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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 19th Nov 2012, 6:46 pm   #1
timewave
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Default Rusty Grub Screw Removal

My pneumatic Clark Mast recently started to play up so I decided to check the seals and of course the job was not as simple as I thought it might be.

Each section of the mast has an aluminium casting which holds the rubber seals at its base. The grub screws hold the casting in place within the tube section. Normally these screws have a protruding piece of metal which has a screwdriver slot in it. The idea is that the grub screws are screwed fully into the casting which is then fitted into the tube so that the screws align with holes in the tube and then the grub screws are unscrewed sufficiently to be level with the exterior of the tube,thus holding the casting in place. Most of these protrusions on several of the sections have been worn or rusted away so they needed to be replaced.

Getting them out proved to be quite tricky. There were several that were flush with the top of the casting so there was nothing to grip. Knowing that they had to be replaced I decided to drill a small hole (approx 1.5 mm) through the centre of the worst ones thinking that I could then inject an easing agent.

However before I did that I spotted my smallest Torx driver and it looked like it might be a tight fit into the hole I had drilled. Sure enough with a fair bit of force and waggling about I was able to force the driver in which of course cut its own splines into the hole. Then with gentle pressure both clockwise and anticlockwise, the screws came out.

This technique might prove to be useful in other aspects of our hobby.
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Old 20th Nov 2012, 9:22 am   #2
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Default Re: Rusty Grub Screw Removal

I like that solution! This is one of the classic problems we've all had at some time or another and this looks like a neat solution.

Thanks.

Dylan
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Old 20th Nov 2012, 9:28 pm   #3
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Default Re: Rusty Grub Screw Removal

A similar trick I've used in the past is to drill a hole in the screw then hammer in the square 'tang' of an old file. the sharp edges of the tang grip the hole and also distort the screw slightly.

Then use a Mole-wrench on the file body to turn it and unscrew the screw. If you're lucky it comes out - if you're unlucky the tang snaps off inside the hole, leaving you with a much greater problem than you started with.
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Old 23rd Mar 2013, 10:01 am   #4
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Default Re: Rusty Grub Screw Removal

ooohh - why use the whole Torx screwdriver - just use a ΒΌ" hex bit and leave it in there.
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Old 23rd Mar 2013, 10:33 am   #5
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Default Re: Rusty Grub Screw Removal

Just spotted something in the post (number 3) above....

Be careful hammering on/with files.

The way their teeth are hardened tries to shrink the outer layer of their steel. It's a bit like safety glass, there is stored energy and files can shatter like safety glass. Only there isn't a window frame to contain them and they can send shrapnel flying. Low probability of happening in normal use, but a rather nasty outcome if it does.

Look at a file and you will see blueing on the tang, showing evidence of heat treatment. It is, but it's a second heat treatment to anneal the tang and undo the hardening the whole thing got earlier. This is to stop the tang being brittle, otherwise it would snap.

The way to put a handle on a file is to tap the end of the handle on a hard surface, and let the mass of the file drive its own tang into the handle. This way there are no blows to the file.

The workshop where I did some early training had as a demo the collected shards of a file which had shattered. Exploded would have been a fair description.

David
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Old 23rd Mar 2013, 1:32 pm   #6
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Default Re: Rusty Grub Screw Removal

Quote:
why use the whole Torx screwdriver
Because it has more pointy edges.
 
Old 25th Mar 2013, 10:52 am   #7
dave cox
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Default Re: Rusty Grub Screw Removal

I can't help thinking that a "stud extractor" is exactly designed for this. The reversed threading, if it works right, pulls the extractor in as you try to undo the the stud. No toolbox should be without a selection of different sizes !

dc
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Old 25th Mar 2013, 11:06 am   #8
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Default Re: Rusty Grub Screw Removal

I've never had any success with stud extractors. They just snap off leaving you with a bigger problem than you started with.
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Old 26th Mar 2013, 4:11 pm   #9
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Default Re: Rusty Grub Screw Removal

The spiral-flute extractors are not really designed for situation where high torque is required. If it's likely to be heavily seized then it would probably be worth drilling with a reverse threaded drill first. Quite often the torque and vibration will release the stud, althought there will ALWAYS be one left that doesn't come out

It's not worth the risk of using a poor quality extractor, as Graham points out, the remaining parts will be impossible to drill out!

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Old 27th Mar 2013, 1:07 am   #10
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Default Re: Rusty Grub Screw Removal

To remove the remains of a very small broken screw that was too small for my smallest extractor, I ground a tapered four-sided blunt point on the end of a broken HSS drill shank and drilled a stepped hole in the screw so that the edges of the steps roughly corresponded with the taper angle. I then tapped the drill firmly home with a light hammer, but not heavily enough to expand the screw. See-sawing the drill shaft to and fro with a small Mole wrench and application of WD-40 did the trick. The intermediate steps meant that grip was taking place at several places within the broken screw and not just on the outer edge. I suppose the steps may also have reduced any tendancy of the screw to expand and jam.
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Old 26th Aug 2013, 10:32 am   #11
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Default Re: Rusty Grub Screw Removal

Quote:
Originally Posted by emeritus View Post
I suppose the steps may also have reduced any tendency of the screw to expand and jam.
That is the problem with spiral screw extractors or similar tools, they expand the jammed screw as they bite in, and then they snap off. I have also had great difficulty in drilling into slotted grubscrew heads, and that is virtially impossible if the knob is still on the radio. If there is a trick to this, I'd like to know it!

I've had success removing rusted-solid grub screws by injecting phosphoric acid, and once the rust is eaten away, a little lubricant will get it moving. I put a Blutack plug in the outside of an immovable grubscrew hole on a plastic knob recently, filled the shaft hole with the acid, put a blutack cap on it, then left it to soak and a few weeks later the grubscrew was completely gone. I had not anticipated that outcome, but it was very welcome!

Cheers

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Old 26th Aug 2013, 11:26 pm   #12
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Default Re: Rusty Grub Screw Removal

I too have successfully removed stuck grub screws from controls knobs using acid to dissolve the screw away. The acid I used was fairly low concentration H2SO4 this worked very well eating the iron grub screw but leaving the brass insert untouched. However I would be unsure of using this method with an aluminium casting.

Jay
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Old 26th Aug 2013, 11:36 pm   #13
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Default Re: Rusty Grub Screw Removal

I always thought that 'easy out" extractors were the reason the spark eroder was invented.

The problem is that it's impossible to resist the temptation to "just try one".

David
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Old 27th Dec 2013, 8:49 pm   #14
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Default Re: Rusty Grub Screw Removal

I hate stud extractors too, snapped loads of them.
Years ago when I was in the motor trade we bought, at considerable expense, a kit for broken stud removal sold by Snap On Tools.
It consisted of a set of high quality drills, locating collars and extractors which looked like left hand reamers, in various sizes.
These worked very well. As the sharp flutes were parallel, it did not spread the stud when tapped in.
I don't know if they still sell them or how small they are made but worth looking for if you have an extraction problem.

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