We Milled our wood Sunday and have made orders for the rest of the supplies.
But I have been wondering how thick to make my cores. We are using ash as the core wood. It’s very close to the weight and stiffness of maple. I have used ash for kayak paddles and its shock resistance, flex and glue up characteristics are something that I am more familiar with.
Currently we are planning to make 5-6 pairs of skis with a couple of snowboards too. For right now I’m using a vacuum setup, but will more than likely go to a bladder press before too long.
The guy that is working with me is 245 lb. I’m 200 lb. I have looked at most of the stats in the gallery and was wondering how much some of you folks weigh (especially the Kams and Kelvin) and how thick you made your cores and what materials you used. It will help us adjust our core setup accordingly with out wasting too much $$, and may help others here as well.
Thanks for the input
Hafte
P.S. If your in the Utah ski areas this year give a shout. It would be cool to see other peoples work, and we can hook you up with some really cool ski area secrets of our local playground.
How heavy are you?
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
How heavy are you?
Last edited by hafte on Tue Sep 12, 2006 1:23 pm, edited 1 time in total.
Hey hafte,
I use Ponderosa pine for my cores. I weigh 170 lbs. My soft/wide powder skis are 10.5 mm at the waist and 2mm at the tip and tail. My medium flex skis are 12mm/2mm. My really stiff skis are 13mm/3mm. It's hard to believe that 1mm in thickness made such a huge difference in flex stiffness, but they're some of the stiffest skis I've seen, and they're quite light. I'll need to try to replicate the charactoristic predictably before I'll really be convinced that a mere 1mm can increase the stiffness so much, even though the physics support it. Oh, my skis are all about 180ish in length. Good luck on your build. What general geographical area of Utah are you located in? I usually pass through Utah 3 or 4 times a year and I always have skis or bikes with me.
G-man
I use Ponderosa pine for my cores. I weigh 170 lbs. My soft/wide powder skis are 10.5 mm at the waist and 2mm at the tip and tail. My medium flex skis are 12mm/2mm. My really stiff skis are 13mm/3mm. It's hard to believe that 1mm in thickness made such a huge difference in flex stiffness, but they're some of the stiffest skis I've seen, and they're quite light. I'll need to try to replicate the charactoristic predictably before I'll really be convinced that a mere 1mm can increase the stiffness so much, even though the physics support it. Oh, my skis are all about 180ish in length. Good luck on your build. What general geographical area of Utah are you located in? I usually pass through Utah 3 or 4 times a year and I always have skis or bikes with me.
G-man
hafte-
I am still getting my mold and materials together so I don't have a ton of info on thickness but I will be reading what you learn with interest.
I am in Orem and will be skiing mostly at sundance (local) and canyons (cheap) and would love to hook up for turns once the season starts. I will be mounting my creations with demo's and hopefully freerides so if you ski alpine a swap might be fun.
Also if you do decide to go with a bladder press let me know if you get fire hose locally. I am getting no love from the fire departments.
I am still getting my mold and materials together so I don't have a ton of info on thickness but I will be reading what you learn with interest.
I am in Orem and will be skiing mostly at sundance (local) and canyons (cheap) and would love to hook up for turns once the season starts. I will be mounting my creations with demo's and hopefully freerides so if you ski alpine a swap might be fun.
Also if you do decide to go with a bladder press let me know if you get fire hose locally. I am getting no love from the fire departments.
- Ben
G-man, that’s cool. Great info. I thought that thickness would play a bigger part in flex than either width or length, and the distribution of the thickness along the length plays a major roll too. Do you know how long the boot/thickest area of the core was, and did you taper the core or do a step down to the tips. I know what you mean about reproducing the flex from ski to ski. Wood is fickle stuff. I think the vertical laminations will really help even things out and give a more consistent ride from one pair to the next.
We’re located in Ogden. North of SLC ~35 miles. We ski at Powder Mountain. It’s a real mom & pop place, but you can’t beat the aspect of the mountain anywhere. If you know where to look there’s always good snow, and tele gear is the easiest/best way to get there. I just love kicking’n’gliding past snowboarders post hole’n to the other side of the ridge hehe.
Ben,
That would be cool to hook up sometime this year. I haven’t been to Sun Dance in years… like almost 40 years! And you didn’t hear any of this about powmow from me!! I fact… it really sucks. We’ll come visit you ha ha ;^)>
Unfortunately, I haven’t had/owned alpine gear in 25+ years. Unless My friend mounts some of these new skis that way trading can’t happen, and he just got some Crispies (sp?) last year so he is really ready to go full on tele this year. I would still really like to see what you are doing though.
I’ll keep my ear open for hose. I may have a real in on that. There are several firemen that patrol at PM and one of my kayak partners knows most of those guys. I’ll keep you posted on that.
Hafte
P.S. I snowboard too, so I feel like poke’n at’m once in awhile is cool cause I’ve been there too.
