Hey guys,
I've got a problem and I'm sure someone on here can help!!!
I've been cutting out the base by clamping a template and cutting around. But when the template is removed we are finding that the base is skewed and thus is useless!!! Any ideas??
Cheers lads
Ross
Ross: skewed in what sense? like the template shifted during the time you were cutting, or the base warping after it has been cut?
its definately the base warping during/after the cut. its not slipping during the cutting, but as soon as we lift off the template and check the base its warped.
Ross:
is it warm where you live? how warm?
interesting behavior... Little Kam and i just ran into this same problem. we were ready to lay up a pair of skis ealier this week and noticed that the base had changed its shape significantly -- warped by 10mm over 175cm length! i drew up a pair of skis with slightly reversed sidecut, and made a thin wood template to cut out the base. the wood template looks fine, no warp there. but after cutting out the base material and gluing on the edges, we noticed that the base was warped, including the edges, yielding a base with one side reverse sidecut and the other with sidecut. oops, that's not right. weird. at first we thought that our template shifted during the cutting process, so we made new bases. come to find out, the new bases we cut out did the same thing, again! ugh!!
so what's the problem? we're not quite sure what the problem is, but i'll discuss what we've observed. i think this is an important topic, and we should all try to put our heads together to resolve it.
I cut out a couple of small (1"x8") test pieces and stuck one in the refridgerator and left the other one outside. I didn't notice any changes, but a) the pieces could be too small to notice a big change, and b) it's not so hot here in Seattle. I've also looked at our finished skis, and don't notice any warpage.
Apparently this is a known and recurring problem. see graf snowboards: (http://www.grafsnowboards.com/phpBB2/viewtopic.php?t=127&sid=578ef7a0e83bf6ffdb2fc30717ce7f57)
The coefficient of thermal expansion for UHMW is 130-200 x10^-6/k. (For comparison steel is 12x10^-6/k). (source:http://www.goodfellow.com/csp/active/static/A/Polyethylene_-_UHMW.HTML) This is the percent change in length per degree kelvin or celsius. So for a 180cm ski base, and a 10 degree change in temp, there is a change of almost 4mm! (1800*200x10^-6=.36mm/k)
This is quite surprising and I wonder how they deal with it in heated presses.
kelvin
Nice one guys. Well heres our situation.
We live in Birmingham in the UK, and from what you have heard about the weather over here it is actually about 28-30oC at the moment, and we are working in a lab at Uni that doesn't have any air-con. Its damn hot in there!!!!!
The first 2 i cut out I cut with long strokes as it were (ie cut about 50cms at a time) off the roll and when i took off the template it was warped.
Next we tryed cutting a blank out first and then cut around the template in the same fashion. Results were the same.
So next we tried cutting out a blank and making smaller cuts, cutting both ways. This worked better but it wasn't as accurate. I'm going to give it another go on Monday to see if i can cut it out better.
This would suggest that its an internal stress problem (but i'm sure the heat isn't helping). If a proper solution can be come up with it would help saze a lot of time and money!!!
Cheers for your help guys
Ross
Ross,
that is very interesting. For the skis that BigKam and I have made in Seattle, we have used a router to cut out the bases. I wonder if that makes a difference. I'll look into further.
Kelvin
the more i think about it, internal stress is probably the majority of the cause for the warping. i'm going to give DuraSurf a buzz and see if i can get some information from them. i'll discuss what i find out, but as Ross has pointed out, temperature doesn't help either it seems. if in fact internel stress is the major problem, then one remedy (though not 100% guaranteed) is to 'rough' cut the base material as i mentioned earlier, then let the material sit for a while. afterwards, the final cut can be made and edges applied.
From what I gathered from making p-tex repair patches. The cause of the problem is in the method of cutting.
The p-tex stretches as you cut it with a knife, the sharper, the less this occurs. When I've made patches using a stamp (looks like a cookie cutter made out of razor blades) The p-tex would be the shape intended. Using scissors would warp the p-tex sideways but not significantly. But with a shop knife the patch would never come out straight. The amount of distortion was greatly reduced if I had a very stiff stencil and clamped it down hard, reducing how much I would stretch the p-tex under it.
looking through the various manufactures production videos/pictures, it looks like they are using either die cutters (like a huge cookie cutter) or a router. Neither puts any stretching force on the p-tex.
To reduce warping/stretching but without changing the whole cutting method. How about using a heavy/stiff template and clamping it down very hard. Also cutting with a razor blade or similar that doesnt require much effort to cut, thus reducing the amount it can stretch the p-tex?
Ross:
any more news about the warping behavior?
we're left to believe that we have a bad batch of p-tex. so far our tests indicate that it isn't temperature related, or dependent upon the method used to cut the base material. i called Durasurf and they simply said that it's a rare behavior and most likely a bad batch. anyway, we'll get a new batch of p-tex and see what happens.
let us know if you discover anything...
