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Old 7th December 2010, 09:09 PM   #1
kirk57 is offline kirk57  United States
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Join Date: Feb 2008
Default Looking for advice on Terminator-style tonearm

This winter I've decided to give the inverted Ladegaard air-bearing linear tracking tonearm a try. I am hoping that those who have had success with this can offer advice.

So far I have drilled the larger 3 mm holes, applied tape to the back of the track and put pinholes (approx .3 mm), then used double-stick foam tape to attached the second piece of 3/4" angle AL to the back. The clear air hose attaches to that piece. The foam tape is about 2mm in thickness. There are no leaks around the tape (I used water to check for bubbles)

Using a Rena Air 300 pump (4.5 psi) I am getting no lift at all just using a short section of polished angle AL on top, not even mounting the tonearm yet.

So 2 things come immediately to mind.

1) are the pinholes in the tape the right size?
2) Is this pump strong enough for what I'm doing?

I appreciate any and all advice!

Kirk
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Old 18th December 2010, 03:31 PM   #2
el156se is offline el156se  Romania
diyAudio Member
 
Join Date: May 2006
hi kirk,
- the rena pump si far too powerful for your needs. I run a tonearm build like yours with
a pump that had half the capacity of your rena, and sustain 100 gram carriage
( arm-wand + counterweight + cartrige)
- I'we run a similar test air bearing with 2.5mm holes and 0.5mm pinholes and it was
working with a 550 liter/min pump
If you make no mistakes on building the air circuit, then only reason for failing
is the mismatch of L profiles you are using.

First, make sure the air is exiting the pinholes.
Second, make sure the carriage and the pinhole rail are matching to perfection,
otherwise the 'air cushion' will not form when switching up the pump, thus the
upper rail will never float

help this is helpful,
take care,
robert
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Old 18th December 2010, 07:41 PM   #3
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Join Date: Dec 2005
Location: essex
Ive built a few of these.

The carier and manifold, as mentioned, need to match very well.

I find i normaly need to make each piece from a different length of profile.

The internal and external angles of L section never match. The walls are generaly slightly thicker at the corner than at the edge.

Once you have 2 pieces that match perfectly (manifold top section and carrier) i sometimes lap them together with a little toothpaste or similar.

As for the manifold, i gave up on tape and sticky foam. Its ok for prototype but not good for long term reliability.
I drill the 2.5mm holes with a cheap drill press so that they dont quite go all the way through. Then i make the hole with a 0.3mm drill in a hand held twist drill. This gives perfect holes.
The problem with tape is the holes block, dust sticks to the sticky etc. Also the holes arent perfect so it disturbs the air flow.
My manifolds are now 3 layers of aluminium bonded together with silicone. The middle layer replaces the sticky foam.
Middle layer obviously has the center cut out.
This way you can make very sturdy manifolds with long term reliability.
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Old 18th December 2010, 07:45 PM   #4
diyAudio Member
 
Join Date: Dec 2005
Location: essex
This is the version im using now, not super neat but the best i could do with a hacksaw and a file.

Click the image to open in full size.
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