Losmandy G11 - Ovision retrofit

http://www.astromart.com/articles/article.asp?article_id=663

I posted an article to sum up my thoughts on the topic of the new upgrade and make the basic data widely available.

Hopefully we will get more, and mo' betta', data on the Losmandy yahoo group in the coming weeks and months as additional people opt in to the upgrade. With article available and accessible without being a member of astromart, I am hopeful that if anyone here knows someone considering the purchase of a mount, that they will inquire into whether this alternative is suitable.

regards
Greg N

Glad to see someone ran with my design or one like it that I posted in the Yahoo Losmandy group some year or so ago.

Their product could be better with the use of duplex pair bearings as I had shown in my original drawings. Bearings are as important as the precision of the worm. Rolling noise is something that some seem to ignore.

I hope they chose their bearings well. I only found (2) known types in 1/2 inch size that would take the load and they were expensive. I spent the bulk of my efforts with my mechanical engineer friend working the worm axial load equations. We have some 15 pages of equations to get the result. Took a long time since no one knew what the specs were on the worm bearing loads. Safest way would've been to use the same bearings as Scott, but then we wouldn't achieve the precision and stiffness as we did with duplex bearings each end.

From the looks of their pictures they used the same size bearings as the original? Load not a problem with 5/8 inch bearings, but single bearings each end sucks no matter how you adjust end play.

My design allowed for loading the worm gear though the center window and not through the end. Half inch bearings left more meat (material) to keep the whole assembly more rigid so the housing wouldn't flex. Again, 1/2 inch bearings in duplex pairs each end with TIR of something like .0001 to .0002 or less if you messed long enough.

Scott didn't leave us much to work with material wise for a retro fit. I sent him my design idea about year or so ago. Never did hear back from him but he is a busy man.

I did drop the ball on my effort due to unforeseen circumstances with my time for the last year.

Yeah folks, I'm still around and not dead.

Joe Conway

One of the biggest problems with doing a retro for the worm block is the end blocks. There wasn't enough material to use threaded clamp rings to retain the bearings. If you attempted to thread the blocks for a threaded clamp ring it would break out at the bottom where the threaded mounting studs are.

In one of the pictures on the Ovision site of their retro it appears, maybe, that this is the case. They may have used metric bearings and had a little more allowance for this lack of material. Either way, the original bearing blocks were flimsy and could flex at the mounting studs. There simply is not enough metal at the bottom of the blocks where the studs are.

The end result was I went away from the larger bearings and spent the time I did researching smaller, 1/2 inch bearings. The bearings shown in the second picture, showing the end of my blocks, have an axial load spec. of 72lbs. They have a radial play spec. of 0.0001 inches. I did look at angular bearings that had a axial load spec. of 132lbs, but they were $125 a piece. Times that by 8 and you see the picture there.

It would've been way easier if Scott would've raised up the main gears some to allow for more metal at the bottom of the worm blocks.