One of my boards got put to the test recently with a massive impact. The top sheet has a crack in it but the sidewall is perfect.
If the 305 was ever going to crack it would have been on this board.
That would work but it's overkill imo. A sturdy cooking pot is sufficient and you get the bonus of seeing what's going on inside if you use a polycarbonate lid. Just check your local classified ads and I'm sure you'll find one for a couple bucks (I paid 10 EUR for mine).
did anyone try the Smooth-On 300 instead of 305/310? Did a test with 305 today and the 7 minutes pot life seemed looooooooong. Less than half of it would be enough for me.
As far as I understand, a shorter pot life would make less bubbles.
had a look at all the Smooth-On products. And I found 65D. It has a very short pot life of 2.5 minutes, so something to work quick :)
What I like about it compared to 3xx: A bit softer (65D instead of 70D) and a much higher elongation break of 20% (instead of 5/7.5%). And it costs exactly the same. Sounds good, doesn't it?
From my exprience the bubbles are caused by the heat generated as the urethane starts to kick. A shorter pot life may mean it kicks harder/faster? If this were ther case I would expect more bubbles.
IMO as it kicks it gets hot and this is when the bubbles form. Its quite an aggressive process.
I reckon something slower would generate less heat and produce less bubbles.
Not to harp on lol but the answer IS a pressure chamber guys. Invest, enjoy incredibly dense sidewalls and move on to the next problem.
The company I buy my PU at is an expert at anything PU-related. They pour parts all day long. I've had a few discussions with their lab technicians about the bubbling and they said it's usually all moisture related. Curing parts under pressure just shrinks the bubbles, but they're still there. When they're pouring large parts which do not fit into one of their pressure chambers, they set up a room with a de-humidifier. The tips they gave me were to seal the channel in the woodcore and to pour the sidewalls in a room with low humidity.
I thought about building a pressure chamber, but I would rather use a piece of pipe than a rectangular box. Kind of a waste of space but much safer. But then again, I get good results with the species of wood I use the most even without sealing the channel.
I buy it at www.asma.at. They usually do castings, but they were kind enough to sell me some. I always buy large quantities (30-40kg) though, cause it gets much cheaper then.
