New OTA build

[mountainstorm]

So after getting my telescope back into working quality [see here] it reminded me that whilst it's beautiful, and works pretty well; it's a tad on the heavy side.

This isn't a major problem if you have a permanent/semi-permenant setup (as I did when I built it) but it's inconvenient now.  For reference the OTA weights in at 19.5kg, the mount is over 5kg and requires a 10kg counterweight.  I've no idea how heavy the Meade Giant field tripod is - but its heavy, probably around 15kg.  Overall a bit much for an 8" Newtonian.

My plan is to adapt it into a simple dobsonian, or perhaps modify the mount and go for an unusual GEM setup.  

To that end I've knocked up some test pieces for the mirror supports and thought I'd share.

Main mirror cell

You can see the markings of how I'm refining it for the actual mirror cell; narrower in the middle and wider at the edge to allow me to move the bolts in towards the centre slightly.  It's 18mm plywood and works on a pull bolt system (I don't like springs).  The bolts in the edge go into insert nuts and will hold three mirror support clips.

On the bottom theres some nice thumb screws to allow collimation.

For those which wonder how the pull bolts work this picture should explain.

I've embedded a M12 done nut in the bottom piece (drill a 12mm hole and chisel out a hexagon.  I've drilled a very shallow 12mm hole in the mirror plate to let it sit and rotate as the M6 pull bolts are adjusted.  Works well (different from how I did the mirror cell on my original OTA).

The secondary cell looks like this

Another M6 bolt this time with two 50mm washers; one attached, the other floating on a plastic (reduced height) dome cap.  The wooden diagonal block is an offset of broom handle and will have a 60mm circle of perspex attached; which will in turn have the secondary glued to it.  I'm still waiting for some thumb screws (like the ones on the primary) to replace the adjustment nuts.  The pull bolts are M3, so tiny.

I also plan to cut the edges off the two washers to make them into rounded triangles; which should allow me to fit the whole lot behind the secondary (vertically as well as horizontally).  The threaded connector will have the veins welded onto it.

As I progress and refine the design I'll post updates.