Please review my design

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Gents,

I am getting to build this beast. It is a cross between a Teres and a Redpoint turntable using a Teres Bearing. It will be machined from solid aluminum billets and filled with lead shot and silocone fluid for damping. The arm pod will be set for an SME IV tone arm. I have the aluminum and want to get started milling it. Could you have a look and let me know it you see anything obviously wrong. I don't want to ruin $500 of aluminum so let me have it.




An externally hosted image should be here but it was not working when we last tested it.




An externally hosted image should be here but it was not working when we last tested it.
 
yup, it's big and fugly...

a couple of difference in opinion...cosmetics aside.

lightweight plinth for minimal energy storage (and more uniform energy release, cause it has to go somewhere). Heavy weight plinth for a "brute force " approach to dampening. (and more random energy release at sometimes the wrong times).

Personally I like a homogenous material for platters, all teflon, all acrylic, all aluminium...

I think the bearing, if drawn correctly looks to be a non-inverted type. This may help create a significant amount of friction. Consider an inverted bearing (which I believe the Teres is/was), with the pivot above the centre of gravity of the platter.

just a couple of thoughts.


stew

PS: I can't build a damn thing, but you did ask for an opinion:D
oh, have a look at this....
 

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Teres bearing is non-inverted.


Your design looks good and is fairly close to the Teres idea, just in alu instead of cocobolo. I think ?? that redpoint might have some kind of system where you can tighten the screws down through the teflon into the platter and that that adjusts the sound? I could be wrong on that.

Are you going to have a simple weight or a screw down clamp? Are you going to dish the platter slightly to allow for that, and the contact between LP and platter?

No. 9 lead shot I believe is the one to go for.

What are you going to use for a motor and controller?

Do please allow yourself a second arm pod - even if you have no plans for it right away, its going to be much cheaper to make it now rather than later. Just leave a blank plate on the top that you could drill out later to suit a different arm.

I know I've fired a lot of Q's back to you, but I think you should decide these things now and get them sorted before the platter comes off the lathe.

Fran
 
Thanks for the input Fran and Stew. I will be using a Teres Clamp so the teflon will stand proud of the platter by .060" creating the same size dish as the Teres. I called Redpoint and they said that their screw pattern is just set to maximize flattness when the teflon is attached to the table. He also didn't know any adjustments of the screws for sound. I am using Mark Kelly's controller with the same motor as Teres from the recent group buy. Stew, #9 shot it will be. Keep them coming gents.
 
Teres Bearing...

sorry for the error. I've been concentrating on fixing the the turntable in the pix I posted. It definitely needs an inverted bearing.

Regardless I still like inverted bearings, although perhaps a little more difficult to make or get, because you need to feed the bearing some lubricant, and be able to collect it in a well....

I still like traditional looking turntables, so cosmetics aside, the rest opf your design looks good.

woodturner suggested the #9 shot, not I.


A very interesting project. Once it comes to fruition, I am sure it will sound very good.

stew
 
I'd keep the "right way up" bearing (I can't see any benefit in an inverted bearing and there are at least two significant downsides). I would however try to get further separation between the upper and lower radial load surfaces, or reduce the side thrust, or both. Take a look at what Dave Garretson has been doing with idler pulleys to reduce side thrust, it's quite interesting (Dave posts on VA).

Why Teflon? What benefits do you think it has? I can't see any apart from it being very "dead" but I question why you would need that much deadening.
 
BTW, the Teres bearing kinda simulates an inverted type because it goes right up inside the platter, ie the whole actual bearing sits on the plinth with a big threaded stub underneath that holds it to the plinth.

The DIY teres controller should do the trick nicely - although the teres trick of a LED sensor to control speed is very nice indeed.

I think you're pretty much there to be honest. If the teflon sounds horrible, you could always get someone to turn some cocobolo into a disc that would fit in place of the teflon and it might liven up the sound a bit.

Both pods will sit on the table free of the plinth, right? Allow a way at the bottom of both to adjust the level (3 adjustable feet - i used 3 M6 grub screws with some rubber material melted into the allen head - which give s a firm grip on the surface). You will need this to get the tape you will be using to drive the motor to ride level. Likewise for the arm - more things that are adjustable the easier it gets!

Other than that I just can't see anything. Of course there is always an element of risk in DIY!!

PS, please don't make the outside of the platter a polygonal shape like either redpoint or galibier - IMHO thats horrible.

Can you get the alu anodised?

Fran
 
Just to be clear, the DIY controller has nothing to do with the Teres design other than the use of a Maxon DC motor.

It does not use a servo loop like the Teres does so it does not suffer from the dynamic wow problems associated with slow servo loops. On the other hand it has no correction for thermal drift, so the long term speed stability is not as good.
 
I knew that, but its good to be clear! I think thats what algar-emi called the group buy so thats why I went there.

A friend of mine actually was in on that group buy - I'm looking forward to seeing how it performs in the end.

Kilwattski: do you have the machining capability for this yourself or are you going to your local friendly machinist? Did you manage to get one billet of alu big enough for the platter, or are you making it up of a number of discs? What way are you going to have the holes for the lead shot done ie sealing them afterward?

