knot my skis
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
knot my skis
punched out a couple pairs of skis this week for some friends. still using high-quality wood as usual .
sprinkled one pair with a touch of aluminum, and glitter too.
cooked them in the press at 190F for one hour. i'm using a zero-camber mold. after cooling to room garage-temp, skis came out with 15mm of camber. outside temp has been cold lately. but smooth looking camber i must say. good flex.
shape is based on the Kaweah. ski shown above has max core thickness of 10mm. second ski is 14mm. wood is mix of fir and pine.
i'm working on another pair right this minute. should finish by wed., then out on the snow by Sat....
sprinkled one pair with a touch of aluminum, and glitter too.
cooked them in the press at 190F for one hour. i'm using a zero-camber mold. after cooling to room garage-temp, skis came out with 15mm of camber. outside temp has been cold lately. but smooth looking camber i must say. good flex.
shape is based on the Kaweah. ski shown above has max core thickness of 10mm. second ski is 14mm. wood is mix of fir and pine.
i'm working on another pair right this minute. should finish by wed., then out on the snow by Sat....
nice looking pair! can you explain a little more how you did the grafic?
i just built a ski made of fir too...didn`t you had any problems with the knots?! as i cut my wood the knots sometimes fell out. and i really can`t use a wooden stripe with a hole in it, right?!
furthermore: did you build something special to enforce the binding area? i am a bit concerned about this because my fir is pretty soft...
cheers
i just built a ski made of fir too...didn`t you had any problems with the knots?! as i cut my wood the knots sometimes fell out. and i really can`t use a wooden stripe with a hole in it, right?!
furthermore: did you build something special to enforce the binding area? i am a bit concerned about this because my fir is pretty soft...
cheers
plywood freeride industries - go ply, ride wood!
cheap and crappy is right! . but seriously, i haven't noticed much of a difference in terms of durability between super-duper high-quality and low-quality wood, except of course, the dent that high-quality wood makes in my bank account. keep in mind that wood does affect the overall weight of a ski, snap, and other characteristics. besides, my skis delam way before the knots become a problem. i put in about 10 days of ski touring on each new pair and i beat them up.
the two new pairs were gifts to friends. they were visiting this past week and wanted to learn to build skis, so i helped out. it was really fun showing them how to build skis. my favorite part was watching them bend and glue the edges. their smiles were bigger than ever when it was time for lay-up, and especially when the final product came out of the press! .
the graphic is simple, as usual. store-bought fabric with printed snow flakes on the pair shown above. glitter was sprinkled over the fabric before the topsheet was laid down. i pressed at 75psi.
as for the knots, i try to keep them away from the binding area. yes, they do fall out sometimes when i profile the core, but i haven't noticed much of a difference. i agree that strength can be compromised, but it's not clear to me exactly how much and whether it's significant. maybe i'll find out someday when i knock out my teeth when a ski snaps in half. modeling the effects of the core with a hole or knot would be interesting. one simple thing we can do is plug a basic core into ANSYS with and without holes --- under three-point bending, for example, and also do a modal analysis --- to observe the difference. i'm sure we'll see a difference, but not sure how much since i haven't done the experiment yet. i believe the other layers make a huge difference too, and maybe they mask the effects of the holes. but i don't know.
like i said for the binding area, i do keep the knots away from there. i've also made skis with an AL binding platform -- a thin sheet of AL which covers the area where the binding is to be mounted. i haven't experienced screws ripping out yet. has anyone experienced this? Kelvin did pull out some screws but he had a pair of foam-core skis.
in the last 6 months i've made over half a dozen pair of skis with the cheapest and crappiest wood possible. the reason is i'm curious. i hope we learn something...
i'll show my latest design sometime this week. it's nothing fancy -- semi-pallet wood mixed with left over pine and fir. AL and some rubber in a few key areas. i'm intrigued by the first few modes of vibration, especially #2.
the two new pairs were gifts to friends. they were visiting this past week and wanted to learn to build skis, so i helped out. it was really fun showing them how to build skis. my favorite part was watching them bend and glue the edges. their smiles were bigger than ever when it was time for lay-up, and especially when the final product came out of the press! .
the graphic is simple, as usual. store-bought fabric with printed snow flakes on the pair shown above. glitter was sprinkled over the fabric before the topsheet was laid down. i pressed at 75psi.
as for the knots, i try to keep them away from the binding area. yes, they do fall out sometimes when i profile the core, but i haven't noticed much of a difference. i agree that strength can be compromised, but it's not clear to me exactly how much and whether it's significant. maybe i'll find out someday when i knock out my teeth when a ski snaps in half. modeling the effects of the core with a hole or knot would be interesting. one simple thing we can do is plug a basic core into ANSYS with and without holes --- under three-point bending, for example, and also do a modal analysis --- to observe the difference. i'm sure we'll see a difference, but not sure how much since i haven't done the experiment yet. i believe the other layers make a huge difference too, and maybe they mask the effects of the holes. but i don't know.
like i said for the binding area, i do keep the knots away from there. i've also made skis with an AL binding platform -- a thin sheet of AL which covers the area where the binding is to be mounted. i haven't experienced screws ripping out yet. has anyone experienced this? Kelvin did pull out some screws but he had a pair of foam-core skis.
in the last 6 months i've made over half a dozen pair of skis with the cheapest and crappiest wood possible. the reason is i'm curious. i hope we learn something...
i'll show my latest design sometime this week. it's nothing fancy -- semi-pallet wood mixed with left over pine and fir. AL and some rubber in a few key areas. i'm intrigued by the first few modes of vibration, especially #2.
