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Old 8th Jun 2017, 7:39 pm   #1
Colin Boggis
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Question Removing bakelite knobs with rusted grub screws

Has anyone any good tips for removing grub screws that are totally jammed and with badly worn screwdriver slots? I've soaked them 24 hours with plusgas and they are in brass so I expected them to free up but no such luck. Heat seems not to help either. Drilling looks very precarious and I wonder if anybody has a "magic" method?
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Old 8th Jun 2017, 8:42 pm   #2
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Default Re: Removing bakelite knobs with rusted grub screws

A left hand drill bit used aggressively, i.e. push very hard and turn slowly, a battery drill is good for this. I use this method at work for a bit of kit with many M2 countersunk hex head screws, we had a bad batch of screws. Seems I am the one brave enough to push very hard (drill bendingingly hard) to get the job done.
 
Old 8th Jun 2017, 8:49 pm   #3
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Default Re: Removing bakelite knobs with rusted grub screws

Surprising as it might seem, tightening the screw will often break the bond. It is then removed by alternate lightening and loosening, maybe with a good penetrating oil like your PlusGas or my favourite, Acetone/ATF.
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Old 8th Jun 2017, 9:04 pm   #4
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Default Re: Removing bakelite knobs with rusted grub screws

Is Acetone/ATF the same as pure Acetone? I have plenty of the latter. Also I'll have a search for left hand drill bits.
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Old 8th Jun 2017, 9:30 pm   #5
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Default Re: Removing bakelite knobs with rusted grub screws

In the past I've had some success by heating the blade of an old screwdriver to red-heat with a blowlamp, then pushing it *hard* into the screw and holding it there for 30 seconds to get maximum heat-transfer.

If you have 2 or 3 screwdrivers you can have a couple heating while you're using one in the screw. Your aim is to get the screw as hot as possible so do several cycles of the red-hot-screwdriver therapy.

Then dose it with releasing-fluid, which should then have a chance to creep into the screw/knob gap as it cools.

[Sidenote: remember that some releasing-fluids are flammable so keep the blowlamp at a distance!]
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Old 8th Jun 2017, 10:07 pm   #6
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Default Re: Removing bakelite knobs with rusted grub screws

Hi,
I've had some success by putting a hot soldering iron ( temp control on max ) onto the screw head,then applying plus gas .Repeat as necessary!
Cheers Pete
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Old 8th Jun 2017, 10:30 pm   #7
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Default Re: Removing bakelite knobs with rusted grub screws

I would say above mentioned heat-treatment in combination with penetrating fluid good idea. (protect eyebrows!)

You say the screws are in brass; but the screws themselves are presumably steel and rather hard. This, i agree, would make LH drill bit action risky.

I assume that the reference to Acetone/ATF is a mixture of Acetone(or nail varnish remover) and (red) Auto Transmission Fluid?? (Haven't used it myself)

Plus gas is certainly a very good 'creeper', presumably due to low surface tension, and it's a worry that it hasn't succeeded. Don't bother to revert to 'old husband's tales' of paraffin or diesel since both plus-gas and WD are much superior.
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Old 8th Jun 2017, 11:59 pm   #8
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Default Re: Removing bakelite knobs with rusted grub screws

They don't seem to do thread extractors for very small screws, but I have had success by drilling a stepped hole in the screw by using drills of progressively larger diameter and progressively shallower depths, and then grinding a pointed square taper, with a slope corresponding to the steps, on the shaft of a broken HSS drill. This was hammered firmly into the stepped hole so that the edges of the square taper gripped several of the steps of the hole, but not using force great enough to expand the screw in the bore, and then turning it with a small self-grip wrench. If the broken drill is big enough I suppose grinding square flats on the end and using a small tap wrench to turn it would work. Flooding the hole with plus gas or petrol lighter fluid and gently rocking the extractor to and fro so as to pump the fluid into the thread can be more effective than using brute force. Metals are not infinitely rigiid, and if you an get some movement in the top, you should, with patience, be able to pump fluid progressively down the thread.
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Old 9th Jun 2017, 7:25 am   #9
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Default Re: Removing bakelite knobs with rusted grub screws

Quote:
Originally Posted by The Philpott View Post
I assume that the reference to Acetone/ATF is a mixture of Acetone(or nail varnish remover) and (red) Auto Transmission Fluid?? (Haven't used it myself)

50/50 mix of Acetone and ATF. One of the pest true penetrants I have used.


Quote:
Originally Posted by The Philpott View Post
Plus gas is certainly a very good 'creeper', presumably due to low surface tension, and it's a worry that it hasn't succeeded. Don't bother to revert to 'old husband's tales' of paraffin or diesel since both plus-gas and WD are much superior.
Sorry, that is not accurate. Diesel makes a reasonable job and is often used to release seized engines.

