Revelation 10" Dob Mods

[David Smith]

Hi All

Would appreciate any thoughts you have on the following niggles I have with my big scope:-

Finding it difficult to collimate the primary due to the adjustment screws being quite stiff / tight. 2 of the 3 screws seem ok but one is very difficult to adjust. Have tried removing all the screws, cleaning and replacing but still very tight.

Motions on both axes are less than perfect and I keep over shooting as I nudge the scope to track objects. This is especially apparent at high power. Again, have tried removing, cleaning and reinstalling but no better.

Anyone else have similar problems with a Revelation Dob? Have kind of learnt to cope with these but would be nice to solve them.

Thanks

David

[fwm891]

Hi David - short answer is don't worry about the stiff screw/bolt, use it to your advantage. Leave it be. Make all your collimation adjustments via the other two screws.

There is one major benefit from working in this way: your focal plane is always in the same position as the mirror (primary) never creeps forward/backwards up and down the tube as you make adjustments.

That also means your telescope balance doesn't change after a collimation run because the heavy primary mirror is always in the same location.

This technique can also be used with the secondary mirror. Then by only moving two of the three options on each mirror you will quickly learn which of the two screws on each mirror needs the adjustment, and be confident that your focal/image plane is in the same position each time.

My preference would be that when you look at the rear of the mirror cell or the secondary holder use which ever screw in in the vertical line on the mirror (top or bottom) of the cell and fix one of the other two with a lock nut (hopefully it will in your case be the stiff screw anyway).

I've built a few Dob's in the past and found that in the absence of low friction materials for the side rockers or the base pad that a LITTLE silicon polish sprayed on a cloth then wiped over the bearings will ease things. Its small amounts of muck that get onto the rocker box bearings that cause havoc with smooth rotation. Hope this helps.

Francis

[David Smith]

Francis, Thanks for that. Will try the silicon polish on the altitude bearing as this is essentially a plastic tube set on it's side so polishing the surface makes sense. The azimuth bearing is a roller bearing (small rollers embedded in a plastic sheet). Would something as simple as WD40 work on this?

As far as the collimation screw is concerned I had basically been doing as you suggested, collimating with the other two.

David

[fwm891]

The Az bearing would be best if you can dry wipe any muck off the bearings and the upper/lower surfaces they ride between. WD40 is great for most things but here it will act as a dirt/dust attracter because it always stays moist. Use a silicon polish as a repellent for moisture but use as little as possible.

The Alt bearings need to overcome sliding friction so the polish will help here (again as little as possible as a polish build up can take things the other way). The Az bearings need to overcome rolling friction and the length of leverage given by the tube should overcome this easily except when viewing at or near the zenith as the leverage almost disappears in this area with a Dob...

[David Smith]

Thanks again. This will be one of my jobs tomorrow!

[David Smith]

Just a quick up date. Polished the surfaces on both the axes and both have dramatically improved.

Thanks

David