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Teflon or something else ?


John

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I hope this is a straightforward question :smiley:

What would provide the smoothest movement for an azimuth axis where one surface is polished alloy ?. The bearing will be under some load as a 16 kg scope will be on board, if it works. I'm wondering whether to use teflon pads against the alloy surface or some other material. The Meade Lightbridge dobs use felt pads against their large alloy altitude bearings - maybe that would be better ?. If alloy is not going to work as the flat surface I could re-think that too.

Thanks and please feel free to ask me further questions if that helps get a clearer answer :smiley:

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I would not have considered Aluminium ( I assume you are referring to Al ) alloy as a suitable bearing material. It will eventually corode and become rough, Aluminium Oxide is an abrasive aka Aloxite and Corundum. As an azimuthal bearing it will be hidden from view so you will not be aware of it's condition unless your design allows for easy inspection and dismantling. PTFE is quite a soft plastic and will wear quickly against an abrasive surface. It will also creep under heavy load but that can be reduced by increasing the area of the pads.

Probably a better alternative choice would be Acetal which is used as an engineering bearing material. It will have more friction than PTFE but is a bit harder.

Other alternatives for this sort of application are HDPE and Polypropylene but these will have higher friction, with the PP having the better creep characteristics.

Why not go for the usual textured Melamine surface?

Nigel

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Thanks Nigel,

Basically I'm looking at putting together something like this:

http://ejamison.net/refractordobmounts.html

I have a very massive and pretty tall tripod already which has an 8" diameter alloy pier adaptor plate on top of it. I was wondering if the flat surface of that could seve as the bottom half of the azimuth bearing with a matching disk of heavy duty plywood on top, teflon or similar pads between them and the cradle holding the alt bearings on top of the plywood disk. If this is not a good plan then I could bolt an additional, melamine covered, ply disk to the top of the tripod hub and have the cradle ride on that with dob-style teflon pads between them.

It's useful to get such feedback as I'm just kicking around ideas at the moment :smiley:

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I think you are going to run into bearing difficulties with such a heavy load acting off-axis to the pivot point. Have another look at the alternative arrangement that I suggested, the majority of the components can still be made of wood and weight, within reason, is not an issue.  :smiley:

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I think you are going to run into bearing difficulties with such a heavy load acting off-axis to the pivot point. Have another look at the alternative arrangement that I suggested, the majority of the components can still be made of wood and weight, within reason, is not an issue.  :smiley:

Thanks Peter - I've not forgotten your design and still have the details and photo that you sent me :smiley:

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