Well, I attempted to layup my first ski this last weekend and it turned out as a bit of a disaster. Here are some lessons I learned in hopes that others will not have these problems:
1. My press is a one ski press that uses square steel channel instead of I-Beams, and when I started pressing, I there were a few loud bangs. What happened is that the nuts I used to hold it together were standard grade galvanized fasteners, and their fit with the threaded rod was less than tight. Anyway, about 7 of my 9 cross-braces blew out when the threads on the nuts stripped away. Amazingly the press held together through the entire process without the cross braces. I have since purchased higher grade nuts that fit much more snugly and should solve the problem.
2. The core shifted on the base which pretty much made the ski unusable. I thought I had my mold set up well enough to avoid this, but I was quite wrong.
3. I used a mold made of MDF ribs with a sheet of thick plastic running over the entire thing. When the "ski" came out, it had a wavy cross-section from where it had been pushed into the gaps in the mold.
To solve this, I designed a new mold that uses a 2 1"x8"x8' boards stacked on top of each other with tip and tail molds made of 2x4's attached using brackets. (pics to come when i give a full report after the skis are done). I hope to produce camber by placing shims between the 1x8's and the press frame, and letting the bladder flex the 1x8's.
4. The epoxy and resin that only takes a few drops of hardener solution (MEKP I think) sets up really quickly requiring quick work.
5. Finally, and thankfully, if you screw it all up... It is pretty easy to rip apart a ski just after it comes out of the press and clean it up so that you can reuse the materials.
Hopefully next time will work out a little better.
Learn from my first failure!
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Sorry to hear about your troubles. Every one of our skis is a learning experience.
1. What size bolts are you using? We are using 1/2" bolts and threaded rods. Putting washers under your nuts and bolts would help too. Must have been scary when those went.
2. core shift is a tough problem. If you have enough overhang, you can nail the core down to you mold.
3. Our skis have a little waviness due to the ribs also. A good wet belt grind takes most of it out. We have 3/8" of melamine and a 1/8" layer of plastic on our mold and the ribs still telegraph into the base of the ski.
4. You may want to try epoxy instead of polyester resin. If it is that easy to peel apart, it will probably delaminate. On our last ski, I didn't let the epoxy fully cure, and the ski delamed by itself due to the stress in the tip curvature. Epoxy also doesn't smell as bad as polyester resin.
-kelvin
1. What size bolts are you using? We are using 1/2" bolts and threaded rods. Putting washers under your nuts and bolts would help too. Must have been scary when those went.
2. core shift is a tough problem. If you have enough overhang, you can nail the core down to you mold.
3. Our skis have a little waviness due to the ribs also. A good wet belt grind takes most of it out. We have 3/8" of melamine and a 1/8" layer of plastic on our mold and the ribs still telegraph into the base of the ski.
4. You may want to try epoxy instead of polyester resin. If it is that easy to peel apart, it will probably delaminate. On our last ski, I didn't let the epoxy fully cure, and the ski delamed by itself due to the stress in the tip curvature. Epoxy also doesn't smell as bad as polyester resin.
-kelvin
I don't plan on giving up any time soon, and in response to your questions:
Actually, while delaminating the ski wasn't terribly difficult, it did take quite a bit of effort, and the resin was still a little sticky in some spots. I think it should hold pretty well when complete. I had to chip the resin off the edges with a file and chisel where the epoxy had cured. By pretty easy to rip apart, I meant that it took me an afternoon to pull the parts apart and clean up the edges. The core still has some fiberglass stuck to it.
I was using 5/16" threaded rod, and while the regulator on my compressor read 35 to 40 psi most of the time, the bolts popped when I accidentally let it spike to 50 psi. As a side note, I think the pressure may have actually been higher because when I pushed on the fire hose, it felt a more solid than the 100 psi I run in my bike tires. Doubling up the nuts might have helped, and actually I think I might go ahead and double them up with the nuts I have left over.
Actually, while delaminating the ski wasn't terribly difficult, it did take quite a bit of effort, and the resin was still a little sticky in some spots. I think it should hold pretty well when complete. I had to chip the resin off the edges with a file and chisel where the epoxy had cured. By pretty easy to rip apart, I meant that it took me an afternoon to pull the parts apart and clean up the edges. The core still has some fiberglass stuck to it.
I was using 5/16" threaded rod, and while the regulator on my compressor read 35 to 40 psi most of the time, the bolts popped when I accidentally let it spike to 50 psi. As a side note, I think the pressure may have actually been higher because when I pushed on the fire hose, it felt a more solid than the 100 psi I run in my bike tires. Doubling up the nuts might have helped, and actually I think I might go ahead and double them up with the nuts I have left over.
I use polyester resin everyday in fabricating granite counter tops. I have some consern that the polyester is too brittle when cured for use in skis. I will be ordering regular epoxy for my build even though I have 2 5 gallon buckets of polyester sitting in my shop. The work time on polyester is very short, and unpredictably shortened/lengthened by the temperature of the work area. I will be curious to hear how durable skis assembled with poyester are. Good luck. Let us know. -J
Re: Polyester resins. I also have been told that when my granite counter tops are destined for use in a humid environment or if a shower surround is built from granite that true epoxy is the superiour adhesive. Apparently the polyester is not as tolerant of moisture.
I'm not bagging on you for using polyester, just sharing what I know or have been told. -J
I'm not bagging on you for using polyester, just sharing what I know or have been told. -J