Fran
 
woodturner-fran said:
I knew that, but its good to be clear! I think thats what algar-emi called the group buy so thats why I went there.

A friend of mine actually was in on that group buy - I'm looking forward to seeing how it performs in the end.

Kilwattski: do you have the machining capability for this yourself or are you going to your local friendly machinist? Did you manage to get one billet of alu big enough for the platter, or are you making it up of a number of discs? What way are you going to have the holes for the lead shot done ie sealing them afterward?

Fran

I have access to a Haas CNC Milling machine (see posts 514 and 560 on this thread). My neighbor owns a machine shop and owns a couple of these bad boys. I will write the G-Code and he will run it for me. I have (2) 13" x 13" x 3" aluminum billets and (2) 7" long x 5" od x 3 " id pieces of aluminum pipe. The Red Point is machined from two aluminum billets so I figured I would try the same. If you look at the drawing, the teflon doughnut will cover the 1.75 dia holes for lead shot around the perimeter.
 
Mark Kelly said:
I'd keep the "right way up" bearing (I can't see any benefit in an inverted bearing and there are at least two significant downsides). I would however try to get further separation between the upper and lower radial load surfaces, or reduce the side thrust, or both. Take a look at what Dave Garretson has been doing with idler pulleys to reduce side thrust, it's quite interesting (Dave posts on VA).

Why Teflon? What benefits do you think it has? I can't see any apart from it being very "dead" but I question why you would need that much deadening.

Mark,

I am a novice at this so I figured I would try something from a succesful commercial design (Redpoint) hence the teflon. should it be just solid aluminum? This is good stuff and why I started this thread.
 
There seem to be two schools of thought on interface materials: one is is to place a soft material under the vinyl (typicallly cork or felt), the other is to place a material with an acoustic impedance similar to that of vinyl next to the vinyl and bond this to the higher impedance part (the aluminium). Teflon seems to me to be an attempt to do both at once.

Acoustic impedance is the product of the density of the material and its propagation velocity.

Teflon has the same density as aluminium but much much lower propagation velocity so it's a poor match to aluminium, as are all other plastics.

It has more than twice the density of vinyl but again a much lower propagation velocity (Teflon is just about the densest and also the weakest plastic around) so it's not even a good match to the vinyl.

Almost any other plastic would be a better match to the vinyl and will "grip" it better (except PE which is just about as slippery as Teflon).
 
why an inverted bearing?

consider that an inverted bearing can allow the mass to "hang" if the point of contact between the stationary bearing and the rotating bearing "sleeve" or "body"---the part to be attached to the platter is above the centre of gravity

Once set in motion, the platter stabilizes. If set in motion at an angle, it will remain at that angle until friction slows it down. If set in motion orthogonal to the bearing "shaft", it will remain orthogonal to the shaft. So , it does not rely on any pressure (F/A) laterally to maintain it in a stable condition.

If you rotate below the center of gravity, the bearing "walls" (or bushing or whatever you choose to call it), must take some of the load, and unless the platter is perfectly balanced, it will attempt to precess almost right away.

I agree there are difficulties in making or having made a bearing in this manner. To me it does make sense. But the bearing must be made in such a way that allows lubricant to be pulled up the bearing "shaft" and to allow it to drop back down to a reservoir.

There are good and bad example of inverted and non-inverted bearings out there.
 
Precession is the product of rotational inertia and a torque orthogonal to the axis of rotation. Given that every platter has such a torque (caused by the VTF on the stylus), precession is always present in any turntable system.

This means that static balance is not the determinant of dynamic platter balance, the resistance to orthogonal torque of the bearing is. For a perfect bearing with zero tolerance, there is no difference between outer rotor (inverted) and inner rotor (right way up) except the difficulty in maintaining lubrication in the inverted bearing (and that's a big exception).

As soon as there is any wear in the bearing there is a major difference in the performance of the bearings. With an outer rotor bearing the wear will be distributed around the rotor circumference, increasing the bearing slop and increasing the response to precession. In an inner rotor bearing the wear will occur in one place in the outer shell which actually improves the resistance to precession.

Here's a thought experiment - consider a single point contact bearing with the thrust point located above the COG of the platter (eg no radial constraint). It seems obvious that such an arrangement would be fatally flawed but your argument says that it would be the ideal arrangement. This has to tell you something.
 
The other thing is that the OP has a Teres bearing, and there are a good number of them out there in use and they are reliable and stable in place. Theoretical discussions aside, its one of the better bearings out there. Low tolerance, good mass, well finished <4 thou clearance, can take the high mass of the platter with ease - and from an established system that you know sounds good.

Fran
 
12" cones....

Mark.. as I have no relationship with ABrownSoun, I have no way what they are up to. I provide customer assistance for items already purchased. You might email Perry at Hemp Acoustics to see if it possible.

regarding precession, consider this: spin a child's "top" as friction builds, and inertia in the rotating mass becomes reduced , the top will want to "fall over". Do the same thing , but attach a thread to the top, start it spinning while holding it above the surface that it was spinning on before. Guess what? The orientation of the top to the plane below will not change unless another force acts upon it, even when all the energy has been dissipated and it stops rotating.

stew
 
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