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.640-26 tap for 3C collets?

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  • .640-26 tap for 3C collets?

    Hello, a very kind friend recently gave me a dozen NOS Hardinge 3C collets, all new in the box and cellophane. I would like to use these on my SB 9C lathe, but I am lacking a drawbar. I have found various plans for these on the web, and I already have a 3MT>3C spindle nose adaptor.

    My question is this: Does anyone sell a .640-26 tap which I can use in making my drawbar? My threading mojo is not very good , and internal threads are something I am yet to attempt....I suspect I will get much better (and more immediate) results from a tap (if one exists).

    My intent is to thread a small tube for the collet threads, then braze/solder/weld/pin this to the business end of a bar. Is this viable for a collet drawbar?

    One final question, where can one aquire custom-ground 3C collets? I would like a couple custom fit for Mod.98 Mauser firing pins. Many Mausers were souveniered from WW1 and 2, but many had the firing pin tips snipped off as a crude demill. I'd like to be able to accurately machine down the broken bit and add a new piece to give an effective repair.

    Thanks in advance for any thoughts, ideas, or advice!

    Regards, Ken

    Spandau
    Senior Member
    Last edited by Spandau; 02-17-2009, 02:08 AM. Reason: added image

  • #2
    You might be able to talk Hardinge into making custom collets, but they would almost certainly be several hundred dollars apiece. A better possibility might be soft blank collets that you could machine yourself, but I've never seen any blank 3Cs for sale. I expect the most likely scenario is to make a split bushing you can insert into a larger-size collet to hold whatever odd size you want to hold.

    A tap may exist for that thread, but it will likely be quite expensive. For the cost of the tap, you could make a huge number of "test pieces" perfecting your thread cutting ability.

    Note that the drawbar would more correctly be called a "drawtube." It ought to be hollow so long stock can pass through it (yes, you will want to do that).
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.
    Don't own anything you have to feed or paint. - Hood River Blackie

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    • #3
      You may want to look at one of these. It might be a bit overkill for a firing pin but I think you can machine this collet to a custom size to fit your needs.

      http://cgi.ebay.com/NEW-3C-3-STEP-PO...3A1%7C294%3A50

      This is not my listing and I have no affiliation to the seller and cannot verify the quality of the product. etc. etc.

      Just passing on the information.


      On EDIT. center hole probably too large for your application.
      regards

      3t

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      • #4
        Thanks for your help gentlemen! I guess I will have to roll up my sleeves and master internal threading. I will look into the split bushing, as a couple of the collets I have are close to being able to hold a M98 firing pin. I too have not come across any 3C collet blanks.

        Regards, Ken

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        • #5
          When i was tooling up my lathe as you seem to be i needed to make that cut for a draw tube, i did everything i could to find a way around cuttin the threads my self . i spent a couple evenings in the basement reading and trial cutting threads first i did outside threads fitting them to nuts. then later i did the inside tube cut fitting it to a collet. I never could understand all the stuff in the machinery manual about thread fits , so i just fit it to the part. I am in the lower portion of the talent pool here , if i can get it in an evening or two so should you.
          The cutting tool i used for the inside cut was a ground tap with one cutting tooth on the end , it worked well for this application, the tap was broken so i had nothing to lose , that way i didnot need to worry about getting the point correctly ground as it was already ground.
          scariest thing to hear " I am from the government and i am here to help"

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          • #6
            What Alguy said....

            Yeah, don't be scared off by threading, internal or otherwise. Use slowest backgear so things happen (relatively) slowly and have at it.
            ----------
            Try to make a living, not a killing. -- Utah Phillips
            Don't believe everything you know. -- Bumper sticker
            Everybody is ignorant, only on different subjects. -- Will Rogers
            There are lots of people who mistake their imagination for their memory. - Josh Billings
            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
            Don't own anything you have to feed or paint. - Hood River Blackie

            Comment


            • #7
              Making collets isn't that hard either. There was an HSM article about it. Actually two. One was about 3c collets and the other was about 6k collets. I don't remember the issues offhand but I think you can find them in the article search.

              matt

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              • #8
                I made a tap for the 3c collet tube. If your interested I still have some of the 3/4" tubing left (4140 steel) and if your interested I can tap the tube and sell you the length that you need. Mine was made for my South Bend 9". Heck I can even supply the drawings for the South Bend unit and the hand wheel for the collet closer. Here is a link to the closer drawings I made: http://www.wswells.com/data/prints/prints_index.html

                Pm me if your interested!!
                Mcruff
                Senior Member
                Last edited by Mcruff; 02-17-2009, 08:14 PM.

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