Building an ER collet chuck from scratch for a Myford ML7

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arnoldb:
John, Stew - Thank you - much appreciated feedback!

At least a little less elbow grease on that then :D

Kind regards, Arnold

arnoldb:
Well, new start today...
Cleaned up the new chuck body:

Then switched to the 4-jaw and drilled consecutive through-holes to 16mm, and tried my hand at an action shot while drilling on fast back-gear to 19mm (my biggest drill) to spindle-depth:

And bored the register to size using a carbide tipped bit that I honed on a bit of emery:

After this I bored out for thread run-out in the back; slowest back-gear speed & PLENTY of lube with frequent stops to clean out the swarf ribbon. Thought it might be more difficult, but came out well. Then I set up the change wheels for the internal thread, and set up for the single-pointing. Decided to stop there, and do the thread tomorrow when I'm fresh.

Cheers, Arnold

:nrocks: :nrocks:

Gerhard Olivier:
Nearly back on track again Arnold. I used my collet chuck again yesterday and I think you are going to get a lot of use out of the ER collets- one of the big points is that it doesnt take up as much space as a 3-jaw chuck.

"Fresh" for the single pointing sounds like a good idea.
BTW that looks a nice piece of metal ?big bolt

Gerhard

sbwhart:
Going well Arnold :thumbup: it will be a real useful bit of kit when complete.

Cheers :beer:

Stew

arnoldb:
Thanks Gerhard, Stew :)

Gerhard yes - a bolt... Slightly over sized for my modeling needs :lol: - nice steel as wel, but a regular bugger to get a decent finish on.
Stew, I've been literally dreaming of getting a collet chuck - seeing them used so often just pushed me, plus it seems (from another forum) this build has started a bit of :proj: Didn't know I was opening a can of worms here without going fishing :lol:

Well, a good result for today :) :ddb: :ddb:

This afternoon I started by turning the spindle thread in the chuck body. A close-up down the register and thread - the pool of cutting fluid in the back is collected in the thread run-out:

Once I was happy the thread was well-done, I unscrewed the 4 jaw with the chuck body still in it and tried to screw the whole assembly onto the spindle from the collet chuck body. The register was a touch too tight, so I turned it around again, and used some emery & oil to open up the register a bit more. With the next test it fit very acceptably.

Removed the collet chuck body from the 4-jaw, and screwed it straight to the spindle. Then turned down the nose end to size for the collet closer nut:

Once again the undercut using a parting tool - slowest back gear speed, as this steel is fairly tough:

Threading nearly done:

I tested the final thread size by trying to screw on the closer nut after cleaning the threads thoroughly on each attempt. Once it screwed on full way, but slightly stiffly, I used a fine triangular needle file just to give the threads a final cleaning - after this the closer nut spun on easily, but not loosely.

Now came time for the internal taper for the collet. I first tried the following to set the topslide to taper:

Something "felt" wrong at this point :scratch:, so I tested a couple of different collets and got readings all over the show :hammer: :smart: They are all already slit and spring loaded, so there would be differences. I settled on trusting mr. Myford :D, and just set the top slide to 8 degrees, making sure the boring tool was set dead on center. I know there are other ways to set an accurate angle on the top slide - but was not about to go down that route :coffee:. A blue test while the hole was still slightly undersized would suffice, and that's what I did, using the 10mm collet and a known-good piece of 10mm silver steel, long enough to be clamped on it's entire length. First off, blued the collet and inserted in closer, then inserted test bar:

Then screwed the collet up tight into the chuck,carefully keeping the collet from touching the chuck initially and keeping it from rotating as I did this. Reversed out the collet, once again preventing rotation and trying not to let it "drag" in the chuck - got the following blue marks in the chuck proving that the entire length of the collet was clamped adequately and evenly:

After this I turned the taper to just under full-size and carefully smoothed it off using some emery superglued to a wooden dowel & oil. Then I played around with removing the chuck, installing it, chucking up different workpieces repeatedly in different rotations and a whole combination of the previous. Biggest run-out I measured was less than 0.005 mm (less than half a division on my 0.01mm guage) - that's about 0.2 thou - I think that's acceptable :headbang:.

Some cosmetic work externally (well, it's not a beauty :lol:) and here is where I left off for tonight:

Tomorrow I'll cross-drill a couple of holes to take a tommy bar in the chuck body, as it is too smooth. At a later stage, I'll knurl a ring grip on the body as well; first need to get some knurling wheels and build a tool :dremel: :proj:

So, that's my version of a collet chuck; pretty it's not :lol: , but, like Stew said, I really think I'll enjoy this addition to my workshop in upcoming projects.

:beer: , Arnold

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