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

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  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20697
    • Katy, TX, USA.
    • BT3000 vintage 1999

    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
  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20697
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #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

    • woodturner
      Veteran Member
      • Jun 2008
      • 2047
      • Western Pennsylvania
      • General, Sears 21829, BT3100

      #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

      • LCHIEN
        Internet Fact Checker
        • Dec 2002
        • 20697
        • Katy, TX, USA.
        • BT3000 vintage 1999

        #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

        • E. J. Hansen
          Handtools only
          • Apr 2003
          • 2
          • Shakopee, MN, USA
          • BT3100

          #5
          Looks like this is what I need to do to my BT3100. Blade elevation won't change but gearing all looks good. Elevation shaft (? my term) rotates but the motor unit won't raise or lower. In disassembling, I can now manually move the blade/motor unit elevation with the front crank but am finding fine metal shavings in the threads of the elevation shaft. My conclusion is the threads in the aluminum are shot. Does this diagnosis sound correct?

          Which solution is easier helicoil or timesert? I have zero metal working experience. Should I attempt or find a metal worker to help?

          TIA for your input and help!
          Eric
          Eric
          E. J. Hansen

          Comment

          • Black walnut
            Administrator
            • Aug 2015
            • 5405
            • BT3K

            #6
            IMHO Helicoil is not only easier, one less maching step but also better suited for the application. Only you can answer your last question. I never drilled a hole in metal until the first time. I never tapped a hole in metal until the first time. I never handcut a dovetail until the first time. Do you have a drill press with 1/2" chuck and a vise or clamps to fixture the workpiece to the table with the elevation hole inline with your drill quill?Setup is 90% of the battle here. A drill will follow the tapped hole. Tapping a hole in aluminum is easier than steel. Practise on hardwood if you have any offcuts...
            just another brick in the wall...

            Boycott McAfee. They placed an unresponsive popup on my pc.

            Comment

            • d_meister
              Established Member
              • Feb 2009
              • 179
              • La Conner, WA.
              • BT3000

              #7
              Originally posted by LCHIEN
              Anyone else done this repair and have comments?
              I took my BT3000 to Texas from California for a big yacht job in 2006. While there, the threads went away. Thanks to this forum, I learned about the heli-coil fix and the specs, so I bought the kit. I soon realized that the set-up and execution were beyond the scope of the tools I had in the van, so I found a machine shop that was willing to do the installation.
              I lower the saw blade every time after I use the BT to prevent damage to the blade as well as self injury, and it's been fine ever since.

              Comment

              • nicer20
                Established Member
                • Sep 2007
                • 360
                • Dublin, CA
                • BT3100

                #8
                Since it is aluminum which is fairly soft, I wonder if drilling 19/32" is a necessary step. Can you directly tap the existing damaged hole, with the new helicoil tap?

                May be it is important to clean off the damaged threads and that is what the 19/32" drill will do.

                Just asking to learn.

                Comment

                • LCHIEN
                  Internet Fact Checker
                  • Dec 2002
                  • 20697
                  • Katy, TX, USA.
                  • BT3000 vintage 1999

                  #9
                  Originally posted by nicer20
                  Since it is aluminum which is fairly soft, I wonder if drilling 19/32" is a necessary step. Can you directly tap the existing damaged hole, with the new helicoil tap?

                  May be it is important to clean off the damaged threads and that is what the 19/32" drill will do.

                  Just asking to learn.
                  I think its very difficult to run a tap into a hole that is smaller than the core diameter (minor dia) of the tap. Taps can't take off more material than thread width.
                  The helicoil external thread minor diameter has got to be bigger than the major diameter of the original threaded hole, or the helicoil will disintegrate.

                  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


                  • capncarl
                    capncarl commented
                    Editing a comment
                    Correct, there are machinist charts that tell which drills to use for what taps with different drills for different percentages of threads desired. I can vouch for these charts and how difficult it is to cut threads in a drilled hole when desiring a high percentage of threads. And undersized hole is nearly impossible to tap. Aluminum is not that hard to cut treads when the proper size drill is used, but bolt threads are usually cut with 3 taps, taper, plug and finishing. Helicoil tap kits usually have 1 size drill and 1 tap. The threads it’s tap cuts are not that deep but they are engineered so the coil that is threaded into it to tighten up precisely the size as the bolt that it is intended for. One thing that I haven’t heard mentioned is the helicoil tap is not intended for a tap through configuration like you use on a bolt tap.
                • Black walnut
                  Administrator
                  • Aug 2015
                  • 5405
                  • BT3K

                  #10
                  Reference capncarl's comment, yup there is a whole book devoted to all sorts of wonderful information. Machinerys Handbook. Problem is the price is rather steep and for as much as a woodworker would use the information probably not worth the price. Charts can be found with a bit of looking. IIRC I even have one uploaded to my website... if only I could recall where.

                  I should have qualified my opinion in a previous post as to why I think Helicoil is the better option. If you look directly at the marketing materials for the timesert it explains how the lower few threads expand to lock it in place. I think for a tapped hole where the screw moves often having a tight spot in the thread is a bad thing. Adding to that the extra step, although with a through hole application maybe not necessary, the need to counter bore makes it more work to use.

                  Helicoil on the other hand is simple: drill, tap, insert with provided tool, and break off tab. Done. I would add some blue locktite to the hole first though, not the insert. It might not hurt to use JPW on the elevation screw and keep it in the insert for a day until the locktite cures. The JPW will act as a release agent should any locktite migrate to the inner threads. Placing the elevation screw in will help it cure since locktite is an anaerobic adhesive, in that it cures in the absence of air.
                  just another brick in the wall...

                  Boycott McAfee. They placed an unresponsive popup on my pc.

                  Comment

                • nicer20
                  Established Member
                  • Sep 2007
                  • 360
                  • Dublin, CA
                  • BT3100

                  #11
                  LCHIEN, capncarl & Black walnut : Thanks for all these insights. Learning everyday from all you guys. Can't thank you all enough.

                  TC

                  Comment


                  • Dedpedal
                    Dedpedal commented
                    Editing a comment
                    Same here. I think you may have messaged me last year about miter slots for the bt3000. Sorry if I didn’t get back with you. I’m still learning this format myself. Feel free to try again.
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