1. I've previously pointed out the loose fit of the Dec and Ra shafts in relation to the the needle bearings. It's has been pointed out that this looseness if needed in order to get the shaft through the needle bearings and when the clutch is tightened this looseness should not matter.? However, this looseness results in the shaft having just two points of contact per the drawing, and means it's rotation is ever so slightly off axis. This was determined by inserting the shaft into freshly greased needle bearings and removing it without rotation.?
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2. I have previously pointed out how sensitive setting the worm mesh pressure is. +/- 0.0005 to 0.001 makes a big difference in the ability to finger rotate the worm in order to move the ring gear. The closeness of the mesh has a direct relationship to backlash.
3. I and Michael Herman have found that changing out the thrust bearings from the stock Losmandy to ones sourced from McMaster can have a significant effect of ease of rotation resulting from a better worm ring gear mesh. I have also found that a large PHD2 error in the 2600s or higher range is most likely due to the thrust bearings. It should be noted that the stock Losmandy and McMaster thrust bearings have been measured to be the same thickness, but they do differ in their construction. The stock Losmandy bearings have a crimped edge which is not even in diameter the case of those I have. This implies that the rollers are not pointing to the exact center of the bearing, resulting in an off axis force as a function of rotation. I greatly reduce this error with the McMaster thrust bearings.
4. The ring gear rotates on a bushing (in the case of the G11 this is brass). With the clutch off off I have found that the ring bearings rotates easily through 360 degrees.?
5. With the clutch tightened I have found that the if the worm is meshed at the CWD position there is a tight spot when the axis is rotated 180 degrees. This tightness can result is a stall at the 180 degree position, but regardless represents a variation in the backlash as the axis rotates.? This is the Dec axis.
CWD position where the worm mesh was set. Even distribution of grease.
Grease distribution at 180 degrees of ration. In my case I had a stall at this point.?
So what causes this to occur. I believe that the clutch plate being off axis by virtue of the needle-shaft loose fit, produced off center pressure? on the ring gear, which has some degree of movement by virtue of riding on the brass bushing, that forces the ring gear into the worm as it rotates. Hence the worm mesh and backlash changes as a function of rotation
Peter
