The Giant Binocular

[woodchucker]

Hey Charles, when wood working and hand planing, I will often chamfer the edges to start to avoid tearout. That way there is no 90 degree edge to blow out. It definitely works. I'm wondering if a small chamfer would help, and keep maintaining that chamfer anytime you work through it. And looking at that scratch, could the chip have lodged and dragged?

 

[savarin]

Hi Jeff, the bevel is the chamfer and thats the idea to stop chipping. I dont know what caused this one as there was still a small chamfer there.
I heard the chip go and the screech as it dug the scratch and thought Oh bugger! but a lot stronger and for longer than that.
Inspecting the grinding tool it looks like it could have been a chip of the glass tiles but I'm not sure.
Theres also about 10Kg of weight on the tool which may also have contributed so the next wets will be a lot lighter, say 6Kg
We will see.

 

[rwm]

Would a scratch like that cause much of a visible artifact?

 

[savarin]

probably not but it hurts to see it

 

[savarin]

Managed to remove the scratches but had to go back to 400 grit.
took 3x15min wets but got there.
Then back to 600, 800, 1000, now just starting 1200 grit.
Fingers are crossed it doesnt chip again.
I still have some thickness left in the tiles so I can still go back if needed.
no pics, it looks the same as the first mirror.

 

[savarin]

Done, both mirrors ground.
Next grind the aluminium puller disks, shouldnt take long.
BUT, polishing and testing the mirrors will be a long job.

 

[wachuko]

Those are great news.

Even if the same, we love photos, if not too much of a hassle.

 

[Eyerelief]

Done, both mirrors ground.
Next grind the aluminium puller disks, shouldnt take long.
BUT, polishing and testing the mirrors will be a long job.

I'll know if I see any pictures of my house here in Texas on the interweb that testing went well. Guess from now on pants are in order around here.
Absolutely fascinating work you are doing!

 

[savarin]

Started grinding the puller plate. I decided to just use 120 grit as the small scratches will leave a key for the glue.
The surface has been pre-generated using a diamond saw leaving a very rough surface.
I need to get the radius of curvature to read 0.065mm on the spherometer, at the beginning it was 0.088mm so thats a lot of metal to remove.
setup, the sharpie lines give me a good idea of where the grinding starts.

15 mins, hardly any wear. Some, but very slow, I expected it to be a lot faster than this.

Moved the tool outwards a little more and stuck 15KG of lead weights on the tool.

This tool is what I used to grind the tool to grind the rear of the mirrors so it should grind the aluminium to the same curvature, if I get the position correct. After 1/2 hour it still hasnt started to wear the centre.

Another 30 mins and it just started to wear the middle

and got to 0.083 so its flattening which is what I want.

another 45mins and got it to 0.070

Looking better but still too deep in the centre.

Still a heck of a lot to go but I got bored, just standing there watching, sprinkle of grit, spritz of water, repeat over and over.
More tomorrow.
I really expected it to go way faster than this.

 

[woodchucker]

slow and steady... better than fast and wrong.