Storing your pitch lap between uses.

[mura_gadi (Steve)]

Hello,

Can I ask how people keep their laps and mirrors stored between polishing sessions?

John Dobson's youtube video states that once made, the mirror and the pitch lap are married together till coating.

I can understand keeping the cold press for shape, but I'm not sure about collapsing the channels down. If they collapse due to a long cold press I would have to re-form the channels anyway and then a new pressing.

If they're separated for storage, I assume I only need a quick 1 hour cold press before restarting.

I'm happy to reform channels etc after 2-3 hours of use, but, having to do channel work due to storage seems a little tedious.

thoughts, ideas and suggestion welcome.

MG.
Ps. Would there be any point in freezing the lap to halt tar movement, that way you could leave a few days between sessions. You just have a 1-2hours defrost time instead and a cold press before starting?

[Rod]

Hi Steve

I do what you suggest and leave lap and mirror separate. Then press and rechannel before use. I usually give it a scuff with a brass brush and add micro facets with a Stanley knife too. I don’t want the mirror to stick to the pitch and ruin the lap.

I wouldn’t freeze it. That’s what I do when I want to remove the pitch. It can break off as it warms up at a different rate to the night plaster.

Some people store it in the fridge. I haven’t tried that.

Rod

[mura_gadi (Steve)]

Thanks Rod,

Just poured a lap with mixed results, failed when I applied too much pressure too soon to the pitch and lost a lot of my main square channelling.

However, made a major score, remembered I had read about John D Upton using a "hot channel cutter" with good success.

Chopped the end off a medium screw driver and hit it with a blow torch. About 10sec of heating near the blue tip and it ate out the channels for about 1/2 the horizontal main grooves in one heat (8" lap).

Really neat, fast and without any mess. (I used a very long smooth tapering on the screwdriver end)

Hassles with rechannel are no longer an issue! Tyvm for your reply.

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In regards to the Stanley knife approach, have you tried metal flyscreens for a cold press fine groove on the squares? (or the green shade cloths?). I have just used a Stanley but wanted to try the flyscreen and forgot. Might be too uniform is my only thought.



Thanks
MG

PS. Nice tips for the tar breaking due to uneven defrosting rates, hadn't considered that at all. The wire brush I completely forgot about... must be getting to the "list" stage of life.

[Rod]

Hi Steve

Yes I’ve used flyscreen and it works but don’t use metal screening, it will scratch the mirror. Use nylon fly wire. If you overwarm the pitch you can pull a lot of pitch off and damage the lap. So I find the Stanley knife approach better for me. I prefer cold pressing to warm pressing so the knife suits that approach too.

A lot of this stuff is trial and error till you find a set of techniques that work well for you.

Rod.