Modified English, Cross-Axis mounting?

[Rusted]

Has anybody had direct experience of building or using a cross-axis mounting?
I'm thinking this is the only sensible way forwards to mount my 10" F/8 Newtonian, 7" f/12 and 6" f/10 H-a refractors simultaneously.
Swapping such large, long and heavy instruments is very difficult even with block and tackle.  Each needs different counterweights/balancing.

Pros:
Massive OTA load capacity.
No meridian flip/reversal.
Whole sky access without obstruction.
Suitable for long and heavy instruments.
OTAs can be opposed instead of using counterweights.
Needs no massive, central pier in the observatory.
No dangerous counterweights at head height.

Cons:
Very bulky. Needs plenty of room.
Unsuitable for "mobile" use. Fixed observatory use only.
Needs a very tall Northern pillar. Lateral loads only? Simple A-frame?
Needs a stiff polar axis to avoid flexure.
Must avoid floor/building contact vibrations through TWO piers.

So why not build a Cross-Axis? What haven't I thought about?

[Peter Drew]

Yes I have.  None of my usual mounts, not even a Fullerscopes MkIV,  was really up to the job of carrying a 12" F8.5 Newtonian so a "Cross-Axis solution seemed a worthwhile project and one that I had been mulling over to try out a motion damping scheme.  Being experimental it was floor standing and the mainframe was in 3" x 2" wood.  There was no South pillar, just an angled bearing plate.  The base was an "A" frame and the North pillar was a braced "goal post" carrying the top bearing.  The polar axis was a length of 4" square 1/4" wall steel tubing with stub axles at each end.  The friction damping discs were 18" diameter made from MDF faced with aluminium, variable friction was supplied by adjustable PTFE brake pads.  The cross-axis was a stub axle on one side of the polar tube carrying the telescope and a counterweight shaft on the opposite side.  The main object of the exercise was to try out the damping scheme which worked well, the construction has since been dismantled pending a final engineered version when it comes to the top of the "to do" list.

Photos of the mount are currently locked on a defunct computer.     ☹️  

[Rusted]

1 hour ago, Peter Drew said:

Yes I have.  None of my usual mounts, not even a Fullerscopes MkIV,  was really up to the job of carrying a 12" F8.5 Newtonian so a "Cross-Axis solution seemed a worthwhile project and one that I had been mulling over to try out a motion damping scheme.  Being experimental it was floor standing and the mainframe was in 3" x 2" wood.  There was no South pillar, just an angled bearing plate.  The base was an "A" frame and the North pillar was a braced "goal post" carrying the top bearing.  The polar axis was a length of 4" square 1/4" wall steel tubing with stub axles at each end.  The friction damping discs were 18" diameter made from MDF faced with aluminium, variable friction was supplied by adjustable PTFE brake pads.  The cross-axis was a stub axle on one side of the polar tube carrying the telescope and a counterweight shaft on the opposite side.  The main object of the exercise was to try out the damping scheme which worked well, the construction has since been dismantled pending a final engineered version when it comes to the top of the "to do" list.

Photos of the mount are currently locked on a defunct computer.     ☹️  

Thank you Peter.

A quick search produced three excellent pictures of your Cross-Axis research project on CN.
Though I have no need for your interesting friction device because I have clutches in the wormwheels. Lovely big OTA!

I have a whole stack of sturdy, metric, 4"x8" [scrap] box section alloy tube in fine condition and up to 2m long just waiting to be "repurposed."
Lengths of 2"x8" box section too. I'd imagine the 4x8 is easily stiff enough for the very long PA.
I'd plate the middle of the PA with 10mm thick alloy. After stuffing the 4x8 tubing tightly with laminated marine ply.
Timber would eventually shrink if it was used as internal reinforcement where the Dec axis goes through.

Reusing the same 50mm bore flange bearings and wormwheel drives as my present GEM should be fine.
Dec axis at above eye height would suit the refractors but leave the 10" f/8 Newt EP rather high up unless I move it well down its saddle.

I imagine a 4"x4" timber A-frame would do for the north bearing support. It being subject to lateral loads only[?]
As the whole set-up would be raised onto the first floor I'd have to provide adequate support for both bearings while isolating them from the building.
The low, South bearing would have to resist quite a lot of linear thrust. Another 4x4 A-frame with a brace down to the ground might work.
It should be quite "epic!" in a classical observatory sort of way.