scrapyard turntable

[bulgin]

Scrapyard...

Hi Marco

I admire your ingenuity. Salvador Dali would have gone ape and bananas all at once😀

Looking forward to further developments

Cheers

bulgin

 

[deduikertjes]

I understand that the Thorens type bearing cannot take much more than 1 or 2 kg without excess friction and wear.

Ok, but with a well balanced platter, this wear should be on the bottom plate of the bearing only? (I've once seen widia bottom plates for this bearing for sale). Then I could drop in a little teflon plate which I can exchange when it is worn. Right or wrong?

After casting the plinth, did you have to clean it up- remove material from it, or is it just 'as cast'? What concrete did you use, and why will you not use it again?

I did go for a distinct lo-fi look. So I took it out of the mould, and that was it. If you want a smooth finish you either have to make a very smooth mould and/ or will be looking at a lot of work with the grinder.

I used fibre reinforced concrete meant for the top layer of floors, so it sets to a plane and smooth surface and it densifies itself.

This particular type I wont use for my kitchen sink (I will use it for other things though). This type is especially for great strength. It allows constructions up to 5 cm in one go (the normal type for floors allow 1 - 2 cm at most). So from a construction type of viewpoint its is very good. But: it does NOT give a smooth surface on top (where it is not confined, but open to air). I think a smooth surface is important for a kitchen sink (as I have 6 meters length of sink, I don't want to do too much grinding).

greetings, MArco

 

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Hi Bulgin

I admire your ingenuity. Salvador Dali would have gone ape and bananas all at once

Kind, very kind...

Looking forward to further developments

I'm building the phonoclone. I've left some space in the plinth for it, so I can have very short leads from arm to phonopre. I believe that will do something for the quality.

I also planned to do some more concrete casting: a sort of shelf or bottom plate for the turntable to put in on. In this plate I'll leave 3 cavities, where the feet of the turn table will land. These cavities I want to fill with rubber, air bubbles, or something to decouple the turn table from the surface. Still thinking on that one.

greetz, MArco

way of topic: how is life in the Mother City nowadays. I lived in cape town for parts of 1994/1994 and 1996.

 

[jrevillug]

Thanks for that.

Certainly putting a teflon disc in the bottom of the bearing will reduce the wear associated with the heavier platter, but it probably won't reduce the extra noise and friction.

James

 

[bulgin]

Scrapyard

Hello Marco

Cape Town is fine. A bit windblown but that's the south easter (aka the Cape Doctor)😀 After all the rain we've had, the warmer weather and sun now is superb.

I can't compete with you guys, hehe😎 The closest I can get was a regulated clean powersupply built underneath and into the 301's plinth. Oh, and I've made a new armwand.

Regards

bulgin

 

[deduikertjes]

I can't compete with you guys, hehe

😕 😕 Have you gone bonkers??? You make cartridges!!!

I cannot even dream that I can do that (i whish I could, than I can have my complete hifi chain made by myself. stupid: I forgot the drivers of my speakers.

Marco

 

[deduikertjes]

Certainly putting a teflon disc in the bottom of the bearing will reduce the wear associated with the heavier platter, but it probably won't reduce the extra noise and friction.

Due to the laws of physics, every bearing will have extra friction with additional platter weight. The Thorens bearing as well. And yes, extra friction gives extra noise.

But... bearings designed for larger platter weights do suffer from the same laws of physics. Is there anything special with bearings designed for heavier platters except for the extra hard materials and probably the closer tolerances?

Marco

 

[jrevillug]

The larger size ball that the spindle rests on is another thing, but apart from that I can't think of anything. However, a PTFE disc is quite soft, while most bearings for heavier platter will use hardened or stainless steel, or something even harder.

Just a thought, you will probably find that the extra mass gives more benefits than it causes problems.

James

 

[deduikertjes]

The larger size ball that the spindle rests on is another thing

For the record: the Thorens spindle doesn't have a ball. It pointed in a rounded sort of way (so the profile is comparable with a ball on the end).

while most bearings for heavier platter will use hardened or stainless steel, or something even harder

Harder material gives of course less friction but: How hard can we go. I suppose we don't want to get harder than the spindle material or even close to it, to prevent the spindle from excessive wear (a bottom plate can be exchanged after all).

Does anyone know how hard we can go for a bottom plate in relation to the hardness of the spindle of a Thorens?

greetz, MArco

 

[AuroraB]

Based on pure logic, the trust plate, if yo use one, should be softer than the end ball, loose or fixed. Otherwise the wear will be on the ball, which you don't want.
If you look at the DIY-Teres thread, the Teres bearing uses a loose trustplate, - several versions have been tried, -PTFE, Delrin, brass, bronze, all claiming to have somewhat different sonic signatures, which I cannot comment, as I haven't finished my own yet.
Oil bronze or PTFE makes sense to me.. and the average Teres platter is usually a LOT heavier than a Thorens platter.

