How to strengthen this knob

[WotEver]

Hi all you engineers...

 

Bakelite knob with the (1/4”) shaft broken off...

 

Bakelite knob with the broken shaft superglued back into place...

 

That glued shaft would never survive if pushed into service so I was thinking of trying to very carefully drill a small hole down through it into the knob body, then inserting something like a 2mm drill bit along with plenty of Araldite. 

 

Does that sound like a good plan? Any better suggestions?

 

Would I be better off cutting off the glued shaft, drilling the knob body, Aralditing a 1/4” steel rod and then filing a flat on it?

 

Thanks,

Tony

[Nut]

sugru

for the win

[David Schweizer]

24 minutes ago, WotEver said:

Hi all you engineers...

 

Bakelite knob with the (1/4”) shaft broken off...

 

Bakelite knob with the broken shaft superglued back into place...

 

That glued shaft would never survive if pushed into service so I was thinking of trying to very carefully drill a small hole down through it into the knob body, then inserting something like a 2mm drill bit along with plenty of Araldite. 

 

Does that sound like a good plan? Any better suggestions?

 

Would I be better off cutting off the glued shaft, drilling the knob body, Aralditing a 1/4” steel rod and then filing a flat on it?

 

Thanks,

Tony

 Yes, that would be my preferred solution, buit I would probably use brass which is easier to work, and it will still be stronger than bakelite.

 

 

 

[Athy]

Would a new one be expensive to buy?

[GUMPY]

Assuming the knob is fairly solid and not hollow I would have drilled a hole into the knob and shaft, tapped both with a suitable thread (2.5mm?), filed ends flat,  inserted a threaded rod (cut down machine screw) and reassembled with super glue.

Edited February 1, 2019 by Loddon

[Chewbacka]

Get a long dome head bolt where only the end is threaded the same diameter as the bit that broke off, cut it to the length of the existing knob moulding from the front face of the knob.  Then file a flat to match.  Drill a hole right through the knob, and glue your new shank in place.  Before glueing in place you could even paint the dome black to match.   Or see if you can get a new one on eBay.

[dor]

I think i would drill through the shaft and knob, perhaps even try cutting a thread, then glueing in a threaded rod, i.e. a bolt withthe head cut off.  Perhaps cut a slot in the end so it can be screwed in with a screwdriver.

 

Superglue just isn't what it used to be since the H&S mafia made the manufacturers reduce the strength.  Commercial or medical stuff is much stronger if you can get hold of it.

 

ETA: cross post with Loddon!  (great minds think alike.)

Edited February 1, 2019 by dor

[GUMPY]

9 minutes ago, dor said:

Superglue just isn't what it used to be since the H&S mafia made the manufacturers reduce the strength.  Commercial or medical stuff is much stronger if you can get hold of it.

Gorilla glue seems to be the best of superglues

[David Mack]

I used to get a lot of emails about this, but the spam filters seem to be more effective these days...

Edited February 1, 2019 by David Mack

[WotEver]

28 minutes ago, Athy said:

Would a new one be expensive to buy?

Sadly unavailable as far as my googling informs me. It’s over 50 years old and it appears that all originals have been scrapped. 

Just now, David Mack said:

I used to get a lot of emails about strengthening my knob, but the spam filters seem to be more effective these days...

So... I wondered who’d be first

[rusty69]

The perfect excuse to buy a 3d printer. Though not sure you can print Bakelite.

2 minutes ago, WotEver said:

So... I wondered who’d be first 

Bet you thought it wood be me!

[Alan de Enfield]

Having read the title I was going to suggest Viagra.

[Onewheeler]

The knob looks like a bog standard old fashioned radio control, with an integral shaft. The shaft looks like the same as used on a standard potentiometer. Knobs with grub screw available on Ebay e.g. https://www.ebay.co.uk/itm/2-VINTAGE-BAKELITE-VALVE-RADIO-KNOBS-BRASS-INSERTS-GRUB-SCREW-FIXING-35MM-DIA/113603357901

 

Search "knob vintage radio" and cut the shaft off a pot?.

[WotEver]

31 minutes ago, Onewheeler said:

The knob looks like a bog standard old fashioned radio control...

