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 Post subject: Rethreading a hole on Bakelite
PostPosted: Dec Sun 29, 2019 10:34 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
A hole of one of the screws for the rear cover was damaged when I got this radio and after removing the rear cover a couple of times, the threads seem to be gone. I used Loctite Form-a thread twice but it did not stick to bakelite. I was thinking of crazy glue but after it dries up I will have to use a wood screw which would look out of place because the remaining screws are metal screws. Short of mechanically rethreading the hole, is there any other compound that could work?


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 2:07 am 
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Location: S. Dartmouth MA 02748-1225 USA
Find how much depth is left in the hole, it should not be threaded all the way to the bottom. Select a coarse thread screw the will fit the remaining hole for both diameter and thread. For example 10-24. drill the hole for 10-24 tap size not bolt size BUT drill slightly oversize from diameter on the tap drill list. Probably will need a set of NUMBER Drills. Use a 10-24 starter tap and cut maybe 5 threads, back out and then use a 10-24 Bottom tap take 1/4 tun back out, take another 1/4 turn blow dust out often.

Bakelite does not like fine threads because it is brittle, nor does it like and pressure from forcing the tap or by forcing a self-tapping screw, that is because the Bakelite is old and very hard. When new molded it still was not fully polymerized (soft).

You can drill the tap hole much deeper and use a longer machine screw if need be. Try to keep the drill, taps as straight as possible.

May have to take the sharp edge off of the drill bit so it will not bit too fast or use a bit ground for plastics or soft metals.
A small, fine "slip stone" is used to take the sharp edge off, only takes a couple of passes, note the bit will not cut metal very well once the edge is removed.

You can work up in the size of the hole by drilling progressively large bits, then the bits should not bite, removing a small amount of Bakelite at a time.

The drilling and tapping should not need a lubricant.

Try the screw all the way down, if it begins to bind, use the tap and press ever so lightly off center to gently enlarge the hole as the bottom tap is run in...

If the fastener boss is broken away I have found that 24 hour cure resin of J-B weld is the strongest and adheres the best. With JB I have made dams of plastic packing tape to mold the JB, peel off the tape when cured... Use a Dremel with a dental burr to make hatch lines for the JB to grab...

YMMV

Chas

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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 4:49 am 
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Joined: Aug Wed 24, 2011 4:35 am
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Location: Sunnyvale CA
radioer wrote:
A hole of one of the screws for the rear cover was damaged when I got this radio and after removing the rear cover a couple of times, the threads seem to be gone. I used Loctite Form-a thread twice but it did not stick to bakelite. I was thinking of crazy glue but after it dries up I will have to use a wood screw which would look out of place because the remaining screws are metal screws. Short of mechanically rethreading the hole, is there any other compound that could work?


Fill it with JB-Weld, then drill and tap.

Brett


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 10:21 am 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Chas, Brett, I thank you both.
What I used to fill the hole was Patten two parts compound which as I said did not adhere to bakelite. Taping the hole to create new threads calls for a long and blind search to get the proper tools because the bits that I have for work I did on my cars were bought in NJ, now I am in "no man's land" called Athens,Greece.
Do you think a wood screw could create some threads in the Patten compound and provide decent strength, or, even better, a wood screw working it back and forth to create new threads on the bakelite hence ending up using a wood instead of a metal screw?
Happy Holidays to members.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 11:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Nr London, England, SS1 3PT
Nothing to lose. How about cleaning the hole and partially filling with JB Weld and then taping in the screw cleaning away any excess. Could put a tiny smear of oil on the screw thread as a release agent.

Another trick is to poke some strands of fine wire in the hole before winding in the scew. It is really making it a jam fit and will stay there and just be replaced the next time the back is taken off. Wont work if the back is warped and you are expecting the screw to pull it flat. I just use strands of wire pulled from radio cable.

Gary


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 11:39 am 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
I thought of your second suggestion using strands of fine wire or even fine shreds of a toothpick. As of your first suggestion, the problem is that the screw pushes the paste further in and since the other end of the hole is closed, there comes a point that the screw does not progress any further and that way it does not even provide any hold. At the end, I will have to use this solution, it is quick and I will not have to redo it that often.
Thanks for your thoughts.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 1:28 pm 
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Location: Norfolk, VA
PC7 or JB Weld has always worked with bakelite. I've filled holes in bakelite, phenolic, and Benelex with the stuff. JB Weld taps best, but if you shove a nylon screw in the hole first, it drills a lot easier. The softer nylon guides the bit better too.

My go-to:

Image

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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 5:51 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Quote:
I am in "no man's land" called Athens,Greece
OH, that kinda makes a difference as for finding vendors for tooling.

