School me on collets for the Atlas lathe, 3c, 3at,or both?

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Uncle Buck

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I understand the benefits of using collets on the lathe and their greater accuracy instead of chucks, but I have always had a poor memory regarding the Atlas lathe and collets. As I recall Atlas/Craftsman lathes when made were supposed to take 3at collets and not 3c collets. Unless I am mistaken 3at collets can be hard to find and are expensive when they are found these days. Could a guy use a 3c collet instead? If not, why not, do they simply not fit the closer and flop around?

Anyway, if you are in the know on collets maybe you might further my knowledge some. It would be appreciated. Clarity on the whole Atlas collet thing in particular would be greatly appreciated.
 
So far 27 people have looked at this thread and not one knows anything more than I do about Atlas collets for lathes? Man, I am some disappointed guys.......
 
Uncle Buck,

Since my father-in-law went into hospital a month ago, and then died, my wife has been stuck in San Antonio caring for her mother. And I've been out there about 3/4 of the month (three trips so far). So I'm not keeping up with anything fun much. :-(

Anyway, the collets that Atlas originally supplied for the 10" and 12" machines were the 3AT. They aren't too difficult to find. I have a complete 1/32nd increment set plus extras all acquired within a few weeks. What's hard to find are 1/64th increment ones. I found that Bass Tool here in Houston still stocks them and in 1/64th increments. Downside is that price is about $21 each. The draw tube is a little harder to find but not unavailable. There was a guy making an adjustable length one with ball thrust bearing that I bought first. It works fine. I later found two originals from different decades.

The differences between the 3AT and 3C are (a) 3C is about 3/8" shorter than 3AT so a fixed length draw tube that works with one will be too long or too short for the other. This can be solved by having two different length thrust bearing/centralizers. (b) threads are the same pitch and only 0.003" different in OD (3AT is the smaller) so a draw tube tapped for 3C works fine on 3AT. (c) closer taper is significantly different (3C is shorter) so to use both, you need two adaptors. Both type adaptors to fit 3MT spindle taper show up frequently on eBay.

All that being said, I do not like the 3C. I have some because of the afore mentioned problem finding 1/64th increment 3AT collets. But probably due to the shorter closer taper they seem always to jam in the adaptor when tightened. When you loosen the draw tube, you have to bang on the handwheel to get the collet to release. The 3AT ones release just by loosening the draw tube.

So you can use either or both so long as you have the proper adaptor and proper length draw tube.

The lever type closer for the 12" is extremely difficult to find. The actual draw tube assembly is the same for both 10" and 12" but the lever and the mounting brackets are different. I have most of a 10" model (everything that works with 12") but have been looking for nearly a year for the lever and brackets to convert it. I have the Atlas drawings and may eventually give up and make them.

Robert D.
 
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This thread isn't too old so I'm posting another question: I have some Precision Brand collets that don't work in my collet closer. My Royal, Hardinge, Sutton collets work fine. I see the Precision Brand collets are a little longer, maybe .08" measured in the collet adapter. What is the deal with the Precision Brand collets? Do they make a taper adapter for them that's different?

Also, here's a little more info from a nice ramble by D. Turk on another site, 2008:

The 3AT (atlas) has a different taper on the front of the collet so a 3 AT will not work in a 3C nose piece and vise versa. There is about .05 to .08 difference in the thread diameter also but the same pitch thread. What I have found is that the grater taper on the 3AT collet requires a lot more force to close and hold a work piece. The 3C collet on the other hand has a less taper and so takes significantly less draw bar force to hold the work piece. I am not sure if the steeper angle of the 3AT collet affects accuracy much but in my mind it has to. One thing that is different is because the of the grater angle on the 3AT collet it takes less movement to close it. In the cast of the 3C it reacquires more travel of the collet to close it. Just some odd thoughts about the two collets.

I personally do not like the 3AT but do like the 3C. Then I am predigest as the 3C 4C 5C collets were patent by Catarac which led to Hardinge. Least I know the 5C was patent by Catarac which Hardinge acquired when they purchased Catarac. That patent by the way ran from 1920 to 1927 and as Hardinge wonted big royalties for the use of there 1 inch collet no lathes other than the Wade 8A used a 1 inch collet till 1938 when the patent time had ran out. By the way Wade got around Harding patent by patenting there own collet. What Wade did was lengthen the thread 1/2 inch but other than that was exactly the same as the Hardinge collet. In fact Wade offered two draw bars for their lathe so you could use either there long threaded collet or you could get a longer draw bar and use the shorter Hardinge collet. The wade 8A came out in 1928. Ya and I have one. Just a little history guys that I think for the most part is correct.
 
I have a set of NOS Precision brand 3AT collets that I bought for my lathe and I've been curious to know where they were made and by whom. I don't think they are quite as nice as the name brands like Hardinge, Sutton, Royal, etc. but they seem to be adequate and are pretty common on ebay. My collet adaptor is also a Precision brand.
 
These are not 3c collets, bt I figured I would post anyways. These are called EC collets and you can sometimes find them and the chuck for a reaonsable price. I use them on my atlas lathe quite often when I need to turn and part off pieces in a succession or really want the accuracy and the ease.

IMG-20130206-00032.jpg
 
Artemetra,

My 3AT collet collection includes Precision and half a dozen other brands. After you posted your question, I compared the Precision ones to several of the others and the others among themselves and find quite a length variation. Both between collets of the same brand and between different brands, and both in LOA and in the length of the taper. I have 3AT collet drawings from three different sources, Logan, Hardinge and unknown. None agree on all dimensions. None show how long the threaded area should be. And aside from the Hardinge, the other two are missing some other dimensions. So my take on all of this is that if you have two alike with different brands or of different ages, it's a minor miracle! I found three distinctly different versions made by Precision. I didn't compare each of the other brands among themselves but wouldn't be surprised to find some of them don't exactly match.

I have never seen what I would call a collet chuck for a 3AT. Only handwheel operated and lever operated draw tubes. Aside from the little European ER types and the rubber-flex types, all of the collet chucks I've seen have been for collet sizes too large to fit into the spindle bore (like 5C). Where did you find it? Could we have a photo? As for the difference in length making some of the collets unusable, I have a 5C collet chuck for my Atlas, and it would easily handle the length variation that I found (about 1/8" total) if it were for a 3AT. It would be inconvenient to have to readjust it but the lever type closer I have would also have the necessary range. And the handwheel one would just screw on a few more threads.

Two comments on the D Turk paragraph that you copied in. I don't find that the difference in taper (about 3 deg. per side) makes the 3AT any harder to close than the 3C. I do find that the 3AT collets are self releasing and that the 3C are not. With the handwheel closer, to release a part held in a 3AT, I just have to loosen the handwheel. With several 3C's, after loosening I have to hit the handwheel with something to get the collet to release. Consequently, despite the better availability of 3C, I decided to go with 3AT. Second, his statement about the difference between the threads is approximately the difference in millimeters. He should have said so as at first I thought he was 'way off in left field.

Robert D.
 
Here are pics. Logan 820, 1946, I think the collet closer came with the lathe. No markings on it. The other pictures show both of my collet types. Left is the Precision Brand collet. Obviously longer. The Precision collet sticks out of the adapter too far even when fully threaded, unable to cinch down on the work. The closer has a stepped diameter, which is the depth stop. Now I'm thinking of machining a ring to "lengthen" the step and put the closer back by the longer diameter. If that works I'm golden.

Logan Collet Closer 1.jpg Logan Collet Closer 2.jpg Precison Brand vs Hardinge Brand 1.jpg Precison Brand vs Hardinge Brand 2.jpg
 
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