17.12.2021 Another shutter slide rethink. KISS!

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Friday 17th 41F, heavy overcast and thick mist. No chance of any imaging today!

I have decided to simplify the skate wheel support for the shutters. Making pivoted bogies would drastically shorten their effective wheelbase. Perhaps leading to tipping of the shutters. My desire to spread the load between more wheels can be achieved by accurate placement of the axles on a straight line. The flexure of the tires can even out the loading between four wheels. 

It works for hefty skaters. Wearing inline skates for repeated aggressive maneuvers. Rollers skis have only one wheel at each end. So they will probably work for my humble, dome shutters. 

A closely spaced pair of wheels, at each end of the inverted channel, will do the job. Being so close together will reduce the differences in wheel loading between pairs. 

I shall cut down the 50x200mm box section to make 100mm deep channels to hold the wheels firmly. 

Or not. I found some 50x140 box section hiding in my scrap heap instead. Which made more sense than the 50x200.

The DeWalt "Metal" jigsaw blades were a complete waste of time. I mixed lamp oil with light "cycle" oil and adding copious quantities the fine toothed, saw blades. Still they became worthless in seconds as they built up aluminium in the teeth. So I looked for alternatives in my shrinking stock of [short] jigsaw blades. Standard length blades hit the inside of the box section on the out stroke.

Straight toothed "Laminate" blades worked really well. These have an aggressive, staggered, tooth form of different tooth lengths of medium pitch. 

I used a medium speed on the saw and sloshed the lubricant along the cut line and in the cut slot as I progressed. Half an hour later I have two 70mm deep x 49cm long channels. 

The second image [Right] shows suitable spacing and axle depth in the channel to provide clearance.

The cut edge was typically wavy for a sloppy Bosch jigsaw. These edges will be straightened by filing or sanding. The mock-up shows the "axles" resting on the cut edges. In practice the axles will be securely clamped through holes in the channel webs. With spacers to load the bearings against tipping. 

I used the profile's extruded back edges. Rather than the wavy, freshly cut edges for all my measurements. Once the wheels are fitted they will become completely invisible. Being hidden by the nested channels. A test run proved that the slide's rolling movement was silent, friction free and smooth. I must hope the same holds true once the wheels are mounted on their axles.

 The third image [Above left] shows the channels drilled and the wheels mounted on 8M x 60mm stainless steel bolts. The assembly is inverted in this view. The bottom channel, in which the skate wheels run, fits inside this channel with room to spare.

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