Thinking of re-building base for 10" skywatcher dob...

[GWING (Greg)]

Originally Posted by mental4astro

Hi Greg,

The first thing to do to improve the movement of your scope is to clean all the bearing surfaces, regardless if it's just the altitude or azimuth bearings that are bugging you. Dobs often are neglected in this aspect and end up sticky and hard to handle.

And it doesn't matter if the bearing surfaces are laminate or aluminium, they all get soiled.

*Use something like methylated spirits (denatured ethanol) or isopropyl alcohol and with a soft cloth clean well these surfaces - these don't leave a greasy residue. You'll be surprised at how much dirt you'll remove.

* Wipe over these surfaces with as good a high quality car wax as you can get. If you don't have a car, you'll have enough wax to last til your grandkids retire,

* The Teflon pads only wipe over with the alcohol. DONOT wipe them with the wax! If the azimuth bearing material on the ground board is of the roller type, take your time to clean as best as you can with the alcohol.

Is the bearing material on the ground board Teflon or the roller type?

Reassemble your scope and you'll notice straight away an improvement.

Clean these components first and let us know how you go. It is far cheaper and easier than choping and changing components, and the improvement in action is really, really significant.

I clean all the bearing surfaces and wax the laminates once a year on my 3 dobs, and I am ALWAYS surprised at the improvement in their action. Cleaning is all the maintanence that is required really. I look after my scopes, yet the bearing still need a little attention.

If you are still unhappy with the azimuth movement after cleaning, if the ground board bearing is of the roller type, you may like to change this for some virgin Teflon pads. The only other modification to be done after that is the Ebony Star laminate on the base of the rocker box. This last one is a last resort.

Thanks Alexander! I will give your idea a try first. Yes, they are Teflon on the base board according to Celstron who sells SkyWatcher here in the USA, but they don't know if it is the better Virgin material. Cheers! -Greg

[GWING (Greg)]

"Thanks Alexander! I will give your idea a try first. Yes, they are Teflon on the base board according to Celstron who sells SkyWatcher here in the USA, but they don't know if it is the better Virgin material. Cheers! -Greg"

Alexander,
I gave your suggestions a try today and the improvement by just cleaning and waxing was remarkable (No wax on the teflon). The Alt. is buttery smooth now and the az much better. The telflon pads on the base board are 1"x3/4" by 1/8" thick. I may still replace them with Virgin PTFE Pads from Scopestuff http://www.scopestuff.com/ss_tp41.htm I did notice the original pads are not beveled and so the base borad must be shaving off little tiny pieces making teflon dust. That was likely slowing things from smooth movement. Do you think I could step up to the 1"X1" by 1/8" size pads or should I stick with the origianl size?
Thanks again! -Greg

[Amunous (Michael)]

I replaced the teflon bearings as i was having heaps of trouble with the up and down motion of the scope.. going up or down it would "stick" and then suddenly jump over what it was stuck on. it was very hard to accurately point to anything. so i replaced them with skateboard ball bearings.

smooth as butter now. you do have to tighten the handles a little more now as its a bit too smooth. but once it wears in and you get used to it. no dramas at all.

[mental4astro (Alexander)]

Originally Posted by GWING

Do you think I could step up to the 1"X1" by 1/8" size pads or should I stick with the origianl size?
Thanks again! -Greg

The old adage: "if it ain't broke, don't fix it"

Leave it alone is my thought. Mohammed went the whole hog and got the virgin Teflon and Ebony Star, and the result was magic for him. If you replace the whole lot like he did, you'll gain something, but the balance between cost/benifit is what you need to deal with for yourself.

If your scope was a big beasty, say 16" or more, then reworking the mount may be a more viable option - better quality laminates, virgin Teflon, the 15lb/sq inch rule, etc. The stiffness requirements of these large dobs is less problematic in smaller apertures.

The 15lb/sq inch rule is the size of Teflon pads for the weight of the item they are carrying. The altitude pads will be smaller than the azimuth ones as the alt. will just be carrying the OTA. The az. pads have the OTA and the rocker box.

As an example, if the OTA weighs 45lb (45 pounds, or approx 20.5kg), then the total area of the Telfon used will be 3sq inches. The is then divided into four for each of the four pads used to carry the OTA. Remember that you'll need to take into account the area lost to the counter sinking of the screw heads that hold the pads in place.

Now, the rocker box adds another 15lb to the OTA total, so the area of Teflon used on the ground board totals 4sq inches. BUT, there are FOUR pads here on the ground board, not three - the fourth is a 'doughnought' shaped ring that goes around the pivot bolt to stop the bolt from crushing in the ground board and rocker box base toghether.

Michael, sounds like there may have been some other problem with your altitude bearings to change the whole lot for skate board bearings. I bet it's smooth as now!

[Amunous (Michael)]

yeah the teflon bearings just weren't cutting it. its soo smooth now. i too looked at making/changing to a different base. but this solved all my problems.