Yes! it is internal tensions from the manufacturing process!
I am using snowboard grade ski base from ISOSPORT and they told me that due to the manufacturing of snowboard bases you get internal tension that might cause problem. When they make these wide material they in some way weld to sheets together and therefore get tensions in the material.
What I do is that I make base templates in MDF (20 mm thick) and then clamp the routed base on to it. Then I mount my edge on the base and it comes out perfekt. The edges are so stiff that they keep the base perfectly straight. I always check so that my edge/bases are perfectly matching each other!
Coming up soon: hendryxskis.se
Rock on!
Henrik
Henrik:
thanks for your thoughts, and welcome. we're excited to see hendryxskis.se. please forward some of your work to show...
as far as the base material is concerned, it's rather irritating there internal stress issues. i like your method of trying to minimize the behavior, but even after you attached the eges, and then remove the MDF template, isn't there enough stress to cause the edges to warp with the base? i guess we'll have to try your method and see what happens...
thanks again for your thoughts...
Hendrik.
what adhesive are you using to attach the edges? -thanks
i can't answer for Hendrik, but we use SuperGlue. just a dab every 10cm or so...
Hello everybody!
No, the edges do not warp with the base. This is due to the big differences in elasticy modulus. The edges are much stiffer and stronger than the base so the edges keep the base perfectly straight.
When it comes to the glue I use super glue from R&G germany, r-g-composites.com, blue type.
Henrik
Hendryx the swede finally got his flash finished.
A really informative page, and very interesting with a new brand around! (the 93rd. skibrand?..)
He has got some very
I agree, my first pair of skis, the bremallows don't have any camber, while my second pair of skis looks like it might have 3 or 4 mm, which I would definitely call low camber
the statement about difficult in making low camber skis doesn't make much sense to me either. how is it more difficult to make a low camber ski than a high camber ski? if there is a difference i would expect high camber skis as being more difficult to produce with consistency.
is there a link to the hendryx site?
Try http://www.hendryxskis.se/
Hey, and his workspace is really tiny:
The graphics are nice...I'm wondering whether he uses sublimated topsheets or printed paper laminated above the fibreglass.
Concerning camber his statement is really strange, maybe he wants to express the difficulty to produce skis that actually keep
i like his garphics
but i dont know about the camber?? i think i will pay him a visit, maby this weakend if i have time. His workshop is abot 30 min whit the car from my house.
those graphics are sweet. bertborge, you mind asking how he did his graphics?
camber is an interesting topic. it's unclear to me its specific contribution, although i suspect it has something to do with pressure distribution as well as flex. but what i think might be true is too much camber can be a problem. i'll take the Kaffeines out next week at Whistler and see. they have about 25mm of camber, which seems excessive to me, kind of like double camber XC skis. Kelvin recently reported how strange the DLG's skied. they have about 25mm of camber, too. it will be interesting to note the affect on soft and hard snow. i'll write a few words after the Turkey holiday.
as for the low camber comment, it's not clear why it's difficult to achieve. as Little Kam pointed out, achieving high camber may be more difficult effort-wise. Or is it more difficult to achieve a specific tolerance on the camber? in that case, i can see how it would be difficult to achieve a tighter tolerance for low camber skis because small variations in the camber is more pronounced when compared to the target amount of camber. for instance, if you have 3mm of camber, then a +-0.5mm variation leads to (0.5/3)*100 = 16.7% variation in the camber. if camber has a significant affect on skis performance, then 16.7% may be large. therefore, one has to minimize the camber variation during production and trying to be within 0.5mm and ensuring that the ski does not lose camber for low-camber skis may be difficult. but consider the same +-0.5mm variation for a 16mm camber ski. the percent error is (0.5/16)*100 = 3.12%, so the same amount of change only affects the camber variation of a high-camber ski by around 3%. assuming that the camber is critical, then high-camber skis are more "robust", and in some sense more "friendly" to build. i dunno.
we should think more about this. i'm intrigued by the effects of camber. so far, i like skis with low camber.
I too think camber has a lot of effect om how a ski performs. This winter I'll be doing my master project (I'm industrial design student) on how different shapes affect the joy of skiing. The theory is that varying the 8 floating variables in ski construction (just count) jou can go on making different skis pretty much forever. title of the project is "making skis the snowflake way" (It's kind of strange translated, but it's abot the effect of extreme customizing)
To be able to adjust the camber of the ski, I have built a quite special mould that is adjustable in all directions. It's an amazing piece of machinery. I will keep you posted about the effects of camber or not.. and everything else, I'm testing everything!
endre: your work sounds very exciting. we would love to hear about the progress and results... keep us posted.
Hello everybody!
I see you have problems with my low camber theory. Well, it is not just a theory it comes from testing.