We’re located in Ogden. North of SLC ~35 miles. We ski at Powder Mountain. It’s a real mom & pop place, but you can’t beat the aspect of the mountain anywhere. If you know where to look there’s always good snow, and tele gear is the easiest/best way to get there. I just love kicking’n’gliding past snowboarders post hole’n to the other side of the ridge hehe.
Ben,
That would be cool to hook up sometime this year. I haven’t been to Sun Dance in years… like almost 40 years! And you didn’t hear any of this about powmow from me!! I fact… it really sucks. We’ll come visit you ha ha ;^)>
Unfortunately, I haven’t had/owned alpine gear in 25+ years. Unless My friend mounts some of these new skis that way trading can’t happen, and he just got some Crispies (sp?) last year so he is really ready to go full on tele this year. I would still really like to see what you are doing though.
I’ll keep my ear open for hose. I may have a real in on that. There are several firemen that patrol at PM and one of my kayak partners knows most of those guys. I’ll keep you posted on that.
Hafte
P.S. I snowboard too, so I feel like poke’n at’m once in awhile is cool cause I’ve been there too.
It's cool to see some Utahns here. I grew up in Tremonton, UT way up north and first started skiing at Beaver. I'm living in SoCal right now but plan on heading up to Brighton and Alta this winter so maybe we can all get together.
As for my stats. I'm 5'7" and about 135 lbs.
As for my stats. I'm 5'7" and about 135 lbs.
- Kam S Leang (aka Little Kam)
You are right!hafte wrote:I thought that thickness would play a bigger part in flex than either width or length
I am sure that a lot of you are engineers, but in case people are looking looking for more insight....
The stiffness of a rectangular section ski will be proportional to the width and proportional to the cube of the height. This means (as described above) that the ski stiffness will be extreemly sensitive to thickness. For example if your ski is twice as wide it will be twice the stiffness, but at twice the thickness it would be 8 times the stiffness! To put it another way a 12.6mm section should have approximately twice the stiffness of a 10mm section, and a 3mm section would be close to 3.4 times as stiff as a 2mm section.
The exact formula for the stiffness of a rectangular section is given by the expression:
Stiffness = Youngs Modulus * Width * height^3 / 12
I have also done some basic calculations on the relative importance of the fibreglass compared to the natural stiffness of the core with 22oz glass over an 11mm typical wood core. My initial calcs suggest that both the wood and the fibreglass have a significant part to play in the ski stiffness. The system is not dominated by one or the other.
I hope that this is useful and that I am not just spewing obvious stuff at people. If it is usefull then when I get a second I will start to compile a few more complete articles on the calcs that I have done...
B.
hafte,
The thick/waist portion of my skis run about 20 cm in length... can't remember off hand just where in that area the pin line falls. I did a standard taper to where the tip and tail curves began, then kept the thickness consistant at 2 or 3mm (3mm was way more difficult to bend than 2mm). I haven't been through Ogden, yet. I've seen your snow covered hills from Interstate 80 and have always wanted to head in that direction to check it out. Sounds great.
Bambi,
Your information is great! Engineering interests me a lot (but, I'm not an engineer), and your examples really help to explain my somewhat vague findings in more concrete terms. The numbers say it all. Yes, it does seem that there are a whole bunch of folks on this site with engineering backgrounds, but I think that there are also a lot of us who really appreciate when someone takes the time to explain some of the 'mysteries' in more understandable terms like you did in your post. Thanks.
G-man
The thick/waist portion of my skis run about 20 cm in length... can't remember off hand just where in that area the pin line falls. I did a standard taper to where the tip and tail curves began, then kept the thickness consistant at 2 or 3mm (3mm was way more difficult to bend than 2mm). I haven't been through Ogden, yet. I've seen your snow covered hills from Interstate 80 and have always wanted to head in that direction to check it out. Sounds great.
Bambi,
Your information is great! Engineering interests me a lot (but, I'm not an engineer), and your examples really help to explain my somewhat vague findings in more concrete terms. The numbers say it all. Yes, it does seem that there are a whole bunch of folks on this site with engineering backgrounds, but I think that there are also a lot of us who really appreciate when someone takes the time to explain some of the 'mysteries' in more understandable terms like you did in your post. Thanks.
G-man
Awesome stuff folks!! This should really help us all dial in our skis quicker.
Bambi, I’m not an engineer either, so this is great. I usually fly by the seat of my pants, and as you can see, build on the experience/generosity of others until I get a feel for what needs to be done. Some calculations would really add a great deal of value here, and seeing your calculations of how the whole composite works together will be very interesting. More more more!!!
LittleKam, I was hoping you would chime in here. I was looking at “The Shit” skis and wondered how they would work for me or my friend. I’m thinking they may be a bit stiff for powder, but as an all mountain crud ski the specs seem about right. I have been skiing 181 Blizzard Titans XXL for the last two seasons, and really love that ski. Super all mountain ski for me.
If you get a chance while your out here give me a shout. PM just put in a new high speed quad chair this summer. Should be ready for this season.
