Ski Builders Forum

chrismp wrote:

gav wa wrote:I have some epoxy that is 65 shore, not brittle at all and costs only $160 for 6 kilo.

Sounds interesting. What shore scale is that hardness on (A or D)?

I had it wrong in the first post, it is 65D. Did some test runs and definitely harder than 65A.
Probably could be better if a little softer really.

dbabicwa wrote:
PS
Smooth 310 trail package 1kg I've paid $30.

If I could find a kilo pack of 310 here in Perth for $30 I would probably use it.

gav wa wrote:

dbabicwa wrote:
PS
Smooth 310 trail package 1kg I've paid $30.

If I could find a kilo pack of 310 here in Perth for $30 I would probably use it.

We can always split the shipping charges

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.

chrismp wrote:Get a big sturdy old cooking pot (I use an old pressure cooker with a 20mm thick polycarbonate lid). Cheap and easy to get.

Something like this?

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).

Hi,

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.

Cheers
Philipp

Hi,

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?

http://www.smooth-on.com/technical_tb.php#plastic

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.

Hi,

read in this forum that a shorter pot life reduces bubbles, thats why I was searching for a faster PU.

The thought that was mentioned was that if the PU kicks faster it has less time to interact with humidity and so on => less time to form bubbles.

On the other hand: the fact that bubbles appear as the kicking starts speak for your theory.

But what would cause the PU to bubble? Part A + B mixed and and cast shouldn't bubble by itself?

So, are there any experiences if a faster PU tends to bubble more or less?

Cheers
Philipp

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.

Also asked the distributor here, the answer was quite clear:
- Vacuum the resin before pouring
- Take one with a longer pot life

@chrismp:
Where do you get the Adiprene from?

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.

30kg? How many Skis are you building? ;)