was wondering whether I might be able to use the inner tube from a tractor tyre. What do you think?
I can answer you this one.
I build one of these. The widest tractor tube i got was 30 cm. So it was stil min. 10 cm to narrow.
I put a layer of PVC and sprinkled it with baby powder to get the tube expand easiliy. But the resaults were disastrous. It wouldnt expand at the tips (ends of the tube) because the top plate wasn't shaped to the rocker table. The tube first takes shape in the original proportions, only when is filled and the preassure starts to rise, it tends to expand. By that time the friction between the tube and other surfaces rises so much, that even with baby powder, the tube will not slide as you would want. It will find one or two places, where it is easiest for it to expand and it will do so on those few places, and there will be rincles between expanded and non-expanded tube.
You must close this press also from the sides, to get higher preassure, or the tube will expand out, or blow.
Fire hose is different, because it has that fabric around it to limit it expansion.
Overal, I made my worst board with this press! The first one I scraped, because it was not worth rebuilding.
Thanks Zob and Stan. You've saved me a lot of time and frustration. Nothing like real experience to go on!
A variation on the bladder idea that I have been thinking about is to replace the bladder with a bag full of sand
The idea is to cover the entire board with the bag of sand, cover it with a thick layer(s) of MFD and then use some sort of screw clamp set up (maybe attached to then of one or more I-beam sections like Stans) to apply the pressure. the idea of the sand is that it would flow over the contours of the board surface and help to distribute the pressure evenly. This would avoid the chance of having you're head ripped off by an exploding bladder/tube and get around problem of the uneven stretching.
Do you think this could work?
Also, how do you make the rocker table surface strong enough to avoid buckling under the big pressures? I was thinking about laminating several layers of 1/4" MFD, maybe 3 or 4 of them to make a solid surface. Would this work ? Is there an easier way?