ER32 Collet Block Design

[sparky961]

Greetings all,

I've recently been working on some smaller precision parts using a lathe collet chuck and collet blocks on a mill.  For this, I've been using someone else's 5C collet block set, and although I find it to be a very nice and extremely useful tool, I'm the type that tries to improve on everything - even if it doesn't need to be improved...

Now, before you go off on me, I'm aware of the ER32 (et al) collet blocks of the Stevenson design at Arc Euro.  They look like a very nice design and from the comments people have made here and elsewhere they seem to be decent quality and fairly priced.  But (there's always a "but") I'm in Canada, and although I didn't go through the whole process of signing up and finding out the shipping rate, I doubt that shipping + customs + local tax + god-knows-what would actually result in a final reasonable price for me. 

Here's a free plug for those people to whom it would make sense though: http://www.arceurotrade.co.uk/Catalogue/Collets/ER-Collet-Fixtures

In my case, I'm considering building my own.  To repeat the sentiments of others, ER32 is much more universal/useful than 5C.

So enough rambling.  What I'm considering is a combination square/hex block.  Why, instead of the typical set of 2?  Well, with the equipment I have at hand and the time it will take I'm thinking making one with the level of precision I'm after will take enough time.  The combination block I'm envisioning would take less time than making separate square and hex ones.  Maybe I'm giving away a great idea for a patent, but I've never had any use for patents.  The long and short of it is that I don't have years and years of experience using collet blocks and I'm looking for some input from those who do on whether this design would work well.

Here's the basic idea:



The finished block would look something like this (without modeling the threads or nut):



In the 90 degree (square) mode, these two images show where you'd clamp and reference:





Now here's where things get a bit tricky.  With a standard hex collet block, I'm thinking the point between two flats would usually sit on the bottom of the vice and function as your reference.  Since we've cut off two of those points, that doesn't work anymore.  The solution is easy though, use two 1/2" (actually anything between about 1/2" and 1" should work) rods as parallels and reference off the flats:



I have quite a few ideas how to fixture this to facilitate very accurate machining, and if I'm not happy with the results thereof I may undertake some surface grinding but I think careful machining will give satisfactory results.  For the use this will get I won't likely harden it either.  Maybe make it from 4140HT to give some toughness.

Thoughts?  Your constructive criticism would be appreciated.

[DMIOM]

......Now here's where things get a bit tricky.  With a standard hex collet block, I'm thinking the point between two flats would usually sit on the bottom of the vice and function as your reference.  Since we've cut off two of those points, that doesn't work anymore.  The solution is easy though, use two 1/2" (actually anything between about 1/2" and 1" should work) rods as parallels and reference off the flats:


.....

Re the last photograph, using that pair of rods will, I think, only work if there's a completely flat base and two jaw faces which extend fully down to the base (which many don't). You'd need to check your vice ....

Dave

[sparky961]

Re the last photograph, using that pair of rods will, I think, only work if there's a completely flat base and two jaw faces which extend fully down to the base (which many don't). You'd need to check your vice ....

Dave

True enough.  The vice that came with my combo-mill is as you describe, and the pictured setup wouldn't work.  However, a small V-block underneath, or a custom V-block with 120 degree included angle would work.  Even a bar with a slot cut into it would work nicely.  Certainly more setup than just the standard hex block though.

I should add that I'm designing this mostly for use in a typical "Kurt" style 6 inch milling vice.  Those jaws extend effectively all the way to the bottom.

[Ugluk]

Why not just make it twelve-sided?
Or am I being stupid?

[sparky961]

Why not just make it twelve-sided?
Or am I being stupid?

Stupid? No... you're just pointing out the obvious fact I should have noticed. ;)

The only potential drawback I can see with this is reduced clamping surface.  But it's not like you're going to be hogging off material when using this.

I like it.  Makes for easier setup.