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Trying to improve EQ5 worm end float


Horwig

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I'm thinking of trying to improve the end float on the dec axis of my trusty old eq5, the rubber thrust washers work up to a point, but I think a solid solution would give a lot less play.

Found this on the web: http://www.iceinspace.com.au/forum/showthread.php?t=4369

Seems a good fix, but shouldn't they be thrust bearings?

Stripped and measured the worm block, I need 6 mm inner, 11 mm outer bearings, easy enough for normal ball bearings, but been trawling the web this morning, and can't see any thrust bearings that small.

So I suppose the question is, would normal ball bearings be robust enough to cope with the axial forces involved?

Huw

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Hi Huw,

These people do small thrust bearings... either Ball or Needle types.

http://www.rcbearings.co.uk/index.php?route=product/product&path=54&product_id=594

http://www.arceurotrade.co.uk/Catalogue/Bearings/Thrust-Ball-Bearings

http://www.arceurotrade.co.uk/Catalogue/Bearings/Needle-Roller-Thrust-Bearings

It would seem though that 12mm is the smallest OD so you may need to bore out the housings a little.

Hope this is of some help.

Best regards.

Sandy. :grin:

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  • 3 weeks later...

Well I bit the bullet, and ordered some bearings from China, deep groove ball races, 6mm inner, 10 mm outer, 2.5 deep. I'd seen a web article where the 10mm bearings were bodged out to the 11.3 or there abouts of the housing by winding insulating tape around the bearing. I tried heat shrink tubing, which was useless, so tried the insulating tape, success, really tight neat wrap. The bearings in their wrap were pressed into the casting, and the tape trimmed cleanly with a scalpel.

post-6754-0-69245100-1397512079_thumb.jppost-6754-0-83942400-1397512081_thumb.jppost-6754-0-82142200-1397512084_thumb.jppost-6754-0-97464300-1397512086_thumb.jppost-6754-0-99424700-1397512088_thumb.jppost-6754-0-29783800-1397512091_thumb.jppost-6754-0-09597900-1397512097_thumb.jppost-6754-0-08972000-1397512100_thumb.jp

Both worms were rebuilt, and they feel nice and smooth, with very little free play compered to the rubber washers. But the true test is guiding, so here goes, 300 focal length, Lodestar through OAG, here's the result on a +-8 pixel graph, and the same on a +- 1 pixel graph.

post-6754-0-10689500-1397512103_thumb.jppost-6754-0-42962000-1397512106_thumb.jp

Before I redid the bearings, the end float on the Dec caused big deflections of about 5 pixels for 10 seconds or more as the mount fought the backlash, they're gone!

The polar allignment was only approx, so ignore the RA corrections, but the rms says it all, 0.21 pixel error, and that's at 300 mm, reckon I'm more than pleased. Now if only that big moon would go away.

Huw 

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I'm thinking of trying to improve the end float on the dec axis of my trusty old eq5, the rubber thrust washers work up to a point, but I think a solid solution would give a lot less play.

Found this on the web: http://www.iceinspace.com.au/forum/showthread.php?t=4369

Seems a good fix, but shouldn't they be thrust bearings?

Stripped and measured the worm block, I need 6 mm inner, 11 mm outer bearings, easy enough for normal ball bearings, but been trawling the web this morning, and can't see any thrust bearings that small.

So I suppose the question is, would normal ball bearings be robust enough to cope with the axial forces involved?

Huw

Huw

Why wouldn't you just use 686 bearings like the CG5 (which is closely related)?

6x13x3.5 or 5 mm

You can get good ceramics here for £4.99 each

http://demonpowerproducts.co.uk/product_info.php?manufacturers_id=&products_id=6430

Works perfect on a CG5 which looks similar to your set up

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  • 2 weeks later...

Yes, thinking about it, packing the bearings with plastic to fit the block is a naff engineering solution, so a couple of hours on the lathe and mill, and I've machined out the block to take some 6x12 bearings I had left over from another project. The alloy cap with the countersunk bolts preloads the bearings to remove end float. It's much easier to achieve a good snug fit than the original threaded packer and lock nut. Everything now feels much more solid, lets see what its like under the stars, whenever they decide to come back.

uw

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post-6754-0-95722700-1398529088_thumb.jp

post-6754-0-61532200-1398529093_thumb.jp

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  • 9 months later...

Yes, thinking about it, packing the bearings with plastic to fit the block is a naff engineering solution, so a couple of hours on the lathe and mill, and I've machined out the block to take some 6x12 bearings I had left over from another project. The alloy cap with the countersunk bolts preloads the bearings to remove end float. It's much easier to achieve a good snug fit than the original threaded packer and lock nut. Everything now feels much more solid, lets see what its like under the stars, whenever they decide to come back.

uw

Just coming to the conclusion that I want to do something to improve the awful backlash in the Dec axis of my EQ5 and came across this thread. I haven't got access to other than hand tools - would you still recommend the plastic tape approach in my case?

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Just coming to the conclusion that I want to do something to improve the awful backlash in the Dec axis of my EQ5 and came across this thread. I haven't got access to other than hand tools - would you still recommend the plastic tape approach in my case?

Hmmm, the feel of the drive was indeed better with the plastic wrapped bearing compared to the standard job, was it a whole lot better in practise, I'm not sure. With the standard nylon washer arrangement, to get rid of float the block had to be very tight. With the bearing wrapped in plastic and well adjusted, it felt a lot easier to turn,. but another variable was introduced, the elasticity of the wrap.

Try it, all its going to cost is a roll of insulating tape and a couple of cheap ball races off ebay. If it works for you great, if not, nothing's broken, you can go back to the standard arrangement.

Sorry for the vague answer.

Huw

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Huw

Why wouldn't you just use 686 bearings like the CG5 (which is closely related)?

6x13x3.5 or 5 mm

You can get good ceramics here for £4.99 each

http://demonpowerproducts.co.uk/product_info.php?manufacturers_id=&products_id=6430

Works perfect on a CG5 which looks similar to your set up

Huw

Why wouldn't you just use 686 bearings like the CG5 (which is closely related)?

6x13x3.5 or 5 mm

You can get good ceramics here for £4.99 each

http://demonpowerproducts.co.uk/product_info.php?manufacturers_id=&products_id=6430

Works perfect on a CG5 which looks similar to your set up

Ya, I made the same thing.  Ceramic 686 ball  bearings turn your worm to very smooth and precise one.

Giuseppe

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The problem is that the diameter of the bearing housing in the block is 11.3mm, so to fit 13mm bearings it needs to be machined out. I eventually used 12mm bearings, so less to machine off, and very smooth it is too.

Huw

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Thanks. I was looking for ways to make a housing for a worm gear i found.

I guess putting ywo thick washers is not enough even for 1rpm like speeds..

Can i know if this (housing) can b made with a bllock of aluminum and a latte.?

Pl dont laugh if it's a stupid question..

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Thanks. I was looking for ways to make a housing for a worm gear i found.

I guess putting ywo thick washers is not enough even for 1rpm like speeds..

Can i know if this (housing) can b made with a bllock of aluminum and a latte.?

Pl dont laugh if it's a stupid question..

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No, not a stupid question at all. I have worm drive on my big scope that uses a section of aluminium 'U' channel to hold the worm, with ball races machined into the opposite faces, much like the block from the eq5 above, but larger and easier to make.

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There is probably a way to make the housings for the bearings on a lathe, but a mill would do all the jobs on the block.

Huw

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