Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> ATM, Optics and DIY Forum

Pages: 1
Rockā„¢
member


Reged: 03/18/12

Mirror got scratch
      #5645928 - 01/27/13 12:04 PM

My 1st mirror was completed and sent for silvering to a local silvering glass people.
I am having another 6" glass so i thought to go for F/6 with it. Work was going fine, but at 1000 grit got a little deep scratch. May be abrasive is having ungraded particles in it. It does not got contaminated by me.

Can i ignore this scratch or should i degrade it with 600?


Post Extras: Print Post   Remind Me!   Notify Moderator  
kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: Mirror got scratch new [Re: Rockā„¢]
      #5646291 - 01/27/13 03:45 PM

It is easy to get a scratch when using very fine grit Do not push the wet to long no down presure. Some do not like to go finer than 12 micron . I would fix it now if it is bad .A 6 inch f6 is a very nice size .

Post Extras: Print Post   Remind Me!   Notify Moderator  
Rockā„¢
member


Reged: 03/18/12

Re: Mirror got scratch new [Re: kfrederick]
      #5647356 - 01/28/13 02:32 AM

Thanks, just now i degraded to 600 grit and removed the scratch it and i also completed 800. Mirror is fine now.
As you know it is not possible to go for 1000 grit. Is it possible to move to Pitch And cerium oxide?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Mirror got scratch new [Re: Rockā„¢]
      #5647635 - 01/28/13 09:17 AM

You could polish out after 800 grit (about 14 micron), but it will take a while. It's that last smattering of pits which will consume much time. Not so bad if you have a machine doing the work, but by hand, and if 'walking around the barrel', this could become drudgery. Mere minutes of work with a finer abrasive will save hours of polishing time.

Post Extras: Print Post   Remind Me!   Notify Moderator  
furrysocks
member


Reged: 01/24/13

Re: Mirror got scratch new [Re: GlennLeDrew]
      #5647647 - 01/28/13 09:26 AM

I'm not a grinder at all, but I read in the last few days that the fine abrasives can clump somewhat before they are mechanically broken down, and this can lead to scratches... solution may be to soak a slurry a day or two beforehand. Don't know if this helps.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Rockā„¢
member


Reged: 03/18/12

Re: Mirror got scratch new [Re: furrysocks]
      #5647679 - 01/28/13 09:39 AM

Thanks
@ Glenn i am not using machine , doing with the hand.
@ furry ok i will try to follow your advice to and lets see whether it works or not.

when i touch the 1000 grade carbo abrasive i do not feel like that i am having dust particle between my finger, but as soon as i put it in mirror ans start to grind, i can feel some dust particles done his job.

Will it save my time if i move to polish after 1000 grade??

Edited by Rock™ (01/28/13 09:40 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
furrysocks
member


Reged: 01/24/13

Re: Mirror got scratch new [Re: Rockā„¢]
      #5647689 - 01/28/13 09:44 AM

Not meant to be "advice" as such - just relaying something I read. I can't even quote the source!

You'll have to make your own choices. Grinding and polishing still seems like a dark art, to me!

Good luck, though.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ccaissie
professor emeritus


Reged: 09/13/10

Loc: Whitefield, Maine
Re: Mirror got scratch new [Re: furrysocks]
      #5648697 - 01/28/13 04:55 PM

It is a good habit to gently put the mirror down on the tool, and before allowing gravity or pressure to take over, work the mirror around and distribute the grit for ~20 seconds. Any big grains will get broken up first. If you hear a crunch or two, lift it off and rinse it.

If your grit does have large particles, try mixing it up with water and a few drops of soap. The big grains will quickly settle, and then pour off the top into another jar and use that. I keep my grit in a little cup and brush it on.

I've had this problem with very good grit at 5 microns, and I think it had to do with rough stroking, or maybe clumping of the grit when it got too dry.

But you did the right thing...go back and fix it. Doesn't take too long, leads to happiness, and more practice.


Post Extras: Print Post   Remind Me!   Notify Moderator  
sopticals
professor emeritus


Reged: 03/28/10

Loc: New Zealand
Re: Mirror got scratch new [Re: Rockā„¢]
      #5648813 - 01/28/13 05:43 PM

Quote:

Thanks, just now i degraded to 600 grit and removed the scratch it and i also completed 800. Mirror is fine now.
As you know it is not possible to go for 1000 grit. Is it possible to move to Pitch And cerium oxide?




If you have a scratch free surface after having completed the #800 grind, then its ok to go to the polishing stage. Your mirror will polish up quite quickly using Cerium oxide.

Stephen.(44deg.S.)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rockā„¢
member


Reged: 03/18/12

Re: Mirror got scratch new [Re: sopticals]
      #5649689 - 01/29/13 04:21 AM

Thank you everyone, i tried using settle down larger grit and finally i succeeded in it. I did 1 hour of last 1000 grit and no scratch till now.
But i will not do any more with 1000 grit, i will move to pitch and cerium oxide.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
14 registered and 24 anonymous users are browsing this forum.

Moderator:  ausastronomer, richard7, Starman81 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 715

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics