Machining "Green" ceramics

[MogulTx]

Hey guys... what would you think about machining of green cast ceramics slightly before glazing and firing? Specifically- I am thinking about putting coffee cups onto an indexer and machining specific names into them before glazing and firing. It might be a way to take a specfic set up and add customization at a fairly low cost. What do you guys think?

Monty

(just a concept. I do not yet have the indexer- but i am looking for ways to justify affording one for my 08 PRS standard- and if the noise from that PC router could be dropped even a little bit- it might be worth the cost of a spindle/vfd!!!!!)

[knight_toolworks]

should work as long as you don't break or chip the pieces. they should be easy to cut.

[gene]

The noise level between a spindle and a router is definately worth it

[bill_l]

Monty,

I haven't tried machining after the clay has been bisqued but I have made 3D plaques by allowing the clay to dry to a "leather hard" state and then machine a relief using the Bot. Don't believe that this would work for a mug on an indexer but I might give it a try.

Bill

[steve_g]

Monty:

I recently learned (at the Austin ShopBot camp) that Marble can be CNC engraved with carbide bits. I haven’t tried it yet but I have bought several marble tile samples. According to Wikipedia, Marble has a hardness rating of anywhere between 2 to 5. According to the CERAMIC TILE INSTITUTE OF AMERICA, INC….

“The MOHS hardness for the bisque shall not be less than 4.0”

This was for tile Bisque fired at 1000 °F Sounds like the definitive answer as to whether or not this is feasible to engrave is … maybe.

I think you should try the cups with a custom jaw perhaps with similarities to the “simple Indexer” Photo I posted on the Austin camp thread.

Nothing ventured, nothing gained! Let us know…

Steve

[MogulTx]

Steve,

That is exactly what I was thinking (the simple indexer kind of idea). Are there plans out there for something like this?

If this is successful, I am also thinking about machining of more complex shapes of ceramic materials.

I was thinking that if an outside clamping /jaw/chuck arrangement could be accomplished from the base, it would have much less tendency to split while being worked. I wonder if it really needs to be green fired first or if it could be sculpted then green fired... then glazed...?

I guess I need to find a a plan for a imple indexer and put one together and learn how to rotate parts while cutting!

[steve_g]

Monty:
I made mine “flying by the seat of the pants”
You’ll need a stepper, Driver, and cables. I chose my stepper/driver combo based on what was already on my shopBot, that way if I was totally disillusioned with the results… I would at least have spare parts! In my case, I needed a Alpha Stepper/driver combo. I found them on EBay. For my first iteration I chose to use a motor direct drive, no gear or belt reduction. This worked fine for very light engraving on bracelets, but not when I tried some heaver material removal… the router bit overpowered the stepper and spun the project. Second Iteration involved a 10:1 gear reduced stepper purchased from a fellow ShopBotter who had listed items on the forum (the best source for compatible parts and support). I don’t know what variety of bot you’re running , but in my case I needed two cables; one from my control board to the driver and one from the driver to the stepper. I foolishly figured that since the cable to the stepper didn’t need to be super flexible (this axis wasn’t moving the cord), … I made up my own. I’m an experienced electronics assembler with proper tools for making up cable assemblies but had no end of difficulties with the pins and shells used on the OM motors/drivers. Buy them from ShopBot.

I hope this gets you thinking and moving in the right direction!

Steve

[paul_z]

I'd be concerned about the ceramic dust. It is a significant heath hazard (silicosis). A lot of the dust will be too fine for normal dust collection systems to trap it.

It may also destroy your bearings. A few years ago I had to destroy 10 2'x2' fiberglass molds. We bought a bandsaw just for this task. It took about an hour to cut up the molds. We used a 2hp dust collection system which exhausted outside the building. The saw looked fine when we were done but every bearing was damaged and some had seized up. The saw was junk (as expected).

[MogulTx]

Thanks Paul. Dust is an issue, and can do a bit of damage, for sure.

[Acmeaviator]

I'd like to hear how your experiment turns out - my wife and I own 12 Paws Pottery and I am the business manager at Funke Fired Arts here in Cinci. I've been thinking of trying the shopbot on some leather hard slabs like a previous poster has done or on machinable wax to create positives for casting negatives of slip casting molds. Imho and experience machining bisqueware is going to present many challenges - the least of which will be the dust. I would give consideration to:

Mounting points and pressure
tool speed and type
any heat-work added by the cutting
lubrication (if any oil gets on bisque it will need to re-fired prior to glazing as it will act as a resist)
the advantages of carving on bisque as opposed to other techniques such as embossing or carving leather hard clay


Please continue posting on this and let us know how it goes:)

[myxpykalix]

One thing you will need to be aware of is vertical and horizontal pressure exerted by the indexer to hold the piece and pressure on the part from the bit.
I encountered this when trying to cut my hollow spirals. To compensate for this i created large dowels that fit into the empty cavity inthe center so that when the bit went thru it didn't just break the spiral from lack of structural strength.

I know you are not going all the way thru but if i was making cups I would have a wooden plug that was as large as the inside diameter of the cup to support it so that the lateral pressure needed to hold the cup in did not collapse the cup

[feinddj]

As far as holding the mug, any four jaw chuck for wood turning will do. Just make a set of jaws that are as deep as the mug in the same profile. using the jaw as an expansion will hold it quite well.

David