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Before you get yourself deeply involved it may be worthwhile figuring out how much thermal expansion you get with the wax before it melts; the shrinkage you see on cooling is partly reflected as expansion on heating. It would be annoying to say the least if you wax pattern shattered your ceramic coating when you heated it enough to get the wax out.Originally Posted by cbass
...I'm in a similar boat to Charper. I will be melting the wax away after I cast around it (hopefully avoiding the need for multiple-part molds....
I hadn't even thought that far ahead
I gues that opens a whole new ball of wax (pardon the pun).
The aproach may very well be to work backwards. Find a wax that doesn't expand too much (ie. a wax made for the lost wax process), then see if it machines.
Carlo
If shrinkage and resulatant crater is the only problem when cooled quickly, you could easily get around this problem and still cool the wax fast. The problem is caused by the center retaining heat and remaining n a liquid state as the edges cool. Because the depth starts high due to the expansion of the wax, the edges cool in the high level. As the wax cools and shrinks, less wax is available to keep the level up. What if you cooled the center?
A peltier(sp?) cooler the center of the pan rests on will cool/chill the center quickly. It may actually form a mound if cooled too quickly. With some experimentation I believe strongly that the crater problem can be addressed without long cooling periods needed at all.
Just use regular lost wax wax but set your machines up in a deep freeze and wear warm clothing.
Not a bad idea LOL.Just use regular lost wax wax but set your machines up in a deep freeze and wear warm clothing.
Actually, cooling the wax before machining may help if it proves too sticky/gummy at room temperatures.
How experimental do you want to be? I have often thought that sawdust reinforced wax might be a good material for making molds for plastic; one advantage would be you already have the mold release agent as part of the mold. I figured take ordinary candle wax that is quite low melting and stir in as much fine sawdust as possible then just let it set. My feeling is that there would be less shrinkage than pure wax and the strength should be much greater. The type of surface finish possible when machined would probably depend on how fine the sawdust was.
Great idea, Geof, I think MDF dust would make an excellent filler. The correct wood/wax ratio would have to be ascertained when using the material for lost wax casting so that it would all get melted/burned out before casting. Though, for goofing around, testing, and prototyping I'd bet a fairly high wood/wax mix could be used. You'd need just enough wax to keep everything together during the machining process.
Back about 10 years ago while I was working at a custom injection molding operation they were testing HDPE/PP coupled with a wood filler. The molded parts looked and felt really nifty. The smell, though, would make you nauseous, even weeks after being molded. These parts were for a company that made office furniture. I couldn't imagine being trapped in an office with the wood filled plastic parts for any length of time. I guess they couldn't either as the project fizzled out before the parts ever made it to market.
HayTay
Don't be the one that stands in the way of your success!
Has anyone thought of, or tried.... drum roll, please... CRAYONS?
I was browsing through the local 'Mighty Dollar' store while my wife was picking out some birthday cards and came across a whole display rack loaded down with packs of 64 crayons for, you guessed it, $1.00 US. The pack, I'm guessing, weighed maybe a half pound. Not bad for a dollar.
Upon further inspection, the crayons seemed to be fairly hard. Anyone who has used crayons know that they run the whole gamut from soft (turn pliable with just the heat from your hand) to extremely hard (after some effort they break with an audible 'SNAP').
Melting all of the crayons together would, no doubt, produce an "ugly" colored block, but would it be suitable for machining? Any thoughts???
If crayons turned out to be a viable solution, someone that worked for a school (hint, hint, nudge, nudge, CHARPER) could probably start a 'Crayon Recycling Program' in the lower grades and obtain the wax for almost free. The only problem is getting volunteers to "peel" all of the crayons before they're melted.Heating or soaking the crayons in water would probably expedite the wrapper removal process. Heating would have the added benefit of kick starting the melting process before the crayons are mixed with any hardeners or fillers.
I've seen crayons available in bulk packs with as many as 3000 pieces, yielding crayons at around 3.5 cents a piece. The 'Mighty Dollar' is still less expensive at approx. 1.6 cents per crayon, though. Suppliers to educational institutions may also offer other incentives, packaging, or discounts for large purchases that aren't available to the public.
Other types of crayons are also available. Several that come to mind are marking crayons and lumber crayons. Additionally, my father used to work in a steel mill and he used marking sticks that melted at specific temperatures to write on the steel. I don't know if they are classified as crayons, or how much they cost, but some of them were so hard (high melt temp.) that when broken they crumbled into chips. These wouldn't be good for machining but the lower temp. ones might be. Just a few of my thoughts, for now.
HayTay
Don't be the one that stands in the way of your success!
so crayons are made of paraffin.....machineable wax appears to be a synthetic wax.....paraffin can be burned out in lost wax castings....not sure about the synthetic wax....
As a bonus, crayons are also non-toxic.
DixonUSA Prang Wax Crayons MSDS
Binney & Smith Crayola Crayons MSDS
Speaking of crayons, here's a funny story from my childhood. When I was a kid, my sister and I had to make sure that we put away our crayons ASAP when we were finished using them. We also had to keep our crayon stashes in a couple of old metal lunch boxes complete with latch. We colored a lot and the lunchboxes were usually full of a wide variety of crayon colors and sizes. Our dog Smokey, half Husky & half German Shepherd in case anyone is interested, was the reason we couldn't leave the crayons laying about. Smokey just loved to eat them, color or brand didn't seem to make any difference. Losing a bunch of used, stubby, warped crayons to Smokey wasn't too bad, but the unopened box of 64 Crayola Crayons with sharpener and 'NEW' colors, left under the Christmas Tree, was another story.
One of the interesting side effects of Smokey's crayon eating was that she used to crap in Technicolor. No kidding, there were all kinds of colorful 'lawn sculptures' in our yard after a crayon eating frenzy! Nothing like a little extra color for the Holidays (Christmas, New Years, Easter, St. Patrick's Day, Fourth of July, etc., etc.)
There was one plus, however, it made it easy to locate the colorful piles for disposal or avoid the 'land mines' when playing in the yard.
HayTay
Don't be the one that stands in the way of your success!
you guys scare me
I LOVE IT!!!!
crayons... It would make a great experiment to try the crayons with varying levels of PE film to get a great consistency..but only after the machineable wax success because I
still haven't made the machinable wax...I need to buy a small stove, my oven isn't getting hot enough and it made me so frustrated, I just quit trying. I have been such a slacker these last 6 weeks.
"Craft is What I do All Day. Art is what I have at the end of it" Jean Weller
Just wondering how much success has been had with this. I worry that wax flash point is 230F and polyethylene mealting point is 270-275F. People have been talking upto 400F.
How often has this been done and without accident?
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