I built a steam box to bend cores. I'll be using it on my next set of cores. The box is designed to put 1/2inch camber into the each ski. The Box holds 2 cores side by side. It's designed to hold up to 3 pairs but right now I have it built for 1 set of cores.
I haven't sourced a heat/steam supply yet and have not cut out an access hole for the steam. Once I decide on that I'll post another pic.
It's a pretty simple design. I use 3/4inch exterior grade plywood. It measures 12 inches wide and 78 inches long. The top opens with 3 hinges. I used 1/2inch threaded rod left over from the ski press to bend the skis. I just remembered I have a set of metal folding table legs left over from another project. I'll attach and post pics later.
I also tried to calibrate points of reference where the rods should be placed over/under the core to get the proper bend. My thought is to have the center rod at the boot center of the ski so the apex of the camber is under the boot center. That's also matches up with my ski press. The other rods are placed at the point where the tip and tail start to bend up, basically the point of contact of the running length. I normally mark the core up where the tip/tail should start as well as the boot center, so I could use those points of reference as well.
I did some reading on steam bending and figure about 30 mins of steaming. Then I'll leave them in the box until dry..... probably over night/next day.
If all goes well I'll be steaming them in the next day or 2.
An interesting idea, pre-bending the cores, but I don’t understand why you would want to do this. I’ve built several excellent skis over the past three years and none have lost their camber. Some skis have over sixty days use and still rock.
The camber (and tip/tail bends) are predictable and come out as expected. The finished skis closely match the press form shape. The sandwich structure is cured in the press and stays set in position. The core materials are forced to comply and the composites hold their shape.
All my skis have vert bamboo cores with triax glass and uni carbon strips top and bottom. All made with QCM epoxy and heat cured (an essential process, IMO).
I would convert your steam box into a ski wax hot box. I think it would be more useful for that purpose.
But what the hell, if you want them pre-bent, more power to ya.
Cheers,
-S http://www.skinet.com/skiing/how-to/diy ... -a-wax-box
This is more of an experiment than anything else. The skis I've made have kept their camber after pressing, but I press at room temp and the skis lose some camber. I should have about 3/8-1/2in camber but I get about 1/4 inch or less out of the press. Losing that little bit of camber is not a killer but I'm hoping that by pre-bending I'll retain more of it and maybe gain a little more pop. But who knows, the press may negate the pre-bending.
From what I've read a heat blanket will fix that problem.... Just not there yet in terms of $$$.
If the steam box doesn't work out, I like the hot wax box idea. I'll let you know if it's worth the hassle.
skidesmond wrote:TI press at room temp and the skis lose some camber. I should have about 3/8-1/2in camber but I get about 1/4 inch or less out of the press.
Do you have the same number of layers of fiberglass above and below the core?
Yes, triax above and below. Also on the last couple I made, I check that the fiberglass faced the correct way above and below the core too. I think you had mentioned that in a previous post.
skidesmond wrote:Yes, triax above and below. Also on the last couple I made, I check that the fiberglass faced the correct way above and below the core too. I think you had mentioned that in a previous post.
Ha, yep, that's what I was fishing for here. That's good your covering your bases.
I think I found one of the reasons for lost camber. While working on the press today I measured the deflection in the beams. The bottom beam flexed about 1/8+ inch. I thought I could live with that much deflection but maybe not.
Well the steam box is already built....... might as well complete the experiment.
Maybe need to re-do the bottom form to give more profile OR and more support in the middle of the press. Adding more support is probably the right thing to do.
My buddy has some more 4inch U channel that we'll be using to beef it up. Probably add 2 more supports and rig it so the front opens downward.... use HD pins or bolts to hold it up....
Update.... Finally rigged up a steam source after the first attempt didn't go so well. I first used some extra wet/dry vac hose to run the steam into the box. The steam nearly melted the plastic. That was a bit of a surprise. I didn't realize the plastic is that weak and an adapter I was using for the hose deformed. So it was off to the hardware store again where I bought a length of re-enforced rubber hose, 1inch OD by 7/8 ID. That worked better.
As for the steam process.... Well this experiment maybe over. I was able to produce steam even from that little tea pot (pics below). The skis did get hot and steam did flow through the box but it certainly did not billow. Not sure if billowing steam is necessary.
I was bummed to see the warping of the tips and tail. I don't think the cores are usable. I'll wait till they cool down and see if the cores retain the camber.
Here's some pics from today (the camera date/time is wrong):
Wisps of steam
Steam Box set up:
warp-age!!
Melted part:
Steamed hotdog anyone? That's Ruby our 2 year old dachshund. I can't work outside with out her wanting to play ball.
The steam box will probably be dismantled and be made into a new planer crib (as long as nothing warped).
It's officially over...... The cores did take on camber...... in every direction!!
Camber:
warped tails:
warped tips:
So the gas tank is hooked up to the grill where it belongs. The tea pot is back in storage in the basement. Ruby is glad it's over too.... time to play ball.
Adding more support is probably the right thing to do.
