Help! Stripped Casting Hole For Speed Control Knob/Screw : (

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FellowCollector
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Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by FellowCollector »

Well, this is a first for me. I've repaired lots of my own phonographs for many years but never encountered this. Someone buggered up the threads in the casting for my speed control knob/screw. Any simpler fixes versus tapping the hole? Worse case scenario is tapping the hole (next size up?) but then the screw threads on my current original speed control won't work? Correct? Any help is appreciated.

Thanks,
Doug

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by kirtley2012 »

It may be possible to fill the hole with some kind of high strength epoxy and tap that, but the strength may be a problem, I can't say I've tried it.
In the past I have had to retrofit parts (original parts from different eras thus from slightly different casting patterns with different screw alignments), in those cases I slightly enlarged the threaded hole, re-tapped it larger, inserted a piece of threaded rod or a bolt, held in place with epoxy or thread lock, filed flush on top and bottom, then re drilled and re-tapped as if making a new hole, this method would allow you to use the original speed control providing you had a tap matching the original thread, but with all that said, if it were mine I would tap it larger and make a new speed control, but saying that I do have access to a lathe.

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by 52089 »

Perhaps you could find or make a grommet to resize the hole slightly downward and then drill and tap as needed?

The only other alternative I can think of would be filling, drilling, and tapping again.

You may want to note what kind of machine it is in case that jogs someone else's brain.

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by Curt A »

You could use a blind threaded rivet nut, assuming that you can find one that matches the size and thread pitch of your speed control. They are inserted with a tool similar to a pop rivet tool, and they provide a new threaded insert. You drill a hole to match the insert size, then squeeze the insert in place with the tool. The result is a new threaded hole.
https://www.baysupply.com/124122/Catego ... z_EALw_wcB

https://www.youtube.com/watch?v=mJSHGYtMS-Q

How to install a rivnut without a special tool:
https://www.youtube.com/watch?v=FJ4gF2tXRBE

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by gramophoneshane »

kirtley2012 wrote: Wed Aug 11, 2021 6:05 pm It may be possible to fill the hole with some kind of high strength epoxy and tap that, but the strength may be a problem, I can't say I've tried it.
JB Weld maybe?
I've never used it so don't know if it's actually stronger than other epoxy resins, or if it's pretty much the same but coloured silver.
It certainly appears to be stronger judging from some of the pot metal repairs folks have done and posted here on the board.
I wonder if flux and solder could be used to coat the thread and then be retapped to fill in what's missing?
Perhaps nickel plating would work too?
I was once given a gramophone to put together for a gentleman after he got everything replated, and none of the threaded screws would fit and everything had to be put through taps and dies so it could be reassembled.

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by JerryVan »

Show a photo of the motor casting where the speed control goes. Having some idea of the thread size and how substantial the casting is in that area, will dictate what kind of repair can be done. Otherwise, we're all just guessing... :?

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by FellowCollector »

Thanks everyone for all of the useful help! The problem, as I saw it at the time, was the speed control knob/screw was unable to catch any threads in the motor casting. No matter how much I tried the speed control was not doing anything but spinning around in the hole. This is on a recently purchased Columbia cylinder Graphophone. So, yesterday morning I decided to remove the 4-spring motor and determine whether I could see anything left of the threads inside the casting hole. I could not see much of the hole with the bed plate installed. With the motor removed and to my amazement I could see some threads inside the casting. So with fingers and toes crossed I inserted the speed control and rotated it clockwise..........it went in PERFECTLY! What the heck?? With this wonderful result I re-installed the big Columbia motor. Got it all together again and.....the dang speed control refused to engage with the threads in the hole - AGAIN... What in the world is going on here?? I can install the speed control with the motor removed but NOT with the motor attached to the bed plate? C'mon.... I called my wife over to look at and discuss the problem. What the heck is going on here? The hole was straight down from the bed plate hole so nothing cock-eyed there...made no sense. So I decided to remove (UGH!!!) the motor again to prove to her that the speed control WOULD go in perfectly. After removing the motor she watched as the speed control could be installed easily and tightened perfectly in the casting hole. So THIS TIME, when I installed the motor again I decided to keep all of the motor mount screws LOOSE. Still I could not get the dang speed control to engage with the casting hole. It was then that I realized that the 4 OIL PIPES that protrude through the bed plate were preventing the speed control from entering correctly into the casting hole. So, I pulled the oil pipes out of their bed plate holes and asked my wife to try installing the speed control. After her many unsuccessful attempts and my holding motor and bed plate up as best I could she finally said "I think I GOT it!".
She did and then I had to spend about 15 minutes trying to re-align the oil pipes so they could enter the holes in the bed plate correctly again. I put everything back together and all is wonderful. When I purchased the phonograph I noticed that the speed control was laying loose on the bed plate but I figured someone simply removed it for whatever reason. I had NO IDEA how difficult it would be to re-install it. This was a first for me. Again, thanks to all for your helpful comments!!

Doug

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by Curt A »

Glad you figured it out...
"The phonograph† is not of any commercial value."
Thomas Alva Edison - Comment to his assistant, Samuel Insull.

"No one needs a Victrola XX, a Perfected Graphophone Type G, or whatever you call those noisy things."
My Wife

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Re: Help! Stripped Casting Hole For Speed Control Knob/Screw : (

Post by AudioFeline »

It is a strange and wonderful world.
Good to hear all is well.

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