Ahhh, but it ain’t

 

t’other side...

[WotEver]

1 hour ago, David Schweizer said:

 Yes, that would be my preferred solution, buit I would probably use brass which is easier to work, and it will still be stronger than bakelite.

 

1 hour ago, Chewbacka said:

Get a long dome head bolt where only the end is threaded the same diameter as the bit that broke off, cut it to the length of the existing knob moulding from the front face of the knob.  Then file a flat to match.  Drill a hole right through the knob, and glue your new shank in place.  Before glueing in place you could even paint the dome black to match.

 

Thanks all for your suggestions. Bearing in mind my own abilities I think one of the two above are my favoured solutions. The brass I like most because it’s an easy material to work. I like the bolt idea because I could drill from the front and easily get the hole centred, but it would spoil the face of the pretty knob. So I think I’ll clearly mark the knob underside to show where the flat needs to be, then cut off the glued shaft, file the surface clean, drill a 1/4” hole etc. 

 

I think if I tried tapping two 2.5mm threads in the two pieces I’d end up with a little pile of broken Bakelite powder. 

 

Thanks loads for the advice

[Jess--]

did the springs and ball bearings survive?

[blackrose]

I'd be thinking about gluing an aluminum cylinder around the outside of the shaft rather than drilling through it, but I appreciate that you're probably putting the shaft into a hole of some description with a flat so that might not work. Might be worth thinking about before you start drilling though.

[bizzard]

Take one block of cheddar cheese.  Carve new knob with it copying old knob. Soak new cheese knob in Elsan blue= formaldehyde over night. In morning, one new Bakelite knob.

[Onewheeler]

2 hours ago, WotEver said:

Ahhh, but it ain’t

 

t’other side...

 

Get yourself a meter from the current century!

 

It may be that the unusual arrangement of a bakelite shaft is to protect fingers from exposure to high voltages were a metal shaft to penetrate to close to the surface. Check first!

 

 

[WotEver]

4 minutes ago, Onewheeler said:

It may be that the unusual arrangement of a bakelite shaft is to protect fingers from exposure to high voltages were a metal shaft to penetrate to close to the surface. Check first!

Good thought, and one I’d had myself. So the plan has changed to something much simpler. I’ll still drill the 1/4” hole but instead of glueing in a metal shaft I’ll use a plastic one cut off a pot - I have plenty kicking around. It also saves both sourcing a suitable piece of rod and filing it once I’ve found it. 

1 hour ago, Jess-- said:

did the springs and ball bearings survive?

One spring, one ball bearing, both a little rusty but serviceable.

[WotEver]

1 hour ago, blackrose said:

I'd be thinking about gluing an aluminum cylinder around the outside of the shaft rather than drilling through it, but I appreciate that you're probably putting the shaft into a hole of some description with a flat so that might not work. Might be worth thinking about before you start drilling though.

Both diameters have to fit something. The larger diameter fits in the hole in the Bakelite case and the 1/4” shaft is secured with a grubscrew to the wiping part of a rotary switch. The top layer of the switch serves as the ‘distant’ support for the end of the shaft. So no, nothing can be any bigger than it is currently. 

[Rebotco]

55 minutes ago, bizzard said:

Take one block of cheddar cheese.  Carve new knob with it copying old knob. Soak new cheese knob in Elsan blue= formaldehyde over night. In morning, one new Bakelite knob.

I tried that once ..............

.....Bloody mouse ate it the same night!  ?

[WotEver]

13 minutes ago, Onewheeler said:

Get yourself a meter from the current century!

Where’s the fun in that? I have several digital meters in addition to an Avo8 and a 1970’s hobby analogue thing. This one wasn’t working (guess why!) so it’s my task to fix it. 

[Sea Dog]

There's a Bakelite Museum somewhere up twixt Dunster and Datchet on the Somerset coast - maybe he'll have a "new" one?  Bit of a rum place mind, and don't go if you have a dust allergy! 

[mark99]

Mmmmmm warm bakelite smell. Anorak warning, dust can contain asbestos.

Edited February 1, 2019 by mark99