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Split Collet in blind hole

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Peter Cook 605/02/2021 18:07:56
190 forum posts
54 photos

I want/need to make a block with a split collet to connect a drive rod to a leadscrew.

The suggested method when making the collet is to use a through hole and leave a flange on the back which can be used to clamp the collet blank firmly in place while drilling the hole for the shaft.

Because of the shape of the block with the leadscrew thread at the back I can't do that. The collet body will be 10mm brass, the block aluminium. The shaft is 8mm diameter

split collet.jpg

I was thinking of supergluing the drilled and tapped collet blank into its hole, drilling the shaft hole and then using heat to get the shaped collet out for finishing.

Will superglue be strong enough to hold the blank in place while I drill the 8mm hole? Will heat be enough to get it out? Or are there better ways of doing this?


Edited By Peter Cook 6 on 05/02/2021 18:09:58

Ramon Wilson05/02/2021 18:23:34
1204 forum posts
306 photos

Hello Peter,

I'd be disinclined to using super glue on the basis that once glued in it may be difficult to remove. I know it does break easy with heat but there's the clean up to consider too though leaving it to soak in acetone soon takes care of that.

Personally if the radius is the same as a cutter I would put the half round section in on the mill after turning, drilling and tapping as one piece on the lathe - still on the stock. The back to the lathe and part off at the split and again at the finished dimension. If an odd size then a boring head.

Just my thoughts - no doubt others will have alternatives for you to consider too

Hope that helps - Tug

Alan Jackson05/02/2021 18:23:51
237 forum posts
115 photos

Just make the collet part too long so that it extends above the surface and clamp it in place endwise with a G clamp or toolmakers clamp while you drill the 8 mm hole. I found this is good enough to hold it in place while you carefully drill the hole. Cut the collet up to suit afterwards.


Edited By Alan Jackson on 05/02/2021 18:24:59

old mart05/02/2021 18:39:25
3398 forum posts
210 photos

Iwould do it the same way as Alan's suggestion.

Peter Cook 605/02/2021 19:18:58
190 forum posts
54 photos

Thanks, the clamping option looks a good one. Not sure the level of precision I can achieve is quite up to Tug's suggestion - although with three to make I might try it.

Thanks again.

Edited By Peter Cook 6 on 05/02/2021 19:19:23

John Haine05/02/2021 19:30:49
4272 forum posts
251 photos

It's a COTTER, not a collet.

John Baron05/02/2021 20:29:27
499 forum posts
189 photos

Hi Peter, Guys,

The way I would make that split cotter is like this.

Drill a hole say 10 mm deeper than the collet length with a tapping size drill say 5 mm for an M6 thread.

Open out the hole to the collet diameter for the length of the collet.

Thread the 5 mm diameter in the bottom of hole.

Drill the collet right through 5 mm tapping size for M6

Drill one half of the collet M6 clearance, and thread the other half M6.

Thread an M6 screw into the collet and screw the whole lot into the bore.

Tighten up so that the collet is locked in the bore.

Then mark out and drill the cross hole making sure that you leave a mm of clearance between the outside of the M6 collet through screw.

Disassemble and clean.

Cut the collet in half by either sawing or parting.

Make sure that you properly deburr the edges of the scallop after parting in half.

If you do it properly it will take a quarter of a turn or less from loose to locked solid on the shaft.


Here is one I made for my Norman Patent tool holder.  12 mm diameter, M6 through screw.  Note the edges at the bottom of the scallop.  Any burrs will cause those edges to dig into the bar that its clamped onto and make it hard to loosen.


Edited By John Baron on 05/02/2021 20:39:24

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