Re: ATM classes and pitch laps (long)

[StepHydro@aol.com]

Guy,

As I mentioned in my previous post to the list, in our JSCAS ATM sessions, 
three people would pour, channel, and press 4 laps of 8" dia in a half hour. 
This can't be done in the old way shown in e.g. Texereau.

Forget forever about making dams of tape, about casting little squares of 
pitch and sticking them on with turps, about channeling with a knife and 
getting pitch all over yourself and the world...forget it all. We are going 
to do this the EASY way, I tell you, the EASY way.

You'll need the following:

A saucepan you never intend to use again for cooking, likewise a wooden spoon.

A square of fine nylon mesh. Buy a bag of lemons and make lemonade. Cut the 
bag up into squares of convenient size for the laps you will be making. I use 
a 12" square for an 8" lap.

A channeling tool. Make one. Get a stick of hardwood about 1 1/4" (30mm) wide 
x 1" (25mm) thick x 22" (55cm) long. Get also two strips of hardwood 1/4" x 
1.5" x 10" (f0r an 8" lap)..do the metric yourself if you insist, my "shift" 
fingers are getting tired. Now, on the strips, double bevel one edge of each. 
The bevel should be about 1/4" long, ending in a blunt "V", and run the full 
length of the strip. These strips will form the channels in the pitch. Now, 
glue and brad the strips to the handle on the narrow edge(of the handle)such 
that there is appx. 1 3/8" between the two "points" of the bevels. I hope 
this is clear. You now have a wooden tool like a double vegetable chopper, 
but not quite as sharp, with a handle on each end.

Some liquid dish detergent and a bar of soft soap, like Ivory.

A tolerant spouse.

Now, let's make some laps:

Clean the tools that you are going to pour the pitch onto. Clean the fine 
ground mirror blanks. Rub the soap well into the ground surface of the mirror 
blanks, coat the tool tops with turps (smells good!!!!). Rub the bevels of 
the channeling tool with the bar soap...get a good coat and don't worry about 
chunks of it sticking about. They won't hurt.

Put the saucepan with the pitch in it on the fire and start it cooking. Not 
too hot, but don't priss around worrying about bubbles as advised by the very 
intelligent but unforgivably anal Texereau. Bubbles do nothing to hurt a 
lap...they are just "micro channels" (forgive me oscilloscope mfgrs). Now 
heat this stuff until it is quite thin (now THAT smells good)and make sure 
that it is consistent in viscosity.

You may want to put a dam of masking tape on your first few mirrors until you 
get used to judging the proper pouring viscosity for the pitch. Once you 
learn this, you will pour a single stream into the center of the mirror and 
it will spread out to the edges, stopping just at the edge in a perfect 5/16" 
thick coat with a nice curve (about f/6) on the top. :-)

Now, take up the saucepan from the fire and stirring constantly, watch it 
until you think it will run to the edges. Don't worry about pouring it a bit 
thin at first; that's better than too thick and having a partial coat to chip 
off so you can start over. You've made a dam for this one anyway. If it is 
too thin, you just won't have the nice curve and pressing it will be a bit 
more of a hassle. It takes practice to get it "just right".

Start the hot water running in the sink. Have your least handy droog set the 
stopper when it gets hot and run about 8" (or whatever you use for that 
depth) of water. Set the mirrors in it to heat them, but don't swish them 
around; you want the soap to stay on them. If you rub it off, be sure to 
recoat before you press.

Now, pour it about 5/16" thick (I don't know how the rest of the world ever 
makes pitch laps, since they don't have 1/16ths of inches lying about 
everywhere) maybe 3/8" at first. Let it cool a bit. Remove the dam as soon as 
you can do it without the pitch pulling away. You want to get to the 
channeling while the pitch is quite soft.

Now place the channeling tool over the pitch, with one "blade" not quite 
centered and press. Press it all the way to the tool surface if possible. If 
not, go on, working fast. We'll deepen those grooves later if necessary. 
Place one of the blades in one of the grooves just made and press again. The 
first groove acts as a guide and spaces the next channel (groove, whatever) 
just right. Continue in this manner until you reach the edge. Turn the tool a 
good 90 degrees and do the same operation again. Wallah!! (I do know how to 
spell the Fr., but some might think I've started talking about musical 
instruments, another of my mad pursuits) you have most of a lap done and you 
don't have a flake of pitch on your hands.

Now, if your channels are good and deep go to pressing. If not, put the tools 
in the hot water and recut the channels when the pitch softens. Do this until 
the channels (grooves, whatever) are all the way to the tool. So now, you 
have these rounded, lumpy squares all over the tool. Looks as if they will 
never be good for anything.

Heat the lap one more time in the hot water (have doofus change it for fresh 
hot water. As a matter of fact, bitch at him for not getting the water hot in 
the first place). Set the lap on your spouses new Corian (tm) countertop and 
rub it well with dish detergent (washing-up liquid to those of the UK'ish 
persuasion) and lower the soapy mirror onto it, and press like hell. You want 
the channels to nearly close and the pitch to somewhat bulge out the gap at 
the circumference. Main thing is that before you are done, the mirror *must* 
contact the lap all the way to the edge. Move it around in a circular motion 
to keep a ridge from developing on the surface of the lap.

