2" shaft mounting: Pt.32: The RA worm, support plate.

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The next stage is making a thin plywood pattern for the worm supporting top plate. The plate itself will be of aluminium and 5-6mm thick. That's the 11.5" RA wormwheel with brass worm in the image alongside. The worm housing is propped on a scrap of pine for checking worm height relative to its wormwheel.

I shall have to move my work site into the shade as it is 78F today [in mid-September] and very unpleasant standing in direct sunshine!

Denmark set a new record for temperature yesterday as did the UK. I much prefer 70F with a nice bit of shade! I have made the plate pattern slightly wider than the wooden housing. I found a much thicker plate of Tufnol but it is remarkably flexible compared with aluminium of only half the thickness. I may still need to brace the aluminium plate to ensure a lack of flexure.

Making the plate from the pattern went well enough. I jig-sawed out the oversized hole for the axis shaft when the pillar drill showed its weakness with a hole saw. The thickest aluminium plate I had in the necessary dimensions was only 5mm. Perhaps 6mm would have been better but I didn't have any. I now need an elegant way to pack up the worm housing by 60mm. I'd hoped for solid aluminium, or even rectangular pipe, but nothing added up to 60mm. I suppose I could order something online.

I decided to use a nice bit of antique oak to support the worm housing. It has been hanging around for over half a century looking for a purpose and now it has a proper home. It was part of old table we bought back in the 60s.

A couple of studs pass through the plate, support block and are threaded into the worm housing. Nuts and washers hold everything tight from underneath the plate.

With the worm now fixed at the correct height and radius I was able to run the worm against the wormwheel with a drop of oil for lubrication. I used a rechargeable drill at low speed for power. The incredible torque applied to the wormwheel cannot be resisted by hand alone.

Everything seemed okay and there was no run-out at the worm as I carefully checked for backlash at various diameters. I need to provide a screw or screws to press the worm into the wormwheel with fine adjustment. An angle profile fixed near the flange bearing will provide a thread or anchor point for the adjuster[s]. Or there is room for a bracket in front of the block where I deliberately left the worm support plate overlong. It is important that the worm arrangements are not struck by the telescope tube or declination assembly. Nor should the worm bracket or adjusters force increased overhang of the OTA.

A visit to a scrap yard produced some 10mm [3/8"] aluminium plate. I was only able to obtain it in 6" widths. Which rather limited its application as a support plate for the top of the 7" cylinder. There was actually quite a lot of the 10mm x 6" width alloy which was sorely tempting as a potential bearing housing material instead of using the oak counter top material. I would need the car to collect the longer lengths and many hours with a hacksaw making it useful. Though a local engineering company would probably make quick and precise work of it with their expensive metal band saws.

Then there is the matter of fixing the metal together. 10mm is not a very large surface to fix edge to edge with screws using simple butt joints. Though strips of alloy angle could also be used to bolt the alloy strips together with staggered butt joints at their edges.

At scrap prices the 6" wide alloy strips would not be cripplingly expensive. I was happy to pay about 10DKK, £1 or $1.30US [equiv] per kilo [2.2lbs] for a few shorter off-cuts of almost virgin alloy plate.

Aside from longevity and shrugging off any damp, I wonder if the conversion to alloy bearing housings is really worth all the extra effort and expense? The oak is seriously stiff and solid in the 2" wall thicknesses I have used so far. The oak will, however, need some sort of coating to remain cosmetically viable in the longer term. I used waterproof glue but have no data on its longevity. The instructions on the bottle just said that it should not be submerged.

Click on any image for an enlargement.

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