3.08.2021 Fibreglass planning.

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Tuesday 3rd 57F, heavy overcast. Completed the shutter brackets. It was easy to put the necessary obtuse angle on them. Simply by laying them over  2" pipe on the ground. Then hitting the 90° angle with a hammer.

I have decided against adding a narrow rib or profile to the dome/slit rib joint. Let's stop messing about and have a small fibreglass, exterior addition. It will be invisible in practice. Except to a drone. I can finish off with glass tissue and a coloured top coat.

I have finally ordered some polyester resin and CSM [chopped strand, glass mat.] Autumn approaches and it would be risky not to be able to do the GRP work when conditions allow. The climate and weather are so highly unpredictable these days and temperatures a complete unknown. 

Polyester resin is best used in fairly warm conditions. Fortunately, the dome will be warmed by the sun. Even if the outside air temperature is lower than desirable. The dome's wall temperature is easily checked with a remote sensing thermometer.

As discussed yesterday, I shall glass over a fairly narrow strip on the inside of the dome and up the inside of the slit ribs. Not an area with easy access but also well hidden from view. So there is no need to achieve a high standard of finish. As would be required on the glossy outside. Besides, it will match the rest of the inside of the dome. 

I can use small, resin pre-wetted strips of glass matt. To save struggling against gravity with longer lengths. The inside of the dome is typically rough glass matt layup. Handy in avoiding reflections inside the dome.

I now plan to fibreglass over the top of the laminated plywood, base ring. A ring of  glass matt will be applied onto the dome just above.  This will lock the base ring in position far more securely than bolting brackets from above. It would also avoid potential leakage points [from using more bolts and brackets] and would help to further stiffen the dome skirt laterally. The cost of the GRP is probably lower than buying lots more brackets.

The overlay of GRP would also stiffen the ring much more uniformly against upward pressures. The entire weight of the dome will be resting on the [14] rotation rollers. Which will run on the underside of the base ring. Distortion of the base ring must be avoided to avoid jerky movement in rotation. The dome base ring acts much like a linear, roller [thrust] bearing. 

The distribution of weight over the many rollers ensures low rolling friction. The rollers themselves have needle roller bearings in their hubs. Each 7" industrial, nylon roller is rated to carry the total dome weight. Their considerable size aids rolling over discontinuities [joints] in the plywood base ring. Moreover they do not rust and still appear brand new after years of use.

There is no need to apply the usual, rolled iron base ring used in conjunction with very small rollers. The effort to get the dome moving is easily overcome with my chain driven, friction roller drive. Which I will carry over to this new dome. If the new and heavier dome requires more effort, I can simply change the drive's gear ratio.

Any condensation on the inner walls of the dome would run off the GRP applied on top of the base ring. The applied GRP will safely avoid the base ring becoming wet. Which in the very leaky, plywood dome has caused wheel spin of the drive roller.

 

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