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 Post subject: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 2:25 am 
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I've been looking through all the super glues on Amazon and end up getting more confused.
I need to create a hard surface somewhat like a screw thread. In fact it is a broken screw thread, on the headshell of a AR-XA turntable. The headshell was made of plastic 60 years ago and invariably the threads get stripped.
I tried some cheap super glue "gel" from the dollar store and it flowed ok but is not rock hard after it dried.
There seems to be a lot of variability with these super glues(cyanoacrylate) as far as thickness. All I need is something that I can flow onto the the remaining thread part and have it replace the broken off thread part. I can then Dremel it to fit afterward. But it has to be hard.

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 2:44 am 
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I wonder if J-B Weld would work.

I have used it to fill extra holes in metal chassis that can be filed and sanded and after paint are an invisible repair.
The point being it's not soft like conventional epoxies. It's rock hard.
It's not supposed to be used on Polypropylene or Polyethylene plastic (poor bonding) but people have used it to repair threads on low stress (torque) applications.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 2:45 am 
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In the shop we used to mix a bit of baking soda with the liquid (not gel type) super glue to get a hardened result. We also purchased a two part acrylic dental casting mix from a dental supplier which appeared to be the same thing, the liquid part smelled like cyanoacrylate and the powder was flour like although it was likely some sort of plastic powder. In any event that stuff was pretty much rock hard when cured and could be worked with tools, and tapped.

You might also consider JB Weld the original long cure types can be drilled and tapped when hard, I've done some repair of automotive parts that I would have thought were impossible.

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 2:51 am 
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Have you ever used PC Woody? it is an epoxy putty with powdered wood filler, I think, hardens well and can be shaped by sanding. I have used it to fill cracks and it is very stable, doesn't shrink noticeably.
It does not absorb stain, dries a Maple color. Is pricey because it is a topnotch epoxy product.

But JB Weld might work well for what you need, so I 3rd Dave and Dennis's suggestions.
Some people like to mix cocoa powder with epoxy, but I'm afraid I'd be tempted to lick my fingers. :x

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 1:24 pm 
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I''ve never tried it, but have heard of the baking soda trick. Worth a test.

This is probably a very small thread (2-56 perhaps?) and a thin blind section. But there are inserts such as keenserts or timeserts which might make a permanent repair.

A custom ID/OD threaded insert could also be made.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 1:58 pm 
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Mr. Detrola wrote:
In the shop we used to mix a bit of baking soda with the liquid (not gel type) super glue to get a hardened result. We also purchased a two part acrylic dental casting mix from a dental supplier which appeared to be the same thing, the liquid part smelled like cyanoacrylate and the powder was flour like although it was likely some sort of plastic powder. In any event that stuff was pretty much rock hard when cured and could be worked with tools, and tapped.

You might also consider JB Weld the original long cure types can be drilled and tapped when hard, I've done some repair of automotive parts that I would have thought were impossible.

I second JB Weld the original long cure. I put my rear quarter panels on my truck with it!!!!

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 2:15 pm 
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J-B Weld. Use the slow-cure type, not the fast-cure variety. When fully cured (12 hours) it is rock-hard and can be drilled and tapped. Will be necessary to build a temporary "dam" around the part to be built up since J-B Weld flows easily before it sets. The dam can be made of masking tape or cardboard.

After J-B Weld has partially (but not fully) cured, it can be easily shaped and carved with an X-Acto knife if needed to remove unwanted excess.

As a suggestion, instead of trying to remake the missing plastic threads, it might be less labor to grind off (with a Dremel tool mill bit) the stub and epoxy a brass nut of the correct size in place. Care must be taken not to get epoxy into the nut threads, but beyond that it should provide a solid repair.

Small-size brass nuts/bolts/washers can be found at hobby stores that cater to model railroaders or R/C vehicle enthusiasts.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 3:32 pm 
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Thank you for all the great suggestions. I should add that the threads are not continuous
around the cylindrical surface, but only use about 20 degrees of arc. There are three threads on the top and two on the bottom. Here is a picture.
Attachment:
headshell.jpg
headshell.jpg [ 44.25 KiB | Viewed 346 times ]

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 3:53 pm 
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OK, the photo helps immensely- I think that most people were envisioning a cartridge-mounting threaded hole. What you have is an "interrupted screw" arrangement which allows partial-turn connector attachment (much like an artillery cannon breech). Why this would be a desirable feature in a turntable escapes me. Probably the designers were just being stupid.

I don't see any practical way to restore these threads: they are under a lot of strain and any attempted repair to the threads will fail. I think that you should consider buying a replacement headshell or adapting the lead connector to an alternate retention method- perhaps a clamp of some sort. Or, just glue the connector in place. That fix will probably outlast both the turntable and you.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 4:15 pm 
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The interrupted screw assembly was needed to get the tone arm contacts to match the headshell contacts. The teeth end up damaged by attempting to screw in the matching contactor too tightly.
These headshells are one-of-a-kind and are expensive to replace. I've had this one for almost 60 years. I was doing fine until about 20 years ago.
The secret to longevity is to press the headshell up against the contactor and then screw in the contactor, instead of using the contactor to pull the headshelll in.

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 10:00 pm 
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Location: Peekskill, NY
How much meat is on the sidewall of the shell, where the threaded boss extends out?
(photo of it flipped over?)


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Wed 23, 2022 11:26 pm 
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If you are not hellbent on preserving the original mechanical design of this part, why not just plug the lead wire connector into the headshell, then secure the union with a dab of clear RTV (silicone) adhesive between the two parts? RTV when cured will provide positive retention but its bond is easy to sever using a razor knife. It would only take a tiny bit of RTV to absolutely retain the pendant connector. This assembly will never be going on a space mission to Pluto so anything beyond what it takes to do the job on Earth is pointless overkill.

There are other ways of accomplishing the same thing (metal-pinning the connector, for example, in the same way some revolver barrels were locked to their frames) but the RTV approach is inexpensive and requires no mechanical skill (if that matters).


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 12:23 am 
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I think it's best keeping it stock. Replacing the cartridge would be a major project otherwise. Also, the headshell needs to stay rigid while playing a record.

The connector on the arm matches four pads with the four pins from the cartridge. The threads are used to cinch up the contact between them.

The headshell was made of plastic in order to have the lowest mass.

I still hope to build up the threads with cement.
Attachment:
sddefault.jpg
sddefault.jpg [ 86.45 KiB | Viewed 270 times ]

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 12:59 am 
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Supposedly stuffing the hole with a cotton ball...then saturating the cotton with superglue makes a hard drillable surface.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 4:27 am 
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3D print a new one and throw that in the garbage.


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 5:26 am 
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There is two-part dental tooth filler that might be usable. It can be purchased on Amazon. It is used as a temporary filler by some dentists. It can be shaped but I do not know the properties on plastics. Tom


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 8:01 am 
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I was going to say just get another one from EBay, then I see they want around 50 bucks! There is one that is a bit cheaper that includes the cartridge and stylus
Wish I didn't toss my AR years ago. (Motor went dead)

Keith


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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Thu 24, 2022 6:43 pm 
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Maybe you could lock it together with a couple of tiny set screws?

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 Post subject: Re: In need of a super glue to form a rock hard substance
PostPosted: Nov Fri 25, 2022 10:28 am 
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I paid ~ 50 bucks for an OEM headshell for my 1974 Lenco B52 MkIV turntable, so 50 bucks for a headshell isn't unheard of, especially if you want original performance as designed...

My 2 cents worth....

73...Jordan VE6ZT


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