• Check out the Annual AK Secret Santa exchange Program, signup before November 23rd in the AK Charities & Christmas forum!

Stripped Knob Reverse Spline

Warren-Oates

Warren-Oates

One Dim Bulb
Subscriber
Got a receiver recently where there was a stripped control. Sometimes the function selector switches will get hard to turn on a 70's receiver. The grease dries out and turns to wax inside the shaft hub. People not knowing any better keep turning the control even though difficult. On a 70's Fisher the knob allows a person to get a lot of torque, eventually the plastic reverse spline inside the knob shears. After the reverse spline is sheared away the control knob just spins with no purpose. You can wad up some toilet paper and liquid nails or the like and do your best to fix it, or, wait for it,,, how about a 3D printed reverse spline adapter insert. The insert seems to work way better than TP.
 
Register to hide this ad
I printed the adapter in PLA, it seems good enough, but I think PETG with carbon fiber would be superior. The tolerance is tight, I had to work this on and off 12 times before it would easily go on and off the the splined shaft. The cross member inside the insert is for an extra measure of toughness. The back flange is for extra holding power when you JB weld the insert into the old knob.

Spline_Adapter.jpgSpline_AdapterB.jpg
 
This should work to fix any stripped out reverse spline in a knob. If your lucky a simple 5/16 drilling and you are all set. if the plastic inside the old knob is hopeless and ripped apart you might have to dig a lot of it out and the simply fill the whole cavity up with JB weld. Let the weld cure and drill a centered hole of 5/16 (or perhaps even 21/64 if you have it). Unfortunately the STL file is too big to post here, 4.5 meg, but if you want the adapter just PM me and will email it over to you so you can print what you need.

Note ** the adapter will fit very tight going on the first few times, just work it part way on and off a few times and it will free up a bit. Use a tiny amount of silicone lube if you need. Eventually it will slide right on and fit very tight.
 
Last edited:
I think this is a great solution. I just ordered a 3D printer and this seems like a perfect use, along with capacitor spacers and banana plug mounting plates. What software do you use to 3D model?
 
Namlook said:
I think this is a great solution. I just ordered a 3D printer and this seems like a perfect use, along with capacitor spacers and banana plug mounting plates. What software do you use to 3D model?
Click to expand...

Use a Bambu printer, enclosed cabinet. Solidworks is where the modeling is done. I know one of the big companies offers a free version of modeling software for personal use. Autodesk Fusion 360, I think is free for personal use.
 
Figured out how to reduce resolution a bit, so I can post the STL files in the thread (in ZIP format). File should still work fine for printing. Kind of like reducing the quality of picture online, the jpg looks just as good as the bitmap with much less file size.

So here it is if anybody needs to fix a knob.
 

Attachments

crispycircuit said:
A small drop of Super Glue Jell will work....
Click to expand...
I`ve had over the yrs. very good results using a decent, like plastic rated JB Weld 2 part epoxy and coating the control`s shaft`s spline with silicone spray for ease of future knob removal and scooping the just mixed epoxy about halfway or less depth into the knob`s hole and carefully inserting the knob to the shaft eyeballing to make sure of proper non-crooked alignment, and leaving overnight for full cure.
 
That's a great fix, OP. You could probably sell those on ebay or Etsy.
My go to for bonding plastic, with very little or no gap, is Loctite 401. It's a cyanoacrylate specifically designed to bond polymer.
 
Wow. This is exactly the solution I’ve been looking for. Have a Sansui 9090DB with 2 knobs that have stripped plastic inserts. Original replacement knobs go for insane $70-80 with shipping on that auction site. I don’t have a 3D printer nor do I know anybody with one though. Would you be willing to sell me a couple of these inserts?
 
You must log in or register to reply here.
Back
Top Bottom