From: "Banich, Howard" <email@example.com>
Subject: RE: Re: Mirror box bottom light baffle / Sawdust + 3M undercoating.
OK, here are the steps I went through:
1.) Created and saved lots of clean sawdust while working on an assortment of
2.) Bought two cans of 3M automotive undercoat spray and read instructions on
3.) Practiced on scrap wood until I was comfortable with the process. I
needed the practice to get an even spread of the sawdust and to control the
spray - it comes out fast and thick.
4.) Bought a grated cheese dispenser - this made spreading the sawdust evenly
5.) Practiced on scrap wood again. Much easier, and it was his point I knew
this technique would turn out well (let the practice pieces dry overnight so you
can see the finished texture).
6.) Removed the primary mirror from the mirror box. Stored it in its shipping
box and covered the box with a shop towel to protect from over-spray.
7.) Removed mirror cell and altitude bearings, and covered them with shop
towels to protect from over-spray.
8.) Rough sanded all the areas I intended to spray. I used 80 grit sandpaper
and did the sanding by hand - nothing major, just enough to roughen the surface.
9.) Masked off all the areas I did not want to spray. I used painters masking
tape and covered the outside of the scope with newspaper and made sure to plug
all the bolt holes so spray wouldn't sneak though to the outside wood finish.
10.) Read spray instructions on the can again.
11.) Sprayed on first layer of 3M undercoat.
12.) Immediately sprinkled sawdust on the still wet first layer. Made
sure the sawdust was sprinkled evenly.
13.) Sprayed on the top layer of 3M undercoat, making sure I completely
covered the sawdust from all angles. The first layer was still wet at this
14.) Let dry for about a week, then reassembled the scope.
From step 6 it took me an afternoon to complete. By itself the 3M spray has a
pebbled, flat black finish when dry but with the additional roughness of the
sawdust it comes close to eliminating light reflection, and I'm very pleased
with the result. Hope this is what you were looking for, and good luck if you
decide to give this a go.
It was pretty easy to do. I sprayed a layer of the 3M undercoat and then
immediately sprinkled on the sawdust while the undercoat was still wet. Then I
sprayed on the top layer, making sure I covered the sawdust from every angle.
Clean sawdust is important as it's easier to spread than dirty sawdust.
Also, I used a shaker container made for sprinkling grated cheese on food to
sprinkle the sawdust, which turned out to be important to get it spread evenly.
Because this was the first time I'd tried this method I first practiced on scrap
wood to make sure I was comfortable with the technique.
As you probably know, spray painting anything involves some pre-work. I took
out the mirror, mirror cell and removed the altitude bearings so all I was
working with was the wood mirror box. I rough sanded every surface I was going
to spray and then masked off everything else. This took longer than the actual
spraying but helped the procedure turn out nicely.
Aside from suppressing stray light, I like the rough and very black finish
contrasted to the beautiful wood finish of the outside of the scope. Looks cool!
I'll use this technique again on my next project.
20" Obsession #038
West Linn, Oregon
Heated Secondary - not wired up yet.