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Dob bearings


acey
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I went to a local plastics engineering company and was able to get 2x 18" squares of 3mm teflon, etched one side for application of adhesive, for 10 earth quids per sheet. My initial plan was to make two discs that ran against each other, but then decided to make two circles of 1" squares instead, thus using a fraction of the material and still getting a jolly good bearing. I also use a dry silicon based lubricant to eliminate "stiction".

Edited by yeti monster
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I didn't know you could stick it effectively if you etched one side, instead I drilled holes through my bearing points, countersunk the holes deeply, and attached them using little screws.

It did also occur to me to use silicon lubricant on my dob's base because I started out using felt pads (which were a failure, nowhere near as good as PTFE) - I actually wanted Pledge or something similar, having slipped over like a clown more than once on laminate flooring after someone's been polishing furniture! I don't know how effective the silicon spray really is but between that and three PTFE bearings of about an inch square my dob's azimuth adjustment is as smooth as I could have hoped for, and way smoother than I thought it would be.

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hi acey, i used ptfe rod cut into 25mm lengths and inserted them into holes drilled in the radius of the bearing cut outs , they are then trimmed to the radius of the bearing discs. i inserted 8 in each side ,this gives 8 x 8mm pads the rest of the 8mm flexible rod was coiled into a circle as my base board bearing, see my other recent posts for more info ,

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The dry silicon lubricant was recommended by my local bearing factor, to whom I turn to for all my bearing needs. They put me onto the plastics engineering people when I explained about building my Dob mount. The idea being that a dry lubricant doesn't pick up debris like a conventional "wet" lubricant would in such an application. I have found it to be very good at elliminating the "stiction" that caused me hassle with the tiny movements required whilst tracking an object.

this is how I set out my bearing pads:

DSCF6777.jpg

Edited by yeti monster
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When I mentioned "lazy susan" at the bearing factors, he just gave me a rather funny look!

I tried a pair of encapsulated bearings I had in the shed, for my alt. bearing, but they were too free, I was unable to apply the required friction to maintain position without inducing "settling". it was just too frustrating trying to get an object into the centre of the FOV.

I settled for small teflon plain bearings. They proved ok until I started to use "real" EPs, then things started to go all over the place. After an application of paint to the mount, I regained control and when I finally get to fit the hand knobs I'll be able to apply friction more accurately.

Edited by yeti monster
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Lots of great ideas, many thanks. For my 8" I'm going for a low-profile style, i.e. large altitude bearings and minimal rocker box. Haven't made the ground-board yet - given my near non-existent DIY skills I thought to try and get the altitude motion into a tolerable state first. I've heard of using roller-skate bearings - could maybe give that a go while I order up some PTFE. Never made a dob before (or anything else except IKEA flat packs) so it's a steep learning curve - but fun!

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