Let's make a DIYAUDIO TT

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diyAudio Editor
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Well to both our credits, I seem to have communiocated my idea!

With the flat bearing you suggest,, the ball could maybe be smaller than 50mm.

As you say, the flat plate adds more complications, but solves a lot of problems. If others like this approach, I think we should all ask locally how much it costs to make a disk with a 25mm hole and a plate with about a 50mm hole. I suspect that it is easier to make holes in standard sizes (1 or 2" in US) because they probably would use tubular drills with diamond edge.

The hope is by using the construction industry vs. a machine shop, we could save. Wait!!! we could also use granite!!!!
Those granite guys cut holes and grind very flat surfaces all day!!!
I know for a fact that they can cut circles and holes too.
Not cheap, but maybe cheap compared to machining.
 
frugal-phile™
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Variac said:
we could also use granite!!!!

I have seen at least one thread -- and perhaps Dice45 was a participant -- that found significantly negative qualities with granite. But there are other stones, and if they can deal with stone, they can perhaps deal with some artificial concoction we come up with.

Which reminds me i have seen no more on the possibility of recycling vinyl records into a platter... anyone done more than set them in the sun to make trendy looking bowls?

dave
 
Dave,

do you have any idea why i save my loathed records and do not trash them?
Yes, if i have 20cm of it, i will make a platter of it.

Granite: I see nothing wrong with granite as a bearing material if it is glued to huge slab of acrylic or PVC. In fact, i would expect highest precision form ground granite surfaces.And i woiuld prefer granite to many other stones as far as resonance behaviour is concerned.
But my absolute favourite is Diabas (also called greenstone). It is denser than even granite and way less resonant and the esoteric misgivings mentioned below do not apply.

There are some esoteric aspects which vote against granite. Some people, Steward Ono among them, have reported that granite's mere presence, even in small shreds, affect sonics. No explanations, somehow it is (shamanically :) ) incompatible with the human body feeling well. And that removing of he granite piece from the space one is sitting in and listening was removing the stress experienced before.
A TT is meant to make the listener feel well and happy. So, from the esoteric point of view, no vote for granite.

I am reporting this, i do not necessarily second that point. My own TT sits on a thick granite slab for 17 years now. And sonics always have been terrific.
But then, i hate to admit it, but i have problems with chronic headache. Severe problems. Doctor does'n find physical reasons for it. Is it the granite slab? Dunno.
 
Any esoteric objections against using blue grenna? I have a lot of this over when I put a new floor in the hallway.

I would not take the ball to small. If it is used as a radial bearing, then the surface in that "direction" should not be to small. So I would stay with a large ball, 50mm looks about right.
 
It's the stone I put in when I had the hallway renewed. Due to some pessimistic guess (or optimistic, depending on your viewpoint) I ended with about 4m^2 spare. These are slabs 40x40x2 cm. Don't know the exact mineralogical definition, but it is a kind of calcium based stone, found in the caucasus if I remember well. Comes with a green or blue hue dominant. Just kidding really.

Personally, I would stick to glass. If you try to get flat stone, most (cheaper) stoneworkers will give you polished ones. This is not flat. If you want the really flat stuff like the measuring slabs, it will be probably more expensive than glass. Glass comes flat enough for our purpose if you order the correct sort. But it will require building up the needed height.
 
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I was at a stone fabricator a few months ago, and they were surface grinding a slab. I'll bet they can get it pretty flat, even if it isn't a measuring block.

BUT, if float glass is flat enough for out purposes, I'm sure it will be cheaper. Someone should actually talk to a glass fabricator that makes tabletops and see!

I agree, the ball prob has to be pretty big!
 
bearing surface machining

I am glad to see that the group seems to be converging on the aerostatic bearing concept. I think we all agree that the challenge is obtaining a suitably accurate bearing surface, both for the stationary element (stator) and the platter (rotor).

I have a scheme to obtain this result, without the need for super-accurate grinding:

1. Obtain a reasonable (+/- 0.1 mm or so) surface finish on both rotor & stator

2. Pressurize the bearing with a suitable air source. At this time, there will likely be contact at the high points - that is Ok

3. Introduce a fine abrasive slurry into the air supply, and slowly drive the platter with a small motor until the bearing surfaces are lapped smooth.

We can start with a coarse abrasive, working up to ultrafine powders. This could yeild mirror-smooth finishes.

A source of abrasive can be automotive valve grinding compound, and/or optical mirror finishing compound.

