Dome build: Rotation problems.

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Saturday: Woke to thick mist but clearing. The dome is showing a clear pattern of dark edges to the panels from dampness. I checked the moisture content of the dome yesterday and the plywood covering was up around 30% in places. Far too wet to continue sealing the panels. There is hope however thanks to a forecast of warmer weather and sunshine. I shall have to be ready and time the resealing well.

The dome is becoming harder to turn. I resurrected my water hose level and carefully checked all the roller axle heights. My thinking was that one roller was taking all the weight but this proved not to be the case. I added a bit of 4mm ply under one roller base but it made no difference to the ease of rotation.

The rollers were sitting outside under polythene bags for a long time before the dome was finally added. I am wondering if the needle roller bearings have rusted. Though there seemed to be no particular stiffness in the bearing once free of the weight they were carrying.

I discovered that I could move the whole dome sideways against the steering rollers. Though I needed to put some serious effort into a hard shove.

With a cord attached to the base ring I measured an average pull of 8kg to get the dome moving. Once moving the effort dropped to almost nothing and the dome would sail around until it hit a tight spot. Then the pull needed to get going again almost doubled.

I tried pulling some of the steering rollers away from the base ring for greater freedom but this made no difference to the stiffness. Most of the steering rollers hardly seem to contact the inside of the base ring. There is some creaking and knocking from the general direction of one roller but it is difficult to identify the exact location or the reason. It spins freely when unloaded.

After further thought it seems likely the dome has gained weight through moisture build up. The plywood roller track may have softened slightly leading to an increase in rolling resistance. I should pull the axle bolt from the suspect roller and check for rust. It is quite easy to lift the dome locally. Just using a couple of wooden blocks for gaining height. Then a 2' long batten as a lever under the base ring. Not so easy to find a third hand to slip another block in to hold the dome up. The "secret" was to use a 3' lever. So I could tuck it under my arm while I slipped a bit of 2x6 in beside the roller. The needle bearing was fine and greasy.

Click on any image for an enlargement.

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