The benefits of low camber on hardpack is that the skis are very smooth from edge to edge and are very easy to adjust between turns. If you have alook at real World Cup skis you will notice they have a very low camber and infact race skiers break their skis to decrease the camber. Usually these skis have a camber of 3-4 mm and especially skis for speed.
What I mean with that it is hard to make skis with a low camber is that you get a lot of tensions when you heat up a ski to ~120 Celcius, let them cure and take them out and then be used at -10 . I can tell that A former cross country manufacturer here had big problems with the camber at production. They could make six skis in the same press and everybody came out different. This is typically for the european ski manufacturing and I know that you usally do not use these high temperatures in north America.
When it comes to soft snow a low camber ski floats and slide better. This is due to the fact that the tail do not kick up but instead sets in the snow. It is the same theory as for surf boards. The low camber ski also comes closer to a ski with negative camber, it becomes very loose. When skiing on low camber skis in soft snow you only lean over and the skis starts to turn, more like a surf- or skate board, you do not need any initiation of the turn they just starts to turn without any resistance, they simply acts more surfy!
I can tell that I have helped a company with ski designs and I specified them with a low camber. I had prototypes wich were almost flat and they were wonderful but when I recieved the production series they had about 20 mm of camber and it was a completly different ski! They really struggeld in bad snow with a tail that kicked up so much you had to sit on the skis to prevent head butting, in heavy soft snow, they did not slide easy and on the hard pack they did not want to go off edges.
All the best!
Henrik
Tjena Henrik,
Jag bygger p min frsta skidpress nu s jag har inte kommit s lngt. Finns det mjlighet o komma p studiebesk??
Jag ser p bilden att du anvnder en vakum press, funkar det bra?? gr du en skida t ggn??
Tnkte jag skulle ha ringt o frga men det r lttare shr, d kan du svara nr du har tid.
Jobbar du heltid med skidorna eller r det bara "hobby projekt "
PS. din spann teori lter int helt dumm
.DS
what about pop, for a park ski. would low camber reduce the pop by alot?
I'm asking because im just about to make my mould and i plan on using it to make park skis, and to make a pair of powder jumping skis.
pop is a result of how much tension the ski has when you jump of the edge, a no-camber ski wold have as much tension as the concave of your kicker. imagine standing on a ski with 100mm. of camber, that would be like standing on a trampoline. In powder you don't get much pop anway. (unless you have a hard kicker ofc.)
My experience with the stiff upper lips (~10mm camber) and the daddy's little girls (~25mm camber) agree with what Henrik is saying. In soft snow, the dlg's have a tendency to submarine. The DLG's are also fairly stiff, and I wonder if a soft ski with lots of camber has the same effect.
-kelvin
basically i need to use a camber that will work for both powder and park skis, sorta find a middle ground, so im wondering how much pop i will lose in my park skis if i use a lower camber to get better float for my powder skis (since im using the same mould)
Hose-man, I love the table of dimensions, glad you put in all the man hours on it! They will be real useful for all of us here. All die-hard number lovers will love the publication by John Howe, "The new skiing mechanics."
John currently builds his own salomon/freeride skis out of Jay, Maine. He formally worked for Head skis as an engineer. He gives a solid empirical view of ski building in general. If you want to see how his brain works with ski design I recommend purchasing his book.
All though his designs are not as contemporary as ours, in a sense they are with radical sidecuts and tapers. Just a suggestion.
where does one find this book
It was my intent to post the website:
i dont know if this will help, but i have large rolls of snowboard base material that I am cutting skis out of. Rather than dragging a shop knife over the base, i do the opposite. Basically, I lightliy engrave the shape of the ski in the base material, then pierce the knife all the way through at one end and rather than pulling the knife, the knife is stuck into wood underneath and I pull the base. The light engraving gives a guide to follow and the base comes out to the exact shape....I dont know if this will solve your problem, but none of my bases have warped yet
^that's a real interesting approach.
i've found that my bases are no longer warping with any method of cutting. i think it has to do with the colder temps (about 20-30 degrees less).
Hey Guys,
Your sight rocks! My buddy and I are working on a company Avant Skis, which will also be my final/senior project for my BFA in Design at Alfred University, NY.
Has anyone tried a hot knife or blade to cut the base material. Because of the temprature effects I am not sure if it would make the warping worse, but it seems like it would allow the blade to cut with a cleaner edge and cause less stress/stretch while draging the blade??
I have been reading this with great interest, and was wondering which brands of base material you guys are using and if that would make a difference. I have Durasurf available here locally, but would look else where if this is a common problem.
Has anyone tried to heat treat the plastic before you cut out your part to see if the internal stress would relax some after it cools back down. I know you can't tell there is a problem until the part is cut. It looks like a few people already have problem materials and it could be worth a try.
Awesome site guys. Thanks for providing the info. I'm looking forward to making some skis and other toys here real soon.
Hafte
