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Broken screws in bakelit VD101
Old 03-01-2018, 02:35 AM   #1
Dufleuve
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Question Broken screws in bakelit VD101

Hello,

I have a common issue with rusted screw heads that broke and rest of the screw left in the device. Most of the time you can carefully drill out the remains.

In the case of the bakelit Verteiler Dose, I'm afraid to break the box itself.
The screws are M3x5 and you can easily rip off and drill into the bakelit.

Any other trick you may have to get this fixed is welcome.

Thanks
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Old 03-01-2018, 10:54 AM   #2
Yuri D.
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Is some of the screw exposed above or below the bakelite material?
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Old 03-01-2018, 11:06 AM   #3
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Unfortunately when they are this far gone, chances are diminishing that they can be successfully restored. It all depends on the level of corrosion.

Remember that the screws are not screwed directly into the bakelite, there are threaded steel bushes moulded into the bakelite which will be equally corroded as the screws. If the corrosion has gone too far, the thread has turned into rust and can not be properly restored (Typically the bakelite will crack around the bushes because they will have swollen).

If you can, break of the heads of the screw by applying force with a screwdriver. If the screw can not be broken, use a centre punch to indent the centre of the crew head and drill away the head until the lid can be removed.

Before you drill into the crew stem, flatten the screw stump level with the bakelite surface using a small hand held grinder (Dremel or equivalent). Use a centre punch to get a dent dead centre of flattened section of the screw. If the dent is slightly off centre, you will be able to correct a little bit with your drill. Start with 1.5 mm, this is thin enough to control accurately and thick enough to give it strength. Use new sharp drills, buy the best quality you can find. You will find that your drill bits do not last very long drilling this hard material, budget for about a drill per two screws... Best to use a small hand held drill at this point, turn your workpiece or your line of vision regularly to ensure you are drilling perpendicular to the surface and straight along the screw thread.

After you are through with your 1.5 mm, go up with 0.5 mm increments until you reach 0.5 mm under the thread size (probably M4). If you can get a 3.7 mm drill, use that to prepare for recutting the thread. Re-cut the thread with an M4 tap. Be careful with the tap, as most attempts fail at this last stage and you are stuck with a broken tap in the hole which you will be unable to drill out.

regards,

Funksammler
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Old 03-02-2018, 03:34 AM   #4
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Thanks FS for the tutorial.

I hope threads are not too far gone as I could unscrew 3 out of 6 screws, one left on the back, two on front.
Front ones will be tricky as they are of the type with a thin unthreaded part, designed to retain the screw in the cover holes.

Cheers
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Old 03-03-2018, 02:09 AM   #5
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I have often wondered if electrolysis could be used to free up corroded/frozen threads.

A general procedure for rust removal using electrolysis is outlined at this link:

http://www.rowand.net/Shop/Tools/Electrolysis.htm

Has anyone tried this on frozen threads?


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Last edited by Hadenuph; 03-03-2018 at 02:15 AM.
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Old 03-03-2018, 11:25 AM   #6
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What works for me is penetrating oil and heat from a soldering iron
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Old 03-03-2018, 01:05 PM   #7
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-use a "kret" fluid for clearing pipes.
-using one of the ways to de-rust
e.g. with a battery and salt electrolyte.
or with mole and aluminum. you have to read more on the net.

bakelite as a plastic should withstand, do not use acid I do not know the resistance of bakelite to acid.
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