2" shaft mounting Pt.47: Firmly planting the base fork.

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My initial plan to add angle profiles on each side of the fork base would not provide vertical stability. It badly needs some downward pressure which might as well provide some rotation for polar alignment at the same time. This will require a division between the fork base and the large bottom plate. Unfortunately I only bought one of the these large 10mm [5/16"] plates from the scrap yard. So cannot simply duplicate the base plate with a central pivot and familiar screwed azimuth adjusters. I do have a little more of the 15cm x 10mm plate but wont have much in reserve if I duplicate the fork tines with doubled plates. Nor will the plate provide enough resistance from the compression of a large, central pivot screw.  

The fork is now sloping backwards by 20° to provide more clearance for the wormwheel. The cross studs and vertical pivot ought to be centrally placed relative to the fork tine base. Which doesn't provide much room the higher they are placed.

I was thinking about having a really sturdy crossbar between the fork tines to resist the compression loads. A large nut and washer would provide the downward pressure via a vertical pivot stud or bolt. I do have limited milling ability on my lathe but would rather avoid milling slots in the fork tines just to fix a crossbar between them.

The original idea was to bolt the entire mounting together without machining. The cylinder rather dented the original plan but was at least optional. I just happened to have a chunk of 7" round stock. Alternative means could have been found for effectively supporting the Declination axis.

Two sturdy, spaced, 15mm studs between the tines would allow a vertical stud to pass between them with a 6" plate resting on top and sandwiched between the tines. The stiff cross studs would help to support the cross plate and simultaneously compress the fork tines together against the edges of this horizontal plate. Or plates, if a bottom plate is added.

Here is an image of the mounting supported from the new 1T lifting strop and 1T chain hoist. The steel hook allows more rapid movement along the ceiling joist than the former, multi-looped cord.


Front and rear sandwiched plates would make a closed box out of the fork and it would all be under heavy compression from the twin, horizontal cross studs. Plus the vertical compression from the central, pivot stud. The tops of the tines are compressed against the sides of the Dec housing by the altitude pivot stud. All helping to avoid flexure anywhere in the fork.

However, first I have to decide on the final fork dimensions and angles. I must avoid contact between the large RA wormwheel and the base plate, fork or large diameter pier pipe.

Materials shortage over. Another visit to the scrap yard produced more aluminium plate in various thicknesses up to 10mm. I now have a second 10mm [5/8"] base plate to bond to the first. A pack of Loctite 'Metal' is on its way in the post.

I have received some useful information on filing and "grinding" aluminium. Files pick up the metal which causes scratches and slow removal of material. Using ordinary bar soap on the file is supposed to help. I've just bought a bar of soap to give this a try. Lamp oil had little or no effect despite being recommended [and highly beneficial] for turning aluminium. The lamp oil had an amazing effect when I was turning the 7" diameter cylinder yet had no obvious benefit on my files. I wonder whether soap would help on the 36 grade angle grinder disks? Might be worth a try.

With the fork slope decided I could duplicate the tines. They are now 20mm thick [0.8"] and look far more substantial. As does the 20mm thick base though it has yet to be trimmed.

Open fibrous abrasive disks have been recommended for cleaning up rough aluminum edges and surfaces. I tried the local DIY chain store but they had nothing like it. Another online search and purchase is obviously  required. 

A 44 mile ride on my touring tricycle produced some goodies to speed up smoothing the aluminium. The card, file brush [bottom] will help to clear aluminium from my files.

I spent another hour trying to level the sawn edges of the duplicated fork tines. Rubbing dry soap on the disks and files is a definite improvement.

The Loctite 'Metal' epoxy should arrive today to fix the plates firmly together. Plates simply held together with nuts and bolts tend to behave more like leaf springs under bending loads. The epoxy should make them behave more like the thicker material the laminations pretend to be. I shall have to have all my G-cramps ready to squash the plates hard together.

Click on any image for an enlargement.

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