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  1. #1
    Join Date
    Mar 2017
    Location
    Melbourne
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    58
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    63

    Default Hercus collet draw tube

    I picked up a genuine Hercus 3C collet set at the Bendigo swap meet last weekend. A nice complete set with the storage stand and all. After cleaning it up I have found the thread in the collet end of the draw bar to be in poor condition. Probably not so unusual. I thought I might make a new one. A bit of research suggested the internal thread (collet end) is an odd thread of 0.635" x 26TPI, so that will have to be cut in the lathe. The external thread at the other end is 3/4" x 24TPI, which I can get a die for, but will probably also cut that on the lathe (maybe use the die to tidy it up).

    Anyway, my question: can someone direct me to a supplier of the tube stock?

    The tube is a thick walled tube, or hollow bar, 19mm OD and 13.75mm ID. This gives a wall thickness of 2.6mm in round numbers. Getting 19mm OD tube is OK, but the thickest wall tube I can find is 1.6mm - which is just too small for the internal thread (and leaves a pretty thin wall on the external thread). I believe the original tube was mild steel.

    I'm in Melbourne. Happy to buy a longer length if need be (maybe make a few tubes for others, or just cut off a length if someone else wants to share the 'experience').

    You may also have some alternative/better suggestions to solve my problem.

    Thanks in advance, Tony.

    PS. the internal thread of 0.635" x 26TPI is mighty close to 5/8 x 26TPI BSB (for which taps are available), but not quite. Some research suggests a tap of this size may end up with some very tight collets.

  2. #2
    Join Date
    Nov 2008
    Location
    Perth WA
    Age
    65
    Posts
    5,821

    Default

    Have a look here Tony - Round Tube 4130 Chrome Moly Stocklist Information

    Is the thread in the draw bar restorable? Picking up the thread would probably be tricky but armed with a jeweller's loupe and a bright light along with a smallish boring bar, you might get there.

    Bob.

  3. #3
    Join Date
    Mar 2017
    Location
    Melbourne
    Age
    58
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    63

    Default

    Quote Originally Posted by Anorak Bob View Post
    Have a look here Tony - Round Tube 4130 Chrome Moly Stocklist Information

    Is the thread in the draw bar restorable? Picking up the thread would probably be tricky but armed with a jeweller's loupe and a bright light along with a smallish boring bar, you might get there.

    Bob.
    That is a very handy mob to know about. Thanks. I'll give them a call and see if they can help. I wonder if they have a min order value? There is a place in Melbourne I get silver steel from - min order $200.

    Yes, will try and pick up the existing thread. Tricky operation. Some of the thread is actually missing (broken off), so that's why I thought I'd have a go at making one.

    Thanks again, much appreciated. Cheers, Tony

    Sent from my SM-G955F using Tapatalk

  4. #4
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    200

    Default

    Could you just bore out the thread and then silver solder in a bushing turned to size. Then bore your ID and re-cut the thread?

    Might be easier and cheaper than buying a new piece of tube.

    Otherwise you could just dock off the damaged thread bit, silver solder in a length of steel, drill/bore and then face to length and recut your internal threads.

    Nothing to lose trying.

  5. #5
    Join Date
    Mar 2017
    Location
    Melbourne
    Age
    58
    Posts
    63

    Default

    Good suggestion. I was also contemplating drilling out a solid bar - if I couldn't buy a tube of the right dimensions. The tube is 15" long, which presents it's own challenges to drill out, say 13mm. The bushing idea would be quicker and easier.
    I also thought that if I could buy the right sized tube, I could make a few, as others may interested in one. Maybe....
    Cheers, Tony

    Sent from my SM-G955F using Tapatalk

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