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  1. #1
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
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    831

    Default Metric Collets for an Imperial Wohlhaupter boring head.

    My "go to" boring head is a really nice UPA4 Wohlhauper with a full set of imperial collets for holding various sized boring bar but there has been times when I could have used some of the metric tooling that I have, the only one that sort of crosses over is the 5/16" which for some reason also holds 8mm. The size that I would use the most is 16mm so I am making one and probably a 12mm at a later date.

    Wohlhaupter Collet 1.jpg
    The material is Bohler K245, 30mm diameter.

    Wohlhaupter Collet 2.jpg
    The blank machined ready for heat treatment.

    Wohlhaupter Collet 3.jpg
    Wrapped in stainless steel foil and heated to 840 degrees C.

    Wohlhaupter Collet 4.jpg
    After quenching in oil and tempering at 180 degrees. I forgot to get a photo of cutting the slit in the milling machine with a ball nosed end mill, it does not go right through to the inside diameter, there is about 1mm left at the base of the groove, this will be cut though after finishing the I/D and O/D.
    More to come tomorrow.

  2. #2
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    831

    Default

    Honing the I/D to 16mm, I had only left 0.1mm in the bore for finishing and I was a bit worried that it would not clean up after distortion from hardening but as it turned out it cleaned up easily, this material is very stable during heat treatment.
    Wohlhaupter Collet 5.jpg



    Grinding the O/D to 0.875" between dead centers on a mandrel using a tool post grinder. The O/D had an .008" grinding allowance which also cleaned up quickly, probably within .002"
    Wohlhaupter Collet 6.jpg


    The final process - cutting the slot through using a 1.0mm cutting wheel which is actually about 1.4mm thick.
    Wohlhaupter Collet 7.jpg

    Wohlhaupter Collet 8.jpg
    Attached Images Attached Images

  3. #3
    Join Date
    Apr 2012
    Location
    Healesville
    Posts
    2,129

    Default

    G/day Techo, would you give us a bit more detail on the honing please, maybe i am being a bit dim but i just can't workout what you have done there. Aaaand some pictures of that Sunnen would be g8 also

  4. #4
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    831

    Default

    Hi Shed, the honing machine and the honing process is very simple and very precise, the honing mandrel holds an abrasive stone that is pushed outwards by a retractable wedge when the spindle motor clutch is engaged via a foot pedal. The wedge is under constant spring pressure which is adjustable to suit the size of the mandrel in use.

    This is a typical Mandrel assembly.
    Attachment 401061

    This a short video of the machine in action on another job. https://www.youtube.com/shorts/F8i51cxC5t0

  5. #5
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
    Age
    64
    Posts
    4,887

    Default

    Is this in a home shed?

  6. #6
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    831

    Default

    Yes it is Peter and thanks for sending the grinding wheels.

  7. #7
    Join Date
    Mar 2013
    Location
    Mt Pleasant SA
    Posts
    126

    Default

    Hi techo, not wishing to be a killjoy regarding an otherwise nice job but Bohler in their literature on K245 use an example of a collet. They temper the wearing portion at 200-250 C for 59-62 HRC & the spring part at 500-550 for a hardness of 42-47 HRC. In that light your collet might be a bit on the brittle side. Perhaps a second tempering for safety? Some sort of compromise between springiness & wear resistance? Nice job tho'.

  8. #8
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
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    Default

    Correct, but not really an issue with this type of collet that is not threaded and has very little room to move, it is virtually a transition fit in the boring head and has a maximum of .0005" clearance on any of the 16mm tooling that I have so as soon as the locking screws make contact with the collet it is locked up securely.

  9. #9
    Join Date
    Sep 2008
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    Riddells Creek, Vic.
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    Default

    The finished 16mm collet next to the 5/8".

    Wohlhaupter Collet 1.jpg

    This is the 12mm collet ready for hardening with the 1/2'' Wohlhaupter collet alongside, this one required a bit more work with the addition of a carefully located 3mm drilled hole right through lengthwise.

    Wohlhaupter Collet 2.jpg

  10. #10
    Join Date
    Apr 2012
    Location
    Healesville
    Posts
    2,129

    Default

    I reckon that i am the only dumbo here that doesn't know what the hole is for?
    Drive pin? Coolant?
    Techo ?

  11. #11
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
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    831

    Default

    BC, the hole is there to allow a slight amount of flex in that area. Once the collet is hardened/tempered and finished inside and out I will cut through the thin webs left between the slot and the bore and between the bore and the hole as per the photos in my first post above. I think Wohlhaupter used this method instead of just a square cornered slot, to reduce any chance of cracking.

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