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...... Bubble ......

Bought the bubble from Paul Felski, it was cheaper than the one from Fred Barton and the postage was a LOT cheaper.

It has some minor imperfections in the top as you can see by the uneven reflections of the light, but you don't notice those when it's assembled. It's very easy to see small scratches etc when looking at only the bubble, but with the motion and flashing lights in the brain you could have much bigger imperfections that wouldn't show up.

Disaster! - over tightened one of the screws and cracked the bubble. The acrylic gets stretched in forming the bubble, that puts tension in the material, so once it cracks the crack tends to open up. Pushing as hard as i could the crack wouldn't close up, but i figured glueing it up at it's narrowest point would at least stop the crack from spreading any further. Glued it back together with Weldon-3 and turned it so the crack was at the rear, it didn't look too bad (but decided to buy a replacement anyway).

Warning the Weld-on is much thinner than water, even with the smallest needle on the syringe it still pours out without applying any pressure.

To avoid this happening again, the self tappers will be replaced with machine screws in tapped holes. Drilled out the holes a little larger and tapped them with M3 thread for clear screws, The M3 is a nice fine thread so even though the bubble is thin, there is still enough material to cut a thread in. A normal drill bit tends to bite into the acrylic, even at slow speed an electric drill has enough torque to push through and crack the acrylic. So it's safer to do it by hand.

The plastic is soft enough that you can drill a small hole by just spinning the bit with your fingertips. That way if the drill bit does bite it just stops spinning and you can back out and try again.

Used a clean new tap, again just finger pressure was enough for such a small hole in soft material.

Cut three screws to the correct length, only found round head screws so far but will replace them with countersunk. Or could just use metal screws, they would be no more visible than the old screws. Wont be using a screw in the 4th hole, now at the back.

The Barton bubble was nearly perfect, still a few light scratches could be seen when looking at the bubble on it's own, but again, not visible on the completed brain.

Kept the cracked bubble and renamed it "the stunt bubble", may use that when going to events where there's a chance of damage, and keep the other for when it's sitting safely at home. If the same bottom plate can be used for both bubbles they could be swapped easily without disassembling the brain.