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

[wa5cab]

Artemetra,

Thanks for the photos. That is a fair amount of length difference. But about the same as the max delta-L out of the assortment of 60 odd collects that I have. For reference, all three of the collet drawings that I have agree that the length from the left (threaded) end to the large end of the taper should be 2-5/16" AKA 2.313".

However, if that amount means the difference between working and not working, the spacer/pilot/thrust bearing next to the handwheel on your closer is too short or thin for your spindle. I have three handwheel type collet closers. Two are Atlas originals, one early and one late, that I finally found after some time looking. The first one that I bought has the handwheel and spacer adjustable. So I can use it on 3AT or 3C collets. My rule-of-thumb for adjusting it is that when the draw tube is screwed about half-way onto the collet (typically 7 or 8 threads) the pilot should be against the end of the spindle and the collet should be fully in the adapter but not squeezed any. If you make a spacer to go between the thrust bearing and the wheel of a thickness such that the above rule is met for the rest of your collets, the Precision ones will work fine. You will probably need longer flat head screws.

Robert D.

 

[Artemetra]

Thanks Robert, interesting thoughts. Basically I think I can work it out now - but not quite like you put it. The thrust bearing on this setup isn't doing anything. Maybe that tells me that the wheel collet closer isn't original to this lathe. Somehow, the tube hits a shoulder inside the spindle, and that is the stop. The thrust bearing is a couple inches back from the rear of the spindle, not touching anything when you have a collet with workpiece tight in it. If you were to somehow push it all the way in, the wood would rub on the cover anyway. So Maybe I can make a larger spacer for behind the spindle that will use the bearing, or just a little sleeve that goes inside the spindle. I'll post when I get to it.

 

[VSAncona]

I have three handwheel type collet closers. Two are Atlas originals, one early and one late, that I finally found after some time looking.

Robert D.

Robert -- Do you have any photos of your early Atlas handwheel type closer. I'd like to find one for my Atlas lathe and it would be helpful to know what I'm looking for. The one I have now works okay, but I don't think it's original to the lathe. It's an inch or two too long.

 

[wa5cab]

Artemetra,

Either you collet closer wasn't made for the lathe you have or it is missing a part. Or both. All handwheel operated drawbars and collet closers I have ever seen for any make machine take the thrust against the left end (or the top on a vertical mill) of the spindle, not against some shoulder down inside the spindle. I think that your closer is missing the actual thrust bearing. Possibly the nose of the draw tube is stopping against the left end of the adapter. I never saw any hollow lathe spindle that wasn't the same ID throughout.

Try this. First, with the adapter loose, load one of your shorter collets into it. All threads and the relief groove should be visible. If not, your adapter is too long. Then, put the adapter into the spindle nose, load a collet into the adapter as far as it will go without pulling on it, slide the drawtube into the spindle, and screw it onto the collet 7 or 8 turns. Pull lightly to the left on the handwheel and measure the distance between what I was calling the thrust bearing on your handwheel and the left end of the spindle. As a check, push to the right on the handwheel and the collet should come out of the adapter a little ways. This confirms that the drawtube nose isn't hitting the adapter when it is where it belongs. Make a steel or stainless steel thrust bearing about 1/4" larger in diameter than the drawtube and a little longer than the measured distance mentioned above. Bore it until the ID is .005" larger than the diameter of the drawtube. Bevel one end at 45 deg., leaving just a barely visible flat on the end, and gently deburr. Temporarily assemble everything and tighten the drawtube until the collet is just beginning to compress. Mark the top of the handwheel so that you can count turns and back it off until it comes loose. Shorten the thrust bearing until the answer is between 7 and 8 threads engaged when it goes tight. That should allow you to use all of your collets.

Robert D.

 

[wa5cab]

VSAncona,

I have in Atlas catalogs of various dates seen three different Atlas 3AT collet drawtubes. The photo shows what I think are the second (left) and third (right) variants. The first was very similar to the second except that the handwheel was round instead of octagonal. The thrust bearing on #2 is crimped or swaged so tightly to the tube that it is immovable. I may end up having to machine it off. I am not certain how #2 was made. One would assume that probably the handle was cast, the tube machined from heavy wall tubing, and pressed into the wheel. But in the bore I cannot see a parting line so it could have been cast as one piece and then machined. In #3, the wheel is cast aluminum. The alloy steel tube was pressed in and secured with a short Allen set screw. The thrust bearing on #3 was actually made by the person whom I bought the drawtube from but looks like the photos. It is a bare slip fit on the tube, about .002" running clearance. #2 is probably cast SS. I do not know the purpose of the two holes in #2's wheel. They may not be original as they are sloppy and both need deburring both sides.. The OD of the two draw tubes are not quite the same. #2 is 0.772" and #3 is 0.745".

Robert D.

 

[iron man]

Forgive me for asking but I have never used a collet in my life if I could not four jaw it and get it accurate I would give up. But I still find it interesting, since the Atlas has a MT3 tapper cut into the head why cant you use the much cheaper MT3 mill collets??? they seem to come in all sizes and making a rod to tighten them up would be a walk in the park.. Ray

 

[VSAncona]

Forgive me for asking but I have never used a collet in my life if I could not four jaw it and get it accurate I would give up. But I still find it interesting, since the Atlas has a MT3 tapper cut into the head why cant you use the much cheaper MT3 mill collets??? they seem to come in all sizes and making a rod to tighten them up would be a walk in the park.. Ray

You certainly could use the MT3 collets with a drawbar for short workpieces. The advantage of the 3AT collets is that they tighten with a hollow draw tube, so you can have a long piece of stock passing through the tube. If you're making a bunch of identical small parts, it's easy to simply turn a part, part it off, loosen the collet and slide your stock through for the next part, re-tighten the collet, and start turning. There's no indicating required.

- - - Updated - - -

Robert -- Thanks for the photos. Mine looks different than both of those. I'll try to take a photo my setup and see if anyone here can identify it.

Vince

 

[Artemetra]

Robert, that's hilarious! I made the very part you describe, with those exact details, before your post. It works like a charm. All the collets, not just the long Precision ones. You're right, there was something missing. Thanks for the help!
Btw, I wanted to get the collets going for this lathe because they are the WAY TO GO! Iron Man, try the setup (buy the parts you need if you don't have them) it's a sweet way to go. If your lathe can use a lever-style drawbar/closer, well then you're in the money if you have to make more than three pieces or so.

 

[Restorer]

View attachment Collet Adapters.pdf

The attached PDF shows basic dimensions for each collet configuration.

Manufacturers take liberties and change dimensions especially in Asia.

Hope this helps. Perhaps Nels can copy the drawing to the lathe download section.

 

[wa5cab]

Ray,

In addition to what has already been written about long stock, there is one other issue between 3MT (or 2MT) and 3AT (or 3C) collets. AFAIK, no one makes 3MT collets in increments smaller than 1/16". If your need or interest in collets is for holding milling cutters, neither that nor the drawbar being in the way is any issue. It's relatively easy to buy end mills in 1/64" increments with shanks in 1/16" increments. And the 2MT or 2MT collet sets are cheaper both because they are easier (and cheaper) to make and there aren't as many of them in a full set. But if you need collets for holding small work pieces, 1/16" increments just isn't good enough.

Robert D.

Forgive me for asking but I have never used a collet in my life if I could not four jaw it and get it accurate I would give up. But I still find it interesting, since the Atlas has a MT3 tapper cut into the head why cant you use the much cheaper MT3 mill collets??? they seem to come in all sizes and making a rod to tighten them up would be a walk in the park.. Ray