cnchillstar
super member
Reged: 12/29/08
Posts: 102
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Hi, I notice all high level GEM mount applying a very strong counter weight shaft. ME-38mm, others like AP and mountain, even with a 40mm diameter.
If they are threaded to Dec shaft and rotate together, it seems that Dec shaft is relatively smaller female thread to have it in. or the counter weight shaft just link to Dec body and doesn't rotate?
maybe for small GEM mount like eq6 or even lasmandy G11, it will be threaded directly to DEC axis. but I check AP document(when assemble with Dec encoder) and meade max mount, find it seems that the counter weight shaft is link to DEC housing only and will not rotate.
anyone who use those mount know the details?
what will be the advantage or disadvantage for each method from mechanical view?
thanks!
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Mike Clemens
Post Laureate
Reged: 11/26/05
Posts: 4289
Loc: Wasilla, Alaska 61N
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I can speak for the massive shaft of the AP1200... it links only to DEC body. As a matter of fact, when i remove my CW shaft it usually instead starts to unscrew the big DEC end-cap from the DEC body itself.(the thin black ring seen at end of CW shaft: http://www.robincasady.com/Astro/users/SteveNightingaleAP1200.jpg )
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historius apochromaticus
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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thanks for help! is there any disassembling picture on internet for AP mount? I found some for lasmandy G11, every mount has their mechanical design....
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Sky Captain
Metal Whisperer
Reged: 11/07/04
Posts: 7195
Loc: Issaquah, WA.
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Quote:
maybe for small GEM mount like eq6
Though not stock for an EQ6, I needed a stronger & longer shaft than the little 18mm that came with mine. It's now 32mm stainless shaft.
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Equipment Overload!
Kerry
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Sky Captain
Metal Whisperer
Reged: 11/07/04
Posts: 7195
Loc: Issaquah, WA.
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Here is a breakdown of the shaft I designed and built.
In the photo, the lower stainless pin has 1/2" threads on one end and just slips into the mount head the same as the old shaft that retracts into the mount head.
The upper 32mm shaft is tapped for the same 1/2" threads and just screws on to the exposed 1/2" threads.
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Equipment Overload!
Kerry
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Sky Captain
Metal Whisperer
Reged: 11/07/04
Posts: 7195
Loc: Issaquah, WA.
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For reference, this shows the shaft not attached to the mount head.
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Equipment Overload!
Kerry
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Billydee
super member
Reged: 01/23/08
Posts: 186
Loc: Winter Haven, FL
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Could it be that the shaft is the counter weight of the weight of the head?
Bill
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hudson_yak
Pooh-Bah
Reged: 11/15/07
Posts: 1106
Loc: Hyde Park, NY, USA
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Quote:
what will be the advantage or disadvantage for each method from mechanical view?
I would say that, at the low end of the market, there's some advantage in Dec bearing forces (whether actual roller bearings or simple bushings) to have the counterweights carried on the Dec shaft. When balanced with an OTA on the other end the forces are probably somewhat more friendly to the bearings, particularly when the scope is pointing near the local meridian. Both bearings are sharing force in the same direction rather than the upper one feeling force downward and the lower one feeling force upward, as would be the case if the counterweight shaft were joined to the housing. Due to leverage such forces could be greater than the twice the weight of the OTA itself, depending on the bearing spacing, saddle height, and OTA configuration, particularly for mounts at the compact end of the spectrum.
Certainly, given a sufficient amount of mechanical engineering and expense, as in the very nice example near the top of this thread, that concern can be adequately contained.
Mike
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Meade 8" LX10
Orion ED100 + Losmandy GM-8 + Berlebach UNI 24
Meade 12" LightBridge
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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Quote:
Here is a breakdown of the shaft I designed and built.
In the photo, the lower stainless pin has 1/2" threads on one end and just slips into the mount head the same as the old shaft that retracts into the mount head.
The upper 32mm shaft is tapped for the same 1/2" threads and just screws on to the exposed 1/2" threads.
thanks,Captain! but how is the thin shaft linked with the black interface? it seems that no thread on that end.
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cnchillstar
super member
Reged: 12/29/08
Posts: 102
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thanks,Mike! I think same with you, I will post a new thread about bearing, please give your professional comment!
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Sky Captain
Metal Whisperer
Reged: 11/07/04
Posts: 7195
Loc: Issaquah, WA.
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Quote:
thanks,Captain! but how is the thin shaft linked with the black interface? it seems that no thread on that end.
On the stock Atlas shaft, there is a small threaded on ring that keeps the retractable shaft from falling out. In the photo, I added a red arrow that shows the machined step in the threaded pin. To the left of the arrow, the pins diameter is similar to the stock Atlas shaft which is 18mm, but I found that I was able to up this diameter to 19.5mm for a tighter fit. The reduced area to the right of the arrow mimics the small ring added to the end of the stock Atlas shaft that keeps it from falling out.
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Equipment Overload!
Kerry
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Sky Captain
Metal Whisperer
Reged: 11/07/04
Posts: 7195
Loc: Issaquah, WA.
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This shot shows how the pin inserts into the black hub on the mount and won't fall out because of the machined step pointed out in the previous posted photo.
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Equipment Overload!
Kerry
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