Gina

Yep - great thread

Thanks very much for your offer, I'll let you know. Meanwhile, I think I'll print a couple of test parts to try the RTV Silicone Gasket Maker. Going by the instructions, I think this stands a chance of working. I think you're right about the O ring being too hard to compress and seal properly. Closed cell sponge should be much better.

Me too.

I have a tube of this RTV Silicone Gasket Maker - looks like it might be better than the clear or white stuff.

Strange thing is that the dome is leak free and only has 4 bolts into threaded holes in the PETG and sealed with silicone sealant. There is a 3D printed ring on top of the dome flange.

Both good ideas - thank you - but I think I'll have one more go with the O ring and 3D printed parts. I can make the flanges a lot thicker and double up on the number of bolts. I have observed that most pipe flanges have a very large number of bolts to hold them together. The current leaks might be due to the remaining silicone sealant on the body top part.

I wondered about more bolts. 16? 24? Currently using 8 but with 120mm ID they're still a couple of inches apart (ooh I love mixed metaphors measurements!).

I could do with some good ideas and I seem to be fresh out of them!!! Maybe I should shelve this project and do something else...

Printing a new base with thicker flange, for what it's worth. I guess I might as well try to forget about getting this thing imaging until I solve the sealing problem.

I presume you mean the 3D printed flangesd may be too thin. You could be right. Though the worst leak is at a bolt.

Most of the clouds have departed and the sun is out so it would seem that forecast is probably right. However, it also seems the chances of having the ASC working for tonight is vanishingly small

Added white grease profusely and reassembled. Still leaks. Not as badly but evident in two places around the flange. So that's another idea gone. I'm thinking the only solution will be to make the flange joint permanent and if I need to repair anything inside I'll just have to either break it apart or saw it open.

I agree but to produce a smooth groove is not easy. 3D printing is not necessarily perfect.

The O ring has arrived and I've assembled the ASC with O ring dry and it leaks but I haven't been able to find where by testing with soapy water. It isn't easy to see bubbling down in the flange channel where the O ring is. There is certainly no bubbling round the cables or tubes. Guess the next thing is to take it apart again and grease the O ring and try again.

Still have clear skies forecast for the dark period overnight in spite of current total cloud cover with some of it very dark and looking like rain. There will only be a short interval between moonset and sunrise though, and in view of that I don't think I'm going to "bust a gut" to get it all working by tonight. Slow and steady generally gives better results. The O ring is scheduled to arrive this afternoon. New base plate has printed fine and I'm installing the cables and other parts. I think I can use the present top - I've got most of the silicone sealant off it. The inner ring that retains the O ring will also raise the camera to allow for the thickness of the O ring. I also have the electronics to sort out.

I doubt it!

Printed those parts and now printing a new base plate.

You have green beer in SW France??? Or is it lime juice?

Hope you haven't forgotten the entrance doorway!

Looks great - coming on nicely ? I could have done with a digger too when I built my observatory and we too have clay 20-30cm below ground level.

Same here!

To retain the mirror flat surfaces on the 3D printed parts I think I shall design and print two rings to hold the O ring in place - one inside and one outside with the outside one having the clamping holes.

Yes, I've come to that conclusion! Though this was squeezed between 3D printed parts. I have some 4 core screened cable I can use for the USB and that can go through a grommet.

I'll bear that in mind, thank you, but I want to get the ASC working again for tomorrow night if possible as it's forecast to be clear.

Clamped and sealed with silicone sealant - oodles of it. Should have sealed alright.