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View Full Version : Lathe Collets...A Success Story



Arbo
04-20-2006, 12:08 PM
I noticed recently that there has been alot of talk about workholding with collets on a lathe. I thought I would share my story and experience here. It is hardly a cheap solution, but if the need arises, this is one way to "skin the cat".

I own a Southbend Model A. I got a pretty good production run going of about a thousand parts for a customer. I am still working on the parts, but am meeting demand. All I had at the time for workholding was a four jaw chuck. Obviously, it was out of the question to dial in a thousand identical parts. So, I started looking at collet chuck options to fit the lathe. Some of you may remember that I asked a few questions here when the search was on. I finally settled on the ER32 collet chuck from Little Machine Shop mated to a cast iron back-plate. When the items arrived, I was dead set on making this the best set-up I could. The first thing that I checked, was to be sure that the registration diameter was concentric with the collet taper. To do this, I chucked a one inch piece of 1018 in the four jaw, and turned a section to exactly .750" diameter. This, of course, guaranteed that that piece of work was running concentric to the spindle of the lathe. With that piece staying in the chuck, and the chuck on the lathe, I attached the collet chuck to that work piece using the .750" collet. Then, I indicated the registration diameter on the back of the collet chuck, and found that it was .007" out of concentricity. I removed and replaced the chuck several times, running the same test, and got the exact same results each time. This proved to me that there was a definate run-out problem that needed a remedy before proceeding. The cure was a quick pass on the registration diameter with a carbide boring bar. The collet chuck was still attached to the .750" piece that was being held in the four jaw chuck while I did this. At that point, I ran the Starrett Last Word across everything one more time, and found that everything seemed to be dead nuts on for concentricity.

The next step, was to mate the back plate up to the spindle, and get everthing running true and repeatable there. I did the basics, by making sure that the spindle threads were clean and all. I threaded the back plate on to the spindle, and the first thing that I noticed is that it did not bottom out on the spindle boss the way it should. I turned the back plate around, and cleaned out the first few threads with a boring bar. That problem was quickly remedied. Again turning the back plate around, it now bottomed out on the boss the way it should. I didn't even bother checking to see how it was running, because all of the exterior surfaces were to get machined anyway. I started out by turning the registration diameter to a light press fit to mate with the freshly bored registration diameter on the collet chuck. I don't remember the dimensions at this point. They were really unimportant to me, as long as the two matched. I then got a nice face cut on the mating face of the back plate, and turned the OD to about .002" under the OD of the collet chuck body. Now, I removed the back plate from the lathe, transferred the screw holes on the collet chuck to the back plate. When I did the hole transfer, I marked the chuck and back plate with a marker so I knew which holes mated where after drilling the back plate for the screws. I was really carful when using the transfer punches, and then setting up with a wiggler to locate the punch marks for drilling. It went fine, but was time consuming. I really wanted everything as perfect as I could get it.

I got everything together, and mounted the chuck on the lathe. It was the moment of truth. I had a nice piece of .500" drill rod that I set up in the collet chuck, and ran the indicator on it. I am showing TIR of .0007". Quite frankly, good enough for me!

Overall, I am satisfied with the performance of the chuck. It makes for a very convenient workholding option. As most know, the ER32 collets go up to .750", and so does the Southbend through hole. It makes a pretty good common sense approach. I must admit that the quality is what is normally expected of Asian imports, but is not offensive to me in any way. If you have read this far, you have figured out that I had quite a few hours in making things right before I put it to use. To date, the approximate $400.00 investment has paid for itself if you don't count my time running the parts. It is a simple one operation to make the parts that I'm running right now, so now my time is finally worth something again. I hope that this may help others in the future who are looking for a fairly accurate work holding option.

BobWarfield
04-20-2006, 12:38 PM
Nice project. Any pictures?

BW

Doc Nickel
04-20-2006, 03:57 PM
I agree- photos?

I have an older Logan I don't use much, though I do use collets on the other machine quite a bit. I've been toying with the idea of buying one of those Bison 5C chucks they keep advertising in ENCO, and making a backplate for the Logan.

An ER collet might take a bit more work, but might be a better setup.

Doc.

Alistair Hosie
04-20-2006, 04:07 PM
Well done Arbo it's nice after all your effort to gwet such a good result.Your friend in Scotland Alistair

Arbo
04-20-2006, 04:08 PM
I didn't do a very good job of documenting the installation progress. As a matter of fact, I didn't take any pics of it at all. I will get a shot of the collet chuck in place, and post them later. If there is alot of interest shown, maybe I can work something out to document things better.

HWooldridge
04-20-2006, 08:40 PM
The overhang aspect is not good but I solved this problem by buying one of those 5C holder packages from MSC for about $40. This kit consists of two holders, two lock rings and a lever closer. One holder has an hexagonal exterior and the other is square for use in a 4-jaw. I made a manual-type closer bar for the collets to fit the inside thread. In practice, I clamp the hex holder in the 3 jaw and indicate the inside of the collet-holding taper with a dial. If it's out, I tap a bit with a soft hammer until it's true and re-tighten. I then put the collet in the holder and slide the bar thru the spindle to tighten the collet on the work. The bar is in tension with the rear of the spindle so the setup is pretty secure when everything is tight. This works well for the type work I perform but of course, is not as rigid as a typical collet chuck.