Rubber mold for pitch lap

[dark star]

Cutting the channels in a pitch lap for polishing a telescope mirror is always a nightmare. So I started to think about making a mold to pour the pitch in to, so it would already be formed in to squares with channels between them. Does anyone know how to go about doing this? Also where to buy silicone rubber if this is the right thing to use? I am aware that someone in America sells something like this, but ordering from America is not likely to come cheap, and I would find it interesting to do this myself. Although silicone rubber seems rather expensive!

David

[JamesF]

Could you do a sort of variation on the "lost wax" method, making a positive form in wax, then using that to make a negative and finally using the negative to make the pitch lap?  I imagine you might not need to melt the wax in this instance.

Perhaps this sort of thing would do for making the negative form?  http://www.ebay.co.uk/itm/Polycraft-Rubber-Liquid-Latex-Rubber-Used-Mould-Mold-Making-Masks-SFX-/230686264823

James

[JamesF]

If you only wanted a one-shot mould then perhaps you could use plaster of paris for the negative form, but I imagine it would be awkward to remove.

James

[laser_jock99]

Rubber car footwell mat?

[LeoLion]

How about kitchen sink matts (still to be found on Ebay !) :smiley:

[Glasspusher]

How about kitchen sink matts (still to be found on Ebay !) :smiley:

 Yes, they work fine. I have used one, see my thread about making a 12 inch mirror...http://stargazerslounge.com/topic/75093-making-a-12-inch-mirror/page-3

John

[dark star]

Actually, despite a lot of searching I have never managed to find a kitchen sink mat that would do! Plus my next project is hopefully a 20 inch mirror and I doubt I could find one big enough!

I have found a shop in the centre of London called Tiranti which sells sculptor's supplies including lots of different types of silcone rubber that can be used to make molds. Addition cure silicone seems to possibly be the right type.

There is no rush, as it is likely to be a very long time before I am at the stage of making a pitch lap for the 20 inch, I haven't got the glass blank yet! If I don't come along something I can use I will probably have a try at making the mold out of silicone. I could make a wooden lattice type frame to pour it in to. The beauty of it would be I don't see why it could not be used to make different sized pitch laps. In fact if I made it say 25 inches I could theoretically use it to make this size pitch lap as well (not that I am ever likely to do this!).

David

[fwm891]

Found this link:

http://www.pitchlaps.com/

[skybadger]

I tried the kitchen sink mat approach and found that when I went to remove it, it had buried itself below the surface of the pitch and lifting it out pulled away the edges.

I also found a rubber mat with circular holes punched randomly in it  when I collected some ATM stuff - seems someone else found that to work.

Car mat sounds a sound idea- pitch can't get through then.

Mike