开云体育

To those of you who have actually tried placing one or multiple Bellville? springs on the worm shaft, do you compress it by squeezing both worm blocks together? Seems to me if the spring is flattened you lose spring action and if you don't completely compress it, there is play in the worm shaft. Any thoughts appreciated from people who are experienced playing with the old worm.

Tom

Thanks Michael, I have a collection of them as well. Without any Bellville washers I used a c clamp to hold the blocks on either end of the worm and placed a feeler gauge between the gear housing and the block further from the motor. That way I only had to gently pivot the block against the feeler gauge while I tightened the bolt under the block. No lateral worm movement.

Hi Tom,

The reason the Belleville discs improve PE is that they force the bearings to rotate in a predictable way with the motion of the worm. Left to their own devices the ball bearings tend to stall then start again in unpredictable ways likely when the clearances are taken up by misalignment in the worm and bearings. Placing a light load on bearings is a well documented mechanical engineering practice for precision mechanisms and many bearing manufacturers have engineering notes on the practice. That is how I found out about this many years ago when I applied the idea to my HEQ5-Pro/Sirius and EQ6/Atlas mounts 6-7 years ago back in my EQMOD says.?

Another good idea I had but didn't try due to updating to OPWs was to fix the worm blocks to the worm cover to in essence make the cover a rigid bridge between the blocks to make backlash easier to do. The way to do this would be to use a pin on the top and cut a slight recess under the existing grub screws on the cover to set the blocks in the cover well aligned with the outer bearing which is being preloaded by the Bellevue disc. By bridging the blocks they would move as one making backlash easier to set well. The other thing to try to achieve is to locate the gearbox output shaft as closely on axis as possible with the worm shaft.??

--

Chip Louie - Chief Daydreamer Imagination Hardware

Here's an extreme example of the problem. This is a worm block commonly found in up market Celestron Nexstar mounts made in the first decade of the 2000s, like the Nexstar GPS Alt/Az and CGE mounts.?

While playing with on of these I notice there was a lot of play in the worm. Tightening the adjustment screw until the play disappeared produced a horrid notchiness like a out of round tire.?



Digging into the design of the block, this what I discovered. The block is one piece. In order to assemble it one end was bored to let the worm and the adjustment en bearing pass through it. The outer diameter of the worm is larger than the bearing fitted to it. Thus the bearing is left to float around in its seat.?

George,

You have it mostly right, it is fine for the worm to ride on the inner bearing surface. The purpose of the threaded cap is to take up the end play but this design cannot compensate for material expansion/contraction as temperature changes. So just as with the HEQ5-Pro/Sirius and EQ6/Atlas mounts you can use a Bellevue disc spring to allow for dimensional changes with air temperature changes. The worm is riding on the inner bearing so we will need a Bellevue disc with an outer diameter to match the outer bearing shell, just a bit smaller actually and the cone can be seated on the threaded plug which is tightened just enough to take up half the spring height no more. This will force the bearings on both sides of the worm to rotate at the same speed as the worm and take out any end play while also allowing some expansion/contraction for thermal changes. This works great but you must find the correct size Bellevue disc spring and ensure that the sprung bearing can move in the bore under the threaded cap/adjuster.?

--

Chip Louie - Chief Daydreamer Imagination Hardware

George,

The grinding was probably the cheap or damaged bearings they use in the Chinese mounts. I had a new Sirius HEQ5-PRO that had been assembled with the RA tapered bearings so tight that the cheap Chinese bearing seats were permanently damaged. I had to use a strap wrench to loosen the retainer. I replaced all of the larger tapered rollers on RA and DEC with SKFs and the mount was fantastically smooth. I had used Bellevue discs and precision ABEC7 bearings for the worms and Timken deep groove bearings elsewhere for the worm wheels. Huge improvements in movement and PE. The belt drive was a big help to, I loved doing the EQMOD stuff but the Atlas had no chance to carry the payloads I wanted for imaging so before I went down the road I did with my 2x Sirius mounts I dumped them all and bought a used G11.??

--

Chip Louie - Chief Daydreamer Imagination Hardware