Resin Addict Forum

I'm new here, so please bear with my ignorance and forgive errors of protocol! I have done some simple filled polyester casting using a vacuum chamber, but not for some years. I have been asked to produce letter stamps for impressing in clay, which can be stiff enough to need a tap with a mallet to make an impression. The easiest way to make the moulds is for me to carve them in wood (I'm am much more competent at carving than casting, believe me). The letters, about 20mm high, would them be sanded flat on their backs and mounted on wooden sticks to aid use. I doubt ordinary filled resin would be strong enough, but could I get away with some kind of toughner in the resin, if this does not make it too brittle. Otherwise I have seen urethane resin, which claims to be really tough; would this be a better bet? If none of these will work I guess I had better start looking at low melt alloys?

Hi dayzombie, welcome to RA!

So will this be used to stamp into cured clay? Certainly even a resin with a metal filler I wouldn't expect to be strong enough. You are probably going to have to look at things like metal machining to get that kind of strength.

Hi Mang,
No, not cured clay (and certainly not fired!) It will be used when the parts (usually bricks) are freshly moulded. I understand that the clay for this can be pretty stiff compared with what is thrown on the wheel, but nothing like it is when ready for firing.
Rus

Oh in that case I would expect plain polyurethane to be strong enough. You just need to make sure that the backing minimises any flex. At 20mm in height the letter details are going to be plenty large enough so that there's nothing fine that could potentially be worn out over time.

Thanks Mangozac,
I was intending to bed the letters on epoxy resin on the end of wooden handles, so that should avoid flexing. Is the urethane resin liquid or paste-like when it is ready to dump in the mould? Can I just spread it in and level it off? I assume I will need to treat the wooden moulds with something to prevent it sticking.

It would be good news if I could use resin. I have cast a few letters in low melt alloy (tin/bismuth) but the surface tension means there is loads of alloy to smooth off the back, and the stuff is hellishly expensive!
Cheers, Rus

I'm not completely clear on exactly what you're planning to do. You want to make a mould out of wood and cast the polyurethane into that? That's really not a good idea as even if you use a ton of release spray it will still be really difficult demoulding them from a rigid mould. You really need to make the letters out of wood, take a mould of them with silicone and then use the silicone to create the resin copies.

The polyurethane will be very runny when first mixed. It should be easy enough to smooth off the back - many place a glass sheet sprayed with mould release on top of the open mould to do this.

Yea Im lost as well.... I thought it was to make a stamp out of resin letters to stamp pottery with. this should be fine.

making a stamp out of resin should be easy and quick, although if your wanting to change the lettering im not sure a silicone mold would do as it would be expensive to make a new mold with every new set you need to stamp (unless your only making 2-3 different words).

I can refer you back to the "marking molds" thread where I was making a "stamp" for casting into molds and I think its similar to what your needing. you can make the words, stamp in clay. and them make a resin positive to stamp your ceramics with. you then can glue it to wood for backing OR just stick wood in the resin while liquid and when it dries it will not come off.

Now Im not 100% sure I know what your needing BUT If this is what your looking for Kinda I can help and advise no worries. If I got it wrong Please set me straight and I will also try to help out.