This part is important, so don't let the hot water guy attend to it. You MUST 
get that glass off the lap before the pitch cools. It will stick like it was 
epoxied and you'll have hell getting it off.

Let's say, since this is the first time, that it stuck. Get a plastic spatula 
or egg turner, whatever you might call it. Try to force it under the glass. 
Didn't work??? Then put the whole thing in the other sink and run cold water 
to cover it. In about 10 minutes, take it out and try the spatula again. 
Don't tell me that you used a metal spatula...not really!!! Well, that side 
can now be the back of the mirror. Rough and fine grind the other side of the 
blank and return to this spot in two days.

Still stuck, eh??? Get a piece of pine 2x4 (I'm told that a deal 5x10 will 
work in Yerp) and lay it on the Corian. Hold the mirror firmly in both hands 
and whack the tool on the wood. It will come apart, but will probably take 
chips out of the pitch squares. Get the saucepan hot again and fill them in. 
They will NOT hurt the lap, though I can't say that about your (approximately 
now) wounded pride. Don't worry, this won't happen again until you make your 
16"er. Scrape the bits off the mirror and finish it up with turps, wash with 
soap and water, heat and soap it again. Use the channeling tool to repair the 
chipped and refilled squares. Now go back to the hot water (Doofus asleep??? 
He's got only one job...keep the water hot.)

Now, for the 90% of you who split thelap and mirror apart before they stuck, 
you will have a tool with a nice curve, but the channels will be mostly 
closed. You can guess the next step, eh? Reheat, resoap the channeling tool 
and repress the channels. Now reheat both pieces, resoap the mirror and 
repress. Keep doing this until you have good deep channels and good contact 
over the mirror surface extending all the way to the edge. Now, heat it all 
one more time and get out the mesh. Coat both the mirror and the lap with 
whatever polishing compound you intend to use. CeOx or Zox for most of you, 
rouge for the elite (messy, but it really does make a better surface, and 
isn't that what we want?)

Now, lay the mesh on the warm pitch and press the mirror onto it just until 
the mesh imprints into the pitch. If you pressed too hard, the pitch runs 
over the mesh and captures it. No big deal, just have doofus put it in the 
hot water for a couple of minutes and gently pull it up. If you pull it cold, 
you'll have billions of little pitch chips flying all about the room. You 
might as well try to break the lease, as you will NEVER get them all cleaned 
up.

Now, there are a couple more operations, but they must wait until the pitch 
has really cooled. For now, just put the mirror gently back onto the lap to 
smooth out the micro channels made by the mesh. Don't press too hard, as we 
don't want the channels to close, just get them flattened a bit.

If you didn't have sticking troubles as mentioned earlier, just about a half 
hour has passed, and you have a row of pitch laps on the counter, looking 
pretty good except for that pitch that oozed out when you pressed. After the 
pitch has cooled for maybe 20 minutes (I knew that lemonade would come in 
handy) take the tool outside, and with a sharp knife...I use a kitchen paring 
knife with a short blade... "slice" off the overhanging pitch... NO, doofus, 
NOT right by the car door, in the flower bed!!! Use a quick slicing motion, 
not trying to get the whole lump at once, for it will fracture back into the 
part that you want to keep. Try to remove about ten thou. at a stroke (or .25 
blah, blah) and keep the blade nearly vertical, coming up from under the tool 
and cutting away from yourself. Go all around until it looks neat. I angle 
the cut in about 10 degrees to leave a bit of margin for future pressings.

Now, it is tempting to set the mirror on top of the lap and retire, thinking 
to cold press over night and start polishing in the morn. You can, but you 
will find that all the pitch has squeezed out during the night and all the 
above work will have been merely a practice session. That pitch seems cold, 
but it is really quite soft throughout. Wait until tomorrow, run some warm 
water on the lap for a couple of minutes to get a surface softening, just 
enough that your thumbnail will penetrate a wee bit. Now, set the mirror on 
the lap and walk away for an hour. Come back and charge it with rouge (I 
know, you didn't believe me) er...CeOx. In fewer than 15 strokes, the lap 
will be warmed and purring like a, hmmmm lap.

As you work, the channels will close up. Just run the sink hot again, heat 
both pieces, get out the channeling tool and redo the whole thing. It will 
take less than 5 minutes and will be clean. Something you can't say about the 
old razor blade method. Don't forget to ket it cool twice as long as you 
think it could *possibly* need before working it again.

One final thing. I got tired of the mess of slicing the bulges away at the 
edges after forming the lap. I took a soldering pencil tip and silver 
soldered a brass blade on it. The blade is about 3/8" x 1 1/2" x 1/32 thick. 
I heat the soldering iron and simply slice the overhang off, letting it fall 
back into the pitch pot. Hate to waste it. I also made a V form tip, much 
like a veining chisel, to rechannel with, but I find the heat and channeling 
tool much better.

If you make mirrors smaller than 6" or larger than 12.5", then you'll want 
channeling tools with narrower or wider blades to give the correct size 
squares. For the small ones, I just use a single slip of hardwood and eyeball 
the spacing for what I want on that lap.

Hope this is useful. We've made HUNDREDS of laps like this and would never 
think of doing it the old way.

If I think of anything else, I'll send it along.

Cheers/Don Carron
The TN with red fingertips