Help my Frankenstein spin

July 3, 2009 12:42 PM

What every day (or not so every day) inexpensive (<$75) item, (or part of said item) would make a good turntable spindle bearing?

I'm attempting a DIY turntable build out of repurposed items. For example, the platter = an automotive disc rotor, driven by = floppy disc motor. Tonearm pivots out of hard drive actuators and bearings...

I'm familiar with the 'Altmann' intake valve and sleeve bearing, but for some irrational reason I'd like to try something different. I've read many stories of hobby millwrights carving out beautiful bearings, and I won't be joining them.

Using something for its not so intended purpose is part of the journey on this project. Maybe another automotive bit? (There must be a lot of bits in there, right?) Maybe a home appliance? Maybe something more... industrial? Might anyone think of an item that would allow that disc rotor to spin effortlessly, and silently?

posted by csmason to sports, hobbies, & recreation (13 comments total)

What a neat project!

Very good turntables usually have ridiculously simple spindle bearings; it's a good mechanical principle that, the simpler the mechanism, the more noise-free and easy-to-maintain the machine. Complex systems of ball bearings and spinning rotors are pointless, as there's really no way to completely eliminate all friction, and you usually end up increasing that friction anyhow; the point of ball bearings in machines is usually to regularize the friction in situations where the machine undergoes a certain amount of rough handling, anyway, so they're not really that useful for something as delicate and stationary as a turntable.

My table, an Origin Live kit that I paid $2000 for, has a spindle and bearing which consists simply in:

(a) The spindle, the bottom point of which is tapered sharply to a shallow point; and

(b) The bearing, which is just a cylindrical cavity lubricated with high-grade oil.

The spindle is thus borne on a very hard point which makes contact at a single spot with the flat bottom of the cavity, and stabilized by the walls of that cavity which make light contact with the sides of the spindle. This is actually the most efficient and silent kind of bearing, and it has the benefit of being very easy to construct; all you'd have to do is drill a hole in the mounting where you'd like to bear the spindle and taper the end of the spindle itself. The hardest part would be making sure that the bottom of the cavity is perfectly flat; but you could remedy that by drilling a hole straight through and then covering the bottom of the hole with a flat surface.

It also occurs to me that you could make a fine spindle from a repurposed screwdriver. In fact, if you can find a fine or sharp enough Phillips-head driver, you may not even need to taper the tip of it; it could set perfectly in the bottom of the cavity and spin freely.

By the way: using an automotive disc rotor for a plinth (platter) is probably a bad idea, as metallic discs and especially metallic discs designed for maximum durability and strength are highly resonant, and therefore will pick up vibrations from the contact between the record and the needle and amplify them, causing distortion. The least-resonant material known to man, and a common material for high-grade plinths (and many other items), is solid acrylic. You'll find acrylic in any kind of plexiglass, for example. I'd recommend you find a couple of sheets of plexiglass somewhere, cut them into 12-inch rounds, and glue them together with some sort of rubber cement; they'd be much more likely to form a good, resonance-free platter that way.
posted by koeselitz at 1:21 PM on July 3

I have never given any thought to such a thing, but following on from koeselitz's suggestion, you could use a bradawl rather than a screwdriver for the spindle.
posted by Jakey at 1:38 PM on July 3 [1 favorite has favorites]

If you've got an old hard disk, it will contain bearings for the spindle the platters rotate on. They will typically have all the mechanical properties you're looking for.
posted by Mike1024 at 5:25 PM on July 3

Maybe you could get hold of a woodworking router? Their bearings spin pretty smoothly.
posted by orme at 7:07 PM on July 3

Inline skate bearings are some of the highest bang for the buck bearing wise you can buy. Lots of guys building CNC machines around these cheap yet good bearings. There are several vendors on ebay who sell them in bulk packages of 10-100.
posted by Mitheral at 7:18 PM on July 3

Seconding koeselitz on the plinth material comment— you want that material to be as non-resonant as possible.
posted by a halcyon day at 10:06 AM on July 4

@koeselitz - I think this is what I'm after, but somewhat already constructed. The trick with your idea of a screwdriver / awl is the sleeve it will be supported by. It would have to be drilled with extremely tight tolerances - tighter than to what the screwdriver is manufactured to, which means it likely wouldn't work.

@Mike1024 - I've looked at hard drive bearings. Maybe the one I looked at was too old, but it was quite noisy once a bit of weight was put on it.

@orme - Hmmm.. have to do some garage sale-ing to see if I can find an old one I wouldn't mind sacrificing - my router shivered a little bit with your comment.

@Mitheral - I'll have to take a look at the inline skate bearings, though they're made more to pivot something on an axle extending out both ends.

It sounds like the disc break may be a bad idea, though I had planned on dampening it with some spray on... something. I know I won't be making a world beater here, more a functional conversation piece. Any further suggestions welcome!
posted by csmason at 5:56 PM on July 4

Well, if you can find an old sheet of plexiglass, cut a round from it, and put it on top of the rotor, that would probably cut resonance plenty.

Be sure to update us when you're done. In fact, you could toss some pictures of this and some description of it on a blog and post it to Projects if you wanted.
posted by koeselitz at 7:13 PM on July 4

the inline-skate bearings are not what you want, as you stated they will not take axial loads. I'm not surprised the Hard Drive bearing started squealing, they're designed for perfectly balanced platters which weigh tens of grams, not a brake rotor, which weighs a bit more (!).
A google suggested the following:
(AudiogoN Forum link)
posted by defcom1 at 9:57 PM on July 5

Mr. Rabbit says "VCR head"
posted by rabbitrabbit at 11:03 PM on July 6 [1 favorite has favorites]

I should add: he has actually built a turntable with a VCR head and it works great.
posted by rabbitrabbit at 11:06 PM on July 6

@rabbitrabbit: Innnteresting, will definately check that out!
posted by csmason at 6:44 AM on July 7

The VCR head looks to be a great solution, thanks!
posted by csmason at 9:55 AM on September 3