I'm restoring an old tape recorder. The capstan flywheel is very lightly pitted. I'd like to polish this out.
What would be a suitable polish? Or if it's likely to be too hard for a polish, could it perhaps be sanded first?
It will need to be the very finest abrasive paper, because it needs to have an extremely smooth surface.
Daniele
It doesnt have to be THAT smooth.
However the trouble is, that anything you take off it will slow the tape down.
Th 'pro' approah wuld be to get the spindle off and make a new one, or turn it down and fit a machined sleeve to it.
But for non critical applications, go to Halfords and get some wet and dry of the finest grade - about 600 grit, cut strips and simply wind round the capstan while running.
You can use jewellers rouge or valve grinding compound or even T-cut for a final polish.
Wet and Dry goes to 1200......and on to "Flour Paper".
*Then* it might be worth using rouge etc
Don't you stand a fair chance of unbalancing the flywheel in the process?
Normally I'd turn the capstan on a lathe to get rid of the pits.
P180 paper would probably do the job, leaving a finish smooth enough to polish using a cotton mop on a polisher spindle using an abrasive stick to dress the mop. However the chances are that in the process of sanding and polishing that you will get the flywheel out of shape.
Speed it up, not slow it down.
However, I'd bet that it would make an unmeasurable difference. The pitting's very, very light.
It's not the capstan, it's the flywheel, that needs attention.
Daniele
Capstan flywheel - or capstan spindle? The finish on the flywheel has no functional consequence.
I've been wondering about this. Bearing in mind the OP commnet about a reduced flywheel diameter leading to the tape speeding up, I can only assume that this Teac deck drives on the periphery of the flywheel.
Bob
That would make the tape slower, surely? For a given rotational speed the reduced circumference would reduce the speed of the tape...
Tape capstan used to be the most precisely machined surface in an average household, taking anythng off the capstan will affect tape speed if its the part in contact with the tape bewtween it and pinch wheel.
Adam
Not even where the belt makes contact with it? I imagine it must have only a tiny effect, if any, but since the flywheel is meant to be smooth and not pitted, it seems better to restire it to that condition.
Daniele
Is it on a face a drive belt or pulley bears on?
They're normally made of a casting alloy - unfortunately sometimes Mazak which can develop pits if kept in adverse conditions - although not normally in a house. Now obviously if you grind these out in some way you'll also alter the diameter and therefore speed. I'd be inclined to fill them with good body filler then just smooth that down.
'Fraid not Frank, Smaller diameter =faster rotation for a fixed peripheral speed.
Bob
Yebbut elsewhere the OP has mentioned a belt drive to the flywheel.....
Huh, idiot. Just got my head working......
It would help if you properly described what bit you are actually talking about. Do you mean the peripheral surface of the part the tape wraps round, against which it is held by a pinch wheel and thus pulled past the recording heads?
If so then I'd leave it alone unless the pits have sharp edges which might damage the tape. The capstan surface should be almost mirror smooth. Some of the advice you've been given such as 180 grit it bleedin' absurd. 180 grit is rough as a dog's arse. 1000 grit is what you'd call a fine grit but even that, or in fact any grade of abrasive paper will destroy the original finish. You get surfaces that smooth by fine polishing with things like high speed felt mops containing very mild abrasives in a slurry form.
If you remove material and decrease the capstan's diameter then the tape speed will slow down NOT speed up. This is hardly rocket surgery. Smaller diameter = lower peripheral speed for a given diameter not the reverse. It's the capstan that drives the tape not vice versa!
If you remove the pits then the tape will no longer run at the right speed which is fairly pointless. You'll also never remove them without machining even if they're only a few thou deep. You can't polish off large amounts of metal like that by hand and have any hope of keeping the capstan truly circular. I've spent half a lifetime polishing crankshaft journals in race engines so I know what it takes to remove a given amount of metal and what surface finish you end up with. Half a thou is a shed load to remove by any sort of polishing even when you're rotating the part on a lathe. You're normally only talking about the odd tenth of a thou or even fractions of a tenth for the final polishing operation.
The most I'd do just to make sure the pits didn't have sharp edges is go over the surface very lightly with a fine metal polish, or even toothpaste, and a cloth. Try on an old capstan first to make sure that even this doesn't just lead to scratches.
He did. He said it's the flywheel. You then spend the rest of your post ranting about the capstan. Perhaps you could spend slightly less time being angry and slightly more time reading?
If he reduces the diameter of the flywheel and the flywheel is driven by a belt then reducing the diameter of the flywheel will speed the tape up.
Piddling about with the flywheel and flatting it in an attempt to remove pits (which is just about inevitable if one does it by hand) will introduce "wow". It depends if the aim is to have a working tape recorder or a pretty one that doesn't function properly.
If something is driven by a belt then it's a pulley not a flywheel! It might well be a pulley that's attached to a flywheel but it clearly isn't the same thing. So you clearly don't know for sure which bit he/she is talking about either. Until he/she makes clear which bit is being discussed, what it's made of, whether it's functional or decorative, whether it contacts the tape or a belt or not we're all pissing in the wind here.
It's the flywheel. You obviously know f*ck-all about tape recorders.
No, it's a belt drive to the edge of the flywheel.
I know exactly what he's talking about. But then unlike you I know what the inside of a tape recorder looks like.
No, you're flaming away with unrighteous anger because you don't know what you're talking about.
It's quite common on tape recorders to have a flywheel as part of the capstan assembly which is a cylinder in shape - and driven by a flat rubber belt, so no actual pulley. On some, the motor driving this will have a stepped shaft, and the belt moved from one to another to change speed. No actual pulley on that shaft either. Sounds quite crude but works ok in practice. Of course more upmarket machines will have a directly driven capstan or capstans where the motor is driven by an oscillator etc to achieve speed changes. But then this usually means separate motors for the feed and take up spools too - so more expensive.
Excellent. Profanity *and* personal abuse.
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