RA,
i'm using natural top sheet over cloth. for smooth look, i put three layers of materials between top sheet and bottom of the cattrack: one layer of 1/16 AL, 2 layers of P-tex based material (old stuff laying around). The key is to make sure no debris gets squished into the top sheet, so keep the surfaces clean.
i'm using natural top sheet over cloth. for smooth look, i put three layers of materials between top sheet and bottom of the cattrack: one layer of 1/16 AL, 2 layers of P-tex based material (old stuff laying around). The key is to make sure no debris gets squished into the top sheet, so keep the surfaces clean.
BigKam - quite a few of your skis seem to have ~10mm thick cores. With 22oz glass I would expect these to be very soft.
Are you typically using additional reinforcement? Do you like soft skis or are my assumptions wrong?
I have made 1 pair to date with a 10mm poplar core and I found it to be a little soft round the binding.
B.
Are you typically using additional reinforcement? Do you like soft skis or are my assumptions wrong?
I have made 1 pair to date with a 10mm poplar core and I found it to be a little soft round the binding.
B.
Thanks BK,
I saw your latest Kewah - looks pretty cool - did you try to locate the rubber damping at points of high shear under natural vibration or did you just put them where you felt it was needed?
I just pressed a second pair this evening which went a little slow but I think it was OK - the garage where we were working was freezing and the epoxy was really solid and hard to work with.
B.
I saw your latest Kewah - looks pretty cool - did you try to locate the rubber damping at points of high shear under natural vibration or did you just put them where you felt it was needed?
I just pressed a second pair this evening which went a little slow but I think it was OK - the garage where we were working was freezing and the epoxy was really solid and hard to work with.
B.
YES! this is exactly what i did. it's the strain/shear-rate that i'm after and it seems to work, but don't quote me on this -- assume i know nothing .Bambi wrote:I saw your latest Kewah - looks pretty cool - did you try to locate the rubber damping at points of high shear under natural vibration or did you just put them where you felt it was needed?
i mumbled something here: http://www.skibuilders.com/phpBB2/viewtopic.php?t=1029
anyway, i considered the natural vibration of the ski. it's pretty much an educated guess without having to plug the entire model into something like ANSYS. (BTW, i'm ging to try this next, but it'll take some time.) and the trickiest thing is the boundary condition. what are your thoughts on this?
this summer a good friend/colleague and i measured the mode shapes of one of my skis. WOW! it was eye-candy and gave some insight: target the area of high-strain.
Did i get this right - you experience delamination after only 10 days of skiing on a new pair!?bigKam wrote:cheap and crappy is right! . but seriously, i haven't noticed much of a difference in terms of durability between super-duper high-quality and low-quality wood, except of course, the dent that high-quality wood makes in my bank account. keep in mind that wood does affect the overall weight of a ski, snap, and other characteristics. besides, my skis delam way before the knots become a problem. i put in about 10 days of ski touring on each new pair and i beat them up.
I agree with Alex, a 10 day life span is quite short.Alex wrote:Did i get this right - you experience delamination after only 10 days of skiing on a new pair!?
What kind of delam do you experience bigKam? Is it just edge delam or do you experience delam of de sandwich construction (so between the wood and fibreglass layers)?
10 days of touring can be tougher on a pair of skis than 100 days inboundsEasy wrote:I agree with Alex, a 10 day life span is quite short.Alex wrote:Did i get this right - you experience delamination after only 10 days of skiing on a new pair!?
What kind of delam do you experience bigKam? Is it just edge delam or do you experience delam of de sandwich construction (so between the wood and fibreglass layers)?
True, but I ski out of bounds (even in bad snow conditions) and I ski snowparks. I still expect my ski's (normal factory ski's) to hold up way more than 10 days. I also expect my home builds to hold up longer than 10 days, but I have yet to build my first pair (after building and testing a prototype). The touring/hiking should not make that much of a diffence right?Idris wrote: 10 days of touring can be tougher on a pair of skis than 100 days inbounds
It could also be that bigKam used to destroy factory ski's in 10 days, in which case it isn't much of a surprise that he destroyes his home builds in the same amount of time.
I am still very interested in Kam's explaination and the type of delam which occures.