Hafte
Bambi, I’m not an engineer either, so this is great. I usually fly by the seat of my pants, and as you can see, build on the experience/generosity of others until I get a feel for what needs to be done. Some calculations would really add a great deal of value here, and seeing your calculations of how the whole composite works together will be very interesting. More more more!!!
LittleKam, I was hoping you would chime in here. I was looking at “The Shit” skis and wondered how they would work for me or my friend. I’m thinking they may be a bit stiff for powder, but as an all mountain crud ski the specs seem about right. I have been skiing 181 Blizzard Titans XXL for the last two seasons, and really love that ski. Super all mountain ski for me.
If you get a chance while your out here give me a shout. PM just put in a new high speed quad chair this summer. Should be ready for this season.
Hafte
I'll try to put together a more comprehensive article and associated spreadsheet for people to play with. Also I would definitely be up for meeting up to check out each others skis sometime this season - perhaps some of you can show me how to ski - I'm not called Bambi for nothing!
Unfortunately I am normally based on the east coast and I think most of you are out west, but I will do at least one week over there - probably in Utah.
B.
Unfortunately I am normally based on the east coast and I think most of you are out west, but I will do at least one week over there - probably in Utah.
B.
Hafte-
You warmed my heart when you said powder mountain. I grew up in Layton and skied pow mow till I left home. Too many fun memories to count, but a few are:
Riding the old blue bus back up the road from the backside.
Skiing hard for 14 hours, without a break, with my friends on "central ski day" (never failed to get sick the next day).
Getting towed by a patroller on a snowmobile to the top of sunrise ridge.
Freezing on hidden lake lift.
Poaching the cat skiing area with long traverses off of "the crotch rider".
I remember the first time I was at snowbird and saw people racing for first tracks, I didn't get it, I had been spoiled. I haven't back to powder for any of the recent improvements, but it is on the list for this season, so lets definitely get together.
I appreciate any help on the fire hose and will let you know if I find something. If you need any other info on local (SLC) fiberglass or lumber suppliers let me know I would love to pass it on.
p.s. To answer the original question 6'1" 190.
You warmed my heart when you said powder mountain. I grew up in Layton and skied pow mow till I left home. Too many fun memories to count, but a few are:
Riding the old blue bus back up the road from the backside.
Skiing hard for 14 hours, without a break, with my friends on "central ski day" (never failed to get sick the next day).
Getting towed by a patroller on a snowmobile to the top of sunrise ridge.
Freezing on hidden lake lift.
Poaching the cat skiing area with long traverses off of "the crotch rider".
I remember the first time I was at snowbird and saw people racing for first tracks, I didn't get it, I had been spoiled. I haven't back to powder for any of the recent improvements, but it is on the list for this season, so lets definitely get together.
I appreciate any help on the fire hose and will let you know if I find something. If you need any other info on local (SLC) fiberglass or lumber suppliers let me know I would love to pass it on.
p.s. To answer the original question 6'1" 190.
- Ben
I have made a couple pairs of ash cored skis. Ash is awesome wood to work with, and they ski really well. However, the cores are about 11mm or 12mm thick and about 130mm wide in the center, and they are exceptionally stiff. As an example, in about 2 inches of corn or soft snow I can throw my weight back and ride completely on the tails of the skis while dragging a hand in the snow behind me for balance. I made a pair of maple skis that are about 13 or 14 mm thick, but only 100mm wide in the center and they are really stiff too (but extremely powerful to ski on). I weigh about 180 and ski with a normal alpine setup. If you are working with ash, I would recommend making a set of cores at about 12mm thick if you are making a 120mm wide ski, then seeing how they feel from there considering you sound like sizeable dudes .
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Chris Downing
- Posts: 15
- Joined: Sat Sep 30, 2006 12:05 pm
- Location: Waitsfield VT
- Contact:
DD
I'm 270 lbs. Alpine ski coach at GMVS, and I always like my skis soft flexing, but torsionaly stiff. You will find a softer ski wil break down faster.
downing design
stiffness calculation
I am not an engineer, so is it Stiffness = (Young's Modulus * Width * ((height^3)/12))Stiffness = Youngs Modulus * Width * height^3 / 12
or (Modulus * width * (Height^3))/12 ?[/quote]
Either way is fine.
I am putting the finishing touches to a spreadsheet that automatically works out stiffness profiles based on simple core dimensions, which I try to make available either on this site or by uploading somewhere and giving a link. It will also output a deflection at centre due to a point load so that you can crudely compare a potential design to overall stiffness of pair of skis that you like.
B.
I am putting the finishing touches to a spreadsheet that automatically works out stiffness profiles based on simple core dimensions, which I try to make available either on this site or by uploading somewhere and giving a link. It will also output a deflection at centre due to a point load so that you can crudely compare a potential design to overall stiffness of pair of skis that you like.
B.
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Chris Downing
- Posts: 15
- Joined: Sat Sep 30, 2006 12:05 pm
- Location: Waitsfield VT
- Contact: