DIY TT design

[Tee-Rex]

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

[livemusic]

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!

[Tee-Rex]

Speaking of Galibier - anyone have an idea why the multiple screws on top of the Galibier and Redpoint platters?

Livemusic - do you mind if I drop you an email?

Cheers
-T

[livemusic]

T,
Galiber stuck with idea, that bolts are superior for the platter layers connection - make sence, but the bolt heads are not necessary to be exposed, compromising platter-record contact, IMHO...
You are welcome to email me.
Shalom,
Michael

[InDaGroove]

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

[Tee-Rex]

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

[InDaGroove]

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

[Tee-Rex]

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

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

[InDaGroove]

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

[Tee-Rex]

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