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

[LCHIEN]

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 90º 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



I think this kit $50 or so lacks the drill bit but includes a handful of helicoil inserts

Alternate kit at Amazon:




I was curious how it works.
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.

[LCHIEN]

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.

[woodturner]

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/

[LCHIEN]

Anyone else done this repair and have comments?

[E. J. Hansen]

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

[Black walnut]

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...

[d_meister]

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.

[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.

[LCHIEN]

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.

[capncarl]

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]

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.

[LCHIEN]

Buy a 20 year old Machinery's handbook on eBay, the data doesn't change all that fast esp for common fasteners. Save a lot of Money.
Amazon: Machinery's Handbook 31, $88
eBay Machinerys Handbook 25 (1996?) $18.completed. + $5 shipping (book rate should be cheap)

But I have to say, I got a MH21 and an MH26 and hardly ever use them... too much information. I use that little black POCKET REF by Thomas Glover which is about $10 new and it usually has the info I need.
https://www.amazon.com/Pocket-Ref-4t...78207965&psc=1

[capncarl]

Too much information is a very good way to describe the Machinist Handbook. You could easily spend more time searching through this book than it takes to do the job! My handbook was sold years ago at a car swap meet along with a truck load of other things I no longer used. I do have a couple of old small ref manuals to fall back on but the internet is still my go to for stuff like this.

Borrowing a statement I saw on Gold Rush, from Freddy Dodge. It goes something like this… If you keep over thinking this it will bite you in your as.

[nicer20]

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

TC

[Dedpedal]

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.