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

301, 401, plinths and assorted idler stuff
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Dave the bass
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#46

Post by Dave the bass »

Lee S wrote: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:
^^^ Only just seen this :lol: Yeah! Tell 'em Bro!

Big up the Goldring/Lenco Massiff.
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thomas
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#47

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:)
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#48 why machine it??

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If a weight has hit it on the face and has actually dented through to the back all you need is it being laid on a polished steel surface and put under a hydraulic press - if one used a (for arguments sake) fifty ton press with a 3" diameter ram and on the inside of the platter place a smaller, say 1/2" diameter piece of steel right on top of the dent then the tonnage you can apply in that one place is phenomenal - you will have not removed any material at all then so the platter should still be in balance or at least no worse than it was before the accident - as for it slipping on the tapered spindle just ensure it is not 'bottoming' out on anything - you can check this with some engineers blue - put a thin film inside the taper and at the bottom end of the base around the tapered hole - if it is bottoming out then all you need do is lightly stone the bottom so it can sit on the taper properly - hope this makes sense
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Greg
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#49 Re: why machine it??

Post by Greg »

DewiSant wrote:If a weight has hit it on the face and has actually dented through to the back all you need is it being laid on a polished steel surface and put under a hydraulic press - if one used a (for arguments sake) fifty ton press with a 3" diameter ram and on the inside of the platter place a smaller, say 1/2" diameter piece of steel right on top of the dent then the tonnage you can apply in that one place is phenomenal
Sounds good. Where do you suggest we and in particular Thomas access' that very useful service?

Actually, I don't think you are getting what is required here, but I'm happy to eat my words if you can explain adequately. Please have a go!
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thomas
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#50

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I had the inner surface of the platter checked for tolerances on a lathe- the chap doing it knew his stuff! The ding on the 'outside' actually didn't distort the inner surface...

My suspicions have moved on to the idler wheel; I must admit the Garrard is in my loft presently as a spare, but I've been waiting a while for a cheapie substitute to show up on epay!
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#51 Re: why machine it??

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Greg wrote:
DewiSant wrote:If a weight has hit it on the face and has actually dented through to the back all you need is it being laid on a polished steel surface and put under a hydraulic press - if one used a (for arguments sake) fifty ton press with a 3" diameter ram and on the inside of the platter place a smaller, say 1/2" diameter piece of steel right on top of the dent then the tonnage you can apply in that one place is phenomenal
Sounds good. Where do you suggest we and in particular Thomas access' that very useful service?

Actually, I don't think you are getting what is required here, but I'm happy to eat my words if you can explain adequately. Please have a go!
eyes down look in for a full house :D

I will do my best for you

1) when your car has a 'dint' in the wing a good bodywork man can 'tap' the back of the dint until it reforms into its original shape without the use of handfuls of filler compound i.e. a Rolls Royce bodywork man or any really competent bodywork man for that matter

2) unless the platter had something seriously heavy dropped on it the same applies in that 250/300 tons applied to the back of the platter over the dint would be enough to force the dint back into position whether it wants to go or not it has little choice in the matter -

3) thus as no material has been removed from the platter if it was balanced before it was struck by an unknown object it should be after

4) because the spring in the metal may allow it to spring back a thou or two when the ram pressure is released from the platter when this is measured using a Dial Test Indicator if it has dropped back say for arguments sake three thou then placing either a three, four, five or six thou brass shim under the platter or even Aluminium plate then repressing the platter should take it past it's normal position then when the pressure is released it will spring back exactly where it should be

5) using a Dial Test Indicator with 0.0001" (a tenth of a thousand of an inch) resolution it would be possible to get her back as near perfect as possible

6) another possibility would be to keep the ram pressure on the back of the platter for perhaps a week then there is less likelihood of it springing back at all because the metal will give even more under sustained pressure rather than a quick burst of it then letting the pressure off

7) now for the platter slipping on it's tapered spindle - these tapers cannot fail to grip unless something is restricting it - if the spindle has a seat/landing/step directly under where the taper ends on the spindle guaranteed that's why it is seating properly and needs locktite to help it grip

