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Old 16th September 2013, 12:46 AM   #611
bgruhn is offline bgruhn  United States
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Location: Medfield, MA, USA
Quote:
Originally Posted by vynuhl.addict View Post
Bill,


No worries, I've abandoned the smaller tube, 10mm is bang on on all aspects, the smaller tubes were just steps backwards but worth a try as in this hobby it's a process of ruling things out as much to solidify ruling them in to begin with. The arm stands as is as best, and that brass shim makes a real difference vs secured bearings that are locked at their inner axis.




Colin
Colin, Great!
As I may have mentioned a while back, my arm doesn't use any of your design features save two, 4 bearings and loose fit on the axles. My solid axles are aluminum. Their diameter is turned to provide the same loose fit that you have with the brass shim. There is a boss at the inner end which locates the inside bearing. The outside bearing is located by a friction fit brass ring which on assembly is pressed onto the axle far enough to space the bearings 5mm apart. My bearings are free to slide together on the axle but the diameter of the glass tube and gravity keeps them 5mm apart. Yes I think that the loose fit of the bearing on the axle is a key to the performance of the arm. In a sense it makes a self aligning bearing of sorts. If there is any small runout in the rotating assembly due to eccentricity of either bearings or tube, the clearance between bearing and axle will tend to compensate and permit unconstrained rotation. This explanation is pretty much off the top of my head and may not be sustained by rigorous analysis.

On another subject now, cartridges. I've had a couple of ADC XLM 2 (or3) carts hanging around in my junk box for years. I inherited them. Out of curiosity I just bought one of the low priced RXL/RZD styli advertised by Amazon. Diamond eliptical. Placed it in service a couple of nights ago. On this arm it easily equals or exceeds the Ortofon OM with OM10 stylus. A very nice cartridge. It tracks well at 1 gram Thanks to the surface of the glass and the polished corners on the bearings. Saw some bearings at a hobby shop over the weekend. Didn't have a loupe with me but feeling the corners with my finger nail said that they could be better than the ones I had to polish.
Rgds,
BillG

Last edited by bgruhn; 16th September 2013 at 12:55 AM. Reason: Correct typo
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Old 16th September 2013, 01:16 AM   #612
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Siddley:

Sorry, I should have been more clear. Tungsten carbide is much harder, you can get lengths to 1 foot long here without much trouble. If you do order a piece make sure it is ground and polished and have them cut it to your exact length. If you want to go a step further you can get some super fine diamond lapping compound on ebay ( pretty cheap ) and spin the rod in a lathe and get a mirror finish.

A quick check on ebay (USA) under " carbide blank " shows a 7/16" diameter x 12" long piece for $79 which would be just about perfect.

Someone here who wants to make an " ultimate " attempt at this arm should scoff this up quickly. I already have a piece of 1/2" x 12".


ChrisG139:

Nice arm you made. But do not form any opinions about the arms performance until you ditch the fiberglass tube. If you want something quick and much better ( and cheap )get yourself a piece of " drill rod " which you can get from most tool supply houses. Even this is not ideal because it is not hardened. When you are happy with the performance go for the tungsten carbide rod--- you will be a very happy camper !!

Joe
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Old 16th September 2013, 01:28 AM   #613
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Just be careful with any dust created by tungsten carbide as it is a known carcinogen, but I guess nowadays what isn't?.


Colin
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Old 16th September 2013, 01:48 AM   #614
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Bill,


To me thats part of the beauty of this design, we have a bearing system that works well and needs to be pretty much done a certain way, but each is free to design his or her own carriage ideas and tastes around this and still have success as long as the laws if physics are also adhered to mass wise. I've been trying to out do myself on the bearing arrangement with no luck, it works damn well as it stands and obviously is the important cog in the equation.

For the fiberglass tube being used, it will be enough for now to get started but Pyrex. Or quartz will be ideal and still leave money for more records .

Colin

Last edited by vynuhl.addict; 16th September 2013 at 01:51 AM.
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Old 16th September 2013, 01:54 AM   #615
Siddley is offline Siddley  Spain
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Quote:
Originally Posted by hottattoo View Post
If you want something quick and much better ( and cheap )get yourself a piece of " drill rod " which you can get from most tool supply houses. Even this is not ideal because it is not hardened.
Joe
Hey Joe ( sorry, couldn't resist that - I'm a huge fan of Hendrix )

The nearest equivalent to drill rod in the UK is precision ground " silver steel " - even without heat treatment it's pretty hard and I use it a lot for tool making. I really doubt the surface hardness would be an issue in this application.

What is going to matter is that it rusts. Not as badly as some steels, but it will corrode. How fast it corrodes is going to depend on your climate.
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Old 16th September 2013, 10:06 AM   #616
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Hi All
Re the fibreglass tube-as I stated, I was only using it temporarily until the glass arrives this week. I've already used the 10mm glass tube and, as Colin mentioned, I'm doing a bit of experimentation. watch this space........
chris
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Old 16th September 2013, 01:37 PM   #617
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Tungsten Carbide- located a UK supplier but they only supply in 4" lengths!
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Old 16th September 2013, 03:15 PM   #618
Siddley is offline Siddley  Spain
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Quote:
Originally Posted by ChrisG139 View Post
Tungsten Carbide- located a UK supplier but they only supply in 4" lengths!
That's the best I could do as well Chris.

You might want to get your hands on a dead printer and strip the chromed steel rods that the printhead rides on out of that - they really are good stuff.
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Old 16th September 2013, 03:26 PM   #619
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Hi,

Siddley:

One other advantage to using tungsten carbide is that it is only slightly magnetic. This may be an issue with the cartridge only 2 or 3 inches from the carriage support, and of course the corrosion factor of tool steel is a problem.

About 2 years ago I built a magnetic levitation turntable bearing using 2 very strong n50 ring magnets which was used to float a 45 lb aluminum platter ( works very well ). I used a 5/8" diameter mirror finished tungsten carbide shaft 6" long and I was concerned about the magnetic field traveling through the shaft and interfering with the cartridge as it got close to the end of the record. So far no problems. Even when surrounded by 2 105 lb lift magnets the top of the shaft was only slightly magnetic.

Joe
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Old 16th September 2013, 06:01 PM   #620
Siddley is offline Siddley  Spain
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Ever thought about titanium Joe ? its non magnetic, doesn't corrode and the aerospace grade 6ALV barstock is pretty dimensionally constant with a surface finish which is quite good. Would be roughly a third of the cost of tungsten carbide.
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