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Old 21st Jul 2005, 10:40 pm   #1
brianc
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Question Rusted grubscrews in bakelite Knobs

Hello all,
What is the best way to loosen grubscrews that have rusted in bakelite control knobs? I have a set which has 7 knobs, 5 of which have rusted screws. Unfortunately, they are about 0.5 inch long and the whole length is in the threaded bit of the knob. I am really reticent to attempt to drill them out as they are so long and the set is too good to risk a bodge. Is there a miracle method?

Cheers,

Brian.
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Old 21st Jul 2005, 11:04 pm   #2
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Default Re: Rusted grubscrews in bakelite Knobs

I hope you haven't damaged the scewdriver slots in the knobs in your attempts to remove them.

Turn the knobs so that the screws face upwards and build a circular dam of plasticine or blue tack round them. Fill with your favourite de-rusting fluid and wait several days before attempting to remove the screws. It may help to TIGHTEN the screws a bit before loosening them.

Suitable de-rusting fluids are WD40, penetrating oil, diesel fuel and brake fluid, but check that they won't damage the knobs first.

Application of heat from a hair dryer, or towelling soaked in boiling water may help.

I always replace slotted grub screws with grub screws having internal heaxgon heads. So long as you use the correct size of Allen Key it's just about impossible to damage them.

If you can grip the shaft with a small pair of molegrips to stop it turning it may be possible to twist the knob off, particularly if there is no flat on the shaft.

It's very difficult to drill out screws in situ. Where the pot or switch can easily be replaced I have been known to saw through the shaft leaving as much as possible of it in the knob. I then grip the shaft in a machine vice clamped to the table of the drilling machine. Drilling out the screw is then easy.

Good luck with the job.

Graham.
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Old 21st Jul 2005, 11:13 pm   #3
mickjjo
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Default Re: Rusted grubscrews in bakelite Knobs

I've had this problem a few times, The first thing to try is a drop of oil left to soak overnight. If they still won't move the next stage is to apply some heat, a soldering iron may work if you can get a good contact with the screw head. Recently I had some Cossor knobs that failed to respond to this treatment , but eventually an old screwdriver heated red hot in a gas flame did the trick, and both the knobs and screws survived intact .

Regards, Mick.
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Old 21st Jul 2005, 11:22 pm   #4
brianc
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Default Re: Rusted grubscrews in bakelite Knobs

Thanks guys. I will try the WD40 overnight tonight. I was a bit concerned about the oil causing the bakelite to swell somewhat and make the situation worse! BTW, it is absolutely impossible to saw the shaft off as the knobs are on variable caps, switches and a filament rheostat from the twenties - this is the reason why I want to do things correctly.

Cheers

Brian
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Old 22nd Jul 2005, 7:57 am   #5
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Default Re: Rusted grubscrews in bakelite Knobs

To add to it all, heat is good, and tapping the screw with a small punch can loosen the corrision.
I do not buy expensive penetrating oil; some DERV when I change my fuel filter, or a 50% mix of paraffin and engine oil or LHM* is just as good, and does not evaporate.
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Last edited by Darren-UK; 15th Jul 2011 at 2:11 pm.
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Old 22nd Jul 2005, 9:19 am   #6
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Default Re: Rusted grubscrews in bakelite Knobs

First class advice from everyone there Brian. They can be a problem but once well soaked with some form of easing fluid the job becomes much easier. The red hot screwdriver idea usually does the trick after an overnight soaking. Regards. JOHN.
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Old 22nd Jul 2005, 9:21 am   #7
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Default Re: Rusted grubscrews in bakelite Knobs

Another tip is to use a proper Instrument Screwdriver with a blade having parallel edges rather than being diamond shaped. The end should be square to the shank with no rounded corners. If necessary grind it back to be a snug fit in the screw slot, otherwise all the force is concentrated at just two points in the slot. The screwdriver can be given a light tap with a hammer, both to crack the rust and seat the blade firmly in the slot.