 

[deduikertjes]

Oil bronze or PTFE makes sense to me.. and the average Teres platter is usually a LOT heavier than a Thorens platter.

If you look at the pictures, I use TWO stacked thorens platters. The top one I plan to fill with either Acryl, concrete or even some other substance to increase inertia.

I would love to use concrete as it is cheap, heavy and relatively easy to work with. But then, the whole concoction becomes heavy (which is good) but the bearing issue is not trivial any more.

I'll be looking in the Teres thread, and studying the magnetic supported bearing. It might be a good solution to take much of the (Extra) load off my magnetic levitation.

Marco

 

[AuroraB]

Hm.. even two standard Thorens platters is a lot lighter than the average Teres of 7-8 kg....but someone had a point here, about the max load of a standard Thorens spindle.

If you go to www.teresaudio.com and look in the "Information" section, you should find details of the Teres bearing, - I think it's still for sale. 20 mm dia takes a whopping higher load than any standard Thorens.

As for motors,- if you concider leaving the synchronus path, the dutch co Premotec still makes the brushless DC motors Philips once had, - similar to the Maxxon's so often promoted in other DIY threads.

 

[deduikertjes]

One possible solution to this is to lift some of the weight of the platter with magnets, while using the bearing to locate it. There is a thread on here about someone using magnets to totally levitate a Linn platter, but in there I posted about relieving the bearing of some of the weight of the platter.

I'm investigating this option. It looks very promising though it requires some precision for which I don't have the tools. It will have to come down to recycling something which is suitable.

The first thing which comes to mind is using loudspeaker magnets. The problem will be in locating them EXACTLY concentric around the bearing. Another option is inserting small super magnets in a ring as I have read in another thread around here.

Still thinking on this one. Anyone advice?

MArco

 

[dario54]

Hi Marco,

compliments fr the wondefull realization
I had the same idea some yrs ago (Thorens 160 subplate integrated in a concrete block)
I ended up to the subplate fixed by screws to a huge concrete block used fr pavimentation paths in gardens😱 😱

re the trustplate, I suggest u to look on eBay, Joel (Thorens specialist) sells fr peanuts a Widia trustpate that maybe the solution fr yr problem

You can also ask him about max weight allowed...

Keep us informed and good luck, Dario

 

[deduikertjes]

I've restyled the arm board and arm post a bit. This definitely is better (easier VTA adjustement; better mounting of the arm board on the plinth). Improved the looks a bit too...

Marco

 

[Mark Kelly]

Does anyone know how hard we can go for a bottom plate in relation to the hardness of the spindle of a Thorens?

You need to calculate the maximal stress in a Hertzian point contact of dissimilar materials.

The relevant calculation is available online through the brilliant work of Anton van Beek at TribologyABC.com.

If you need a guide to how to use the calculator, just post the radius of the spindle end and the material from which it's made and I'll run you though it.

 

[deduikertjes]

If you need a guide to how to use the calculator, just post the radius of the spindle end and the material from which it's made and I'll run you though it.

Wow, thank you, I'm impressed. It would be great to find the right material for the bottom plate.

The spindle has a diameter of 10 mm, and the end is pointed in a rounded sort off way (so the end resembles one half of a ball).

I've no clue as of which material the spindle is made. Sure it is some sort of steel, but what alloy?

MArco

 

[deduikertjes]

and the end is pointed in a rounded sort off way (so the end resembles one half of a ball)

On better inspection: there seems to be a little ball in the end of the spindle. I never saw it due to the oil on it.

The spindle and sub platter is from an old Thorens with a composite rather than metal sub platter (I think it was a TD150).

MArco

 

[deduikertjes]

Dissapointed

Today I did a quick test with a magnetic bearing.

In a loudspeaker shop I'v bought two compensation magnets (the ones you can put on a driver so it can be put close to a TV set) with a diameter of 9 cm. The shop owner told me that would be more than strong enough to lift a heavy platter.

Nope, it is string enough to lift a single Thorens platter, but not the stacked one I use. Let alone it would lift a stacked platter filled with concrete or something similar.

Besides that the overall thickness of the two magnets is to large. I have to replace at least one of them with a ring of neodym super magnets.

To be continued ...

MArco

 

[Mark Kelly]

The spindle has a diameter of 10 mm, and the end is pointed in a rounded sort off way (so the end resembles one half of a ball).

I've no clue as of which material the spindle is made. Sure it is some sort of steel, but what alloy?

That's all the information you need, alloying steel does not change its modulus appreciably. Since the force required to be supported by the bearing is an unknown we can use the calculator to determine the maximal force which can be supported by bearings with different materials.

The remaining data required are the modulus and the shear strength of the possible counter materials. I'd suggest we look at Teflon, Delrin, bronze and steel for starters. If you intend replacing the ball with a ceramic one we then need to do the calculations again with the different material pairs. I don't have time to do this right now, Ill return to it this afternoon.