From: [email protected] <[email protected]> On Behalf Of Davidspain via groups.io
Sent: 10 December 2021 10:35
To: [email protected]
Subject: [Losmandy_users_io] Futura losmandy G11T

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Acabo de pedir la losmandy G11T al proveedor Valkanik en espa?a, con suerte en unos meses la estare disfrutando ????, que ganas de tenerla!!

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Derek,

The ring gear measurements were made with the clutches tight, so all the thrust bearings, washers, are surrounding contacts are all snugged down. I now use Michael Herman's high friction discs, so it is not necessary to overly tighten the clutch knobs to avoid slippage during mount operation.

I have my original RA and Dec blocks plus 3 new pairs I bought from HGM at different times over the last few years. They all have the same holes and thread sizes, but are not precisely the same size, off by perhaps 0.01" or more in height, though I haven't logged all these dimensions. Thus the need for shimming if the blocks are too short for the ring gear involved. If the blocks are too tall you may have to perhaps sand down the bottoms, or shim under the bottom thrust washer, but I haven't seen that situation yet with my parts. How close you have to get is what I am questioning.

John

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Recently did another rebuild of my G11 (with non-spring-loaded worms) as I wanted to replace the 3” ID thrust bearings and the 3” ID thrust bearing washers which were a bit scored. Also, I had a stubborn 80 second error (1/3 worm period) which I could not figure out, so I replaced the current RA worm with an old one I had good results with previously. I replaced the thrust bearings with Koyo NTA-4860 bearings which were 5/64 or 0.078” thick. For some reason I was unable to find the same 3” ID washers which Losmandy used which are 0.045” thick, so I used an INA TWA-4860 with 0.030” thickness, and a Koyo TRB-4860 with 0.060” thickness, which together total 0.090” thick, same as the two original washers.

The RA worm blocks were changed out to another set where the right block was honed out a bit to allow the right bearing to slide back and forth as compressed by the Belville washer. As a new test, the bearings were replaced with McMaster-Carr part 2342K163, which are permanently lubricated, and have a black plastic seal over the ball bearings.

A micrometer was used to measure the various parts positions to try and determine the exact center of the worm axis and center of the ring gear. This issue has probably been discussed before, but I was wondering how close is good enough for best RA periodic error behavior and proper function of both axes. All parts were at approximately 50F, the temperature in my unheated workshop.

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The following measurements and determinations were made:

Diameter of worm shaft inside of bearings: 0.400”

Radius of worm shaft: 0.400”/2 = 0.200”

Thickness of ring gear: 0.300”

Midpoint of ring gear: 0.300”/2 = 0.150”

Thickness of black anodized base plate: 0.329”

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With these values in place, the centers of the worm and ring gear can be determined by measuring the distances from the bottom of the base plate to the top of the worm shaft and top of the ring gear, respectively (see pics). The calculations then are as follows:

Top of worm – 0.200” = Worm center position

Top of ring – 0.150” = Ring gear center position

For the RA drive prior to disassembly:

Top of worm: 0.856” – 0.200” = 0.656” at worm center

Top of ring: 0.807 – 0.150” = 0.657” at ring center

Centers difference = 0.001”

The worm top surface measurement appeared consistent whether done on the left or right side of the brass worm teeth in the central area, thus no tilt.

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RA drive after reassembly:

Top of worm: 0.846” – 0.200” = 0.646” at worm center

Top of ring: 0.805” – 0.150” = 0.655” at ring center

Centers difference = 0.009”

Note the top of the worm measurement had dropped by 0.010”, which appeared to be too much. I also saw that my original blocks now in use had a bare aluminum bottom, while the newer blocks I bought later were anodized black on all surfaces. So, it would appear all worm blocks are not identical. To remedy this centers discrepancy, I bought some 0.005” brass shim stock which I trimmed to fit under the blocks and folded one time to get twice the thickness.

RA drive, second assembly after shimming:

Top of worm: 0.856” – 0.200” = 0.656” at worm center

Top of ring: 0.805” – 0.150” = 0.655” at ring center

Centers difference = 0.001”

This difference is now the same as originally, though the worm is 0.002” lower than before disassembly.

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Now for the Dec drive:

Before Disassembly:
Top of worm: 0.856” – 0.200” = 0.656” at worm center

Top of ring: 0.806” – 0.150” = 0.656” at ring center

Centers difference = 0.000”

After Dec Drive Reassembly:

Top of worm: 0.850” – 0.200” = 0.650” at worm center

Top of ring: 0.805” – 0.150” = 0.656” at ring center

Centers difference = 0.006”

Here I’m not sure of the reason for the worm drop, since the same blocks were used. One layer of 0.005” shim stock was used under the blocks and new measurements were performed.

Dec drive, second assembly after shimming:

Top of worm: 0.854” – 0.200” = 0.654” at worm center

Top of ring: 0.805” – 0.150” = 0.656” at ring center

Centers difference = 0.002”

Again, the worm center is dropped by 0.002” from original position.

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So finally, the question is what difference between worm and ring gear centers really plays a factor? I think 0.01” off seems significant and needs to be adjusted. After shimming, the worm centers are very close to the ring center but have dropped a tiny bit and are essentially on the other side of ring dead center. During previous mount rebuilds, I had never made these measurements, so I do not know what they were when the mount was new. I would assume the scoring I saw on the thrust bearing washers would drop the ring center a bit, but all seemed to return to the same position with the new thrust bearings and washers.

So again, how close is good enough and will the worm being centered higher or lower on ring gear amount to anything? Since my blocks are fixed, the positions should remain the same. With the floating or spring-loaded worms, I assume the relative positions can vary by some degree. Now waiting for some clear skies to check out the performance of the above modifications.

Any comments appreciated.

Thanks,

John

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Morning all,

I am having no success with using the ST-i guider for use my my G11/G2 modified. ?I have tried PHP, which does not work well once guide star is selected and even have gone back to SBIG's CCDOPS, which I used with my ST-5c pretty well successful in tracking and controlling the G11. ?I am not sure where/how this problem I have with the ST-i & G2 combination comes from or whether is is just plain incompatibility or most likely operator error. ? Also, ?if someone has a cheat sheet on their set & control. I would appreciate having a copy of it.
Thanks for any assistance,
Doug

On Dec 9, 2021, at 9:50 AM, Doug Askew <doug@...> wrote:

?Morning all,

I am having no success with using the ST-i guider for use my my G11/G2 modified. ?I have tried PHP, which does not work well once guide star is selected and even have gone back to SBIG's CCDOPS, which I used with my ST-5c pretty well successful in tracking and controlling the G11. ?I am not sure where/how this problem I have with the ST-i & G2 combination comes from or whether is is just plain incompatibility or most likely operator error. ? Also, ?if someone has a cheat sheet on their set & control. I would appreciate having a copy of it.
Thanks for any assistance,
Doug

On Dec 8, 2021, at 7:40 AM, Ian Taylor <robert.ian.taylor@...> wrote:

?You need one that looks like the one below. The square end plugs into the Gemini 2 and the USB plugs into one of the USB2 ports on the ASI-Air Pro.?

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