Max Skis-2013
Posted: Sat Apr 13, 2013 7:09 pm
Hello!
I had attempted to build a pair of skis two years ago with mitigated results, but I got experience and it was a lot of fun! It was for a final project for grade 11, which is the end of high school here in Quebec. I had some other projects going on and didn't have time for skibuilding. I recently got back on it during the fall, and started profiling cores. I could not get a straigth core, it was always slanted laterally by 0.5mm. WOAH! Bad news.
So I completely redid my router bridges rails (and they were as perfect as possible) and did some further testing. I realized that my table was slanted, which made my router bridge and therefore made the cores slanted. I then rebuilt a new, and overkill, table which allowed me to get a straight core.
I had vacuum pressed my first pair at a local technical school, but I no longer had access to the vacuum setups as I had not decided to attend it in the end. One of my friend had built a pneumatic press, and he told me it was fully functional at 40 psi without any deflection. That would be perfect! But no, the press was complete crap. It was built with 2”x2” steel tubing, 8 inches wide. There were only 5 ¼” aluminium rods supporting the top steel tubings, and the bladder was the kind of stuff used to help kids float in the pool. I pressure tested the bladder, and it started leaking at 6 psi. I went to my ski hill, and managed to get some of the tubes used for the snow canons. They had extras, so they gave it to me for free thanks to my father who is in the ski patrol. I built a decent bladder with them and tested the press.
The supporting rods were bending like crazy at 20 psi, and the bladder was leaking quite a lot (I was at 10psi after 30 min).
I flipped all the middle sections laterally, added two other tubes and used some 5/16” annealed steel rods to have a more decent/usable and (I hope) much less dangerous press. It worked a lot better, and I did not have a significant amount of deflection at 40psi.
I bought some biaxial carbon fiber at 5.5oz, which were put top and bottom of the core, with some 2” wide strips of uni on either side. Poplar with maple sidewalls, profiled at 2.3-11.5-2.3 (I will verify the middle thickness when I will get back home; I am at my cottage right now). Wood veneer on top, with a polyurethane varnish to finish it up.
The pressing was a REAL PITA. It was one ski at a time, and the epoxy has a 12h cure at a minimal temperature of 25 celcius. But my basement floor is at 15, so as we had some electric house heat source, I used them to have a decent temperature! The bladder was still leaking, and I had no way to repair it. It was built with two layers of membrane, which made reparation of the inner membrane almost impossible. I had pretty tight deadlines to be able to present this pair at my school’s science fair, so I could not replace it in time to be able to press both skis before the fair. I pressed with this bladder, and had to restart the compressor every 30 minutes to be able to get enough pressure. Of course, my compressor automatic shutdown was broken, so I could not just leave it open (It is now repaired, and will be installed with another control valve soon enough). I did not sleep of the whole night. My Cal 3 class on the following day was really interesting…
To make the end short, I won second place and public’s choice at the science fair (350$ less to pay!!), and have been shredding the skis for about one month. They have minimal camber with rocker tip and tail, and (almost) no tip, which was not intended but rather resulted from the lack pressure during their cure cycle. It made them somewhat dangerous in the moguls, but it did not impact them on the groomed runs. I had a couple of other good skiers try them (aka level 3 and 4 ski instructors, etc…), and I skied them a lot. The main comment I got was that they are hard to pivot, as if the skis were too stiff torsionally. It seems that it always wants to set its edge and just follow the curve of the ski. It is also quite short, which makes for an interesting combination. They are super stiff, and the skis do not have that much length on which to bend, which sometimes made them “track”. I personally found that it was hard to be able to generate a lot of rebound in the transition between two curves, probably due to the combination of not enough length, and too great stiffness. On the other hand, they are really cool park skis, as they are super light and are stiff enough to be able to have a good edge hold on ice in between the sections of the park (that park design really sucks).
There are some more pictures on there, I will post some more soon:
http://s1312.photobucket.com/user/maxim ... sort=3&o=0
I just bought a planer, and will start playing with it as soon as I have some free time. I have started a pair of fat skis for a friend. I will keep you posted on that in the following weeks. Sadly, ski is almost over. But that means more building time!
