Removing bakelite knobs with rusted grub screws

[mark pirate]

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.

I have used this method when all else failed, it certainly works, but you need the right size tip and wait until it is smoking hot!


Mark

[AmateurRepairer]

I will go for the soldering tip method, seems to be the best course of action. The chassis slides out on the Bakelite rails but I’ve heard if they rust they can be a pig to slide off, should I just use WD40?

Thanks all

[emeritus]

Petrol lighter fuel (e.g. Ronsnol) is very penetrating and can be easier to find than plus gas. Don't expect a badly-siezed screw to come free immediately: after a good soaking of solvent you may need to firmly attempt to turn the screw to and fro to progressively pump the solvent into the threads.

[ThePillenwerfer]

I've now tried acetone on a bit of scrap Bakelite and no harm was done to it.

[Radio Tech]

You could try this, use a drill bit the same size as the grub screw to just take the flats off what the screwdriver fitted in then use a decent 2mm drill bit to drill a hole exactly in the centre of the screw then start going up in 1/2mm sizes until you have almost drilled out the screw, you then have a chance of using a left hand tap to tap a thread in then use a left hand screw to finally draw the grub out. But be patient and take your time.

Ken

A left hand drill bit is handy for this sort of thing, push in hard at a low speed so it jams in unlike normal drilling practice.

[NottsIan]

A warm solution of Alum will disolve the screw and not touch the brass bush. Takes a very long time though. (days!)

[ajgriff]

The merging of today's thread with one from three years ago has got me (and a few others it would seem) a little confused.

Alan

[GrimJosef]

If the pot shaft is steel then anything which dissolves the screw will, presumably, end up attacking the shaft too.

Cheers,

GJ

[AmateurRepairer]

Has it been merged Alan? I think it’s a server issue.

[ajgriff]

You may be right of course but it seems odd that the server managed to mark your thread of yesterday as having been 'moved'.

Alan

[David G4EBT]

It's easy to be wise after the event, but as often as not, the problem of stuck grub screws can be avoided by using the correct screwdriver, which I think is rarely done. If the wrong screwdriver is used and it slips out of the slot, it's all downhill from there and the question then morphs from "How can I removed a stuck grub screw?", into "How do I remove a chewed up grub screw?"

On the question of screwdrivers, they must be the full width of the screw, the tip ground to have straight sides and as thick as the slot will accept. The handle should be as long as possible to ensure maximum torque. I arrived at that conclusion after many failures over many years due to picking up whatever screwdriver would fit -as often as not one of those daft little neon testers. Then the penny dropped, and I went to the trouble to grind screwdriver tips to suit 2BA/4BA/6BA grub screws and always press down really hard on the screw as I twist the driver to prevent it slipping out of the slot. If it won't move, as often as not, a few drops of Plus Gas overnight will do the trick.

I've attached a diagram to illustrate why using the wrong type of screwdriver will not end well and why the correct one maximises the chance of success.

Which is all well and good, but what about when the damage is done and the slot is all chewed up?

The only way I've managed to deal with that is to drill out the screw, starting with say a 1.5mm pilot hole, dead centre, but the chances of drilling a pilot hole exactly centred freehand, are slightly less than zero in my experience. The only way I've succeeded is by making a drill guide on the lathe from steel rod turned to the same diameter as the hole into which the grub screw fits, then drilling the guide on the lathe with a 1.5mm drill bit. The diameter of a 2BA screw will have a 4.85MM clearance hole, 4BA will be 3.75mm and 6BA will be 2.9mm. The easiest way to check the diameter is with 'number' drills. 2, 4 and 6BA 'number drills' are Nos 10, 24 and 32, which I guess most wont have.

EG: https://www.warco.co.uk/drill-access...rill-sets.html

When the guide is inserted into the hole in the knob, the next challenge is to use the guide to drill the pilot hole. As often as not, there won't be enough clearance between the cabinet and the know to be able to use even a small Dremel type drill, which makes it necessary to resort to using a flexible drive shaft which Dremels and cheaper alternatives often come with, like this sort of thing:

https://whiterosetools.com/products/...xoC7K4QAvD_BwE

Having drilled the pilot hole in the grub screw, I then use progressively larger drills to open up the hole - 2mm, 2,5mm, 3mm etc, up to the taping size of the screw, which for BA screws are: 2BA = 4mm. 4BA = 3mm. 6BA = 2.3mm (which equates to a No 43 Number Drill). When the screw has been drilled out and the knob removed, a tap of the correct thread can be used to clean up the threaded hole in the knob.

I appreciate that these notes will be of limited use to many who have little in the way of workshop facilities and don't know anyone who has, but stuck knobs and chewed up grub screws are basically engineering problems which call for an engineering solutions. I only arrived at these conclusions after a long journey littered with failures, characterised by frustration and exasperation with connotations of Basil Fawlty.

Hope it might help or interest someone.

Best of luck.

[Gabe001]

I had a similar problem, a chewed up grub screw and a knob that wouldn't budge.

I ended up scooping out 1-2mm of the bakelite around the grub screw until I could grab and turn the screw manually with fine tweezers.

Once the grub screw was out, and replaced with a new one, I filled the gap with milliput (superfine) and painted the 'filling' with acrylic paint of matching colour to the rest of the knob. Almost impossible to notice unless you know about it.

David, you should consider making a few YouTube videos of these specialist techniques of yours if you ever have time. They would make for some very educational viewing.

Gabriel

[G6Tanuki]

I forced one particularly stubborn knob off by drilling a hole into its face, tapping it and fitting a grease-nipple: a few strokes from my grease-gun 'hydraulicked' the knob off the spindle - and I found that once the end of the grubscrew wasn't bearing against the spindle any more it unscrewed quite easily despite the mangled slot.

(The tapped hole was subsequently filled with car-body-filler and painted over)

[emeritus]

Further to #52, I have found that many vintage screws have narrower slots than the blades of what ought to be the correct size of modern screwdriver blade. Dad's pre-war wooden-handled screwdriver is a perfect fit. This is particularly the case for the smaller sizes of Nettlefolds brass woodscrews. I have ground down the blades of a couple of modern screwdrivers to better fit the older slotted screws.

[Tractionist]

Brake cleaner has latterly impressed me - it's very very searching ..... but I've never tried it near Bakelite.