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Old 12-01-2009, 04:36 PM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,476

Originally Posted by nightstalker View Post
been giving spme thought as to how mount the alt encoder
any thoughts most welcome .. I might make up a bush and slightly oversize the hole in the mounting mounting bracket to allow a little bit of adjustment.. though I'm pretty sure the centre of rotation is at the intersection of those two lines.

The tangent arm is 2mm brass I had a piece of lying around .. A little heavier than I would of hoped for
Hi Graham,

Looks good. Rather than increase the overall circumference of the mounting hole,
you might want to consider milling it into a slot whose major axis is parallel to the
cross bar on the Alt trunnion. That will allow you to move the encoder side to side.
For the vertical axis, you might want to consider some mechanism to raise or
lower the entire bracket itself. Rather than fasten it directly with wood screws
onto the cross bar of the trunnion, possibly insert a couple of self-threading
brass inserts into the crossbar first. Then fasten the bracket into the self-threading
inserts using machine screws. One can then adjust the bracket in the vertical
direction and then fix it in place with appropriate washers and hex nuts.

Scott Tannehill posted a procedure in PowerPoint format entitled
"Version 4.0 Locating ALT axis on Dobsonian.ppt" which you can find in the
Files section of the Argo Navis User's Group.
this can be useful to help center the encoder.

The 2mm brass for the tangent arm is a bit heavy-ish but should be fine.
Refrain from fastening the far end solidly to the side of the rocker.
Use a shoulder screw on the side of the rocker and carefully mill then file a
slot with a transition tolerance in the end of the tangent arm that just slides over
the shoulder screw.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
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