DIY TT design

Hullo,

Below attached is a design for a table I'm going to build.
Plinth material - high density aluminum alloy, leadshot damped.
Platter - Acrylic topped with teflon. Leadshot damping is an option I'm considering.
Bearing - All bronze. Ceramic ball and haven't decided about the thrust plate yet.
Motor - DC pll controlled - maxon or like.
Arm pod - same material as the plinth but haven't decided on the arm board itself yet. I was considering carbon fiber.

So, first, I'd appreciate comments on the design. Plus, specific suggestions on:

Arm board material?
Thrust plate material?

Thanks,
-T
 

Attachments

  • tt1.zip
    98.8 KB · Views: 399
T-rex,
1. Bearing - way too small. You have to deal with complex vibrations, caused by large and imperfectly balaced rotating mass, with the side load appied (belt tension). Look at the Teres/Galiber bearing - they have a large diameter and substantial lenghts, in order to stabilize the platter and absorb vibrations by means of the oil layer, spreaded along large contact area.
2. Armboard - I made one for my friend from aluminum-acrylic-aluminum sandwich, bolted together. It cost me 300 sheckels at one of the south Tel-Aviv local workshops and does very good job.
3. Feet - fix the ajustable rods with the counter nuts and make the supports wider. It must be very stable/rigid in both planes.
4. Motor - I'm happy with the Teres motor/controller, but the controller may be superceeded by simple variable resistor. Do not go for a cheap motor though - it is a critical part.
5. Platter - lead shot loaded platter is way superior.
6. Thrust plate - I use delrin, but ceramics/tungsten may be better.
Good luck with your project!
 
Not much time this morning to cover everything, but two things...Thrust plate- if the ball is off center just slightly, hard surfaces are not good. I was using Ceramic/Carbide, and had this problem. The ceramic ball actually ground a divot into the carbide, and a small flat appeared on the ceramic ball. I went back to nylatron (google it) for a thrust plate, and I can send you some if you would like.

Multiple screws- I have a teflon top layer, and used 48 screws. Teflon is not stiff- if enough screws are not used, it will "come up" (for lack of a better description) between the screws, especially if the mating surfaces are not dead flat to begin with.

Colby
 
Thanks Colby.

I'm attaching the newer plan, after many hours of thinking and reading a lot of info. I some how came up with some parts very similar to the Teres principles. Chance or fate? Some things just make sense to me.
Anyways, wrt the platter. Leadshot filled and topped with Teflon is the plan. Either Acrylic or aluminum platter body, still considering. I thought gluing the teflon on top of the platter body. Do the bolts really make a difference?

As for the thrust plate - I believe the platter will reach 15-20kg. Would the Nylatron hold? How does it compare with Derlin? Thanks for the offer on the Nylatron, btw.

I was thinking to center the ball using a recess in the bottom of the bearing shaft. What I don't understand is why does the ball need to have minimal friction with both upper and lower surfaces. I'm thinking it can be held tightly by the shaft recess, and spin freely on the plate.

TNX
-T
 

Attachments

  • tt4.zip
    66.9 KB · Views: 290
The design looks much better- not much I can add, but if you'd like to see my design and pictures, they are in a nearby thread "intro from newbie TT builder".

Gluing teflon sounds next to impossible, although McMaster-Carr does carry an adhesive that will bond teflon (spendy, I think).

I came across a chart of plastic characteristics today at work, and discovered that nylatron is not the best material for a thrust plate. Here are some comparisons for you...

Compressive strength (10% deflection), PSI: (higher is better)
Delrin 150 (Acetal Natural)- 18,000
Delrin (Acetal Teflon Filled)- 13,000
Teflon- N/A (Forgetaboutit!)
Nylatron- 10,000
Peek (very spendy)- 17,000
Phenolic (bearing grade)- 50,000
Cast Acrylic- 17,900
Ultem 1000- 22,000

Coefficient of friction (Dynamic): (lower is better)
Delrin 150- .25
Delrin- .14
Teflon- .07
Nylatron- .13-.16
Peek- .34
Phenolic- .21
Cast Acrylic- N/A
Ultem- N/a

I brought home a piece of Ultem today and swapped it with the Nylatron. As an experiment, I counted the seconds it took the platter to reach a dead stop after turning off the motor (Teres).
Nylatron- 28 seconds, Ultem- 40 seconds

I was goin to include a comparison of the divot produced, but it appears that my ceramic ball has indeed developed a small flat on the bottom from grinding against the carbide. But it looks like the Ultem holds up much nicer.

