Ready to Grind

[yobbo89]

It took me all week to make this tool. 2 days waiting for the Plaster to fully cure, then 2 coats of epoxy and then gluing the tiles.. I think i might just spend extra and buy dental Plaster next time so I don't have to spend so much time waterproofing.. . Any how I got this 8 " glass at a good price so I can get some practice before I move onto the 10" that I obtained from Joe (Ozeclipse) . Have not decided on an f ratio yet, I was thinking maybe f 4.5 , I don't know if that's reasonable for a first mirror.

[JayTee]

It's so awesome to see you attempting this.

Just remember the longer the focal length the easier it is to achieve your f ratio. That's why I stopped mine at f/7.5 - - I got tired.

[Bigzmey]

Good luck!

[messier 111]

a great project, keep us informed of your progress.

[helicon]

This will be a challenging project but should have a great outcome. I'm sure it will be a fantastic feeling to gaze at the universe with a glass of your making.

[SparWeb]

Please post about your progress. I'm keen to see how it goes.

[yobbo89]

about 15+ wetts in, getting tired xd , I've settled for f4.7. final read out will be 1.05 mm on the sphereometer, I'm currently at 0.25, so about to 1/4 way there, using chordal stroke with tool on bottom and 80 grit which is a little slow, should of got 60 grit for hogging.

[yobbo89]

Almost at my target !, I have 270 microns to go, currently at f6.4


Dial needs to come around to 3.21

I end up putting grout in between my tiles to add a little tension for the water and grit as most of it was getting flushed out un grounded beforehand.

[AstroBee]

Very cool to see you attempting this. Even if it turns out to be a failure I'm sure it was a learning experience. This is almost a lost art among the younger generation.

[yobbo89]

I've been following some guides here

https://stellafane.org/tm/atm/grind/rough.html

I'm at about 75% completed to reach my sagita all done with 40% overhang on chordal stroke and 80 grit, should move up a grit and complete the other 25% and use less overhang?

[yobbo89]

I did a few laps of 20% over hang, work back to 40% then push back out to the outside of the mirror again .

On the ball, f 4.79 , 959.7mm fl

Time for a good scrub and rinse for the next grit

3.21mm on the sphereometer was my target

[JayTee]

My goodness, that went fast.

Well done,

[AstroBee]

Congrats!
So once you are completely finished polishing, where do you send it to get silvered?

[Graeme1858]

On the ball, f 4.79 , 959.7mm fl

Is that a spherical pun?

[yobbo89]

Congrats!
So once you are completely finished polishing, where do you send it to get silvered?

looking online There seems to be a few here in aus, i think most are south aus or nsw and a couple in nz, i'll have to do some research, joe recommended a place but i forgot the name.

[yobbo89]

I'm on 120 grit doing normal 1/3 strokes, it seems i have a little bit of a gull wing curve, here's the pencil test.

So the high spots are 20% from the edge, not sure if I should go back to chordal stroke to correct or do Normal stroke with the tool on top since I have a hole in the center.

[yobbo89]

So close! , so now I grind with the tool on top to get the hill out.

[yobbo89]

I'm a few hrs in at 180 grit, well I'm stuck trying to get this bubble out...

[yobbo89]

I Have only two tiny defects left which I'm gone leave,it's better then before, I guess it really pays to inspect the glass for bubbles prior to grinding. After some hours on 240grit I'm ready to move on, currently down to f4.62, 924.5mm fl , reflection test in the sun yields spot on, moving onto 400 grit with the tool on top to not further shorten the f ratio as in fine grinding it is still possible to change slightly.

[a100171]

I Have only two tiny defects left which I'm gone leave,it's better then before, I guess it really pays to inspect the glass for bubbles prior to grinding. After some hours on 240grit I'm ready to move on, currently down to f4.62, 924.5mm fl , reflection test in the sun yields spot on, moving onto 400 grit with the tool on top to not further shorten the f ratio as in fine grinding it is still possible to change slightly.

20240615_094150.jpg

It is a really amazing project. I don't think I would have it in me.