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panzerholz plinth?

No.. it is solid all the way across. It is immensely stable and has the advantage of simplicity. Your acrylic platter sounds like a lot of work.
What I was trying to achieve was the most simplified and stripped down design. Hopefully others will look at it and realise that they can build something similar themselves.
 
Well they were a lot of work for someone else at the machine shop I suppose I can't remember what I did with them, must be in the loft somewhere I guess.

Moving most of the mass to the edge of a spinning thing, even if it means making it lighter as a whole, means it's much more difficult to change it's velocity. For a given total mass, in that way, you can be much more stable. A large mass on its own is only a little more stable really than a lighter mass assuming the mass is distributed evenly in both of them. I can't remember all the math now but assuming you could make the platter infinately light across its diameter and only have all of the mass at the edge it would have a moment of inertia 12 times higher (or so my sketchy memory says) that is what a car fly wheel or a water wheel in a mill tries to achieve. Obviously the extremes are not possible, you just can't have an infinitely light hub! But you get my drift. Good solid maths making things better for no more outlay just like the math for the material damping did.
 
I do and did take your point but my design had to 'design out' other constraints , eg , I wanted to use ring magnets that were as wide as possible ( for reasons due to the properties of ring magnets ) The 100mm magnets were chosen both for that factor and that they were the ones available in the thinness that I wanted. If you start searching online for ring magnets you will see how very few wide and yet thin magnets are available. Thicker ones dominate but they were too strong for my needs... the platter would have had to weigh 30 kilos to counteract their opposing force.
The magnets I chose ( by the physics of it ) chose the weight of the platter. If I went down the route you suggest ( and i did do the maths ) the platter would have had to be over 140mm high and that I didn't like the look of. It also greatly increases the cost of the billet of aluminium that you have to start with only to leave most of it as swarf on the workshop floor.
The bottom line of it for me is that I achieved the design 'look' I wanted for an amount of money that I was willing to commit and the physics of the design are close enough to good enough for my purposes.
It spins at two requested speeds smoothly and silently and , it is so 'massy' that nothing in its drive train has any detectable effect on speed stability. The sheer weight of the platter and the belt drive system smooth out any momentary anomalies in the speed.I doubt that there is any wow or flutter nor any bearing noise. The platter is also so massive that it seems to be sonically dead...no hint of ringing.
Also I should mention that the electronics controlling my motor are accurate to within a ridiculous n'th of a degree and have the grip of the devil on the motor speed.
 
Helen Bach said:
Luverly job, Joe. I hope it sounds as good as it looks (or, I hope it doesn't 'sound' at all!)

May I use a pic as an exemplar of what can (should) be done, all credit given?

Just as a tiny comment, no criticism intended, I understand that the carbon fibre is an aesthetic consideration, but will not add to the goodness of the Panzerholz. The non-rectilinear design also reduces modal density.

One question, the magnetic bearing, is any part of the spindle magnetic? Could it have an effect on MC carts? I ask because I am looking at a design for a bearing which uses an oil-based ferrofluid and neo-magnet to keep some oil between the ball and thrust plate. However, the steel spindle becomes magnetic. I may try a non-steel ball, but just a thought!
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id be interested in your thoughts using panzerholz as a tonearm board,ive used it in the past and it sounded very good.
my current turntable uses a 5mm aluminum plate on top of a block of 21mm mdf.
 
Be interested to hear about the magnets and the properties of the larger diameter that make them more suitable, you got any links?
 
Oh , I see, given the mass and the fact that it's being driven anyway how much real difference does that make? I'm loving this thread, learning more stuff. I spent last night looking through some of the links Joe posted and got the calculator out to work through some of the magnetism equations. I do love getting the calculator out.
 
Ok... whilst I am posting up useful links.
If you combine the pulley calculator link....https://www.blocklayer.com/pulley-belt.aspx
with this O-ring supplier link..https://www.polymax.co.uk/o-rings/rubber-nbr-oring
with a small element of judicious jiggling between the two and the use of Pi to determine the O-ring diameter you find that you can buy , say , 320mm x 3mm o-rings ( which you will use for drive belts ) for the princely sum of 56p each ( thats pence ! ) . So that would be 25 drive belts for £14 with free delivery on top of that sweet deal.
The higher end turntable manufacturers will charge you up to £33 EACH in some cases
You can imagine....I have a very large stack of spare belts

https://www.ebay.co.uk/itm/Michell-Engineering-Orbe-SE-Turntable-Drive-Belt/182807503191?_trkparms=aid=555017&algo=PL.CASSINI&ao=1&asc=20170907081254&meid=1dd58c8293a04ecf9aa9c97bbe4a16b6&pid=100281&rk=7&rkt=12&&itm=182807503191&_trksid=p2045573.c100281.m3567 for a 56p o-ring

http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=232218259734 .... £39 !!!! ...for a 56p o-ring
 
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orangeart said:
Oh , I see, given the mass and the fact that it's being driven anyway how much real difference does that make? .
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I am no expert... you need either Mark or Simon but, With a variable field you might get an effect you would liken to the cogging of a motor and you could get a wave like ride across the two opposing fields resulting in the platter rising and falling or almost vibrating. As you intimate the mass of my platter would go quite a way to eliminate those possibilities but it was, from my point of view better to design them out in the first place . So.. wide ring magnets it was.
 
I tried different size magnets when I did my rega, measured the platter height with a jewel probe run out gauge. It was 100ths of a mm, slighter lower with wider rings. Neither was worth worrying about.
 
sq225917 said:
I tried different size magnets when I did my rega, measured the platter height with a jewel probe run out gauge. It was 100ths of a mm, slighter lower with wider rings. Neither was worth worrying about.
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Interesting, so in all the theoretical problem, even with your lighter platter, turned out to cause less runout than that of the record warp probably did? Remind me, did yours completely levitate or just take some of the friction of your thrust plate?

I'm starting to feel the need to build a deck again...I've got a half built phono stage somewhere...
 
I’m in the process of developing a new type of magnetic bearing. I should have a prototype running in a week or so - awaiting the delivery of some magnets.
 
YNWOAN said:
I’m in the process of developing a new type of magnetic bearing. I should have a prototype running in a week or so - awaiting the delivery of some magnets.
Click to expand...

Sounds interesting, is that something you are planning on marketing?
 
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orangeart said:
. I'm especially interested in the build of the bearing and the math you had to do for the levitation.
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I had forgotten that I'd done this.. when I didn't quite believe the maths I resorted to empiricism and built a jig.

Aluminium tube the width of the internal width of the ring magnet is glued to a board.

Place one magnet at the bottom of the tube and place the other magnet on the tube to oppose the other magnet.

Place the jig on a suitable set of scales and press the top magnet down towards the bottom magnet and check the reading you are getting on the scales.

I was looking something around a 5mm gap between the two magnets and a reading on the scales of 15 kilos. It was dead on.

The bigger tube was for the magnets I ended up using... on the smaller one I have put two 60x40 magnets to show you how much they stay apart with no weight on them.

Those magnets are just pushing each other that far apart.

IMG_1183.jpg
 
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I do like a good jig, so much so I have a workshop full of them..
You asked me about a polisher, we may have one in the works, what is it for ?
 
You literally can’t have too many jigs. Today I made a jig that needed another jig to align it :).
 
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