-Max
I had attempted to build a pair of skis two years ago with mitigated results, but I got experience and it was a lot of fun! It was for a final project for grade 11, which is the end of high school here in Quebec. I had some other projects going on and didn't have time for skibuilding. I recently got back on it during the fall, and started profiling cores. I could not get a straigth core, it was always slanted laterally by 0.5mm. WOAH! Bad news.
So I completely redid my router bridges rails (and they were as perfect as possible) and did some further testing. I realized that my table was slanted, which made my router bridge and therefore made the cores slanted. I then rebuilt a new, and overkill, table which allowed me to get a straight core.
I had vacuum pressed my first pair at a local technical school, but I no longer had access to the vacuum setups as I had not decided to attend it in the end. One of my friend had built a pneumatic press, and he told me it was fully functional at 40 psi without any deflection. That would be perfect! But no, the press was complete crap. It was built with 2”x2” steel tubing, 8 inches wide. There were only 5 ¼” aluminium rods supporting the top steel tubings, and the bladder was the kind of stuff used to help kids float in the pool. I pressure tested the bladder, and it started leaking at 6 psi. I went to my ski hill, and managed to get some of the tubes used for the snow canons. They had extras, so they gave it to me for free thanks to my father who is in the ski patrol. I built a decent bladder with them and tested the press.
The supporting rods were bending like crazy at 20 psi, and the bladder was leaking quite a lot (I was at 10psi after 30 min).
I flipped all the middle sections laterally, added two other tubes and used some 5/16” annealed steel rods to have a more decent/usable and (I hope) much less dangerous press. It worked a lot better, and I did not have a significant amount of deflection at 40psi.
I bought some biaxial carbon fiber at 5.5oz, which were put top and bottom of the core, with some 2” wide strips of uni on either side. Poplar with maple sidewalls, profiled at 2.3-11.5-2.3 (I will verify the middle thickness when I will get back home; I am at my cottage right now). Wood veneer on top, with a polyurethane varnish to finish it up.
The pressing was a REAL PITA. It was one ski at a time, and the epoxy has a 12h cure at a minimal temperature of 25 celcius. But my basement floor is at 15, so as we had some electric house heat source, I used them to have a decent temperature! The bladder was still leaking, and I had no way to repair it. It was built with two layers of membrane, which made reparation of the inner membrane almost impossible. I had pretty tight deadlines to be able to present this pair at my school’s science fair, so I could not replace it in time to be able to press both skis before the fair. I pressed with this bladder, and had to restart the compressor every 30 minutes to be able to get enough pressure. Of course, my compressor automatic shutdown was broken, so I could not just leave it open (It is now repaired, and will be installed with another control valve soon enough). I did not sleep of the whole night. My Cal 3 class on the following day was really interesting…
To make the end short, I won second place and public’s choice at the science fair (350$ less to pay!!), and have been shredding the skis for about one month. They have minimal camber with rocker tip and tail, and (almost) no tip, which was not intended but rather resulted from the lack pressure during their cure cycle. It made them somewhat dangerous in the moguls, but it did not impact them on the groomed runs. I had a couple of other good skiers try them (aka level 3 and 4 ski instructors, etc…), and I skied them a lot. The main comment I got was that they are hard to pivot, as if the skis were too stiff torsionally. It seems that it always wants to set its edge and just follow the curve of the ski. It is also quite short, which makes for an interesting combination. They are super stiff, and the skis do not have that much length on which to bend, which sometimes made them “track”. I personally found that it was hard to be able to generate a lot of rebound in the transition between two curves, probably due to the combination of not enough length, and too great stiffness. On the other hand, they are really cool park skis, as they are super light and are stiff enough to be able to have a good edge hold on ice in between the sections of the park (that park design really sucks).
There are some more pictures on there, I will post some more soon:
http://s1312.photobucket.com/user/maxim ... sort=3&o=0
I just bought a planer, and will start playing with it as soon as I have some free time. I have started a pair of fat skis for a friend. I will keep you posted on that in the following weeks. Sadly, ski is almost over. But that means more building time!
-Max
