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DIY Air Bearing Linear Arm
DIY Air Bearing Linear Arm
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Old 30th January 2015, 01:54 PM   #21
niffy is offline niffy  Europe
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Wow Super.

Your attention to detail is astounding. Well thought out and beautifully crafted. It makes your ball race arm look tiny.

Niffy
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Old 31st January 2015, 04:10 AM   #22
drumdoctor is offline drumdoctor  United States
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Are you using a NewWay bearing? Or did you build the actual bearing from scratch?
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Old 31st January 2015, 01:59 PM   #23
super10018 is offline super10018  United States
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I bought the New Way air bearing from here

https://www.motionusa.com/online/sho...s/air-bushings

They sell shaft for $9.00 per 25 mm. I bought mine from

MetalsDepot® - T303 Stainless Steel TGP Shafting

The diameter tolerance is +/- .0005". New Wary 's requirement is +/- .0002-.0007". It is much cheaper. Then, I used 2000 grit sand paper and put the shaft on a drill press to sand it to mirror shine.
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Old 1st February 2015, 01:45 AM   #24
super10018 is offline super10018  United States
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I added my damping device today. I have a pair of u-groove ball bearings in hand so they are prefect for the job. The string is polyester thread. It can be stretched a little. I moved the device from back side to front because it is more effect on the front and it is easy for me to install the device. I made two small buckets as weights. The buckets weight 1.7 gram alone. If I want to increase the weight, I can add lead shot pellets. Each pellet is 0.1 gram. If I want to damp different low frequency, I may attach a piece of rubble band with the thread to make it more stretchable and combine with different weights. But I don't see the reasons to do this so far. The cartridge I used was Dynavector 17D3. It is high compliance and recommended VTF is 1.8-2.0 g.

Before I installed the damping device, I had the 17D3 on the arm. I was wondering why the sound was kind of dull and boring. The high frequency didn't sound right. 17D3 never lacks micro dynamics but is some what weak in bass. After I installed the damping device, it really opened the sound. High frequency was really wonderful and natural. The sound came to life. The bass was very well defined. The damping weight I used for 17D3 was 1.8 gram. In the meantimes, I also increased air pressure to 42 psi to make the arm stiffer.

I think my damping device is better than silicone oil damping device.

1. Silicone oil is messy. Mine is complete dry device.
2. Silicone oil damping is non-directional. Mine is directional. I really don't see the needs for damping all directions except the direction which is parallel to the bearing shaft.
3. It is hard to guess how much damping force you apply with silicone oil. Mine is very straight forward by the weight.

On my air bearing arm, it may not be necessary to use damping device for some of cartridges. It may be ideal still to add light damping to reduce distortion and noise. I will try different high compliance cartridges later on.
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Old 1st February 2015, 07:33 AM   #25
vynuhl.addict is offline vynuhl.addict  Canada
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Hi Super,

The Dynavector 17d3 would fall in the Medium compliance at 15, most MC carts don't ever get out of the medium territory. I'd be curious to see how a true higher compliance cart such as the Shure M97 would fare, the cantilever is far more elastic so would be affected by mass. None the less it is a nice project my friend, I would get my hands a little more wet but the $195 for the linear air bearing is a bit much right now :/.

How do you find the sound compared to a mechanical arm?, do the gains outweigh the added complexity?


Colin
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Old 3rd February 2015, 12:46 AM   #26
super10018 is offline super10018  United States
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Hi Colin,

Actually, I am not satisfied with any ball bearing designs. This is why I made my air bearing arm. I don't like two glass tubings and one ball bearing design because it is not a safe design. The carriage can very easily drop off the glass rails and damage cartridge. It happened to me. Luckily, the cartridge was fine. Its friction is simply too high. In reality, once the bearing is not centered, its friction on one side can get too low while it actually requires higher. And on another side, the friction can get too high while it needs lower friction. It has shortcoming of Cantus's design, various VTF, too.

I don't like Clear audio's approach because the arm pivot is not stiff enough. It can move forwards and backwards. I also don't like Cantus style, that is what I have now. Cantus style ball bearing design has stiffer pivot but still not enough. It has different force of damping on two side of ball bearing so its VTF varies. Of course, both Cantus' and Clear Audio's are very safe for cartridges. All the ball bearing designs require low compliance cartridge to work best. I have my own idea about ball bearing design. I think it is better than all the designs I mentioned above, but I have to actually do it to approve if it works better than other designs. And I don't think I will do it because I think air bearing is the best solution for linear tracking arm.

Comparing air bearing, ball bearing designs have one advantage. Ball bearing designs are mechanically grounded, while air bearing depends on arm and bearing to absorb resonance. Anyway, ball bearing arm can still sound very good under the right combination. I believe that for arm design, there are nothing absolute and everything are relative. Everything are about optimal in relation to other factors.

Air bearing arm's trackability is superior to any other means for linear tracking arm. With a damping mechanism in place, air bearing works very good with wide range of cartridges. Its sound is so well defined. I asked myself why we need a pivot arm. My air bearing arm is much quiet than ball bearing and has much less distortions. I thought about magnetic leviation linear arm, but it was just a thought. If it works, it can be comparable with air bearing arm and can even be better because it doesn't need an air compressor.

I don't make things complicated if I don't need to. But one thing for sure, I won't make any arm in its full length. Linear tracking arm must be short to work best. A short arm makes things a little complicated because you need a retractable mechanism. If a short arm makes things complicated, I would certainly say it is worth to do.

I also can't stand rough finish. My most advanced tools are a band saw and a drill press. Otherwise, I may make the arm even nicer both looking and functionality. Roughness doesn't mean simplicity.

Last edited by super10018; 3rd February 2015 at 12:53 AM.
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Old 3rd February 2015, 07:53 AM   #27
vynuhl.addict is offline vynuhl.addict  Canada
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Hi Super,


I think in the elegant simplicity department we North Americans couldn't even nip the heels of the Europeans in that department, many American things are profoundly overtly engineered in the bigger is better philosophy, but there are exceptions, Apple being one.


The air bearing makes sense, though as you point out it's now entirely up to the arm to dissipate internal resonances vs the mechanical ground of the bearings. I'm not bashing your design which is very similar to the ESP linear arm, just looking for the info to justify the cost . Speaking of mag lev, that's what I've been working on lately, it's although a lot more complex from a stability standpoint :/.



Colin
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Old 3rd February 2015, 10:28 AM   #28
Hiten is offline Hiten  India
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Pardon me as this is not related to the thread. I think it was a British designer whose talent made a turnaround for Apple Co. British designs are good. I like them. Some designs are iconic.
Regards.
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Old 3rd February 2015, 06:37 PM   #29
super10018 is offline super10018  United States
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Update:

I am using 1/16” latex tubing to feed the 40 psi air to the bearing. But I am always afraid that the latex tubing can’t resist high air pressure because I destroyed one with 50 something psi air pressure. I just bought 1/16” Tygon ND100-65 medical plastic tubing from Amazon. The tubing is almost as flexible as latex and its working pressure is 55 psi. It should have no problem since I even added some damping. A little resistance from the tubing should be beneficial.

I will rise the air pressure to 50-55 psi. The bearing will get stiffer. I also will rise the compressor output air pressure to 90 psi. My compressor runs highest pressure 80 psi with temperature at 105 F so far. Therefore, I can run the compressor even higher pressure. It is time to put high pressure on. I highly recommend Tygon tubing.
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Old 4th February 2015, 11:31 AM   #30
Max Headroom is offline Max Headroom  Australia
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How much acoustic noise does the leaking air cause ??.

Dan.
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