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Old 16th Sep 2021, 6:20 pm   #1
vinrads
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Default Making /casting knobs for the AWA

Having cast two knobs ,I paid a visit to a friend with a lathe , explained what I needed to do , the solution was to drill a hole to take a brass bush , this was glued in and tapped 4ba thread , The AWA is looking splendid with its full compliment of knobs . Mick.
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Old 16th Sep 2021, 7:35 pm   #2
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Default Re: Making /casting knobs for the AWA

hi mick, looks good, did you have a thread on how you cast them?
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Old 16th Sep 2021, 7:40 pm   #3
Lloyd 1985
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Default Re: Making /casting knobs for the AWA

Nice one! They came out well, and certainly look the part on the radio (nice radio by the way!). Bubbles in the mould and the final piece are always a problem, eliminating them totally would need a vacuum chamber, which is probably out of reach of most of us restorers, but making the mould with the knob face up keeps the worst bubbles away from the face of the knob, and then turning the mould upside down to cast the final piece makes sure the bubbles end up at the back of the knob out of sight! I'm guessing this is how you made yours too

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Old 17th Sep 2021, 8:04 am   #4
vinrads
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Default Re: Making /casting knobs for the AWA

Thanks Lloyd ,I was pleased how they turned out as you say I cast them face down ,
Hi Kevin this the stuff I used the mould is made of casting silicone rubber ,the the hard part is getting the ratio of 9.75/1 you need a steady hand ,don't be in a rush give it two days to set . Mick.
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Old 17th Sep 2021, 9:49 am   #5
Lloyd 1985
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Default Re: Making /casting knobs for the AWA

That’s the same stuff I’ve got, it’s pretty good so far! Is it 9.75/1 by weight as well? I’ll admit I did mix it wrong the first time I used it, took ages to go off!

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Old 17th Sep 2021, 5:57 pm   #6
David G4EBT
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Default Re: Making /casting knobs for the AWA

They look spot on Mick and the radio looks bonny too!

The main challenge (apart from having one good knob to use as a pattern), isn't so much casting the knobs, but getting the spindle mounting hole to be perfectly concentric and exactly perpendicular to the knob. If it's just 1mm off centre when rotated, that become 2mm swing from side to side, which is noticeable - even worse if the spindle hole isn't knob.

It's next to impossible to drill a perfectly concentric & perpendicular hole in the knob with a pillar drill, less still with a hand drill, but by using a lathe as you did with your chum, it is. The brass insert can also be drilled either 1/4" (the usual size for vintage British or American vintage radios) or 6mm for continental ones.

As the casting medium I've had quite a bit of success using Plastic Padding two-part epoxy 'Super Steel'.

It sets rock hard, can be drilled, filed or turned.
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Old 17th Sep 2021, 6:13 pm   #7
Bazz4CQJ
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Default Re: Making /casting knobs for the AWA

I guess that that mix ratio is actually 9.75:1.00 ? That's a measurement of around 1 in 1000, so that pretty much ensures that it would make a difference whether you use volume or weight as the measure... or maybe not, at least for purposes of making knobs for a radio .

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Old 17th Sep 2021, 6:25 pm   #8
Lloyd 1985
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Default Re: Making /casting knobs for the AWA

That's the problem I had with the knobs I made for my Ekco A22, I tried to cast the new knobs with the pre-drilled and tapped insert, so it would come out of the mould and be ready to fit, after a little bit of sanding, to the radio. It's not so noticeable on the volume and wavechange knobs, but the tuning knob is awful!!! I'm going to have another go when I get time, this time with better jigs that become part of the mould. I would use the lathe, but the chuck on mine is too small to accept even the volume knob!

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Old 18th Sep 2021, 8:36 am   #9
vinrads
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Default Re: Making /casting knobs for the AWA

Quote:
Originally Posted by Bazz4CQJ View Post
I guess that that mix ratio is actually 9.75:1.00 ? That's a measurement of around 1 in 1000, so that pretty much ensures that it would make a difference whether you use volume or weight as the measure... or maybe not, at least for purposes of making knobs for a radio .

B
Measurement by weight is recommended . Mick.
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