401 platter 'dinged'- can it be skimmed?!

301, 401, plinths and assorted idler stuff
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thomas
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#1 401 platter 'dinged'- can it be skimmed?!

Post by thomas »

After cleaning out and oiling the motor & bearing I've finally figured out why I've always had speed stability problems with this 401- the platter has been dropped at some time in its life and there's a subtle 'ding' in it I can just see when its spinning. Also, swapping out just the platter solves the stability...
So I was wondering how feasible it would be to get the inner side 'skimmed' but then presumably it would need rebalancing afterwards.. any thoughts, please? Anyone have a lathe?! I would pop round to my local machine shop, sadly, manufacturing industry is a bit scarce darn sarf in Kent..
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Thomas
ps hoping to get to Egg- currently doing my first ever 'breadboard' (D3a, Tx, 2A3)!
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pre65
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#2

Post by pre65 »

I would offer to help but my lathe is just not up to the accuracy needed,and not big enough to swing a Garrard platter.
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#3

Post by cressy »

hi thomas, in principle it should be 'skimmable' but it depends how deep the ding is and where abouts on the inner rim it is. it would need a big lathe and a skilled operator though! as far as i know the platters were statically balanced but not dynamically balanced. however greg would be the person to ask about this, he knows a heck of alot more about them than me. if its a subtle ding rather than a chunk out of it then you might get away with it. if you can get it done at reasonable money then its probably a good thing to try as platters tend to be pretty scarce. but i doubt it would be cheap, skilled lathe operators are pretty scarce too!
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thomas
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#4

Post by thomas »

Hi again
The 'ding' is ever so slight but the paint is chipped below the strobe markings as if the platter had hit a 'corner' of something and its barely just discernible visibly when spinning. Dunno how much would have to be skimmed off, probably not much. The phrase 'operator skill needed' is now starting to worry me a bit!
Curiously, what the platter does when playing is a regular, subtle slowing and speeding- the strobe light shows a regular 'pulsing' of the lit platter markings and even more curiously my cloth ears can hear this...wobbly piano or keyboards, usually...
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shane
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#5

Post by shane »

According to this, 401 platters were only balanced statically. What is more of note is that the tapered hole for the spindle and the inner running surface were machined in the same operation to ensure concentricity.

http://www.audio-talk.co.uk/phpBB2/view ... 3979#33979
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#6

Post by thomas »

Thanks for that article- v interesting reading!
I've taken the plunge and rung a machine shop who skims brake housings for £12 a go- gulp- I guess my precious platter is scrap anyway so what have I got to loose?!
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#7

Post by pre65 »

thomas wrote:Thanks for that article- v interesting reading!
I've taken the plunge and rung a machine shop who skims brake housings for £12 a go- gulp- I guess my precious platter is scrap anyway so what have I got to loose?!
£12. :wink:

I don't know how it would be set up, but if the machinist does not use a dial gauge to check for absolute concentricity then you (or the platter) are doomed. :shock:

The diameter as is does not want to be increased one iota, only the "ding" needs the most subtle bit of machining. That is why it needs to be done by an "expert". :wink:

Someone into model engineering might be suitably skilled, and enthusiastic enough to have a proper go.
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#8

Post by Lee S »

For £12 you could get a Lenco GL75 which is a damn site less complex and finnicky than a Garrard and IMHO sounds better anyway...... :wink: :lol:
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thomas
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#9

Post by thomas »

Thanks pre65 for the tips I'm more than a bit doubtful about this..!
Not sure I can get a Lenco for £12?!!
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Nick
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#10

Post by Nick »

pre65 wrote:
thomas wrote:Thanks for that article- v interesting reading!
I've taken the plunge and rung a machine shop who skims brake housings for £12 a go- gulp- I guess my precious platter is scrap anyway so what have I got to loose?!
£12. :wink:

I don't know how it would be set up, but if the machinist does not use a dial gauge to check for absolute concentricity then you (or the platter) are doomed. :shock:

The diameter as is does not want to be increased one iota, only the "ding" needs the most subtle bit of machining. That is why it needs to be done by an "expert". :wink:

Someone into model engineering might be suitably skilled, and enthusiastic enough to have a proper go.
Why does the absolute diameter matter? I thought it had a speed control?

Can't it just be centred with the headstock to the spindle hole?
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pre65
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#11

Post by pre65 »

Quote "Why does the absolute diameter matter? I thought it had a speed control?"

Indeed it does, but if it is centred properly (and I mean properly) then there need be no change in the diameter, or perhaps just 1/4 of a gnats todger.

Quote "Can't it just be centred with the headstock to the spindle hole?"

Yes it can, but you make it sound like that is an easy thing to do. You have to hold it somehow. I doubt if most chucks would have the required accuracy, and bolting it on a faceplate (my preferred option if my lathe was big enough) would need setting up with a dial gauge to ensure it was running true.

All in my umble opinion of course.
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Nick
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#12

Post by Nick »

I am sure you are right Phil, I am happy to defer to your experience on this matter. I was just thinking out loud that the requirements of a disk drum skim would be similar to the platter in that it would need to be centred.

In the past I am sure there wound be loads of local machine shops who could do it, or someone who was a machinist who could have done it in his lunch break for a pint.

Its much the same problem as me and Ali are having finding someone to make a chassis for the static amps.
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thomas
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#13

Post by thomas »

Well I'm over to Sidcup machine shop tomorrow so we'll see how it goes....!
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#14

Post by Mike H »

I would imagine if you had a face plate with a hole in the centre, which precisely matches the spindle size :?:


 
 
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pre65
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#15

Post by pre65 »

Mike H wrote:I would imagine if you had a face plate with a hole in the centre, which precisely matches the spindle size :?:


 
In principle, yes !

But, the taper would be facing the wrong way. :?

Unless you made a dummy spindle with the taper reversed ? Still reckon you would at least have to check it with a dial gauge.

Precision turning is a lot more skilled than most of whot I does. :wink:
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