The pouring urethane sidewall thread

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gozaimaas
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Post by gozaimaas »

MontuckyMadman wrote:Why did you use al?
Weight issue?
Scrap material?
Seems like steel would be cheaper and easier.
Primarily weight.
Steel would not be any easier, it would in fact be harder to cut and fold, you might get away with a few less braces but thats about it. A steel box would be too heavy to move around by myself.
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dbabicwa
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Post by dbabicwa »

chrismp wrote:@dbabicwa: thanks for sharing your findings! We always degas the resin and hardener seperately before mixing them...this also reduces the amount of bubbles. How did you seal the channels in your samples?
With epoxy sealer, two coats.

The bottom example was sealed but than slightly sprayed with a hair spray.
Didn't leave it to dry hence extreme foaming...

The word from a kiteboard factory is they do not seal Paulownia wood, they just use fast PU. I don't think they pressurize it latter.

You can see this on Cabrinha video posted on my links at Aug 22, 2013 5:10pm.

I think that epoxy is good, but PU is better.
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MontuckyMadman
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Post by MontuckyMadman »

prolly easier to get a pressure vessle. Like a big tube maybe.
Big and heavy.
My AL tig welding is not as good as yours, and yours was sorta blown out at the ends of the welds but kick as job and I'm glad you are getting near perfect results.
sammer wrote: I'm still a tang on top guy.
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tufty
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Post by tufty »

MontuckyMadman wrote:prolly easier to get a pressure vessle
Significantly safer, too. Rectangles are really dded stupid and dangerous shapes to be putting large amounts of pressure into. Compared to tubular or spherical containers, you're concentrating large amounts of force into very localised areas (hence your steel angle bending like it's made of putty and you're plywood box exploding at around a bar of pressure). I would be *extremely* worried about unseen stress fractures after much use.

Very nice tig work, though.
gozaimaas
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Post by gozaimaas »

MontuckyMadman wrote: yours was sorta blown out at the ends of the welds
Not sure what you are referring to there, I am quite capable with the pedal and the welds aren't too hot near the ends which is a common problem for new players when tig welding
gozaimaas
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Post by gozaimaas »

tufty wrote:
MontuckyMadman wrote:prolly easier to get a pressure vessle
Significantly safer, too. Rectangles are really dded stupid and dangerous shapes to be putting large amounts of pressure into. Compared to tubular or spherical containers, you're concentrating large amounts of force into very localised areas (hence your steel angle bending like it's made of putty and you're plywood box exploding at around a bar of pressure). I would be *extremely* worried about unseen stress fractures after much use.

Very nice tig work, though.
There is no denying a pressure vessel is ideal. In my case (and probably most peoples) however it is not a workable solution.
I have achieved a good result here and posted all my failures along the way so others can learn from it and not make the same mistakes
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falls
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Post by falls »

Would it work the same drawing a vacuum rather than creating a high pressure environment in your tube? Vacuum might not deform as much and you could use a thick PVC pipe as your pressure tube? Your way looks to be working well though.

Dbabicwa: looks like some nice bamboo plywood you have. Whereabouts did you get it? I'm down to my last 2 bamboo floorboards and looking for more. Thanks.
Don't wait up, I'm off to kill Summer....
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dbabicwa
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Post by dbabicwa »

Falls,

bamboo sheets are 1220x1800x5 locally here in Perth. $120 each :(
ben_mtl
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Post by ben_mtl »

I'm almost ready to give the PU sidewalls a try, I have a (maybe) stupid questions for those who already use this method :

My plan is roughly : take a core blank, cut a channel on the CNC leaving a thin skin on the "bottom", pour the PU, run it though the planer to remove the "skin" and clean the surface on which the PU was poured, put back on CNC (or on planer crib), profile the core to thickness, DONE ! Basically the same method as DTrain from my understanding.

For the details now :
This method obviously wastes a lot of PU rubber, especially for skis where the thickness difference between the tips and the the binding area is quite big.

Here are the 2 methods I have in mind to reduce the waste, please let me know if it's already been tried and if it was useful or a total waste of time. Let's assume my core thickness is roughly 2mm-12mm-2mm.

- Put core blank on the CNC (planned both sides)
- Machine the sidewall channel leaving a thin skin all around
- Put shims under tip and tail (±8-9mm thick) and keep binding area flat against the CNC bed
- Pour the PU (the tips will get less PU than the bindings area if the PU is quite "liquid" and "self-levels", I don't know yet)
- run through the planer to remove the "skin" and clear the top surface
- Put back on the CNC (flat)
- Profile to thickness
- Done !

Another option would be :
- Put clean core blank on CNC
- Machine the channel full depth in the bindings area, but shallower (3/4 mm) in tips and tail (progressive transition of course, same "profile" as the desired final core profile)
- Pour PU
- Clean top side on the planer
- Top side becomes bottom side
- Profile to thickness
- Done !

What do you guys think ?
A bad day skiing is always better than a good one at work...
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chrismp
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Post by chrismp »

Both methods should work. I've tried the second one with success. Just make sure to make the channel 2-3mm deeper than the final sidewall thickness to leave some room for error.

I'm back to routing a full channel though since I found generating the necessary toolpaths more of a hustle than spending a few bucks on PU. ;)
Dtrain
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Post by Dtrain »

Ben,

If your using the 790. It is pretty thick. You can just do your full channell, and pour less in the tips. The stuff won't run like water. Just make sure your on a perfectly flat surface. Do basic first, and then see if you advanced ideas are worth while.
ben_mtl
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Post by ben_mtl »

Dtrain wrote:Ben,

If your using the 790. It is pretty thick. You can just do your full channell, and pour less in the tips. The stuff won't run like water. Just make sure your on a perfectly flat surface. Do basic first, and then see if you advanced ideas are worth while.
I'm gonna keep it simple first. I was just trying to optimize the quantity so I could get 2 pairs of skis done from the 1.5 Qt kit :p
A bad day skiing is always better than a good one at work...
Dtrain
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Post by Dtrain »

A person could theoretically route his profile upside down into the core. Sidewall only.pour.plane to flat. Flip it over and profile. I dare someone to try.

Yesterday I wrecked my new core on the cnc. stupid human error. All that time and money wasted. It never gets easier. It's always something. My ski building slogan ha become

"tommorows a new day"

I might have to put that as my next base graphic. LOL
gozaimaas
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Post by gozaimaas »

I did another core yesterday and packed up the ends 8mm before pouring to create a low point in the middle. This worked perfectly to reduce the amount of waste PU in the tips.

I start with a 20mm core and rout a trench 16mm wide and roughly 17mm deep, dont try to cut too close to the bottom.
I then fill with PU to a few mm short of the top, place it in the pressure chamber and leave it to cure.

The board I did yesterday is a 175 and I mixed 700ml of PU which was more than enough.
I am going to work out a system where I can predict how much PU I need to mix by running a piece of string along the inside edge of the trench and applying the formula to this measurement.
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dbabicwa
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Post by dbabicwa »

ben_mtl wrote:
Dtrain wrote:Ben,

If your using the 790. It is pretty thick. You can just do your full channell, and pour less in the tips. The stuff won't run like water. Just make sure your on a perfectly flat surface. Do basic first, and then see if you advanced ideas are worth while.
I'm gonna keep it simple first. I was just trying to optimize the quantity so I could get 2 pairs of skis done from the 1.5 Qt kit :p
I would use 310.

790 is rubber. 310 is plastic. 790 is quite soft. 310 is hard as.

After that try fast one like 305 as gozaimaas is using.
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