[Bob Shaw]

Sounds pricey.

I've got a 20kg box of hot melt glue. I might give that a go.

[awerby]

I doubt that the glue would improve the machinability of wax much - if at all. It's rather gooey in its pure form, so it's unlikely to harden the wax. PLA filament is rather pricey I agree, but it's also available in pellet form much cheaper, as well as in the surplus prints I mentioned that seem to be proliferating out of control.

[Bob Shaw]

The stuff I've got is industrial glue for plastic (I think). Its very hard as it comes.

Having said that, its glue. So when it gets hot it gets tacky.

Worth a small batch just to see.

I agree about scrap PLA though. That sounds promising.

[crazybrit]

Bumping an old thread.

What are people using for molds?

I wouldn't mind coming up with reasonably accurate blocks (say 1*2*3) but I'm not sure if trying to create a mold of this size is the best approach?

I'd read the top surface will sag as the wax dries and so usually requires facing so the mold would have to be slightly taller.

I'm trying to do this on the cheap and so was thinking of just making something out of some scrap wood, maybe old melamine covered shelving but I'm not sure how easily the wax would release if the mold has a fixed bottom.

I've seen other people just pour into a large disposable aluminum baking pan and then hand cut.

[awerby]

Not sure about wooden molds, but if you try that and it works, let us know, okay? What I've done is recycle the blue machinable wax I've bought from places like Freeman supply using steel baking and loaf pans, depending on the shape I needed. The stuff shrinks quite a bit, so it releases easily. The problem is that if cools quickly, you get a sinkhole in the middle of the block, or at least a big dip. To combat that, I've put the pans in the oven filled with chunks, run it up to 300F or so to melt it, then turned it down to cool slowly, turning it off after a while and leaving it there until it's fully hard.

[Bob Shaw]

One thing to note is, I made a large flat plate (maybe 14" x 14" and an 1" thick) and after machining about half the thickness away in various places, the plate bowed upwards at the edges by about 1/2" each side.

Which meant that for the purpose of using it as a pattern for casting a resin 'negative' it was pretty much useless.

I think my issue was casting the wax in a thin plate and letting it cool naturally (i.e. quicky).

To avoid the internal stress I saw, it would need to be cooled much more slowly.

Or allowed to cool and then reheated to some 'stress relieving' temperature and held at that temperature for a while.

[routalot]

That happens with lots of materials when an amount has been machined away.It would probably be better to cast a slightly oversize version of the final shape you need and to add the fine detail at that point as you would be allowing much smaller forces to impose themselves.