types of optic molds

[Ray Laubs]

Ive been toying with the idea of getting some optic molds made out of good ductile cast iron. The thoughts I have concerning the materials used to make them are thus:

regular cast iron or steel will scale more easily. Iron based molds need to be cleaned as rust can occur, perhaps a real light shot of vegatable oil as a preventive.

ductile will not scale as easily, cost more per pound than reg cast.

aluminum will sap the heat out of your gathers, all the heat sinks Ive ever seen are made from aluminum. I used to weld about every type of metal and know that the heat transfer in aluminum is phenominal.

bronze is smooth, cost alot, and doesnt rust, less cleaning

Anyone care to add to all of this?

[Jon Myers]

chilling the glass is why I go into a optic mold. (but I could be doing it wrong)

[Dave Hilty]

Originally posted by Jon Myers
chilling the glass is why I go into a optic mold. (but I could be doing it wrong)

Most of the postings here have talked up the wonders of finely cast brass optic molds. I've only ever used Steinert cast aluminum & I'm wanting to try something in brass for the same reason that Ray hints that aluminum chills too quickly. If the brass doesn't suck (transfer) the heat as quickly as the aluminum then the parison would conform to the shape & fill the points rather than chilling so fast that you never fill the voids.
You can always go in hotter but then its harder to control & easier to blow too thin up close to the pipe.

Which material has the slowest rate of heat transfer?

[Ray Laubs]

Originally posted by Dave Hilty


Which material has the slowest rate of heat transfer?

Thats a good question. I know at the foundry, cast iron melts slower than the steel we charge as a base. On that note, I would assume that cast iron has a greater resistance to heat transfer.

[Michael Stoddard]

We keep our big cast aluminum mold next to the oxy-propane torch and blast it with that for a few seconds if we want to avoid excessive chilling. Works great. I'd still do it with other metals, too. On the down side you have to have two people in the shop.

[Kenny Pieper]

Surface texture, shape and rib detail are much more important. Cooling of the glass has more to do with how long you spend in the mold than the material that it is made out of. The filling of the mold correctly has to do with the setup of the bubble and glass temp. I would never want a mold that could rust!

[Greg Frankhouser]

I'm like Kenny. I use the mold TO chill the glass. Gather, 1-2 block rolls, sloppy into the mold, out and still have some working time before re-heat.

I've never learned how to blow INTO an optic, only use it to form the bubble that I blow out later.

YMMV

Greg

[Greg Frankhouser]

Just another thought. If the mold were made out of "rustable" metal, couldn't it be waxed?

I used to work out of waxed cast iron block, could that not work for an optic?

Feel free, I could be missing something.

Greg

[Dave Bross]

I use cast iron blocks. I spray and then wipe the blocks and other tools with aerosol cooking oil after use and they're fine. Humidity and rust are major issues here too (Florida).

[David Patchen]

Cast iron *blocks*? Not wood? Do you mean 'optic molds'?

I've never heard of iron blocks. Sounds heavy and heat killing.

[David Paterson]

Where can you purchase cast iron blocks?

[Sky Campbell]

Tom Furman was selling them a couple of years ago. He designed them and had them cast. I have several sizes sitting behind the back of the marver. I keep them lightly waxed and they work great for some of the production items I make.


Hello Tom where are you?

[Jeff Hoover]

Tom seems to have redone his website ( http://www.fuhrmanglass.com ) recently and eliminated the page with the iron blocks. They used to be $22 and $32.

[Dave Bross]

They were a one time deal when a friend of Toms' was teaching iron melting in a craft/vocational course.

Might be a good Tom and Ray joint project to create some more? I've been thinking about talking to the little foundry here about doing some more, but Ray seems better positioned to to get it done than I am. I would definitely buy more if I could get them. Tom was charging around $20 for them.

They do cool the gather and that's part of what I like about them. About the same amount of cooling as a wet wood block. They were pretty common in the old W. Virginia style of working.

Tom just got back from England so he may be busy catching up.

[David Patchen]

Sounds perfect for students. "Try burning the crap out of this block kid"

I'd be curious to turn a gather in one. Were they super heavy or very think so not bad?

[Scott Dunahee]

They're table or marver blocks. The block stays stationary and you move the glass in it. They are awesome.

They are solid cast iron so quite heavy.

BSD

[Larry Cazes]

Are they lined with cork?

[Scott Dunahee]

beeswax

BSD

[Dave Bross]

Or your favorite flavor of spray cooking oil.

Once they get a slight bit of any kind of carbon in the pores of the working surface they work just as slick as can be.

Makes me wonder if an iron optic wouldn't be a very sweet thing for the same reasons.

[Larry Cazes]

Ahh....seasoned like a great old skillet.