Bearing Question

[Tal]

I've pretty much just started construction of my own turntable, heh i'm trying for extremely high quality, but this being my first project its been a little slow.

Right now I already have a 5lb acrylic platter, 1 1/2 " thick, which I'm having milled and am balancing. And I've already had a spindle made.

my question though is about the bearing. right now I have two RS608 high precision bearings, but i've noticed that all high end turntables use a ceramic thrust plate, and steel ball.

so i'm not sure weather I should go with that approach or just stick with the two bearings i already have.

Any help or comments are appreciated

[FastEddy]

" ... but i've noticed that all high end turntables use a ceramic thrust plate, and steel ball. ..."

Those very hard steel balls are there to achieve a tiny point of contact at the top and bottom of the ball (the steel ball being very close to a perfect sphere) ... this tiny point of contact acts as the upwards thrust bearing (to keep the weight of the turntable from sliding further down inside the lateral bearings. The hoped for result is very low friction from the very small point (thrust bearing supporting the weight of the turntable).

I have heard of and many others have seen various very hard materials, including diamond, used as the point where the ball sits in order reduce this friction even more.

For my money, anything greater than Rockwell 70 or 80 hardness (ceramics could work) for this thrust plate (the point where the ball rests) would probably be overkill, but your goal of "extreme high quality" may lead you to use something harder.

Assuming that your "two RS608 high precision bearings" are the lateral bearings (top and bottom of your spindle (shaft)), then a round, case hardened, steel ball bearing sitting on a hard ceramic disc at the bottom of the shaft would probably not be "extreme".

[vinylkid58]

I would stay away from caged ball bearings, if that's what you are refering to (RS608); rumble from the bearing assembly will probably transfer thru to the record.
A simple plain bearing is realively simple and cheap to make. The bearing would consist of a 3/8" polished shaft, supported by a steel or ceramic ball running on a Delrin or teflon thrust pad, and a brass housing with oil bath. This should support a 5lb platter without any difficulty. You may be able to incorporate the spindle that you've already had machined, depending on it's dimensions. The tolerance between the shaft and the housing is the important part.

Jeff

[FastEddy]

" ... A simple plain bearing is realively simple and cheap to make. The bearing would consist of a 3/8" polished shaft, supported by a steel or ceramic ball running on a Delrin or teflon thrust pad, and a brass housing with oil bath ..."

Delrin = ... Teflon = ... glass filled Teflon =

Brass tubing for the outer bearing guide = ... the absolutely best is something very few folks have ever seen = hard coat black anodized (ceramic) aluminum = very hard bearing material = Rockwell 80+ = hundreds of millions of cycles or rotations without any signs of wear. If used for both shaft and sleave, a lapped, running fit must be done on a lathe using diamond grit & Singer sewing machine oil and will take several hours work but the resulting shaft / bearing set can run dry for years.

Consider another approach as well: cut down automotive intake valve stem and valve guide. Hard shaft, long life bearing, machine shop lapped to a very good running fit = very long life and very low friction =

vinylkid58 is absolutely correct about caged ball bearings (for the lateral, top and bottom rotating bearings. If they ever run dry, rumble sets in that never can be fixed without total replacement. The same applies to "caged" roller bearings ...

BUT that little hard ball bearing that the whole thing rests on (above) is going to be required. This is not a "caged" set of ball bearings, but a single, small diameter case hardened, high carbon steel ball serving as a thrust bearing on a hard ceramic plate or Teflon disc.

[FastEddy]

Another unusual shaft and bearing set seldom used but that works very well:

Case hardened steel shaft running in ... wood !

It turns out that one of the best bearing materials is wood. Consider that for more than a century that mold board plow tail wheel on your grandfather's farm plow had a wooden bearing race, usually of hard oak ... just had to keep 'er well greased.

Now the automotive intake valve stem could have a very hard wood guide ... something like purple heart or coca bola hard wood would do this trick. You might want to "hard ball align" the hole to fit, but then lubrication can be any light oil.

[vinylkid58]

Now the automotive intake valve stem could have a very hard wood guide ... something like purple heart or coca bola hard wood would do this trick. You might want to "hard ball align" the hole to fit, but then lubrication can be any light oil.

Didn't the original Volkswagen Beatle have wooden valve stems?
I seem to recall someone in high school with a really old Beatle, having
all of 38HP.

Jeff

[Tal]

I think if I go with the plain bearing way (which its loking like I will) I will have a new spindle machined for that purpose, the one I have probably wouldn't work best for it.

and I though is was the thrust plate that was supposed to be ceramic...but delrin you say? I'll have to look into that.

now sorry if this is an obvious question then, would the spindle have a divot in it to hold the ball in one place, to spin on the thrust plate? or is the ball allowed to float freely in the bearing?

[FastEddy]

" ... Didn't the original Volkswagen Beatle have wooden valve stems? ..."

Urban legend, possibly. Cheap steel as far as I know. (So was the horse power rating of 36 HP, really more like 30.)

Wood has decent compression strength, resilance to shock, absorbant to lubricants, etc.. Celulose is quite the material.

John Deere stopped using wood as bearings in plow wheeles ... in 1967!
......

Delrin is available in varying degrees of hardness ... Delrin is used extensively for model building and mock up of mechanical devices ... sources are any good machine shop.

Glass filled Teflon can also be obtained from quality machine shops and is notorious for being a very hard bearing surface that "self lubracates" ...

[vinylkid58]

Originally posted by Tal
I think if I go with the plain bearing way (which its loking like I will) I will have a new spindle machined for that purpose, the one I have probably wouldn't work best for it.

Way cheaper to buy hardened precision ground steel shaft, example:
3/8"dia. x 12" long is US$5.77 at http://www.mcmaster.com/. That way you can keep the tolerances for your bearing fairly tight.

now sorry if this is an obvious question then, would the spindle have a divot in it to hold the ball in one place, to spin on the thrust plate? or is the ball allowed to float freely in the bearing?

Machining a cup in the shaft end to hold the ball might be a good idea, not sure if it is really necessary though.

Jeff

[Aengus]

vinylkid58 said:

Way cheaper to buy hardened precision ground steel shaft...

and gave a 3/8" x 12" example. Jeff, how come so long? The longest plain bushing I can find [edit: on the McM-C site] with a 3/8" bore is only 1 1/4" long; even with a very thick platter, surely there's going to be a lot of unsupported shaft?

But I ask purely from a position of ignorance. I've been looking at precision shafting on various sites, and wondered why more people aren't using this stuff. Is it a question of insufficiently good finish, hard to match to bearings, or what? McMaster-Carr even sells it with a threaded end, and in the 1/2" size you can get a 3" bushing and a 6 5/8" case-hardened end-threaded shaft for about $36. Seems like it would be a good solution to the diy bearing problem.

Could some of the machining-knowledgeable forum members give their thoughts on this? Thank you.

Aengus