Making a 10" Dob - Page 2

OzEclipse (Joe Cali) · #21 30-04-2018, 12:00 AM

Hi Logan,

It's a long time since I last ground a mirror (33 years). I don't remember how long it lasts.

When on the course grits, you feel it stop grinding & become smooth when the grit wears down. That's when you change or recharge the grit.

Don't let it dry out. If it gets stuck, really hard to release.

Joe

Rod · #22 30-04-2018, 03:23 AM

Hi Logan

When rough grinding using 80 grit, you grind by sound. When the harsh grinding sound stops, you need to recharge the grit.

You will likely use a lot of 80 on your first mirror.

Rod.

Lognic04 (Logan) · #23 01-05-2018, 08:09 AM

Thanks all, getting closer to having those rings gone, hogging can start soon hopefully! I will use a piece of metal to rough it so that the tile tool that has been used previously gets less worn.

troypiggo (Troy) · #24 01-05-2018, 12:01 PM

Hope you're taking lots of cool videos of the process for your Youtube channel

Lognic04 (Logan) · #25 01-05-2018, 12:04 PM

Quote:

Originally Posted by troypiggo

Hope you're taking lots of cool videos of the process for your Youtube channel

Lognic04 (Logan) · #26 02-05-2018, 08:30 PM

Decided to fine grind the back of the mirror while waiting for a tile tool, Mel Bartels said it is best to do that (but mostly i wanted to have a go at fine grinding!

) Have finished 120 grit, and am going to move to 35 micron tomorrow!

OzEclipse (Joe Cali) · #27 02-05-2018, 10:09 PM

Quote:

Originally Posted by Lognic04

Decided to fine grind the back of the mirror while waiting for a tile tool, Mel Bartels said it is best to do that (but mostly i wanted to have a go at fine grinding!

) Have finished 120 grit, and am going to move to 35 micron tomorrow!

Did he say why?
Joe

Lognic04 (Logan) · #28 02-05-2018, 10:29 PM

Quote:

Originally Posted by OzEclipse

Did he say why?
Joe

He says having a flat back reduces astigmatism.

Lognic04 (Logan) · #29 02-05-2018, 10:47 PM

Some pics!

Lognic04 (Logan) · #30 03-05-2018, 06:29 PM

Wow 25 micron is VERY FINE stuff!!!

Lognic04 (Logan) · #31 05-05-2018, 11:04 AM

Just picked up extra grit, a tile tool and a ring tool! Ready to hog out!

Lognic04 (Logan) · #32 06-05-2018, 08:03 PM

Have been Hogging out with a metal ring tool, and reached about 1.3mm deep. I have now switched to a tile tool to continue grinding! And I have decided to do f/5

Lognic04 (Logan) · #33 07-05-2018, 01:21 PM

I have a tile tool that has a rather different (more curved) surface that doesnt match the mirror. I was thinking of doing normal strokes(CoC) to get the right curve/matching surfaces on the mirror, will this work?

sopticals (Stephen) · #34 07-05-2018, 02:59 PM

Depends how different the curvatures are. If close would be ok as a bit of grinding with #80 grit would soon bring the two surfaces into a match. If a big difference probably not.
You using ceramic or glass tiles on the tool? Ceramic will wear more quickly.

Stephen

xelasnave · #35 07-05-2018, 03:54 PM

Quote:

Originally Posted by Lognic04

Have been Hogging out with a metal ring tool, and reached about 1.3mm deep. I have now switched to a tile tool to continue grinding! And I have decided to do f/5

Dropping the focal length is a confident move well done.

I got to thinking do you or others consider one could make a 2.2 fl?

Every one will probably say impossible but I wonder could you pull it off?

I mean ever one does a hand ground mirror with long fl s but a really fast mirror...It would be good if you could pull off such a feat.. the tube wont mind☺.

Then a fastar configuration?

Maybe you could send it someplace for final figuring so if its best that way it should become apparent.

I wonder ????

Alex

xelasnave · #36 07-05-2018, 04:03 PM

Opps we will need an equatorial mount...I have a mount design that I have been thinking about....more bearings than a car☺ and co sideeing building it in carbon fiber...better thermal stuff and I only have to fiber glass a balse model in effect ..no welding...ao the mount is covered maybe☺
RA and Dec moved by disks of 300 mm radius to make very precise ...at least that the idea.

I should explain it as you could build it I bet.

Plenty to do in astronomy eh☺

Good luck
Alex

Lognic04 (Logan) · #37 07-05-2018, 05:00 PM

Quote:

Originally Posted by xelasnave

Dropping the focal length is a confident move well done.

I got to thinking do you or others consider one could make a 2.2 fl?

Every one will probably say impossible but I wonder could you pull it off?

I mean ever one does a hand ground mirror with long fl s but a really fast mirror...It would be good if you could pull off such a feat.. the tube wont mind☺.

Then a fastar configuration?

Maybe you could send it someplace for final figuring so if its best that way it should become apparent.

I wonder ????

Alex

I reckon it is possible!!!If you can make a mirror, then you should be able to make any f ratio!

Lognic04 (Logan) · #38 07-05-2018, 05:01 PM

Quote:

Originally Posted by xelasnave

Opps we will need an equatorial mount...I have a mount design that I have been thinking about....more bearings than a car☺ and co sideeing building it in carbon fiber...better thermal stuff and I only have to fiber glass a balse model in effect ..no welding...ao the mount is covered maybe☺
RA and Dec moved by disks of 300 mm radius to make very precise ...at least that the idea.

I should explain it as you could build it I bet.

Plenty to do in astronomy eh☺

Good luck
Alex

I am really interested in this design alex!

Lognic04 (Logan) · #39 07-05-2018, 06:00 PM

Quote:

Originally Posted by sopticals

Depends how different the curvatures are. If close would be ok as a bit of grinding with #80 grit would soon bring the two surfaces into a match. If a big difference probably not.
You using ceramic or glass tiles on the tool? Ceramic will wear more quickly.

Stephen

Unsure whether to do normal stroke or chordal?

xelasnave · #40 07-05-2018, 07:13 PM

Quote:

Originally Posted by Lognic04

I am really interested in this design alex!

I have a model in cardboard to demonstrate the idea and I will use it to talk to folk about this and that so let me nail it down a little and I will present you with rather definite.
Needless to say it will be interesting if one could build it in carbon fiber...not because I am taken with carbon fiber but I have experience with making stuff in fiber glass and it seems carbon fiber just replaces the glass and you have a similar process with a suitable resin and hardner.
But I am thinking you could make it up in balsa and over lay that with carbon fiber...sooner or later depending on how many layers it sould be as sttring as steel.
You dont need to weld and it is almost a kitchen table project.
A wild idea but you never know.
Alex