I quoted US fractional tooling and hardware, unless this is a U.S. radio it may have metric fasteners...

I don't relish buying tooling for "one-of" jobs either but once bought I won't have to buy it again...

Consider updating your profile, answers to questions are often predicated by what kind of material you can find/use...

I am sure there are distributors, likely located in the suburbs or industrial areas. They will have a web page, certainly.

A wood screw or a sheet metal screw will wedge and break open the Bakelite boss.

These Google search terms may help: [Athens Greece Industrial material tooling supply distributors]

GL

Chas

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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 8:25 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
this is in reference to Brian's advice. What did you mean by "but if you shove a nylon screw in the hole first, it drills a lot easier", that left me confused.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 8:34 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Chas, using a wood screw I feared could crack the bakelite. I just had a cheap idea, use a plastic screw which, if tight, will deform before the bakelite breaks but of course it will look cheepo.
As of finding a store for what I need in this place, well, it is not as easy as googling it. Take my word, it becomes a never ending exercise in frustration and disappointment, in fact, in the past it took me a lot quicker to get something through a friend in the States than getting an answer from a store here, incredible but tried and true!
I should be updating my profile and thanks fro the suggestion.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Mon 30, 2019 8:48 pm 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 5590
Location: Norfolk, VA
The nylon acts as a filler when you fill the hole with epoxy. Once the epoxy sets, the nylon screw is centered in the area to be drilled. You drill into the nylon screw area. As it is softer than the epoxy, it guides the drill bit, and also allows some depth gauging, as the drilling into the nylon versus drilling into the epoxy are noticed. If you put 10mm of a nylon screw into the epoxy, you know when you've drilled to the 10mm depth - the drilling becomes tougher. it's a great way to limit the depth while also being guided. You can also use a toothpick or wooden skewer - both will drill out well.

I learned the technique from an Electronics Tech that was installing used Benelex Material. Benelex is basically electrical grade 3/8" thick Masonite sheet material. We had a wonderful cache of used sheets, but had holes that needed to be filled or reduced in size so there was no exposed metal when mounting on steel work benches. He used the nylon screw trick with some Hysol Epoxy. After drilling, he had a nice, reduced size hole with only 10% of the epoxy area disturbed by the drilling. We had to use the older, used sheets of Benelex, as the new sheets are 10 fett long, a hard thing to deliver to an aircraft carrier in the middle of the Mediterranean Sea. :P

I'm a lousy graphic artist, but a 2-D rendering of what I mentioned.

Attachment:
bakelite.jpg
bakelite.jpg [ 74.47 KiB | Viewed 1331 times ]

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"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Tue 31, 2019 5:40 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Brian,
I must say that is a smart idea. Thanks for the tip.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Tue 31, 2019 7:13 pm 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4970
Location: Sunnyvale CA
The best solution is as previously described, fill, drill, and tap. Just last weekend I did something that might be relevant. Try dipping the screw in very thin beeswax (heat it up - I used the wax from an old capacitor), leaving a film. Then use the screw, and JB-Weld or equivalent to cast the new threads. Let it set up, then unscrew it. The wax will prevent the screw from sticking.

Brett


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Dec Tue 31, 2019 7:21 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Thanks Brett.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Jan Sat 18, 2020 8:46 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Omak,wa,usa
Hello radioer,
I agree with Brett I have done that many times and chase is right it's hard drill just into bakelite and taping it


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Jan Sat 18, 2020 11:40 am 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Sure, thanks.
I think if the hole was an open end one, it would have made the job easy. In the meantime, JB Weld does not exist anymore in Greece.


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Jan Sun 19, 2020 7:14 am 
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Location: Vancouver Island, Canada
This is worth repeating - don't use a wood or metal screw as they are tapered and will push out on the Bakelite when tightened, causing a bad crack.
There are metal push pins used on some Bakelite radios that work in a straight drilled hole. They stay in place simply by friction.

I haven't tried this, if the original nub is broken off, a small block of wood glued with Super glue to the cabinet will be easy to drill, and will hold a small screw very well. Paint it brown and it will be mostly concealed by the back.

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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Jan Mon 20, 2020 2:29 am 
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Location: Monroe, NC 28112 USA
I have a small stash of threaded brass inserts. Just epoxy them in a hole drilled big enough. Have even salvaged them from old electronics gear going to the dump. Free them with a heat gun or cut them out with a Dremel tool.

Robert


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 Post subject: Re: Rethreading a hole on Bakelite
PostPosted: Jan Tue 21, 2020 4:55 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 93
Lots of ideas and I thank you all. I am still thinking of how to go about using the same screw which at least from the outside looks like the original ones.


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