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  #1  
Old 15-04-2018, 07:22 PM
Tasastro (Bill)
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Location: Tasmania
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Single arm CPC

After deforking my CPC800 I was intending to dispose of the CPC mount. However there was very little buyer interest and no-one was inclined to offer very much, so it sat around getting in the way for a year or so.

I was using the deforked C8 on the NEQ6 and also as a quick set-up on a modified AZ4 with an improved clamping arrangement. The NEQ6 was slow to set up and and the lack of tracking and rigidity made the AZ4 difficult to use at high magnification for planetary work. The aquisition of a C9.25 then started me thinking it would be nice to have a tracking Alt AZmount again, one that could be used with a variety of OTA's and was relatively easy to set up.

After looking at the available options it apeared that the best course might be to modify the old CPC mount. My observations during the deforking strip down were that the drive side arm and bearings were extremely rigid and the opposite arm was almost purely decoration, having only a simple plain bearing with about 0.2mm of radial clearance. Some measurements with a dial indicator and load cell which gave a deflection of less than 0.25mm with 100N of horizontal force on the end of the drive side arm reassured me that a single arm setup was feasible.

I have a well equipped machine shop so the work did not pose any problems. The original drive side mounting plate and axle were utilised with fairly extensive modifications to get rid of the mounting arrangements for the C8 OTA. For mounting of the OTA on the new setup a second hand NEQ6 puck was obtained and machined to suit and also fitted with brass guide bars to improve mount rigidity.

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A handle was made with a recess to contain the GPS.

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I havn't yet had time to try the mount - as usual the weather turned bad just when I completed it. Some quick terrestrial observations with the 9.25 indicate that rigidity is very good and damping rapid.

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To be continued...
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  #2  
Old 15-04-2018, 10:49 PM
casstony
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Neat looking job Bill, I did a similar mod with a CPC11 fork.
I'd like to see more detail on your connection of the saddle to the fork arm.
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  #3  
Old 16-04-2018, 12:23 PM
Tasastro (Bill)
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Quote:
Originally Posted by casstony View Post
Neat looking job Bill, I did a similar mod with a CPC11 fork.
I'd like to see more detail on your connection of the saddle to the fork arm.
Thanks Tony. The job was done over a fairly long period between other tasks and I didn't document the progress. Best I can do is the following...

Since I wanted to keep overhang to the minimum and didn't intend returning the mount to original I decided to modify the existing mounting plates. Initially I sawed and machined off as much of the original OTA mounting plates as possible.

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The image above is the non drive side plate modified in a similar manner as a trial.

Spaces between webs on the mounting face were filled with segments of 6mm aluminium plate Devconned in then faced off flush in the lathe. The holes for saddle mount screws were then drilled and tapped to 6mm into the infill plates and the drive plate. Also the two original mount holes in the drive plate for the plastic dress shroud were drilled and tapped to 6mm.

For appearance, and prevention of dust ingress to bearings an annular shroud was made from MDF (hardened with acrylic laquer) and glued to the drive plate.

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The Skywatcher puck was modified with installation of guide bars and drilling for 6mm mounting screws.

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Original tapered spigot was milled off and saddle base faced off flat.

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Because the axle boss on the drive plate was slightly proud of the surface a gasket was made rather than machining a recess into the saddle face. It also helps damp vibration.

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Last edited by Tasastro; 16-04-2018 at 12:46 PM. Reason: A few corrections
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  #4  
Old 16-04-2018, 06:42 PM
casstony
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So it's a job for someone with metalworking gear/skills. The end result is nice looking.

The mounting plates on the bigger 9.25 & 11 allow for bolting a saddle straight on without much modification.
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  #5  
Old 16-04-2018, 08:56 PM
Tasastro (Bill)
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Quote:
Originally Posted by casstony View Post
.........
The mounting plates on the bigger 9.25 & 11 allow for bolting a saddle straight on without much modification.
They also make deforking/reforking much easier. The CPC800 requires major disassembly of the drive side including a rather nerve-wracking hammering of the drive axle through the bearing while the OTA is attached to the other end.
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