Re: [ATM] Updated pictures of 8"f6 mirror............

["Jerry" <wa4guu@verizon.net>]

Hello Mike:


Just a few points of disagreement. Hee Heee! John will have finished his
mirror and we'll still be debating pitch hardness. Then he will tell us he
used spar varnish.



Mike Lockwood wrote:
The problem is we still have no measure of how the pitch is behaving, 
we can only guess.  And that's what we've been doing.

My reply:
You may be guessing, but I am not. There are the results to give us an idea.
There are several sessions of experience with the lap. Consideration of the
work applied under the stated conditions should say a lot about the behavior
of the lap. If results does not indicate suitability of the lap, we are
wasting our time even thinking about changing pitch or any other property of
the lap. Why would we alter the properties of any thing involved in the
process if it did not impact results? What guessing I have been doing is
what will result using the lap under conditions other than what has been
used in the previous known work sessions.



Mike Lockwood wrote:

In my experience it takes a fairly large rise in temperature (10F or 
more) to make hard pitch significantly softer.  So, I choose to use 
linseed oil to soften my pitch rather than crank up the thermometer.

My Reply:

Why do you think his pitch is too hard? Could it be too soft?  Could it be
just right?



Mike Lockwood wrote:
Keeping my work/testing area closer to the temperature it naturally 
wants to be makes for less air currents when testing, too, and that is 
a big consideration for useful testing results.

My reply:
"Keeping" might be a problem.
John's work area is.... I believe he said a garden shed. In day light the
sunlit wall will have rising air and the opposite wall will be where it is
coming back down. There will be a continual rotation. I think he will be
doing most testing on cloudy days or at night. Or more likely he will bring
it indoors for that. The work temperature will be varying.... lets say
"wildly".



Mike Lockwood wrote:
Well of course other factors can affect the channel closing time (CCT), but 
this is the best we can do over email when we are on opposite sides of 
the world.  Let's face it - most people aren't going to build a pitch 
tester, so this is the next best thing.

My reply:
Obviously I do not think it is the best we can do. I agree most will not
make a pitch tester. Ruling out the pitch tester, channel close time is not
the best. I'm not saying CCT is of no interest at all. You seem to imply
that if the mirror results are excellent but the channels closed "too fast"
or "too slow" a new lap of different hardness is needed.



Mike Lockwood wrote:
If we are ever going to learn to help people with mirrors over this 
list we need some standard questions and indicators that will help us 
determine what is going on.  So I ask again, how long are the channels 
taking to close up?

My reply:
Standards should not ignore results.
John has answered:
	The laps made with a lap mould from pitchlaps.com. Followed the
instructions ok. After a few hours of work the channels are about 50%
closed.
And here we see the vagueness of CCT.  His answer is as specific as can be
expected. Yet if he had said 3 hours you would be no more certain of the lap
condition than if he had said 5 or 6 hours. 


Should I apply the spare varnish with a brush? Do I have to brush in only
one direction? Do I have to use thinner, if so how much?

Jerry

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