View Full Version : 5C Collet threads

01-14-2007, 01:43 AM
Tomorrow I get the great fun of single pointing the 5C threads inside new closer tube.

Speaking of which, I checked my old tube with my trusty Mitu Digi Calipers and found that it was 1-3/8 x 1/8, called my local steel suplier, and much to my dismay, found out that they had it in stock and it would only cost me $12 for 24" cut to order. So I picked it and went to stick it through my spindle to true it up, only to find out, it would not fit. Using a Mic, I find that my original tube, which slides in smoothly, checks at 1.364, only some 0.010 smaller than the DOM which actually checks 1.375. WTF! Who decided to make that spindle hole a few thou under 1-3/8? Lovely, I can't even face the tube so I can run it on centers and turn off the 0.010 (as if that alone on a 24" tube is not bad enough) :( On the up side I got to play co-pilot on a wonderful MoriSeki today that was almost as good as, well, you get the point. I almost felt like smoking a cigarete after watching that thing run... <deep sigh>

Back to my point. The Handbook says the 5C has a 1.238x20 RH thread. What would the major and minor diameters be for single pointing this puppy? Any advice on getting it REALLY right the first time? I’ve turned inside threads before, but with varying success, and I want this to fit smoothly and easily with no slop or bind. I may even decide not to rebuild my Royal Lever and just go with a hand wheel, which places even more importance on good threads at the collet. I have a relatively low use odd-ball collet I’ll be using as a test plug, but I could use some additional help...

Thanks for any help you can provide.

01-14-2007, 08:07 AM
I don't have the book in front of me but I remember making some 5C collet stops and having a difficult time finding information on that particular thread, good luck.

01-14-2007, 08:45 AM
Nobody said it was supposed to be easy. If it was, anybody could do it. 1-3/8" is the most common size for 5C draw tubes, maybe Rockwell had a better idea.

The minor diameter can be obtained be dividing 1 by the thread count, and subtracting the result from the major diameter. In this case; 1/20=0.05. 1.238-0.05=1.188. The major diameter will be determined by the fit of your collets.

The original Hardinge collets are 1-15/64"-20, and that is what they measure. You might want to check the collets you will be using for the actual dimension rather than using some other reference, as they do vary between manufacturers, the Chicom being the worst. At any rate, the best method for determining the fit is the actual fit of the collets on hand. If you have a mixed lot, try one from each manufacturer.

kap pullen
01-14-2007, 09:44 AM
Rockwell probably used standard tube but ran it thru the centerless grinder
to true it up.

That is standard procedure in many cases. Another example is the use of 1.937 tgp shafting in airconditioning units.

You can fact the tube with a pipe center, or a spider, at the tailstock end, chucking inside on the tip of the jaws.

I assume you don't hane a steady because it wasn't
mentioned before.

Use a parting type tool and "back face" down almost to the jaw and finish with a file or scraper.

I c'bore a tube like this to the major thread dia maybe 1/8 inch deep and chase untill the threading tool scrapes the c'bore.

This gets you within a couple thousanths of finish size and ready to start testing with a collet.


01-14-2007, 10:02 AM
If you do have a steady rest handy you could always face it by supporting one end in it. If your tailstock is on center, you could check it first by sweeping it with an indicator, you can use an indicator clamped to a live center to indicate that end in. You turn the center and peck in the end and then adjust the steady rest. This assures that everything is running nice and true. After facing then run as you had planned between centers and finish out od. By the way, keep a close eye on the part up at the chuck end while facing it in the steady. Parts have a tendancy to walk out of the chuck when run in a steady if they aren't running completely true. If it is a light part and your lucky you might get by with no damage, if it is a heavy part it could break your steady rest or you depending on how it feels at the moment. Be careful and good luck.

01-14-2007, 11:44 AM
I have posted this before, but to reiterate, measure your collet thread OD on all your collets before cutting the closer thread. Nothing like 'finishing' the thread and then finding 3 collets won't screw in and 2 are tight while the rest fit fine. I ended up having to coat the threads with lapping compound and running the tight ones in and out repeatedly under power before the collets all would fit. Picking up an inside thread is dicey. Actually doing the threading was a piece of cake IIRC, and it would have been sooo easy to take another 2-4 thou cut for the tight threads before taking the piece out and checking it.

I also had a problem with the closer tube being just a bit over the 1.51" ID of the spindle and had to turn it down before finishing, but the part where the collet threading was done was a separate piece as the ID of the closer tube was larger than the thread diameter. Locktite has held the two pieces together so far.

01-14-2007, 12:51 PM
Kap : What does ( That is standard procedure in many cases. Another example is the use of 1.937 tgp shafting in airconditioning units.)

tgp Mean ? Thanks Chris

01-14-2007, 03:35 PM
T(urned)G(round)P(olished). Shafting with a very good finish diametrically accurate to about 0.01". Not quite as nice as Thompson shafting but cheaper. Sold in 18-21' lengths, wide variety of sizes. There is a numerical designation which escapes me now.

01-14-2007, 05:55 PM
sch Thanks , never would have guessed. Chris

01-15-2007, 05:38 PM
Ok, got side tracked a bit, guess maybe I’ll finish it in the next day or so.

Looks like that’s what I need. So I guess I need to turn the ID to 1.188 and start the thread, going deeper until all my collets fit smoothly (starting with the newest, least used looking thread). My collets are all Hardinge.

I got it all turned and fitted now, with very little slop, just enough to slide smooth. And you are correct, I had no fixed steady to use for cleaning up the end. I sorta kicked getting my mystery steady adapted into "high gear", but in the end, it was quicker and easier to run down and use the Mori. Not sure what the “back face” is about. But thanks for the idea on the major dia c-bore, never would have thought of that...

Yeah, I put off my steady adaptor project till it bit me in the behind. :(

Also good advice, thanks...