The Giant Binocular

[savarin]

Couple of short noisy vids showing the grinding.
I dont know why it published them as shorts though. (Maybe because they are--------------short?)

this one shows the diamond disk smoothing the edge at 90'

Grinding the bevel on the corners at 45'

The mirrors are not quite centered on the turntable so the pulsing of the diamond disk is quite pronounced.
Both mirrors now have their back face bevels done


For the 90' I let the diamond disk free wheel but for the bevels it took way too long so I drove the disk with my drill, mirror moving clockwise and diamond disk anti-clockwise. 5 mins to do each mirror, took way longer than that just to set them up.

But, it was messier with glass dust and water splashing everywhere.

 

[Downunder Bob]

It looks like an interplanetary explorer.

 

[savarin]

Made a shroud for the 45' beveling diamond disk from a large tin can but forgot to take pictures.

Way cleaner than before, no splashes anywhere.
Its a bit wider than I really wanted but I had to ensure there were no chips actually entering the surface.
This is the worst chip and I'm hoping there is sufficient meat left on that edge that it wont cause a proble,.

I wont know till I finish polishing and test it.

 

[BaronJ]

Thanks Bob, I dont know if its persistence or stupidity.
Another spoke in the works this arvo.
I could smell something not right and checked the motor that drives the stroke, it was way too hot to touch so when it cooled I dismantled it thinking maybe a blown bearing as I couldnt turn it.
One magnet loose and one magnet broken into 3 pieces no wonder it couldnt turn.
Now the wait for a new one.
View attachment 461696

Heat from the armature is a major problem for permanent magnet motors. The only way that it can be dissipated is via the spindle core and through the bearings and into the casing. A fan will help by blowing cold air through the motor core.

 

[twhite]

Made a shroud for the 45' beveling diamond disk from a large tin can but forgot to take pictures.
View attachment 466320
Way cleaner than before, no splashes anywhere.
Its a bit wider than I really wanted but I had to ensure there were no chips actually entering the surface.
This is the worst chip and I'm hoping there is sufficient meat left on that edge that it wont cause a proble,.
View attachment 466321
I wont know till I finish polishing and test it.

If there is a slight chip. I have beveled the edge to where it goes away.That way you have a really nice outer edge. I have seen a few people mask the last 1/4” when the edge is messed up.


Cutting oil is my blood.

 

[savarin]

This is the glass tile fine grinding tool. It was cast in the hollow of the mirror so hopefully its not far off the desired radius of curvature.
I've sealed the plaster so I doesnt soak up water (I hope) at least not too much.
Grinding will start tomorow.

 

[savarin]

OK, I couldnt wait and had to make a quick start just to feel good.
Stationary overarm, 1/8" overlap at the edge.
This is after 5 minutes and 3/4 teaspoon of 120 grit.
A small 1" dia patch in the centre hardly touched but contact everywhere else although not as heavy 1.5" outer edge.
One tile not in contact.

This is after another 15 mins and another 3/4 teaspoon of 120 grit.
Much smoother all over with the star on the back side visible, the centre is now starting to smooth and the full contact almost out to the edge.
Still one tile not in full contact but almost.

I am astounded that only 20 mins grinding did this much.
Maybe tomorrow I can work through 4 grit sizes.

 

[Firstram]

I thought this was interesting.

 

[savarin]

The problems with being a total knumbskull.
The grinding was continuing albeit slower than the first hour.
I appeared to have a lot of trouble deepening the curve as it was getting shallower and shallower but still didnt reach the edge. (first clue)
I seem to be unable to read the dial gauge on the spherometer correctly.
Here is the reading zeroed out on a flat surface

and here is the reading on the mirror.

According to this program https://mwganson.freeyellow.com/spherometer/ the reading I need for a 12" f6 mirror is 0.0179"
The dial gauge will read backwards from the flat zero because the mirror is sunken and the gauge probe has to extend further.
Can anyone tell me what the actual reading is on the second image?
My brain seems to be no functional here.
Am I correct in reading it as 0.022?

 

[twhite]

The problems with being a total knumbskull.
The grinding was continuing albeit slower than the first hour.
I appeared to have a lot of trouble deepening the curve as it was getting shallower and shallower but still didnt reach the edge. (first clue)
I seem to be unable to read the dial gauge on the spherometer correctly.
Here is the reading zeroed out on a flat surface
View attachment 467394
and here is the reading on the mirror.
View attachment 467395
According to this program https://mwganson.freeyellow.com/spherometer/ the reading I need for a 12" f6 mirror is 0.0179"
The dial gauge will read backwards from the flat zero because the mirror is sunken and the gauge probe has to extend further.
Can anyone tell me what the actual reading is on the second image?
My brain seems to be no functional here.
Am I correct in reading it as 0.022?

Yes .022
You are a bit deep it appears.


Cutting oil is my blood.