WD-40 however is NOT a penetrating oil but a Water Dispersant. It was their 40th attempt to get it to do something useful. Many of us regard it as snake oil, a triumph of marketing over ability.
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Old 9th Jun 2017, 8:00 am   #10
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Default Re: Removing bakelite knobs with rusted grub screws

Acetone is available either as nail varnish remover or as cellulose thinners
Automatic transmission fluid is also used for power steering systems.

Together they work very well indeed, but remember it will dissolve a lot of plastics.

Diesel, JETA1, and light domestic heating oil all have to have lubricating properties because in use they have to go through (and lubricate) high pressure pumps. Straight kerosene lacks lubricant components.

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Old 9th Jun 2017, 9:18 am   #11
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Default Re: Removing bakelite knobs with rusted grub screws

Acetone and cellulose thinners are different products.
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Old 9th Jun 2017, 9:21 am   #12
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Default Re: Removing bakelite knobs with rusted grub screws

Colin, if you have a dremel kicking around the pointy abrasive bit might be slim enough to give the screw head a dimple to start the drill bit off in a more stable fashion. Risky..

Scim, I would say Diesel is more suitable for unsiezing pistons probably because the cost of purpose packaged penetrants works out more. I don't deny it will unstick pistons, but it can take weeks IME! I also steer away from it for smaller jobs cos it flares up my contact dermatitis (only on one thumb....what the hell!?)

I was cynical about WD previously and trialled Diesel, Paraffin, Simulated Jetfuel mix and 3 in 1 against WD40 (twice) and WD fared best both times. It was only a simple test with old festered steel nuts and bolts. I would say it does penetrate in addition to being a water dispersant, but that's just what i've found (One good thing- it does not contain silicone, and never has, despite what some car forums were saying for a while)
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Old 9th Jun 2017, 9:31 am   #13
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Default Re: Removing bakelite knobs with rusted grub screws

I have never used Hydrochloric Acid in this sort of application, but on loose steel parts the way it eats rust is astonishing. Just don't get it on yourself, or on aluminium
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Old 9th Jun 2017, 9:45 am   #14
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Default Re: Removing bakelite knobs with rusted grub screws

With part brass assemblies acid is a bit brutal, it will usually remove the zinc and severely weaken brass.
Using the different coefficients of expansion between the metals is safe if you can use enough localised heat. Heating the brass should loosen a steel screw but it depends what the Bakelite will stand.
I have part immersed the Bakelite of knobs in oil and heated the brass insert with some success, and I have heard of folk who boil them in washing soda!
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Old 9th Jun 2017, 10:13 am   #15
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Default Re: Removing bakelite knobs with rusted grub screws

I'd try and heat the screw with a soldering iron, and then stick a bit of candle wax onto the screw. The melting wax will flow (capilliary action) into the threads and act as a lubricant/release agent. This should work on copper, brass, aluminium and steel.

I had success with this method on a water tap at a seaside cottage that hadn't been operated in years. I stripped down the tap, but the tap handle was STUCK in the gland area. Heat and candle wax did the trick.
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Old 24th Jan 2021, 2:42 am   #16
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Default Seized grub screws on Bakelite knobs - HELP!

I’ve got a Murphy U198H that is a shed find I bought from eBay.

The grub screws on the knobs on the front and also the wavelength selector on the back have seized on. I’ve left them in WD40 overnight several times to no avail.

Please does someone have any idea how to get these damn things out. Is there some sort of penetrating fluid I need to use?

Many thanks and god bless.
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Old 24th Jan 2021, 3:54 am   #17
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Default Re: Seized grub screws on Bakelite knobs - HELP!

If you can get one in the hole you could try holding the tip of a soldering iron on the top of the screws as heat is the best thing to free things that are stuck. Bakelite is surprisingly heat-resistant.

There is a product called PlusGas (ScrewFix sell it along with Amazon, e-Bay and the like) for freeing things that has its advocates, as does a mixture of 90% vegetable oil and 10% acetone. I don't know how acetone may effect Bakelite though.
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Old 24th Jan 2021, 10:59 am   #18
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Default Re: Seized grub screws on Bakelite knobs - HELP!

I fear the trade-off is between any solvent loosening the corrosion on the screw versus swelling the Bakelite so it grips the screw even more firmly.

In desperation I did once buy an expensive spray-can of dedicated screw-loosening stuff from a car spares shop. It did the trick in 10 minutes or so after a weekend of trying everything else had failed. That was on a steel screw in a steel fitting though.

Cheers,

GJ
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Old 24th Jan 2021, 11:21 am   #19
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Default Re: Seized grub screws on Bakelite knobs - HELP!

I would try the PlusGas. Do a test on a 'not visible' part if the acetone worry's you? I do not think it will do any harm.
You might try a very slight tightening of the screw, before trying to undo it. Problem is if you lose the screwdriver slot in the grub screw...
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Old 24th Jan 2021, 11:35 am   #20
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Default Re: Seized grub screws on Bakelite knobs - HELP!

Never tried it, but is there any mileage in trying freezer spray to shrink the screw a bit?
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