Your other question about the ball turning against both mating surfaces, I can't comment on. My ball is press fitted, and only rotated against the thrust plate. Seems fine to me.

Colby
 
Now this is very interesting information. As always with engineering, it looks like you need to trade off between srength and friction when choosing between these material.

I have read through your thread more than a couple of times... I think it's one of the most interesting pieces of work I've seen around the DIY pages. I do regret no pictures of the final result though:xeye:

Anyways - is your thrust plate flat (was it originally before the divot, I mean...)? I just wonder if the ball is press fitted into the shaft (or, come to think of it, is worked as an integral part of the shaft, that is the shaft comes with a small sphere in the bottom), would the ball still stray off center.

-T
 
I think that friction is not such a bad thing in the thrust bearing, as long as it is quiet and consistent. I may be wrong. For the same reason, I feel that heavier oil is better, especially for a high mass platter. It helps maintain constant speed just as inertia does- while inertia keeps the platter from slowing, drag keeps it from speeding up too quickly when the motor is making a speed adjustment.

If the ball is press fitted into a hole in the bottom of the shaft, and it is on center, it will not move off center when rotating on the plate. The hole must be bored, not just drilled, on a lathe, after indicating in the shaft, unless both features are machined at the same time.

My thrust plate is flat and parallel. I made it on a lathe, but facing on a lathe always creates a small "tit" in the center, especially if the tool is not on center, so the surface needs to be lapped flat on fine grit sandpaper to make sure it is smooth and flat.

Cheers,I was just looking at your design again. The interface between the shaft and bearing is fairly long. Take a look at mine and see how I'm actually using two bearings, near the top and bottom of the shaft. That provides the same stability, but reduces the size of the interface (and drag), and allows oil to migrate through easier. You might want to consider reducing the shaft diameter in the middle section. Keep in mind the assembly procedure- you want to still be able to guide the shaft into the bearing without mis-alignment which could damage the surfaces.

Cheers,
Colby
 
You are right Colby - my head is still spinning from reading some of the Teres threads (oil sump size and should it be worked into the bushing or the shaft, high or low viscosity oil, material of thrust plate etc.)
Anyway, I was going to add an oil sump - say work 1-2 mm into the wall of the bushing at center height, for ~50% of the contact area.

-T
 
Swiss cheese design

I'm curious why the interest in teflon as a platter material?
BTW, I spoke with the Galibier designer about 2 (perhaps 3) years ago about why he decided to bolt the Teflon from the top.
He said because he didn't think that Teflon would hold threads well. That is completely untrue, IMO. I would never build a table with the platter bolted from the top.
Think about the swiss cheese design. The record is coupled directly to a surface with about 48 or so empty spaces below it. As the stylus passes over those areas you would think that vibration would increase due to the unsupported area where the bolt head is. This cannot be good.
As far a thrust plate material, if ceramic doesn't work for you try heat treated PH 17-4 stainless or heat treated 4140.
 
Vinyl-addict,

Well it's a mechanical impedance matching thing. You get vibrations transmit better through the plane where the record and the platter meet, thus damping stylus generated record vibrations. Since the mechanical impedance between vinyl and teflon matches (as do PVC, and to a lesser degree acrylic), mechnical waves transmit easily to the platter where they are damped, rather than being refractured back into the record and the stylus in turn.
See here

BTW, makes u think why not a vynil platter - but I've seen little or no advocats for those, so decided to take the teflon route.

PVC is great btw - I have a heavily moded Thorens 124, in which the thin aluminum top platter was replaced by a ~2" solid PVC. It works very very well.

I tend to fully agree with u about the swiss cheese thing, although I wonder if the effects wont be negligible. I do intend to do my best to bond the teflon to the platter w/o screws.

Thanks for the tip on the bearing. Were u refering to the ball or the plate?

TNX
-T
 
on glueing teflon

Teflon is of course very hard to glue - though perhaps there is a special glue ($$$$?).

Many years ago I used some specially etched (I believe) teflon sheet which could then be glued with 'normal' glue, the glue holding on to the tiny holes. I had it to replace cork pads on an oboe (not sealing pads but for adjustments) and I got from a oboe repair place. I might even have a small piece left, somewhere.
I do not have any idea where to get teflon treated this way now but perhaps if you know it exsists a search would be sucessful.

Or maybe you could etch it yourself!
 
Sounds like worth pursuing. I was actually playing with the idea of playing with the teflon layer bottom in some way in order to facilitate bonding.

