Repairing a BT3 blade elevation that is stripped using a helicoil repair kit

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  • Repairing a BT3 blade elevation that is stripped using a helicoil repair kit

    The elevation screw for the BT3x says is a 9/16"-12TPI threaded rod. It lifts the motor bracket assembly using a threaded hole in the aluminum bracket. This can be worn out and stripped by either extensive use or forcing it when not clean and jammed with dust and debris.

    If its stripped a tap won't restore a stripped thread to working

    Being a thread in aluminum its easy to strip if not cared for or abused.

    The preferred solution has been a helicoil insert; That requires enlarging the hole with a 19/32 drill bit and threading a stainless steel threaded insert onto the enlarged hole and breaking off the tang used for installation.
    So a 9/16-12 tap and tap drill (the original threaded hole) are not needed.
    You need a 9/16"-12 Helicoil repair kit or similar which has helicoils, STI tap, and installation tool, plus a drill (in this case I believe 19/32")
    https://www.truckid.com/heli-coil/9-...AaAjD8EALw_wcB

    19/32" drill bits are readily available for $11 to 17 on Amazon.

    From the FAQ
    [posted by “Knuckles” Brian] I went the HeliCoil route. Thanks to Ed's instructions in the Article section, it wasn't too difficult. It's not something I'd want to do every day. I searched about a dozen auto parts, hardware, and machine shops in this area, and I had no luck finding the 9/16"-12 Helicoil (or clone) kit. I ended up ordering one from a website called Cartools.com. It cost something like $50, shipping included. Wouldn't you know, though, after I bought it I stopped in a local discount tool place that I hadn't noticed previously; they had a clone (Permacoil) kit for $15.

    The next problem was finding a 19/32" drill bit to drill out the lug that the threaded rod goes through. [ed. Note – some helicoil kits include this drill bit]…
    Probably the most tedious (and potentially disastrous) step of the repair was drilling out the hole prior to tapping it. I figured that I only had one shot to drill the hole on the same axis, and I wouldn't know how well I did until "the reckoning" of trying to put it together. I used a 1/2" drill bit to help get the bit centered, and find the axis. I didn't measure the angle, but it wasn't exactly 90 to the table. I had to shim it with some laminated air and a few mosquito wings.


    Once I got the hole drilled and tapped, the insert went in nice and easy, and I epoxied it in place. I made sure to keep screwing the insert tool in and out so that any epoxy that squeezed into the inside threads was "threaded" in.

    ​Doing a little poking around I found this info


    Click image for larger version  Name:	image.png Views:	0 Size:	269.7 KB ID:	852654
    I think this kit $50 or so lacks the drill bit but includes a handful of helicoil inserts

    Alternate kit at Amazon:

    Click image for larger version  Name:	image.png Views:	0 Size:	93.2 KB ID:	852658


    I was curious how it works.
    Click image for larger version  Name:	image.png Views:	0 Size:	348.0 KB ID:	852655​There's a tool that spins it into the drilled and tapped hole. using the cross bar and installation tool. After final installation the cross bar is snapped off, you can see a weak spot where it will break off leaving an unobstructed threaded hole.


    Installation Procedure:
    1. Drill out the old threads using the drill size that is recommended on the thread repair kit packaging. The shank of the tap also lists the recommended drill size.
    2. Tap the hole using the Screw Thread Insert (STI) tap.
    3. Install the insert using the installation tool.
    4. Remove the tang of the insert.
    HeliCoil - Repair Engineering

    Another excellent detailed description
    https://knowhow.napaonline.com/how-t...ipped-threads/

    there are also some You tube videos.

    ​​
    ​Note: I did not do a repair, my saw is working fine. I was just curious about how this repair method worked and this is my research.
    Last edited by LCHIEN; 10-23-2022, 12:00 PM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

  • #2
    This is in the FAQ, but for those of you who don't know, the raising thread is 9/16"-12TPI which means the blade is raised 1.000 inches for every 12 turns of the elevation wheel.

    Or consider it 0.083 inches per turn of the elevation wheel. Since I pretty easily control the wheel to 1/4 or even 1/8 of a turn, I can pretty precisely adjust the height of the blade when making critical grooving or partial through cuts. Consider 1/2 of a turn is .041 and 1/4 of a turn is .020 inches and 1/8 of a turn is .010 inches.
    This works well when going one way creeping up on a cut depth and using calipers. If you reverse direction, don't be surprised to find backlash hysteresis of about .005"
    If the first pass cut is close within 1/8 or 1/16th inch, I can usually dial it right in within .01 of the desired with one adjustment.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment


    • #3
      Personally I still prefer the solid threaded inserts over a helicoil,much less likely to strip out and it is a permanent repair. I did that repair to one of mine maybe 10 years ago and it has worked well.Time-sert is the brand I used http://www.timesert.com/
      --------------------------------------------------
      Electrical Engineer by day, Woodworker by night

      Comment


      • #4
        Anyone else done this repair and have comments?
        Loring in Katy, TX USA
        If your only tool is a hammer, you tend to treat all problems as if they were nails.
        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

        Comment

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