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Old 20th December 2008, 06:22 PM   #11
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Here is a diagram showing how the forces and moments applied.
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Old 20th December 2008, 06:27 PM   #12
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Mine doesnt.

Did you build it yourself?

Are the carrier and manifold perfectly matched?

Tried reducing air?

Strange, we get oposite results!

If anything, i think my normal ladegaard arm did this more.
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Old 20th December 2008, 07:04 PM   #13
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This was 5-th incarnation of my arm.
Matching carrier and manifold is easy if you makes them from the very same piece of aluminum angle. Reducing pressure did not reduce rocking but caused carier stucking.
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Old 20th December 2008, 07:14 PM   #14
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I found using the same piece of angle for carrier and manifold doesnt work as the internal and external angles will be different. The angle is thicker at the corner and thins towards the edge.

When i built my first couple of ladegaard arms i used to get the rocking as the air gap would be thicker at the bottom of the V.

I found there are 2 ways to get a good match, go through all the angle to find 2 that fit together, or lap them together. Lapping will only work if there already pretty much perfect.

If you hold the manifold/carrier up to the light and look at the end, you shouldnt be able to see ANY daylight.

I never managed to get a good match using the same piece of angle, although i know VIC does and his arms are fine.

maybe it depends on who manufactured the angle? Maybe B&Q's stuff isnt that high a quality.

I dunno, but if you get rocking, i bet mismatched angle is to blame, they really do have to be 100% perfect!
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Old 22nd December 2008, 10:37 AM   #15
Nanook is offline Nanook  Canada
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I am a little confused by your diagram and your explanation.

M:=F Xr , where M is actually torque, a vector . It follows the RHR in vector mathematics. The torque created by a (relatively) large F and a large r could , in fact , move the arm "backwards" if there is enough movement permitted by an imprecise gap between the carrier and the stationary portion of the arm, or the gap is large.

I suspect that graeme uk is on the correct path to answering the "rocking " question.


Maybe my neurons are misfiring across the synaptic gap in my brain, in which case please ignore any comments I make.

stew
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Old 22nd December 2008, 06:42 PM   #16
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Match between slider and manyfold may definitely be improved for any ready made angle profiles; I will try lapping. But anyway, all other factors being the same, the rocking moment is order of magnitude bigger for terminator arm. I have rised a bit a point of contact between the arm knife and slider (two tiny bronze prisms are glued to the slider), such as it lays in the same horizontal plane with the air nozzles placed in the middle of slider bottom surfaces; so the rocking moment is virtually non-existent.
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Old 30th December 2008, 09:47 AM   #17
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I started out with Vic's conventional Ladergaard and now have the Terminator. The only time I've heard "elephant steps" is with the conventional arm when there was too much air pressure. The Terminator is very insensitive to air pressure levels and works like a dream. It's a significant step up from the conventional Ladegaard type arm that Vic originally produced - which was very good indeed.

If the inverted arm is causing "elephant steps" then there's something wrong but it's either something Vic has got around or never experienced.
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Old 31st December 2008, 02:37 AM   #18
jkeny is offline jkeny  Ireland
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Quote:
Originally posted by graeme uk
Get the pivot point in the middle of the arm tube, seems to work better.
So the pivot point should be at about 3" & not at the 4" mark as in Vic's terminator pics? In what ways is it better?
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Old 4th January 2009, 04:23 PM   #19
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Middle of the arm tube diameter.

My arm tube is about 8cm long from pivot to stylus.
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Old 4th January 2009, 06:46 PM   #20
jkeny is offline jkeny  Ireland
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Sorry Graeme, I don't understand when you say "middle of the arm tube diameter" - you didn't mean middle of the length of the arm tube then?
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