Graham.
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Old 22nd Jul 2005, 3:23 pm   #8
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Default Re: Rusted grubscrews in bakelite Knobs

I still have some LHM from the days when I owned Citroens. I had never thought of trying it as a penetrating oil but it looks like it ought to work. I'll try it next time I need to free off something awkward.
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Old 22nd Jul 2005, 6:40 pm   #9
brianc
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Smile Re: Rusted grubscrews in bakelite Knobs

Thanks for all the advice chaps. I have managed to remove all the knobs using most of the advice. The penentrating oil removed one, heating the screw after an oily soak got another and the rest I found that I could carefully screw off the shafts. Now I can get on with the front panel - it needs covering with leather with a tooled border arround it! I will have to find a book-binder.

Is it a good idea to replace the grubscrews with brass ones to prevent further problems later (after I have drilled 3 out)?

Cheers

Brian
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Old 22nd Jul 2005, 7:34 pm   #10
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Default Re: Rusted grubscrews in bakelite Knobs

Quote:
Originally Posted by brianc
Is it a good idea to replace the grubscrews with brass ones to prevent further problems later (after I have drilled 3 out)?
Brass will corrode and it is softer than steel. so there is a chance the screw slot will be damaged in atempting to remove it. Faced with a choice between brass and steel I would use steel screws and cut the slots a bit deeper with a junior hacksaw.

However as I said in an earlier post, I now use grubscrews with hex socket heads. They are hardened and have cone or dimpled ends to give a good grip on the shaft. Using the correct allen key it is possible to apply a lot more torque than with a screwdriver (no axial force is needed) and it is just about impossible to damage the socket.

Graham.

Last edited by Darren-UK; 21st Aug 2007 at 11:00 pm. Reason: Fixed quote.
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Old 22nd Jul 2005, 10:40 pm   #11
brianc
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Default Re: Rusted grubscrews in bakelite Knobs

Thanks Graham. That's what I will do.

Brian
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Old 22nd Jul 2005, 10:45 pm   #12
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Default Re: Rusted grubscrews in bakelite Knobs

Quote:
Originally Posted by G4ILN
I now use grubscrews with hex socket heads. They are hardened and have cone or dimpled ends to give a good grip on the shaft.
Can you get these in BA sizes, or do you buy metric and re-tap the knob to suit?

Nick.
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Old 22nd Jul 2005, 10:47 pm   #13
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Default Re: Rusted grubscrews in bakelite Knobs

This site looks to have a useful range of grubscrews:-

http://www.modelfixings.co.uk/steel_grub_screws.htm

B.A sizes included! .

Regards, Mick.
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Old 22nd Jul 2005, 11:25 pm   #14
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Default Re: Rusted grubscrews in bakelite Knobs

I get my grubscrews from:-

http://www.emkaysupplies.co.uk/

They do Metric, BA, BSF, BSW, UNF and UNC.

Graham.
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Old 23rd Jul 2005, 8:29 am   #15
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Default Re: Rusted grubscrews in bakelite Knobs

Quote:
Originally Posted by brianc
Thanks for all the advice chaps. I have managed to remove all the knobs using most of the advice. The penentrating oil removed one, heating the screw after an oily soak got another and the rest I found that I could carefully screw off the shafts. Now I can get on with the front panel - it needs covering with leather with a tooled border arround it! I will have to find a book-binder.

Is it a good idea to replace the grubscrews with brass ones to prevent further problems later (after I have drilled 3 out)?

Cheers

Brian
No, Brian - much too brittle, and they will seize in any brass inserts.
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Old 26th Jul 2005, 12:16 pm   #16
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Default Re: Rusted grubscrews in bakelite Knobs

Thanks boys, tried the WD40 trick on some VERY rusty grub screws on a Cossor Melody Maker the other day and was amazed as they freed up within about an hour of applying the stuff, even though you could hardly make out the slots in the screws for rust.
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Old 1st Aug 2005, 7:56 pm   #17
brianc
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Default Re: Rusted grubscrews in bakelite Knobs

Hi guys

I, like Biggles have also managed to remove the rusted screws without resorting to a drill. Thanks again for all the good advice.

Brian
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Old 11th Oct 2005, 12:55 am   #18
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Default Re: Rusted grubscrews in bakelite Knobs

Why not put a spot of anti-seize compound on the threads when you replace the screws?

Frank

Last edited by Darren-UK; 21st Aug 2007 at 11:02 pm. Reason: Pruning.
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