping long 'bar stock' (actually violin bows) for drilling the ends. As the bow has a gentle bend, it must be held still while drilled to avoid damage.

Also, to allow this to happen, there would need to be a thread and register on the tailstock barrel to fit a chuck, similar to the headstock spindle . Has anyone ever done this? Is it even possible, as in, is there enough metal in the tailstock barrel?

roy entwistle14/07/2019 11:01:45
1005 forum posts

No 2 morse taper so actual bore will be about 9/16 inch

Roy

Mike Donnerstag14/07/2019 11:10:42
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Great - that bore will definitely work for bows up to cello size, and probably most bass bows.

Looking at the Super 7 headstock barrel, it seems to be big enough to accept the headstock thread, but I'd need to fit a separate 'register' so that a chuck can be threaded on.

Once again, has anyone done this? I know it is possible to buy MT2 spindles with the headstock thread, but I would need to use the bore of the tailstock, so using the taper doesn't get me anywhere.

Brian Oldford14/07/2019 11:47:31
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Methinks a specially made tailstock barrel might be your answer. Drilled through as large as possible and made with an enlarged end to accept a standard Myford chuck thread.

You have the machine there to make such an item.

Mike Donnerstag14/07/2019 11:54:55
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Brian: I like that idea. I assume that, to keep the whole drilling setup easy to attach and remove from the lathe, that it would be best to get a second tailstock casting, i.e. the hollow ML7 one? Or, would the Super 7 tailstock casting work?

Also, do you know the thread of the barrel? Is it multi-start?

Mike Donnerstag14/07/2019 11:55:19
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Also, do you know the length of the standard ML7 tailstock barrel?

Bazyle14/07/2019 12:16:40
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Do you need the bow to go though the chuck and down the inside of the chuck and through the bore of the tailstock barrel? As you are not using the morse taper it might be easier to use a plain bar or tube, drill a nice clearance hole then prepare for the chuck. You might make a plastic of wooden clamp instead of a chuck to avoid bruising. Again it might be easier to take off the tailstock, run the saddle down to the end and make a wooden clamp arrangement to mount on that.

Mike Donnerstag14/07/2019 12:20:38
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Interesting, though I like the idea of using a self-centring four-jaw chuck to grip the octagon concentrically (at least within a few thou). Bruising the wood shouldn't be too much of a problem as it shouldn't need to be held tight enough to bruise, and Pernambuco wood is very hard and dense.

The reason I like the idea of the tailstock is that the alignment with the headstock can be easily set and relied upon.

Bandersnatch14/07/2019 19:12:17
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Posted by Mike Donnerstag on 14/07/2019 11:54:55:

it would be best to get a second tailstock casting, i.e. the hollow ML7 one? Or, would the Super 7 tailstock casting work?

Check the cost first. Or perhaps you're seriously rich (based on my experience to replace a broken one some years ago ..... I ended up doing a repair).

frown

peak414/07/2019 20:17:50
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As an alternative and maybe cheaper/simpler method, how about a metal block bolted to the slots on the cross slide, and machined to hold the bow.
Either the block could be made to hold a chuck, or could just have a simple V at centre height with an appropriate clamp, a bit like a normal V block?

Bill

Mike Donnerstag15/07/2019 10:48:06
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Bandersnatch: I can't say I'm seriously rich, though the £100-odd ML7 headstocks seem to be going for on eBay looks reasonable if it's a solution to the stick-drilling problem.

peak4: This was my original idea, though I expect lining everything up would take some time, whereas a tailstock setup would simply slide on and off and I expect its alignment with the spindle axis would be more reliable.

A commercial tool, which is basically only a self-centring vice and drill guides, costs £600-ish and has to be imported from America. It's called the Bow Badger:

And below, in use:

I'm sure there is a better and much cheaper way to do this!

Edited By Mike Donnerstag on 15/07/2019 10:50:04

Robert Atkinson 215/07/2019 13:09:36
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How about a ER32 collet chuck on the tailstock? They will grip a round or hexagonal bow end quite well. You could even make a split nylon sleeve with a hex centre hole if you needed to grip tight without marking. Possible an adaptor tube to slip over the outside of the tailstock barrel and carry the chuck to maintain the full bore clearance.

Robert G8RPI.

Mike Donnerstag15/07/2019 13:27:29
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It's a good idea, in fact I have an ER40 collet chuck with a full set of collets, however I would prefer the self-centring four jaw chuck that I also have because it grips on the flats rather than the corners of the octagon. A split nylon sleeve with an octagon (not hex) centre seems like a solution, though there are so many variations on bow stick size that I would have to make several.

Mike Donnerstag15/07/2019 13:27:56
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Thinking about it, I probably should have renamed this post 'Myford Hollow Tailstock Drilling Fixture'.

Michael Gilligan15/07/2019 15:42:52
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Given the intended use, Mike ... I think you could get away with a slip-on/clamp-on mounting for the chuck backplate, instead of cutting a thread on the barrel.

MichaelG.

JasonB15/07/2019 16:27:23
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Am I missing something as I can't see how you will be able to advance the tailstock mounted chuck towards a driven drill bit if the bow is poked down the tailstock barrel and out the back so no screw can be fitted. Or will you just slide the tailstock or it's barrel by hand?

mark costello 115/07/2019 17:25:34
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Does ER 40 have a square collet available? Or could You make a square adapter to suit?

Edited By mark costello 1 on 15/07/2019 17:26:16

Howard Lewis15/07/2019 17:45:27
2149 forum posts
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As far as I know, only 5C collets can be obtained for square or hexagonal stock.

I wanted some ER32 collets to hold MT shank reamers. So I made my own versions.

No doubt it would be possible to make something similar for square material.

Some time ago there was an article on making accessories that would fit in a round collet, or three jaw chuck, to hold square stock. Cannot recall all the details, but the finished article, was actually the raw material machined and then cut into four pieces to act as the four faces of a square collet..

No doubt, some kind soul will say which Issue of MEW it was in?

Howard

DC31k15/07/2019 17:47:19
42 forum posts
Posted by JasonB on 15/07/2019 16:27:23:

Am I missing something as I can't see how you will be able to advance the tailstock mounted chuck towards a driven drill bit if the bow is poked down the tailstock barrel and out the back so no screw can be fitted.

ML7 tailstock is hollow. Hence why it is not self-ejecting unlike Super 7 which is not and which is.

9/16" bar goes through. 5/8" bar does not.

Barrel diameter is 1".

Make thick washer ID 1", OD 1 1/8". Loctite ID to barrel. Loctite OD to chuck register.

If force of drilling overcomes loctite, use MIG welder.

JasonB15/07/2019 18:22:56
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Thank's DC31K, I can see now that it is threaded externally so no leadscrew to get in the way of the bow.

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