Lightbridge altitude bearing upgrade

[Andrew*]

I'm considering upgrading the altitude bearings on the 16" lightbridge as they aren't that smooth - a bit jerky and difficult. The original bearing is just a strip of felt glued onto the semicircular rim of the base.

I wondered if a strip of teflon would work better.

Has anyone else modified their altitude bearign on their lightbridge - if so, what did you do?

Andrew

[albedo0.39]

Hi Andrew - I'll be following this one closely. Are you on the Yahoo LB group ? If not, I'd really strongly recommend. Heaps of LB only mods and of course people have done all this so can report with experience.

My bearing was also a touch sticky so I duly sprayed the felt in GT85 (as used on all my bikes) and polished the bearing. It's now much better. at £3 a can, it's worth a punt. GT85 is not like WD and doesn't leave a sticky film.

[Doc]

I've often thought about this as well Andrew but from my little experiece that I have it seems that the felt bearings were very well if the scope is balanced correctly.

To much weight on either end and they to have alot more stiction to overcome. But saying that a teflon mod is on the cards oneday.

[calibos]

Just remember that you if you go down this route that it is the Ebonystar and Teflon mod you should be doing, not just teflon alone. Teflon alone will scratch up your aluminium bearings and make stiction 10 times worse. The slightest bit of sand or grit that gets between the teflon and your aluminium bearing will gouge out horrific scratches on your bearings.

I found this out to my cost a few months ago. I wasn't actually performing a true teflon mod. What I was doing was inserting some spare teflon between the bearing and the base rim to take out the slop. As you may have noticed the cutout in the base rim is wider than the aluminium bearing which means the scope can rock backwards and forwards within the bearing cutout. Not much of a problem for visual use where all this means is a little bit of backlash when you move the scope in altitude. However, when one is trying to fit DSC's to the scope, this rocking becomes a very big problem for the altitude encoder as you can imagine.

The teflon piece one each side was to stop this rocking. For the first 5 minutes it worked beautifully. Not only did it prevent the rocking but it meant the scope held at any altitude without any brake even though it was way out of balance, all the while keeping smooth movement with no added stiction. Then all of a sudden....GGCCCRRSSSSHHHHH and the scope got very sticky and grindy when moving in alt. Had a look and some grit or something had got between the teflon and aluminium and gouged the bearing good'o!!

Have since read about guys who thought they could replace the felt with teflon and ended up with the same result.

You need to wrap a strip of ebonystar around the aluminium hub. Problem solved.

[John]

I think this must be a LB 16 issue as the altitude bearings on my 12" seem nice and smooth in their un-modified form. I have taken care to balance the scope properly (no need to use the puny altitude brake at all now ) and I am careful to check that no sand or grit has got onto the felt strips regularly.

I agree with Steve on the value of the Yahoo LB group - a real mine of information

John

[Doc]

I think this must be a LB 16 issue as the altitude bearings on my 12" seem nice and smooth in their un-modified form. I have taken care to balance the scope properly (no need to use the puny altitude brake at all now ) and I am careful to check that no sand or grit has got onto the felt strips regularly.

I agree with Steve on the value of the Yahoo LB group - a real mine of information

John

I don't think this is a 16" problem John as mines balanced very well and have never used the break either and I would say mines very smooth.

[The Warthog]

As I am getting ready to build a 12" dob soon, I have been considering using ABS to ABS as a bearing. I.e. an ABS toilet flange, and a strip of ABS cut from a tube to line the cutout in the box. I realize this would have to be measured pretty finely to avoid slop in the setup, so I am also thinking up ways to shim the whole thing if I end up with slop. Whaddaya think?

[albedo0.39]

ABS toilet flange,

Warthog.. is this what I think it is ?

[The Warthog]

"Don't Call The Plumber yet!"(Toilet Repair Flang)

The one I will use will be one of the simple ones without the rubber expansion ring. I think it is obvious how you could use this as an altitude bearing. The idea is not original with me.

[albedo0.39]

Don't you just love YT ? I never thought I'd be looking at how to fit a toilet flange on an astronomy forum.

It must be to do with the phases of the moon..

Incidentally, I was speaking to the president of an Astronomical Society in Canada today (not sure which one) and he mentioned that his society had purchased an 82" scope and was rennovating it.. (I think that's the size). Do you know this scope ? It's supposed to be the largest in private hands and was built in the early 20th century in the UK.

[The Warthog]

Probably the Royal Astronomical Society of Canada, which has just come to some kind of terms with the developer who bought the David Dunlap Observatory grounds near Toronto. See here: Clear skies ahead for Canada's largest telescope (Forwarded) - sci.space.news | Google Groups

It is actually 74", and the largest telescope in Canada.