[ATM] 12.5 inches BVC mirror - more details

["RM L" <atm@axeinformatique.com>]

Thanks Mel, Jerry and Guy for the advices and encouragement.

I'll give you the details you asked for.

The color in the middle of my tool :

When I created the tool (plywood), I glued a slim round piece of wood in the middle to approximate the desired shape and use less pitch and have about the same thickness of pitch all over.Because the pitch is transparent (yes it's not black and I was surprised about that too. That's what the guy who sold me the BVC gave me), this darker piece of wood shows thru. The pitch is the same texture and color all over :-)

I'm curently working by hand,  tool on top. I'm more confortable this way... Won't the liquid stay all in the grooves if I work MOT ?

What texts am I using ? I only read everything I found usefull on the Internet. A lot of Mel's stuff of course :-)
It's been a year since my last extensive readings, so I'm not that fresh in my mind.

I too find that my mirror looks nice. Just one long hairlike scratch, from a piece of glass that detatched from the border during early stages of polishing.

The pads worked very well. I made a mistake, I did not have enough left to cover all the surface, and that caused zoning. I'd used them again, it worked fast. But it can dig a hole...

I was thinking to enlarge the bevel with a dremel. The guy who does the aluminising says he needs at least a 1/8" bevel. He hangs the mirror upside down and it is held by the bevel on several points... Also, I found appealing to remove some or all remnents of a turned edge that way... If done carefully, why should it damage the rest of the surface ?

The grooves are starting to close on the lap. More on one side than the other. It was my first pressing and polishing after I redid the grooves. So I think they are closing kinda fast.

I don't realy understand how to use a knife edge. I exclusively used the ronchi tester I fabricated. I made gratings of 80, 100, 120 LPI. I get more contrast from the lower lpi (80).

The fuzzy appearance is because the camera is not on a tripod, and is not stable.
Jerry, the part about looking at one line... confused me a bit.

I'm not shure now if I see a crater or a bump in the middle. Is there a concensus on what we see ?
I updated my page. Can you tell me if it's figure A or figure B ?

http://www.axeinformatique.com/temp/Mirror/BVC_Mirror.html

Yes Mel, the mirror is fully polished. I'm ready to go on to parabolisation.
But I'm unwilling to make another lap tool. How should I go about, using the same tool ?

Also I think it may be worthwile trying to diminish the TDE first !?
How much time do you all think it may take do diminish the TDE ?

I'm prepared to press my lap 30 minutes tomorrow morning, then work TOT center over center with about 1 inch overhang.
After 30 minutes of that I would check on the Ronchi tester again. May this smooth out the overal sphere as well as diminish the TDE ?

B.T.W., I live north of Montreal, near St-Sauveur, in the Laurentians.


Thanks very much all, for you are giving me hope.

RML
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