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Old 15th Mar 2021, 9:58 pm   #1
slavedata
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Default Removing remains of shaft from Bakelite knob

The attached picture shows the remains of a steel shaft corroded in to a Bakelite knob. I want to remove this steel without damaging the knob.

Something I am sure people will have tackled before. Any suggestions? A solvent that won't damage the Bakelite? Or drill the steel with a depth limited bench drill?

What has worked for you?
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Old 15th Mar 2021, 10:09 pm   #2
vinrads
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Default Re: Removing remains of shaft from Bakelite knob

Never tried it, rust killer keep giving it a dose over a few days. Mick.
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Old 15th Mar 2021, 10:24 pm   #3
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Default Re: Removing remains of shaft from Bakelite knob

Bakelite isn't as inert as you might think. I'd go for mechanical methods over chemical unless I'd checked the chemistry didn't spoil bakelite.

I'd wrap the outer with something like sticky copper tape and then chuck it up and centre it in a 4 jaw chuck in a small lathe. If necessary, machine-up a small nest to match the draft taper of the knob outer, with a stub for your chuck to grip, or just chuck the outer of the nest.Grind the end of the shaft flattish to make drilling easier, then use a centre drill and drill a fine pilot hole, then a drill to remove the rest of the shaft. A tailstock chuck will make it easy to feed very gently and to limit the depth of drilling. You'll hear the grub screw as you try to cut the end off it (another reason for going slowly and gently with the drill feed.

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Old 16th Mar 2021, 9:59 pm   #4
slavedata
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Default Re: Removing remains of shaft from Bakelite knob

Thanks for that, a Lathe sounds a better approach than a drill. I think the engineering workshop at my old employer the local FE College might be getting a visit.
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Old 17th Mar 2021, 8:56 am   #5
David G4EBT
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Default Re: Removing remains of shaft from Bakelite knob

It looks like it could be held (gently!) in the chuck in the headstock of a lathe, then the protruding part of the shaft skimmed off flush.

It depends on what lathe facilities are available, but for best accuracy to ensure that the hole is concentric in the knob, I'd suggest that ideally, if collets are available, a collet in the tailstock of the lathe would be better than a Jacobs chuck.

Three stages to drill out the shaft after skimming it flat and flush:

1) Centre drill.
2) 1/4" drill bit for part of the depth of the hole.
3) An 'end mill', which is rather like a drill bit but with flat cutting surfaces at the tip.

The end mill with ensure that the bottom of the hole at the full depth won't be pointed as would a drill bit.

A lot of care would be needed to ensure that the drill didn't 'snatch' and wreck the knob in the headstock.

Some pics of my rudimentary 120 year old German watchmaker's lathe below:

1) Centre bit in a collet
2) 1/4" drill in a collet.
3) 1/4" end mill.
4) Tailstock collet drive.

I don't think there's any prospect of using anything other than a lathe, such as a hand drill or pillar drill, with any degree of accuracy.
It's one of those 'ride at your own risk' projects which could be a little thing in a busy day, or could end with tears and tantrums.

Hope that might help as bit.
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Old 17th Mar 2021, 2:40 pm   #6
The Philpott
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Default Re: Removing remains of shaft from Bakelite knob

Question- Would the trick of heating (woodscrews) with a soldering iron before attempted removal....help with a machine screw in bakelite?
(Penetrating oil would seep in as it cools..?)
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Old 17th Mar 2021, 4:41 pm   #7
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Default Re: Removing remains of shaft from Bakelite knob

Might as well give it a go with a little heat and penetrating oil, but go gently so as not to break anything.

Not many lathes are set up for collet chucks at the tailstock end. Most decent ones have something like Rohm milling machine style chucks mounted on whatever size Morse taper shank. Using a short drill has advantages here.... a use for those which have been sharpened many times!

When drilling in, the grub screw will be rather hard and will likely chip your drill, but the repeated clouting the screw gets may do the trick for loosening it. Even if you do machine your way through the protruding part of the grubscrew, the remains of the shaft ought to be free. Meaning you might not need that end-mill, and that using it or continuing drilling is likely not to work withe the remainder of the shaft spinning in the knob's bushing. If so, there isn't a need to machinr further, the stub should drop out.

David
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Old 17th Mar 2021, 5:20 pm   #8
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Default Re: Removing remains of shaft from Bakelite knob

If you are patient you can dissolve steel with copper chloride solution.
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