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Thread: Tiny set screws on new pinions

  1. #1
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    696

    Default Tiny set screws on new pinions

    Hello Shopbot Friends:

    In 2017, I bought a full set of 5 new 20 tooth pinions from Shopbot ($125 total). I noticed today that the set screws on the new pinions are really tiny, and neither the metric or English Allen wrenches fit right!

    I have a full set of metric and English Allen wrenches. The best fitting English allen wrench measures .091" (3/32), but it is a little bit loose. The best fitting metric Allen wrench measures .096", and I can not even force it in........ close, but not quite...... (Hmmmm, added note, .096" doesn't convert into a nice metric,,,,, so this set screw isn't even even close to a metric size.)

    The set screws on my old pinions accept a .125" Allen wrench, and the fit is perfect........

    I am afraid to use these new pinions, especially for holding up my 5HP spindle on the Z axis, as even if the Allen wrench fit right, I can't imagine being able to really torque these things on tight. With the loose fit, I think it would be foolish to hope these would be reliably tight. (Especially since getting at this pinion later, is really difficult.)

    I have thought of:

    1) reusing the best of my old pinions for the Z axis, since I know I can really tighten it and it won't come loose. The best used one is only slightly worn.

    2) drilling out the holes on the new pinions and tapping them with 1/4-20 holes. (I have only done tapping of soft steel before, and had good luck..... but are these pinions hardened, such that I might expect to have problems? I'd hate to mess up my expensive pinions.)

    3) Other ideas????? And I wondered, why on earth would the new pinions have such tiny set screws,,,,, and why would they not match either metric or English wrenches????? (does someone have an adjustable Allen wrench I can borrow??? )

    Thanks, your input is greatly appreciated! Chuck
    Attached Images Attached Images
    Last edited by Chuck Keysor; 04-18-2019 at 10:53 PM. Reason: Noted not a metric size....
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  2. #2
    Join Date
    Mar 2013
    Location
    Memphis TN
    Posts
    703

    Default

    >> but are these pinions hardened,

    The pinions are softer than the rails. I doubt they are mild steel but certainly not hardened.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  3. #3
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    696

    Default

    Thanks,,,,,,,,, I guess the more properly focused question which I should have asked is: With some basic experience in tapping non-hardened steel, can I reasonably hope to drill and re-tap the pinion set screw holes?
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  4. #4
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
    Posts
    7,952

    Default

    Quote Originally Posted by Chuck Keysor View Post
    With some basic experience in tapping non-hardened steel, can I reasonably hope to drill and re-tap the pinion set screw holes?
    Yes...Just do it.

    Machine yourself a jig that will hold each pinion in a cradle square to the drill press quill. If you don't have a drill press, find someone who does. Pull the grub screws out of the old pinion, match up the threads, drill and tap the POS pinions SB sent you and tap them using the drill press quill to hold the tap - by hand. Do not 'power tap' them. There's really not much there to tap...it will go quick. Do NOT do 1/4-20.

    When you put them on, use LocTite Blue...Crank them on good. SB gives you 3 wrenches on new machines so you practically bend them out of whack. That's how tight to make them...
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  5. #5
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    696

    Default

    Thank you Brady. I'll match the thread of my old set screws. I do have a good floor standing drill press and a machinist's vise. (Someone gave me the machinist's vice to get rid of it. I have never used it, but will use it now.)

    Side note, I welded my gantry with the rectangular steel tubing, and am slowly putting things back together after that. I finally got to the Z axis reassembly when I found this new issue of the tiny set screws.

    Thanks again Brady for your guidance, Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  6. #6
    Join Date
    Jun 2004
    Location
    Springfield Mo
    Posts
    811

    Default tap size

    this chart might be handy ... perhaps 1/4 - 28 ??
    Attached Images Attached Images
    The decimal point seems to be the most important on the z axis... x & y not so much....
    ShopBot... Where even the scraps and things you mess up and throw away are cool....

  7. #7
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    696

    Default

    Thank you for the handy chart Curtiss. I'll go out tomorrow and buy a tap, as I don't have the right size in my limited stock. Thanks, Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  8. #8
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
    Posts
    7,952

    Default

    Get yourself a thread gauge too if you don't already have one in your tap and die kit. Don't expect most big box stores to have taps in stock... that would be too useful...
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  9. #9
    Join Date
    Mar 2013
    Location
    Memphis TN
    Posts
    703

    Default

    And... don't waste your money on some no name brand tap. Most likely, it will crack within two turns in steel. Get a Hanson tap. They seem to hold up well.
    ShopBot Details:
    PRS Alpha 96x60x12
    4hp Spindle
    12" indexer
    Aspire
    Rhino

  10. #10
    Join Date
    Dec 2011
    Location
    Piedmont, SD
    Posts
    657

    Default

    the POS pinions SB sent you
    Sounds like your implying that SB's supplier has changed, or altered quality of pinions...
    Are we all expected to go through an hour of re-machining pinions as such going forward, or is this just a fluke?

    jeff

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