Opus 3 Cantus parallel tracking arm - Page 15 - diyAudio
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Old 7th May 2010, 08:34 PM   #141
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Great pics directdriver - that helps a lot.

Fran
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Old 7th May 2010, 10:16 PM   #142
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Hi,

WOW.
Even the most complex cutting lathe seems pretty mundane next to that rig.

BTW, the idea to use convex bearing housings being to reduce contact area?

Cheers,
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Old 7th May 2010, 10:19 PM   #143
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Quote:
woodturner-fran: "Great pics directdriver - that helps a lot."
That's the least I can do as many of my own ideas are half-baked.

The DIY forums are a wonderful community.

.
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Old 7th May 2010, 10:55 PM   #144
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Quote:
fdegrove: Even the most complex cutting lathe seems pretty mundane next to that rig.
Clearaudio has a tendency to over-engineer their gears - after all, how else can they charge people $9000 for such a beast? Conceptually the TT2 arm is really simple and if you take the glass tube out with the armwand, it's essentially a fancy version of the Cantus.

Quote:
fdegrove: the idea to use convex bearing housings being to reduce contact area?
I believe so and I wonder if Clearaudio took into account of Cantus' idea of limiting vertical movement. They are visually similar but I have a feeling CA doesn't subscribe to all of Cantus' design features. I think rounded corners helps the "swinging" inside the tube - not a bad thing.

.
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Old 8th May 2010, 12:43 AM   #145
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Default Linear Motion Bearings

I looked into the linear motion bearing industry and come away with some amazing products. Miniature linear motion bushings. Maybe not as low friction and low noise as air-bearing but it's worth investigating.

IKO Stroke Ball Spline G LS | Products | IKO NIPPON THOMPSON

IKO Linear Ball Spline G | Products | IKO NIPPON THOMPSON

IKO Miniature Stroke Rotary Bushing | Products | IKO NIPPON THOMPSON

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Click the image to open in full size.

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Old 8th May 2010, 01:13 AM   #146
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Hi,

Congrats.

Overcoming friction in a tangential tonearm isn't a big deal for as long at this friction is a constant.

Much more difficult to tackle is to tell the cartridge induced vibrations where to go and stay untill they convert into heat.
No big deal with high compliance carts and their very limited dynamic range but..........

Cheers,
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Old 8th May 2010, 08:12 AM   #147
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Here's a tonearm originally designed for cylinder recordings that uses mechanical bearings.

Phonograph Makers: Norman Bruderhofer & Matthias Menz

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Old 8th May 2010, 05:38 PM   #148
bgruhn is offline bgruhn  United States
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Default convex bearings

Quote:
Originally Posted by fdegrove View Post
Hi,

WOW.
Even the most complex cutting lathe seems pretty mundane next to that rig.

BTW, the idea to use convex bearing housings being to reduce contact area?

Cheers,
Hi Frank et al,

Here is the latest development on my project. Previously said I was going to get better bearings than my junkbox ones. Yesterday I got some ABEC7 bearings with well finished corners (radiused) and light oil lubricant. Going to remove that. Also found in the junk box two 5/8 inch precision stainless steel rods about 8" long. These were originally for use in computer line printers at DEC in Ireland and have been gathering dust for about 15 years. Decided to us them instead of glass V or inside surface of some kind of tube. See the photo at www.gis.net/~bgruhn/audiodiy. In using the rod for rails and resting the bearings in the V between them it was primarily to reduce contact area and to have the contour of the rail constantly dropping away from the bearing for reducing the friction as the arm had to travel vertically. Between the new track and the new bearings, the results are just what I was trying to get. It tracks perfectly, no stick/slip that I can see and easily does so with the Ortofon cartridge. Now to come up with the rest of the design so it looks professional and is a lot more friendly to use than the jury rig it is now. Also need to flush the bearings of oil to use them dry. They didn't have any dry ones in stock at the bearing place. If the link to my web page isn't working try typing the url into your browser plz.

BillG

Last edited by bgruhn; 8th May 2010 at 05:49 PM. Reason: link wasn't working
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Old 9th May 2010, 12:27 AM   #149
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Quote:
bgruhn: "In using the rod for rails and resting the bearings in the V between them it was primarily to reduce contact area and to have the contour of the rail constantly dropping away from the bearing for reducing the friction as the arm had to travel vertically. Between the new track and the new bearings, the results are just what I was trying to get. It tracks perfectly, no stick/slip that I can see and easily does so with the Ortofon cartridge."
Thanks for the update and great picture! I proposed the two rod rail in post#62 and I am glad that it's working well for you. It's great to see something actually working to make music. How encouraging! Please continue to update the progress. Thanks again.

.
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Old 9th May 2010, 02:01 AM   #150
bgruhn is offline bgruhn  United States
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Default Radial play

Quote:
Originally Posted by moray james View Post
Peter: my comments here are given in the context of DIY. Most DIY builders do not have the ability to machine a glass tube. A stainless tube can be machined and polished to a precision inside diametre at any good machine shop or by those with the know how and their own equipment. This would I expect result in satisfactory results. I agree that the combination chosen by Bo is probably offers the best outcome and performance for the reasons you stated.
I had mentioned that the trolley would move up the inside of the tube during sever warps. I was under the impression that it was either Rauna or yourself that spoke about the bearings used and that they have built in play in the race to allow for arm motion. If I am in error then I apologize for misleading readers and stand corrected. I will re read correspondence to see where this impression originated.
At the risk of flogging a dead horse, I raise this subject again. One of the specs of single row ball bearings calls out the tolerances for radial play. The higher class ball bearings abec 7 has less radial play than the lower abec numbers. So if vertical motion of the arm was the only parameter to consider, the lesser bearing would be the one to choose sacrificing smoothness, starting torque, running torque, sticking here and there etc. I have chosen to go with the abec 7 for now and so far it is working out well. What I am commenting on here is my observation of the bearing in actual operation playing a record. It is easy to see that for the normal vertical motion of the arm, tracking a modestly warped disk, the outer ball race remains stationary for radial motion with the inner race supplying all the vertical motion. The outer race continuously is rotating to supply the horizontal motion. It should be noted that the compliance of the cartridge cantilever provides a buildup of horizontal force from zero to some value just greater than the force required to start the bearing rolling. For a very good quality bearing this is very small and approximates continuous motion of the trolley/arm wand. So yes, the bearings do have built in play with the better ones having less (radial) play. I've no idea whether or not Bo calls out a value for this or specially selects his bearing for this but it is there whether or not you might want it.

BillG
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