Compression Mounting nearing completion!

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With the completion of the Declination drive system I could assemble the complete mounting. Not a great picture with so much clutter in the background. I have to keep the hoist tight to avoid the mounting falling over if the beer crate should collapse with the weight. I need such a low workstand to be able to lift the declination housing high enough to insert the polar axis shaft.

The first thing I noticed during assembly was that the brass, saddle support bush no longer fitted neatly over the flange bearing as intended. The Dec wormwheel now gets in the way. I had intended to place the wormwheel at the counterweight end of the Declination axis but changed my mind later on.

I have some cylinders of scrap aluminium now. So could save some overhanging weight if I discard the brass bush. This is hollow at the base to overlap the flange bearing extension. So the hollow itself is additional to the thickness of the Declination wormwheel and its boss. Plus the heavy brass spacer ring which lifts the wormwheel to match the height of the worm. I have arrowed the overhang which could be removed. It is not so much that the 2" shaft will bend more but that overhang requires more counter-weighting. Mass x distance from the fulcrum matters far more than any theoretical flexure over 4" of unwanted overhang.

The wormwheel could easily be moved to the outer end of the Dec shaft just inside the counterweights. It is just a matter of moving the main support plate complete with the Dec drive system.

It's not as if a solid 50mm [2"] stainless steel shaft is going to suffer from torsion problems. The mass of the large and thick wormwheel will beneficially add to the counterweights. Doing so at a greater distance from the fulcrum than in its present position. The Declination drive assembly is no lightweight and will obviously have to be moved along with its wormwheel. The benefits of shifting the Dec drive system are adding up rapidly.

The image shows the work of only a few minutes to move the whole drive system to the other end of the Declination housing. I added a 5kg [10lb] counter-weight to give a sense of scale. The so called Olympic standard weights have considerably oversized holes for the 2" bars they are supposed to fit. The Dec wormwheel is 8.5" diameter.

When I started out on this mounting project I had imagined I'd be using manual slow motion controls. Much later I bought the AWR Goto drive system. This does all the slewing under stepper motor power. So having the wormwheel near the saddle now makes much less sense. There is no longer any need for easy access to extended control rods at the tail piece of a 8' long, classical refractor.

A view inside the saddle showing the previously shown overhang now completely removed. The brass expansion sleeve for the Tollok bush now snugly fits over the bearing extension. This is the minimum possible overhang condition. With the Tollok bush butting up against the flange bearing extension. The OTA now has a 1:1.5 ratio of moment arm relative to the counterweights. The silky smooth freedom of movement of the axes is superb with the large journal bearings well within their load capacity.

Because the RA wormwheel is much larger [than the Dec] it is far more difficult to move to the lower end of the PA shaft. There are serious clearance issues with the PA fork's base plate. Which is more of a problem here at 55N than at lower latitudes.

Talking of which I need anchors for the turnbuckle plate which closes the front of the base fork. The plate tends to slide upwards when the polar altitude, turnbuckle adjustment is tensioned. I wanted to leave the exterior of the heavy fork plates unblemished. A couple of pins in the edges of the front plate could be hidden between the fork blades. The 16mm [~3/4"] altitude pivot stud provides more than enough lateral compression without needing additional cross studs.

Seen from above the PA overhang doesn't look remotely so bad. The final image shows the present arrangement with a stack of empty boxes to give a plain background. 

Click on any image for an enlargement.

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