18.11.2020 Worm housing reinforcement.

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Wednesday 18th. Wind, heavy cloud and possible rain.  

I now realise that my worm support is totally inadequate to the loads being placed on them. The long refractors have such a moment that they suffer from serious lag and overshoot when asked to move to drive and guiding commands. 

Refractors have very heavy objectives in their metal cells placed on the very end of the tube. This has to be balanced at the other end by the focuser and any additional viewing or camera equipment. Which effectively doubles the moment of the objective alone.

I'll need to study my scrap aluminium collection carefully for suitable materials to beef up the worm housings. At present the drive motors are housed in 6mm thick, box section tubes. With the original Beacon Hill worm housings [simple channel offcuts] bolted to the tops of these square tubes. 

I had reinforced these housings with sturdy, motor mounting plates and bearing retaining screws. Thinking I had flexure covered. I obviously hadn't. The drive mounting plates are substantial 10mm aluminium plate trapped by the flange bearings. Quite a  good base but the rest is obviously not up to the task. 

After studying my metal stock I chose some 6mm angle profile. I made it fit snugly inside the motor box section with the inner end pressed against the stepper motor base. The other [upright] leg of the angle is now bolted to the worm housing.This provided the missing reinforcement of the free end of the worm housing. The profile's "leg" inside the box stiffens both the box section and the end and underside of the worm housing. 

Parallel and mutual reinforcement using the same principles as the rest of my mounting. I have no castings. So must use multiple means to achieve the same stiffness from flat plates. A cast, box section is inherently stiff. Assembled plates of the same thickness are not. Not unless they are welded or bonded together. So I must use clamping forces in as many planes as possible. Using the screwed rods [studs or all-threads] themselves to self reinforce the box form. Tensioned rods are inherently far stiffer than a similar rod without.

I mounted the reinforced motor assembly loosely onto its supporting plate. It was easy to add an experimental push-off screw using an eye-bolt, two nuts and an angle bracket to resist the spring tension. The camera is tipped to match the PA altitude angle so the image actually looks upright instead of sloping.

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