I just started wondering what if I just place it on the aluminum platter w/o any bonding - sort of like a mat (a 1cm mat, though). Actually, I can apply some stress in the middle (from the spindle shaft) and from the perimeter (the ALuminum actually being recessed in order to contain the teflon layer. I'm concerned though that pressing though without any pull at the bottom will eventually make the teflon concave, especially as the temperatures change.

I was even playing with the idea of a simple vacuum pull between the 2 layers - but seems too complicated.

-T
 
Thanks for the explanation about the teflon, Tee-Rex. I wasn't quite sure myself why I chose it. I know it is dense and heavy- when you knock on a piece of it, it replies with a dull thud. I knew I didn't want vibration travelling through the platter and reflecting back to the record. I originally used a piece of clear PVC, which is vinyl, for the same reason.

The teflon is very easy to machine with a good surface finish, resists almost everything chemical, cleans well, and basically just looks cool!

Only 40 of my 48 holes are under the record, and I used the smallest screws I could trust (4mm socket-head cap screws) and the counterbores for the screw heads are .250 dia. I think that the swiss cheese effect is quite minimal, especially since I am using a reflex clamp that seems to be working quite well.

Tee- will you be doing the machining yourself? And what CAD software are you using?

Colby
 
Tee-Rex said:
Vinyl-addict,

Well it's a mechanical impedance matching thing. You get vibrations transmit better through the plane where the record and the platter meet, thus damping stylus generated record vibrations. Since the mechanical impedance between vinyl and teflon matches (as do PVC, and to a lesser degree acrylic), mechnical waves transmit easily to the platter where they are damped, rather than being refractured back into the record and the stylus in turn.
See here

Thanks for the tip on the bearing. Were u refering to the ball or the plate?

TNX
-T
I have read many an article regarding mechanical impedance but never one that directly addressed the specific matching to vinyl explicitly, only theory is discussed, as was the link you just offered.
Anyway, have you or anyone you know tried using ABS as a material? I machined 2 platters a couple of years ago, 1 acrylic, 1 from ABS(mainly because I had some ABS laying around the shop), and guess what, I prefer the ABS platter. Before I made it I was to believe that acrylic was the better choice but after hearing the 2 materials, swapping back & forth, I much prefer the ABS platter, to each his own. Acrylic, in comparison is grainy, promotes more surface noise, and is just not as smooth in presentation, in my system at least.
I was referring to a ceramic thrust plate. I mentioned PH 17-4 because you can machine it, then have it heat treated to R62, surface grind it, polish it, and you'll have a great surface for your bearing to ride on.
 
Tee- will you be doing the machining yourself? And what CAD software are you using?

When this design started it was mainly based on wood - but one thing led to another, and I ended up with mainly aluminum. Since my machining capabilities are somewhat limited, I figured I'll do the simple things myself, and have a friend of mine do the more complicated stuff. The bearing is a whole different story - I'll probably pay a precision machinist to make the parts - or, buy a teres or equal bearing. I'm just not sure that getting a machinist to match the Teres spec (0.2 micron smoothness, 5 micron clearance) will cost me less.
On CAD SW - I'll probably do AutoCAD - don't have it myself but have easy access to a PC which has it on. Any other recommendations (for freeware...) are welcome. The drawings I attached earlier are with Visio.

Anyway, have you or anyone you know tried using ABS as a material?
No, but I'm not surprized it sounds better than acrylic. It looks like a very sensible choice, and I guess your listenning experience prooves it is. btw, the platters look gorgeous. Is ABS easy to machine?

-T
 
Tee-Rex said:



Is ABS easy to machine?

-T

Yes it is, very easy. The only thing to keep in mind is that these materials are stressed and when they are machined, they "move". IOW, after you machine the plastic, it will not be completely flat. You can either anneal it prior to machining or rough machine your platter(leave 0.02-0.03 all over), then finish machine for maximum results and minimal runout.
You could make your own bearing by purchasing Ultra Precision Ground shaft and pressing the shaft into an aluminum subplatter or bearing hub. If you look at the picture of my acrylic platter, you can see the bearing hub I machined underneath. I used ultra precision ground shaft for the bearing axle.

The Teres bearing does have a beautifully ground surface that costs plenty as a secondary operation. Unless you have several bearing axles for grinding, the cost would be too high for a "one off" bearing such as yours so the choice is yours, build your own with ground shaft or design your table around a Teres bearing.
Good luck, Frank.