Retrofit ER-32 collet chuck to an Atlas/Craftsman 618

Hey, Rangemaster1. Welcome to the forum! That powered compound is disclosed in this thread:

http://www.hobby-machinist.com/showthread.php?t=24766

I see you're into gunsmithing. A noble trade.
Now I'm wondering if I should post up some amateur acccuracy mods done on this lathe, in the gunsmithing section.

By all means, please do! Gunsmithing is near and dear to my heart as well. I would love to see some of your work in that arena.
 
Hi, Rick. Okay, great, the votes are in. I'll post some when I get a round tuit...
 
Next up was the ER32 high-dollar, high-precision SYIC Techniks 5/16" collet.
It also is much better quality, smooth bore finish, proper chamfering of bore edges, no buffing wheel cover-ups.
But, it also had numerous nano-sized metal hairs emerging from the slits. So, cleaned them out with a fine dental pick.

After fitting to the mandrel and painted. Checked its taper with the dial test gauge, almost dead-on.
Started with a light 0.0005" cut, and let the powered compound make several passes until spark-out.
There was very slight wasp-waist shape, and it was barely eccentric.
It was so close that it cleaned-up on that first cut setting. Finished it off with the craytex, oiled, and put it away.


Last was the 1/4" collet. This one blew me away. :faint:
First, it wasn't a 1/4" collet, it was a 6mm collet marked 1/4". :headscratch:
Then, after mounting, found its taper was so far off, that I had to stop and double-check my setup.
Sure enuff, its supposedly 16° taper angle worked out to 17.25°.
And worse, it was extremely eccentric (by several thou) and WOBBLY! :wantmommy:

Started the cuts, and they revealed the seriousness of the issue.
In this pic, you can see the severe out-of-taper. About 0.005" of the radius has already been ground out, long way yet to go.
Circle #1 - The sides aren't even straight.
Circle #2 - You can see the rough machining. The polisher guy apparently missed this one.
ER32-Grind6mm.jpg


So, decided to stop here for awhile. Let the machines and me cool-off.
Submit this post, and take a nap...

ER32-Grind6mm.jpg
 
Well, time for an update.

I wasn't getting the accuracy I was expecting after grinding the 16° tapers on the collets.

So, decided to repeat the whole mandrel/regrind procedure on the top 30° taper of the collets. Glad I did. Some were way off.

The 3/4" collet top taper had a severely and strangely stepped offset.
ER32-TopGrind-01.jpg

The 5/8", 1/2" and 3/8" collets were close, not as bad, but still needed cleaning up.
The hi-precision Techniks 8mm collet top taper was dead-on.
The hi-precision Techniks 5/16" collet top taper was extremely close.

The budget 8mm collet top taper had the wrong taper and an offset.
ER32-TopGrind-02.jpg

The 1/4" collet top taper also had the wrong taper and a severe offset.
ER32-TopGrind-03.jpg

Next will be as-fitted accuracy measurements...

ER32-TopGrind-01.jpg ER32-TopGrind-02.jpg ER32-TopGrind-03.jpg
 
More updates.

Still not getting the accuracy I was expecting after grinding the 30° top tapers on the collets.

I was thinking that the 16° chuck cavity would be doing the bulk of the centering, and that the nut (with its slight looseness) would naturally center on the collet's top taper, and simply squeeze the collet into the body. It appears that the nut has a greater influence on collet centering than I originally thought. This is turning into a real challenge and learning experience.

So, I decided to chase the metric 40x1.5mm collet nut threads on the chuck body, concentrating on the important thrust side of the threads. Cut a thread relief area behind the threads, did the changegear approximation for cutting metric 1.5mm threads, and synchronized the threading bit to the existing threads.

A couple of 0.0005" skim passes on the thrust side of the threads got them concentric.

ER-ColletChuckThreading.jpg

Fitted a plastic crush/loading spacer inside the collet nut, so that the nut could be align/tightened to the chuck, and checked the runout of the as-loaded nut's 30° taper.

It, too, was a little off, about 0.0010" TIR. So, did a light skim to recenter it.

ER32-ColletNut.jpg

We'll see how this works...

ER-ColletChuckThreading.jpg ER32-ColletNut.jpg
 
Well, this project has been an exasperating learning experience. After all that work to precision grind the collet chuck and collets, testing the runouts were horrible and inconsistent, anywhere from 0.001" to 0.003".

So, suspecting the clamping nut, I fitted a 3/8" test bar by pressing in a collet without the nut. The 16° taper is narrow enough to solidly hold the bar as-is.

ER32-Nut-Minus.jpg

Well, whattya know. I got runout of ZERO at the collet face, 0.0003" runout at the 3" position. THIS is what I wanted.

Sure 'nuff, isolated the problem to the collet nut. Long story short, the clamping nut was made to the wrong dimensions. Its extractor ring was contacting the rear collot groove face when the nut was tightened. The distance from the clamping nut face to the backside of the extraction ring was over 9.5mm, and inconsistent. I believe that for the ER32 clamping nut this dimension is supposed to be 8mm, which would allow for the collet to cleanly penetrate into the nut's 30° taper for the full clamping range. From what I can tell from measuring the inner dimensions of this clamping nut, the feature depths were made to the specs of the ER40 collet system. I shaved 0.030" off the backside of the extraction ring, leaving just enough for it to work, the runouts improved markedly, but now I had no collapse clearance.

Hopefully, this pic identifies the issue:

ER-ColletNutWarning2.jpg

Dang it, I liked that nut. Knurled and large enough to hand tighten, with a handy tommybar hole. So, decided to order (2) ER32 nuts off eBay (The $8 versions).
If you study this pic, comparing the original nut on the left with the new ones on the right, you may be able to see the difference in the width of the 30° contact face, as though it were an ER40 nut.

ER32-Nut-New.jpg

The new nuts were rough inside, with curls of metal dangling from the ends of the threads, and coarse finishing of the extractor ring edges, making collet insertion difficult. Fortunately, the threads and clamping face were like finish ground. Cleaned them up and chamfer/polished the rough extractor ring edges, collets fit much easier now. They also didn't have the telltale notch/mark for the extraction ring, so ground little dimples in the nut body adjacent to the wide part of the extraction ring, per Rego-Fix.

Tried both new clamping nuts, on 1/2", 3/8" and 5/16" test bars. The first one gave 0.0005" to 0.0008" runouts, the second one produced 0.0001" (at collet face) to 0.0003" (at 3" out), much better.

ER32-Nut-SelectNew.jpg

It appears that the clamping nuts have a much stronger influence on accuracy than what I was expecting. Lesson learned.

I'll settle for this second one. For now.

ER32-Nut-Minus.jpg ER-ColletNutWarning2.jpg ER32-Nut-New.jpg ER32-Nut-SelectNew.jpg
 
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