8) this can be easily proved quickly with some 'engineers blue' - with a cotton bud apply a thin film to the tapered bore of the platter and the underneath of the platter bore - clean the platter tapered spindle as clean as you can possibly get it (use some metal polish like brasso) then clean it with petrol or other solvent until it is spotlessly clean - drop the platter onto the spindle and rotate it back and forth - lift the platter back of and you will find 'witnesses' of where it is touching and where it is not - a heavy transfer of 'blue' is where there is a problem -

9) if the only heavy blue witness is on the tapered part of the spindle then it is the finish of the platter bore or spindle taper that is stopping it seating properly - you should be able to see where they are not touching quite easily with the 'lack' of blue in any position -

10) if the tapered bore of the platter is at fault then it just needs polishing until it seats properly - TAKE GREAT CARE NOT TO REMOVE ANT REAL MEAT FROM THE BORE - we are on about tens of thous here not even one or two thou because the amount one or two thou removed will make to where it seats back onto its spindle is not the one or two thou you have removed but probably twenty or thirty thou at LEAST

11) if the 'rough' is on the spindle then it must be removed from the unit and polished until it seats properly - again you must not overdo it because the same as polishing the bore to much applies

hope this explains it more for you

Dewi
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pre65
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#52

Post by pre65 »

I thought the problem on Thomas's platter was on the peripheral outer face ?

ie where the speed strobe pattern is.
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#53

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thomas wrote:I had the inner surface of the platter checked for tolerances on a lathe- the chap doing it knew his stuff! The ding on the 'outside' actually didn't distort the inner surface...

My suspicions have moved on to the idler wheel; I must admit the Garrard is in my loft presently as a spare, but I've been waiting a while for a cheapie substitute to show up on epay!
if the underside of the platter has been machined then the only way of ensuring it's 'truth' is with ground flat surface again with engineers blue - cover the ground plate with a thin film of blue and check it out

now if indeed it is truly flat then the only way out is to 'scrape' the offending raised part using a bearing scraper - again using the blue on a surface plate moving the platter back on forth on the plate - turn it back over and the raised part will be bright blue - gently scrape away the 'blued' area and back on the surface plate again until the whole face is 'blue' - save all the scrapings for weighing the amount of material you have removed so you know exactly how much weight needs to go back on the underside of the platter

yes you will still have the mark on the platter where it was struck but I bet it will be small once the raised bit is removed - and you can always fill it provided the filler has the same characteristics as the base metal
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pre65
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#54

Post by pre65 »

Like Greg, I'm not sure Dewi understands what the original problem was. :?
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Dave the bass
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#55

Post by Dave the bass »

<internet fight-mode invoked>

Nah! You're all wrong, Thomas has solved the problem by bunging it in the loft (where they belong...) and buying an SL1200 which is a lot better anyway.

</internet fight-mode>

:-)

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Nick
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#56

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Instead of just saying the problem was not understood, maybe explaining the problem would help.

Its my understanding the dint was on the outside of the rim of the platter, ie the curved part, so I don't think a simple press would help as you would need a female part to the die that matched the curviture of platter circumferance.

In general though I think small (50 tonne) presses are quiet common and used for general enginearing and motor repair.
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thomas
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#57

Post by thomas »

Nah! You're all wrong, Thomas has solved the problem by bunging it in the loft (where they belong...) and buying an SL1200 which is a lot better anyway.
OOh cheeky!!
Aksherly the sl1200 is in the kitchen, lovely it is too... I've another 401 in the main room with perfect speed control (well as much as a 401 can be... :D )
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#58

Post by DewiSant »

Nick wrote:Instead of just saying the problem was not understood, maybe explaining the problem would help.

Its my understanding the dint was on the outside of the rim of the platter, ie the curved part, so I don't think a simple press would help as you would need a female part to the die that matched the curviture of platter circumferance.

In general though I think small (50 tonne) presses are quiet common and used for general enginearing and motor repair.
you would need two dies an inner and an outer
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Nick
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#59

Post by Nick »

DewiSant wrote: you would need two dies an inner and an outer
Yep, sort of goes without saying :-)

Though I used to design the control systems for super plastic forming presses, they only had a female part (kind of).
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