There may be a residual radial waviness, but the rotor & stator should be perfectly matched.

What does the group think?
 
diyAudio Editor
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The abrasive concept is good I think-how to do it will require a bit of thought.
We could just add a slurry of abrasive between the surfaces and turn it by hand or motor. without trying to blow it in with the pump. The ball part is perfect already, if we do it that way, so we would want to keep rough abrasives away. Maybe we could add the cast epoxy ball socket after, but the motor wouldn't work to turn it until the socket is added. Some are saying that the glass might be smooth enough already. I assume they are talking about float glass, which is made by pouring molten glass over a surface of molten tin I believe. I've always heard that it is really quite flat, In fact, that is what they use to make mirrors! I guess there is ground glass too.

Brigar electronics has a Maxon motor for $29.95
www.brigarelectronics.com

Is it the right sort of thing? Is the price good?
 
All,
it's about full moon (and my corner teeth are growing :) ) and i could not sleep last night. So, there was some idea pestering me. ... based on the posts of Havoc and Mark.

cheapocheapo air bearing. Look at the attached pix. The drawing is in fact a Xsection taken from the 3D model. The components have ballons with numbers in it, the colour of the balloon circle is the same as the numbered component. And, dont pester me with minor hatching errors :)

Here it goes:
1: platter with center hole (no center pin)

2: axial bearing rotor: slab of glass or granite, glued to the platter bottom

3: axial bearing stator: slab of glass or granite, glued into the plinth

4: TT plinth

5: centering plug (centering (1),(2) and (7) to each other)

6: radial bearing stator: brass plug with the spherical bearing surface epoxied on; radially soft-centered to (3) by O-rings or a greased gap or whatever, vertical distance to (3) adjustable via 3 differntial screws (9)

7: radial bearing rotor: a bearing grade ball of 60mm dia.

8: mounting screw to make the ball removable in order to unmount the platter.

9: 3 differntial screws. Inner tap: M4 pitch: 0.7mm, outer tap: M7x0.75, pitch 0.75mm.
REsulting differential pitch: 0.75-0.7=0.05mm per revolution.

The ultimate simplicity of this layout comes from the fact that the only tightly tolerated dimensions are planarity of the flat slabs (any bullet-proof or mirror grade glass will do) and the sphericity of the bearing ball. The epoxied spherical bearing surface of (6) is generated by the bearing ball itself, this fits. As (6) is adjusted vertically to (3), no precision maching is required here. (6) even may be slightly tilted, due to the bearing gap being spherical.

Bearing is adapted to the application. A platter does not face big radial forces. So "soft"-centering via O-rings is totally acceptable. Adjusting the bearing gaps happens via 3 diff.screws (9). So (6) pulls the assembly (1)(2)(5)(7)(8) down via the bearing forces in the spherical air gap between (6) and (7).

The platter (1) cannot perform vertical oscillations and 3D-oscillations are damped by the mere platter height and the flat bearing gap.

Industrial air bearing units usally have either a plane surface and an opposing spherical bearing surface or two opposing spherical bearing surfaces. So that is not new. Adjusting the hollow bearing cup (6)(instead of somehow adapting the spacer (5) to length) OTOH is quite original.

"-With love - from me - to you !" :) .Comments welcome.
 

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Mark,
stay away from that maxon motor! it has a noisy tacho generator.
I just ordered a maxon REmax29 with 24V dc nominal voltage and metal brushes for the commutator. Original maxon price: about 65 ¤ with shipping. I do not toy around, i get what i specified.
The REmax certainly is the ultimate solution. But any ordinary maxon DC motor with between 18Volt and 36 Volt nominally, with friction bearings and a metal brush commutator will do fine.
NO ball bearing please and no graphite commutator. Ball bearing noise and commutator sparkle is undesirable.

I can supply such for ¤10.- a piece plus shipping, i get them from local surplus and then have to remove the gear wheel from the 2mm dia shaft (which is a bit ticklish). ¤10 is without pulley. But pulley should be no problem,
Tomorrow i help a friend to fetch his new CNC lathe. I could ask him to turn pulleys as a first CNC practising job :)

Gilid,
methinks we should be able to obtain slabs with surface flat enough for our purpose. Like bullet-proof bank counter glass. "Plywood" glass :)
But if not, methinks your grinding/lapping procedure is good. We just have to take care that no particle tries to bully its way into one of the air nozzles. Maybe we mount the final nozzles after the grinding process?

