Question about Dynamically Balancing a Platter

[CableMaker1]

I have a question about Dynamically Balancing a Platter. It was encouraged by a forum member to ask the question for all to see so that it can be answered with as many viewpoints as possible - so here goes my question -

I understand that to dynamically balance a platter to a turntable requires drilling holes into the platter. I am sure that mathematics and physics come into play on where to drill the holes - as being a hobbyist myself, I have no plans to do this as it would take a unique knowledge to position the holes in its proper place as I am not privileged in this area.

But the question is why would dynamically balancing a platter for a turntable such as the popular SL1200MK2 (or any commercially manufactured tt from say Thornes, Dual, Technics, Kenwood, Onkyo, etc.) drive the cost up significantly? If one were to drill the holes for a platter that matches to a specific turntable, would the holes be in the same location on the platter for that same turntable that is designed for, and if so, would the cost of the holes be paid for in itself when manufacturing hundreds to thousands of the same TT since the research was already done? Or is it a unique process for each turntable/platter that is constructed and manufactured?

Thanks everyone for your thoughts on this.

[shane]

There's a bit more to it than just drilling holes! Last time you bought a new pair of tyres for your car, the nice man in the boiler suit will have spun your wheels up on a big computerised machine which measured the out-of-balance forces using strain guages on it's shaft bearings and told him exactly where to put the balance weights.Although both wheels look the same, he didn't put the balance weights in the same place on both, because they balance out differently due to slight variations in the materials of the wheels and tyres. Exactly the same principal applies to balancing a platter, except that instead of adding weight by sticking on lumps of lead, we remove it by drilling holes. Working out where to drill the holes is a complex process requiring expensive equipment, but given that most turntable platters are accurately cast and don't go round very fast, it usually isn't necessary to balance them to the Nth degree. The only turntable I can think of off hand that had balancing holes in it was the Lenco L75. Certainly Linn didn't bother, and neither did we. Anyone know if the SL1210 is balanced? I rather doubt it.

[phonomac]

We need to distinguish between static and dynamic balancing.

Dynamic balancing is as Shane describes when the object is spun at a speed usually above its normal working speed, and is normally applied to objects which are a) working at significant speed, and b) are substantially 3-dimensional (think car wheel/tyre, where the thickness is a large fraction of the diameter). The majority of turntable platters are thin in relation to their diameter.

Static balancing means arranging for an object to pivot on its axis of rotation (which is held in a horizontal position) and observing whether or not it consistently stops with one spot at the bottom. That is the heavy bit, and can be lightened by drilling one or several holes. For thin objects static balancing can be sufficient (did it in my student days when we lightened a Mini flywheel for a race engine, and didn't have access to a dynamic balancer - it revved to 8,000 rpm and stayed in one piece and attached to the crankshaft for three seasons! Maybe more luck than judgment!)

In the case of turntable platters, balance will be almost entirely a function of the platter, so any balanced platter will be balanced on virtually all turntables for which it is designed. Platters will need to be balanced individually because of material variation and casting quality. However, again as Shane says given the low speed at which turntables operate (out of balance forces being proportional to speed) and good quality castings balancing isn't strictly necessary.

I don't know if SL1200 platters are balanced, but those of the SL1300/1400/1500Mk2 series, and the SP10 Mk2 and SP15 are.

regards

Angus

[awkwardbydesign]

So why did Lenco consider it necessary on the 75? Rough casting technique? And didn't they discontnue the practice? (Lenco novice!)

[NRG]

The SP10 platter is also balanced...

[YNWaN]

Balancing is usually applied to platters that are not post machined on all surfaces after casting - it may take the form of drilling shallow holes (to remove material) or adding weights. If the platter has cast surfaces and has no balancing the reason is invariably to reduce cost of manufacture.

However, within the context of small scale production, the extra time required to balance the platter should not make much difference. On the other hand, after market platters are usually machined on all surfaces and thought not to require further balancing.

[CableMaker1]

I don't know if SL1200 platters are balanced, but those of the SL1300/1400/1500Mk2 series, and the SP10 Mk2 and SP15 are.


The SL12X0MK-2 and its MK-X Series Varients are not balanced platters. The SL1300/1400/1500MK-2 and the SP10 MK2 (and MK3? I would assume so since it superseded the MK2) from what I read are balanced. I do not know if the SP25 was balanced since it was a cheaper TT. of the SP Series.

For the reasons pointed out here re-enforces my reasoning that I, nor any other hobbyist, should even attempt to drill holes in their platter, unless they have specific knowledge of what they are doing, and such equipment that they can measure to accomplish the task at hand.

Thornes did have dynamic balancing on one of their TT Platters, which was exposed by a storage bidding winner (Darrel Sheets) in an episode of Storage Wars.

Thanks all for your input. It was a worthwhile read for a better understanding of this topic.

[Qwin]

Agree with what has been said - at the speeds involved balancing is not a major issue and normal machining methods should give a part regular enough for the task. Lets not forget, to get it spot on you would have to balance the record and any mat used and also apply a force equal to the stylus presure to the opposite side of the platter to counter act its effect. It depends how far you want to take these things.