16 inch Dob project under way

[Daniel-K]

i just went from this guys

[Daniel-K]

how do i know when its polished enough?

[Astrobits]

Best way to store the lap? I always kept mine in contact with the mirror. Fresh charge of polishing agent and water inside a polythene bag or as tightly under a poly sheet as possible so it doesn't dry out, checked every day if not polishing. However, I would not like to do this with wood based laps Mine were made with plaster and varnished, then wrapped in electrical tape. This was mainly to cover the holes in the plaster that came from bubbles in the mix. It might be advisable to wrap yours with electrical tape, overlapped strips on the back and continuous round the sides. This will prevent anything lodging in a rough surface and falling out at the wrong time.

If you plan to not polish for more than a few days then store separately, clean and dry, the lap ideally in a tin or box with NOTHING on top of the pitch. You will then have to press thoroughly.

It's polished when you can't find any pits using angled backlighting and a 10x magnifying glass ( cheap 25mm eyepiece can work, use reversed ). I always marked the location of the worst pit I could find with a mark on the side of the mirror. Pencil or felt tip marker. I could remember the location in relation to the centre along that radius. A 16" takes quite a time to examine thoroughly.

Nigel

[Daniel-K]

There's a few small scratches but nothing thata concerns me after all its the first mirror

[Daniel-K]

manged around 90 mins polishing, its defiantly gone clearer, theres some small scratches that are there but my polishing place is ideal but its what i have so i have to make do. they dont bother me to much, its really starting to reflect now the picture is after the mirror has had a wash and dried out, total time polishing so far approx 3 hours

[sonic190178]

looks good dan

[Chris]

Thats looking amazing Dan, you're making very good use of your annual leave

[Daniel-K]

Thats looking amazing Dan, you're making very good use of your annual leave

getting a bit done going to keswick with the family on saturday for a few nights

[Rustysplit]

Coming along nicely Dan. The other way that you can check that your surface is fully polished out is by using a red laser pointer angled at 45 degrees then viewing from the side, at 90 degs to the laser, to see if you can see the beam reflecting off the surface. If you can see the beam on the top surface, it needs more polishing. You need to do this test all over the surface. Time spent at this stage will pay dividends later.

Have you tested for a sphere yet ?

[Daniel-K]

Coming along nicely Dan. The other way that you can check that your surface is fully polished out is by using a red laser pointer angled at 45 degrees then viewing from the side, at 90 degs to the laser, to see if you can see the beam reflecting off the surface. If you can see the beam on the top surface, it needs more polishing. You need to do this test all over the surface. Time spent at this stage will pay dividends later.

Have you tested for a sphere yet ?

not yet i think i m going to take the mirror to liverpool astronomical society tomorrow and see if they help with the ronchi. also im running out of cerium oxide were did you get yours from Alan?

[Rustysplit]

I got mine from Galvoptics/image optics. Be warned they are not cheap. You may be better looking on fleabay. Some lapidary supply outlets sell it a fair bit cheaper.