Which brings me to nozzles: they are not yet drawn in my drawings. But they are necessary.
With no nozzles: if the bearing surface is tilted, the air flow is squeezed off where it is most needed, the air oozes out at the opposite side; pressure in the gap collapses and bearing jams. Nozzles ensure that flow of air is limited, be there an opposite bearing surface or not.
And they create a row of elementary bearings, each supporting all others and if one elementary bearing quits, the others remain functional.
 
diyAudio Editor
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Hey, at least someone is thinking. I also sometimes can't sleep- due to a design idea swimming in my head!

I accept that when designing something like this, the project gets more complicated, but I would prefer to keep the fabrication more simple unless we have no other option.

First of all, you can imagine how much I have thoght of this over the years, and I have ended up with the ball attaced to the platter in my current designs- mainly because it can't be too easy to drill a hole through a hardened 50mm ball bearing. I also don't see the need for the centering o rings- the ball will keep the platter from going sideways. I also figured that the platter will be the rotor of the bearing. We could make that optional- either use the 25mm thick disk for the platter like a thicker Rega, or add another disk in another material. Likewise with the plinth, The most basic arrangement would be use the stator as the plinth.
Just have a rectangular piece of thick glass cut and edges polished.with a hole in it (next paragraph) If you want damping, you are free to add it to the bottom.

So, I envision, a 25mm thick 12" dia. glass platter with about a 45mm hole in the center. The ball won't fit all the way into the hole so it sticks down. It is epoxied into the platter hole. The epoxy is filled from above to not add any to the bearing area!
A shaft could be set into this epoxy for the record center hole.
The hole that remains above the ball is completely filled with epoxy, leaving a smooth top surface (with the shaft sticking out)

The plinth is another piece of thick glass with a 30 mm hole in it where the center of the platter is. Another piece of some material
with a 30mm hole is glued under the hole in the plinth to make the 30mm hole deep enough. another (thin) layer is added below this to seal off the hole and create a well.

(The layers under the glass plinth don't have to be glass - could be a disimilar material to help damp. Also the hole doesn't have to be accurate either because it will be lined with epoxy)

NOW, one adds just the calculated amound of epoxy to the well, the platter and ball are coated with a release agent, and the platter and ball assembly is pressed into the well. The epoxy rises just enough to reach the mid point of the ball (equator!)

After hardening , twist off the platter/ball
drill a small through the bottom of the well/socket for air
AND IT IS DONE!!!

NO machining other than the glass, Glass people make circular shapes of thick glass all the time for tables. I don't know about the 50mm hole but I've seen big holes in glass.

Waddayouthink?
 
diyAudio Editor
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R.E. the nozzles

Drilling nozzle holes in the glass plinth would add to the price.
Is it possible that the bearing would still work with all the air coming in from the hole below the ball bearing?

The pump would turn off I think when we are hanging records, so the only tipping load on the platter is the 2 gram tracking force, and the torque of the motor which would be pulling about 25mm above the center of the ball. The platter is about 100 sq inches and is supporting a 4 kilo piece of glass very evenly balanced plus the above forces. Maybe the tipping loading is trivial?

We can try an experiment of course....

No need for laminated bank glass I think. Thick glass is easy to get. Thick float glass? I don't know.
 
Mark and all,

1st,
drilling a hole into hardended steel is no problem with a tungsten carbide tipped drill bit. Apart form that, maybe a half ball or even a ball layer can be obtained.
Or un-hardened balls. Have to consult my ball supplier.
Moreover, it appeals to me to use a slightly bigger ball to form the epoxy surfaces. Bigger by the specified bearing gap. The air needs a bit space to establish a laminar flow.

2nd,
centering the bearing cup of my draft is necessary, i dio want to know exactly where my platter's center is and radial forces can pull the bearing cup sidewards via the bearing ball. And then the adjsuting screws' tips grind over the surface. Oh yes, and now and then i want to transport my TT. Without having to re-adjust the bearing afterwards.
OTOH, radial play is needed so that the bearing cup does not jam in its hole when tilted.

3rd,
as far as i understand your idea (a drawing would help), it could work albeit the spherical bearing gap appears to be slightly off-center to me. I see one point not pleasant to me: nothing keeps the platter from bouncing vertically on the air film (which, let's face it, is a progressive spring).

4th,
to have one air nozzle is simple for sure.
Einstein however says: make anything as simple as possible, but not simpler. Methinks one center nozzle is too simple. The air is flowing thru the spherical gap, then thru the flat gap and then leaving at the outer edge. Thus a pressure belly is created under the center of the platter and specific air flow is decreasing from center to edge and the platter becomes unstable against tilting.

One thing i have to comment to my drawings: air flow (nozzles and air release orifices) is not yet drawn. Trivial to me, so i forgot to mention it : the air has to face about equal gap lengthes (escape path lengthes) in any direction, edgewards or centerwards.
This calls for a ring of air nozzles for the axial as well fort the radial bearing.
 
Mark,
with my last post i have adressed your matter-of-fact points. But after a few hours of sleep, i find me asking myself "who the §$%&! does he think who he is?"
Hey, at least someone is thinking. ....
i should take this as a compliment, But i do not, i feel tense and uncomfortable, reading this: me is the one credited with thinking and the others, are they not? The others, how may they feel reading this?

Mark, stay at home with such killer statements ! :(

For the record, i muse about TTs and tonearms since 17 years and particualrly about airbearing ones! But i found the discussion here quite inspiring, i saw new ideas myself and found me reminded on ideas i had dumped ys ago for forgotten reasons.
Methinks, noone here has the monopoly of good or even original thinking. And to maintain a creative atmosphere, we should have respect for what the other members are coming up with. And.... if i come to think of it ... not brush other ideas aside before they have been fully understood.

All,
selfish me, i apologize! i should have kept my draft back for some days until we have settled on what do we want to achieve, on a technical specification.
Now we are discussing solutions instead of specifications. We discuss how to achieve things. But we do not know if we want to achieve them or not and if we want them, which priority they may have...
Doing so, we are in danger to loose vital specification items out of sight.
Harnessing the horse from the tail, methinks.
 
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I beg for mercy

Whoops, bad choice of words.
I meant someone was working on the problem all night i.e. working harder then the rest of us-including me!-not that no one else had good ideas!!

More like "way to go" not that I am the one to judge others contributions. In fact as I pointed out in my first post- I don't claim to be an expert on turntables or bearings.
So here are some smilies showing my true intent

:) :p ;) :D


Now that I hope that is over, I think it is appealing to think design can be a linear process, it doesn't very often work that way in my opinion.

In this non-corporate environment of DIY I think we can suggest possible ideas to help the decision process. If for instance, my ideas excite people because they can be made without much or any machining, then some might decide to go that way. If others feel that the sound will be compromised, then they might reject the idea.
BUT, when the essence of my idea is based on ease of manufacture, then no one can judge it until they see how it would generally be made. Until we see some options, including your drawings for your idea, it is hard to see what our choices or priorities are. Again, these are not finished designs, just examplesof the concept. In fact I agree with your earlier mention that a drawing would help explain my idea better. I will make one and post it- not as a finished product, but a concept.

With some of these ideas , we can decide what our priorities are- value for money? best turntable possible?, easy to make?

We have the luxury of going in circles a bit . We don't have a marketing deptment telling us what to do thank god.

Of course everyone should contribute technical specs too, I just feel that we can do a bit of brainstorming also

Respectfully ,
Mark
 
Mark,

i have seen creative workshops going into pieces triggered by one such killer phrase. Valuable members just retract their participation. There i am a bit paranoid about the topic :) .
Could be, such statements are triggered by the subconscious and show his intentions, differing from the conscious mind. Best cure is a profound constructive attitude.

To your suggestion: I do not object to having this design on an unsuspended TT at all. Will be cheapocheapo for sure and will work well (provided no plinth suspension is needed).

I do object against having a single nozzle. That will not work properly. That will create a worst case pressure distribution in the bearing gap.

Ease of manufacturing is always welcome.

Quality: AFAIC, i want something better than a Teres or Redpoint to way lower costs.
I do not want something slightly bettering a Rega. At same costs.
 
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Dice:

I think making the plinth suspended or unsuspended can be decided by the maker. also the platter material other than maybe the lower layer being glass.
I'm sure you are right about the nozzles, but I wonder how many are needed? 10, 100?

I want something that anyone can make at home with not too much expensive machine work. I have never heard a Teres, but would probably be happy with something almost as good.

So maybe we all can come up with a simple design that can be upgraded to ultra high end for those that want that.

I found your lecture not to be profoundly constructive so am going to retract my participation for the time being
Perhaps your statements are triggered by the subconscious and show your intentions, differing from the conscious.

If I get around to drawing up my suggestions I will check back in
 
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