DIY Schroeder Tonearm???

[binspaul]

Hello Christian,

What about the magnet holders? Which material suites best ? Do we need to go for a particular thickness ?

Best regards,
Bins.

[bgruhn]

Bins,
If you are going to attempt a single string bearing I think the N35 magnets are not strong enough for a really successful design. K&J Magnetics Inc. has N52 magnets 5/16" x 1/8" (PN D52-N52) $0.43 each. I bought 8 for a total of $10.44 including $7.00 for shipping, USA. I think that was priority mail service.

If you want to try the N35 magnets I think you will be more successful with a split string/inverted Y bearing design. My first attempt was with similar N35 magnets and the inverted Y suspension and was very successful. Even now after completing a single string tonearm I think I like the inverted Y designs better. Please see photos of my inverted Y design at www.apricot.com/~bgruhn/turntable/magarms.html

Bill

[binspaul]

Hello Bill,

Thanks for the suggestions. I will try to implement the 2 string version first. Once, I gets the N52, I will try the single string version.

What is the main platter/spindle bearing you use ? I was not able to find a suitable one yet.

Best regards,
Bins.

[bgruhn]

Originally posted by binspaul
Hello Bill,

Thanks for the suggestions. I will try to implement the 2 string version first. Once, I gets the N52, I will try the single string version.

What is the main platter/spindle bearing you use ? I was not able to find a suitable one yet.

Best regards,
Bins.

Hello Bins,
Odd that you should ask about the bearing today. Just last night I got around to dealing with the bearing design. As I mentioned in another post I have been using ABEC class 7 shielded ball bearings selected for low noise. Stashed away in my materials collection there has been a rod of bearing type nylon and a ~2mm diameter saphire ball left over from my days in the aerospace industry. So I made up nylon replacement inserts to replace the ball bearings. These nylon parts are simple plugs sized to be a tight press fit into the bearing housing. The upper one is drilled for the spindle and reamed to fit smoothly with a hand reamer. The bottom one has a shallow depression made to accept the saphire ball. The spindle is 1/4" dia steel drill rod (USA) aka silver steel. It too has a depression made with a small center drill or countersink bit. I put a small very small amount of cyanoacrylate adhesive into the depression in the spindle chiefly to make the ball captive for easy assembly. Years ago there were great arguments against using anything the least bit compliant in the bearing system of turntables. But now we see increased use of teflon as in the Welltempered TT.
So I am giving it a shot. Only been using the new bearing system for one day now, but the results are far better than I had been expecting. With the stylus resting on the plinth I can turn the amplifier up to full gain and hear nothing from the bearing. This is with the belt removed and spinning the platter by hand. playing records is a pleasure with the noise floor way way down. I think there is some from the motor. Next step is to decouple the motor from the base plate with its own free mounted lead base. I don't feel any great need to push ahead with that project yet.

Go for the nylon/teflon bearing. It could be even longer living than conventional metal based designs. BTW, if you can't get saphire balls, I am sure you will get great results with a steel ball bearing ball.

Bill

[binspaul]

Hi Bill,

What about the bearing model suggested by "Altmann" ? Where can I get the nylon/teflon bearing components ?

Best regards,
Bins.

[bgruhn]

Originally posted by binspaul
Hi Bill,

What about the bearing model suggested by "Altmann" ? Where can I get the nylon/teflon bearing components ?

Best regards,
Bins.

Hi Bins,

I just reviewed the Altmann DIY TT article. I must say that Mr. Altman deserves credit for a well thought out project well carried out. His choice of a motorcycle valve for the spindle is a great idea. The valve guide will work very well for the upper sleeve bearing. I like the idea of using the valve head for the platter support. You should have no trouble with runout of the platter if the valve is properly machined. I don't know what your degree of skill is with tools and materials etc. as well as what your goals are for a turntable and tone arm. If you are striving for a fully completed analogue front end built to rival one of the high priced units, then I would suggest looking for materials and designs different from the Altman project. If you will be pleased with the home workshop look and a TT/arm that performs very well indeed, then follow through with as much of the Altman design as you are comfortable with.

Regarding where to get teflon or nylon:
The web is loaded with suppliers and information on these materials. It comes in plain and filled varieties enough to boggle the mind. I used an unfilled material. For starters look at Industrial Plastic Supply Inc. They have a price of $15.84 for 2 feet of 3/4" nylon rod. You could use the nylon bearing instead of the motorcycle valve guide. I think you can get a quieter bearing this way especially if you run the lower ball in a nylon or teflon seat.
Also, see if you can buy small quantities from local machine shops or engineering firms. There are great numbers of firms making or selling saphire and ruby balls on the web.

Please read up on Bill Firebough,s Amadeus design where he discusses running his round spindle in a square hole in the upper teflon bearing. This is what I will implement soon. I chose the round hole in the nylon as an interim design while I figure out how to make the square hole thing. I believe we can have better performance (rumble etc) with the plastic materials. Possibly at the expense of some bearing life. So after 10 years put in a new bearing.

Best wishes in your endeavour.

Bill

[Badge]

I have been thinking about the magnets. It seems to me that the one string approach is better executed by having the magnets pulling at each other. The string keeps the arm suspended above. With magnets oriented to reject, there are forces that will tend to not only lift but move to the side thus requiring the two string approach. Correct me if I am wrong.

[bgruhn]

Hi Badge,

Yes, you are right. The magnetic suspension does work much better if the magnets are attracting rather than repelling. The 2 string approach is also predicated on attracting magnets. It won't work in the repelling mode either.

Bill

[Badge]

Thanks Bill. Some how I got it in my head the magnets were supposed to be opposing north/south

[binspaul]

Hello Bill,

Thanks for your guidance. Without your suggestions, I would have gone void. Farnell (www.farnell.com) is having a good stock of nylon rods. What is the best diameter for the bearing rod - 15mm/20 mm ? By the way, what is your suggestion on bearing guides ?

Still waiting for my neodymium magnets to arrive....

Best regards,
Bins.