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  1. #1
    casters@claytoncramer.com's Avatar
    casters@claytoncramer.com Guest

    Default M48x0.75 filter tap and die?



    M48x0.75 is apparently the formal designation of the M48 camera filter
    thread.

    I have an Aries Chromacor in my Photon Instruments 5" refractor--and
    it does a great job. But the Chromacor is held in position by
    screwing into the M48 threads of the diagonal. If I want to take
    pictures, I need to remove the diagonal (to get enough infocus). But
    if I remove the diagonal, there's no way to leave the Chromacor in
    place.

    My thought was to build an adapter that would be a 2" ID adapter on
    one end, with M48 threads on the other. Then I could screw the
    Chromacor into the adapter, and use all my normal accessories for
    eyepieces, cameras, etc. without the diagonal.

    But that requires a way to tap an M48 camera filter thread. I have a
    lathe, but not the thread cutting accessory (which isn't cheap). If I
    could buy an M48 tap, I could cut the threads that way. But I am
    having a heck of a time finding an M48x0.75 tap! It might be nice to
    have the equivalent die as well.

    Clayton E. Cramer


  2. #2
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default M48x0.75 filter tap and die?

    On Wed, 14 Nov 2007 09:32:32 -0800, "casters@claytoncramer.com"
    <clayton@claytoncramer.com> wrote:


    I doubt either exist, unless as custom items used with very exotic
    manufacturing equipment. Threads that size are always cut on a lathe or
    something similar. If you can't do it yourself, you could just have any
    machine shop cut some sort of adapter ring that you could otherwise
    utilize. You might even be able to make something yourself- many filters
    have both internal and external threads for stacking. Could you adapt
    one of those?

    _________________________________________________

    Chris L Peterson
    Cloudbait Observatory
    http://www.cloudbait.com

  3. #3
    Dennis Woos's Avatar
    Dennis Woos Guest

    Default M48x0.75 filter tap and die?



    Seems like I have read that the Chromacor is very sensitive to its placement
    with respect to the focal plane? Would it work as well without the diagonal?

    Dennis



  4. #4
    _'s Avatar
    _ Guest

    Default M48x0.75 filter tap and die?

    On Wed, 14 Nov 2007 09:32:32 -0800, casters@claytoncramer.com wrote:


    You have a lathe that can't cut threads?

    You need a better lathe.

    A 48mm tap and die in the thread you are looking for may well cost you more
    than a chinese 7x10/12/14 - if you can find such a thing; and it is
    unlikely that it would work as well as single pointing.

    A possible solution would be to go to someone that fixes (or used to fix)
    cameras, and get a something with a flange with the threads you need. Turn
    a barrel and mount the flange to it. You can drill the holes for the
    mounting with your dividing head.

    What?

    You have a lathe with no dividing head?

    You need...

  5. #5
    Andrew Smallshaw's Avatar
    Andrew Smallshaw Guest

    Default M48x0.75 filter tap and die?

    On 2007-11-14, casters@claytoncramer.com <clayton@claytoncramer.com> wrote:

    I don't think you'll have any luck finding a tap and die that size,
    at least not one that hasn't been custom made for you for more $$$
    than the cost of the thread cutting attachment. The problem isn't
    simply finding taps that big - it is also the pitch. The standard
    metic pitch for 48mm is 5mm, with a 3mm alternative for fine pitch
    threads. 0.75mm is obviously considerably finer than that, and so
    such a tap would be doubly non-standard - not only is it larger
    than normal, it is also an unusual pitch.

    If you don't know anyone with a better lathe my advice would be to
    head down your local high school the next open evening they have -
    the kind meant for parents of prospective pupils, and make a point
    of getting friendly with the teachers of the design & technology
    department. They probably will have such a machine even if it
    rarely gets used, and they are often happy to do little jobs like
    this on an occasional basis.

    --
    Andrew Smallshaw
    andrews@sdf.lonestar.org

 

 

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