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This time I'M SURE I invented a new fixture


Jun 23, 2002
Vancouver BC Canada
Good morning All:
So, the last of the workholding tooling for the DT-2 I'm tooling up for a customer.
Early in August I was all proud of the gadget I showcased then.
Sadly my bubble of self congratulation had to be busted, but it was done so gently that now I'm crowing again.
Again, it's simple in concept...just an ER 20 collet chuck that will be mounted to the TRT 100 on the Haas DT-2 for clamping skinny round slugs and parts

But this one is DIFFERENT;
I modified the Hell out of it so it can do two new things:
1) I built a dead length stop that sits in the chuck body but can be removed at will and can be adjusted for length from the business end instead of from the back.

2) I put in a hardened key and made 7075 aluminum emergency collets that are slit like 5C collets so they collapse only at the front end and cannot rotate, so I can grab small and really skinny little plates when I need to (which is fairly often).

Here are some pictures:
This is a side by side of what I started with and what I ended up with:
comparison old vs new.JPEG
A quick shout out to Frank Mari...nice collet chucks and very reasonable in price.
Obviously the key is not in yet but the slot is burned for it.

Here are the guts for the stop:
layout 2.JPEG

Here are an ER 20 collet and an emergency collet side by side:

Here's the key laser welded in place (it's hardened and I know exactly how wide it is so I can make the collet keyways with 0.0005" clearance so the collet won't rotate at all:

Here's a little collar with prongs that fit in the collet slots like the pins do in a stock 5C emergency collet:

And finally, here's the whole works together, but without the stop in place:
Obviously, the collar is so you can preload the collet and mill or turn or sinker EDM a pocket into it for holding your little tiny robot parts.
Afterward, you pull out the little collar so you can squeeze your parts.

Here's a pretend part of a kind that's very common for me to have to make for these guys...it's 10 mm OD and the round flange is 1 mm thick.
Obviously in production you'd do these on a Swiss with a sub and live tools, but for prototyping, this works well:
So that's it...my big trick.

Tell me what you think.


Last edited:
Marcus, how do you lock the depth stop from the front? Long thin nut driver? Custom tiny crowfoot wrench? Any trick for keeping the stop from turning as you tighten the lock nut?
Hi sfriedberg:
I made the thread for the stop tight-ish so you need to put a 3/16" socket wrench on the hex end to adjust it.
I just use a 5/16" hex driver that's had the center bored out to clear the post, for tightening the jam nut.
It works really well.

To keep the whole thing from just rotating in the collet chuck body, I partially slit the sleeve in four places with a jeweler's saw and pipe tapped the end.
Then I turned down a pipe plug really skinny and burned a new hex hole into it...that's the expansion plug to force the split sides against the inside wall of the chuck body.
A snap ring behind the whole works keeps the stop from shifting axially even if you reef on the collet nut and force the part hard onto the stop.

So it's a pretty simple, easy to make design and it's really robust...I can control the overall height of a part pulled against the stop by the collet within half a thou.


Hi rklopp:
Yep...good eye.
I was too lazy to set it up on the mill and slit it with a saw or set it up on the wire and burn it (actually I was impatient and wanted to see if it would work)
They are pretty disgraceful looking cuts, I do have to admit.

I'll probably keep that one and make a more professional looking replacement for them...I made one of these contraptions for myself when I made the one for them, so they can get the good one.



Hi again rklopp:
Yeah, some of what I knock together "Not for Public Consumption" looks pretty rough...I think we all do it from time to time when we get impatient or have a brain fart.
I've learned to forgive myself.

It's when I have to give myself a good kick in the ass after fucking up a high value part because I got sloppy...that's when it makes me wanna cry!
I'm pretty sure we all do that from time to time too.

So I'll chisel the Bondo back off the statue and try to redeem myself...BTW I got a real good chuckle out of that remark.