Graphite plates for waxing quartz

[JohnA]

Hello all,

I'm not sure if I have revisited this forum since my return from Iraq but if not...Thank you to all who posted words of encouragement for me while I was gone. I came right back to my old job and fell back into the groove in no time.

This question is for those who have machined quartz or even who are currently machining it. The obvious problem in quartz machining is how to hold the stuff without breaking it. Typically we wax quartz to an aluminum plate and machine it that way, however, when the finished part is thin, it tends to break when the plate is reheated to remove the part. We have several methods to overcome this problem but I read elsewhere in this forum that graphite plates were used by someone else in the quartz industry. My question is this: Does graphite expand a lot when heated, relative to aluminum? Would using graphite drastically reduce quartz breakage upon reheat? I know graphite is ungodly expensive but the savings in broken parts might justify the cost of the fixture plate. Any responses are appreciated.

[kkominiarek]

Graphite will expand depending on grade, size, and temperature.

 

check out this link... thermal expansion

 

hth,

[Jaz]

This is kind of off topic but I'm curious. What kinds of parts are made of quartz?

[John Summers]

How about if you make the backing plate out of the same material?

[JohnA]

Quartz is used in high temp applications (1200 C or more) for growing oxide on silicon wafers (just one of the applications). Other materials will either off-gas and contaminate the wafers or melt at those temperatures. As far as using the same material for the backing plate, it is extremely expensive and will break or crack too easily when clamping. I was hoping that graphite was cheaper and not as likely to break when clamped. Thanks for the suggestions and please keep 'em coming.

[crazy^millman]

So I guess a bonding agent and debonding agent is out of the question huh?

[Keith Graydon]

Use a piece of ground steel for the substrate. Or lava rock.

Use Beeswax for larger pieces and Do-All Polymer wax for small pieces.

Heat up SLOWLY to bond and de-bond.

 

-Keith

[67 Yankee]

I have no experience working with quartz, but wouldn't a piece of granite be just about the perfect mounting? Should be easy enough to work into whatever shape you need, and dirt cheap. Seems like the thermal expansion should be pretty close to quartz as well.

[Jeff Kemper]

http://www.handyharmancanada.com/TheBrazingBook/comparis.htm

 

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thexp.html

 

looks like graphite is pretty close to quartz in tempco. a better option would be zirconia, but that's probably not too cheap either. re: backing plate breaking or cracking with clamping: you're cutting thin parts, right? how much clamping force do you need???

 

Jeff

[jmblack]

how about vacuum clamping?

[JohnA]

Thanks to everyone who responded. I think we're going to go with graphite and give it a shot. As far as vacuum clamping goes, the thin parts break as soon as the vacuum is applied...veeeerrry brittle stuff.

 

JohnA