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
Cutting out the base
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
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. anyway, here's what we've observed. you might want to share you thoughts.
first, we think one cause may be temperature effects. i'm down in So. Cal. right now with Little Kam and the temperature in the valley hovers between 90-100 degrees. it's the desert and the humidity isn't that high. we're working in the garage with no air conditioning. and this is the first time i've seen this warping problem, and it's a first for Little Kam too; however, after we inspect one of his more recent pairs of skis, it seems that the warping was already a problem, but it wasn't obvious. anyway, the skis that i've built previously were constructed in Seattle, WA, where the temperature is more mild. Kelvin and i in Seattle didn't notice the warping problem and i called Kelvin a few days ago to see if he can do some tests. our first guess about the cause of the warping is it's temperature related, i.e., the temperature is causing expansion/contraction in the material. for example, between the time the base is cut and when you notice the warped result the temperature has change enough to cause the material to expand/contract to take on a new shape.
if it is temperature related, then this is probably going to be a serious issue. it's an issue because epoxies generate some amount of heat when mixed and even if the base material isn't warped to begin with, adding epoxy will surely cause the bases to warp during layup. yikes. what a pain. so does that mean that the shape of every ski is different than its original design? so, how do they deal with this temperature problem in the ski industry? do they have an environment chamber? i doubt it. perhaps temperature isn't really the problem.
the second observation is this. the base material we purchased from Durasurf comes in a roll that is 30cm wide. when we cut out the bases, we split the material lengthwise making two pieces 15cm wide. we have a couple pre-split pieces of materials laying around and they are warped. perhaps the warping is caused by changes in the internal stresses in the material after they are split. if this is the case, then to compensate for the warping of the final bases, what we should do is 'rough' cut out base material first, let it sit for a day or two to relax, then put a template on it and make the final cut.
anyway, this is what Little Kam and i have observed. i've asked Kelvin to do some tests in Seattle where the temperature is more mild. he's going to also take a look at some of our other skis to see if the shapes were warped and went undetected. i'm sure he'll report back on this. in the meantime, Little Kam and i will do some more tests to figure out the problem and ways to deal with it. i would appreciate if others out there who know something would share...
big kam
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. anyway, here's what we've observed. you might want to share you thoughts.
first, we think one cause may be temperature effects. i'm down in So. Cal. right now with Little Kam and the temperature in the valley hovers between 90-100 degrees. it's the desert and the humidity isn't that high. we're working in the garage with no air conditioning. and this is the first time i've seen this warping problem, and it's a first for Little Kam too; however, after we inspect one of his more recent pairs of skis, it seems that the warping was already a problem, but it wasn't obvious. anyway, the skis that i've built previously were constructed in Seattle, WA, where the temperature is more mild. Kelvin and i in Seattle didn't notice the warping problem and i called Kelvin a few days ago to see if he can do some tests. our first guess about the cause of the warping is it's temperature related, i.e., the temperature is causing expansion/contraction in the material. for example, between the time the base is cut and when you notice the warped result the temperature has change enough to cause the material to expand/contract to take on a new shape.
if it is temperature related, then this is probably going to be a serious issue. it's an issue because epoxies generate some amount of heat when mixed and even if the base material isn't warped to begin with, adding epoxy will surely cause the bases to warp during layup. yikes. what a pain. so does that mean that the shape of every ski is different than its original design? so, how do they deal with this temperature problem in the ski industry? do they have an environment chamber? i doubt it. perhaps temperature isn't really the problem.
the second observation is this. the base material we purchased from Durasurf comes in a roll that is 30cm wide. when we cut out the bases, we split the material lengthwise making two pieces 15cm wide. we have a couple pre-split pieces of materials laying around and they are warped. perhaps the warping is caused by changes in the internal stresses in the material after they are split. if this is the case, then to compensate for the warping of the final bases, what we should do is 'rough' cut out base material first, let it sit for a day or two to relax, then put a template on it and make the final cut.
anyway, this is what Little Kam and i have observed. i've asked Kelvin to do some tests in Seattle where the temperature is more mild. he's going to also take a look at some of our other skis to see if the shapes were warped and went undetected. i'm sure he'll report back on this. in the meantime, Little Kam and i will do some more tests to figure out the problem and ways to deal with it. i would appreciate if others out there who know something would share...
big kam
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/vi ... 0717ce7f57)
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/st ... _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
Apparently this is a known and recurring problem. see graf snowboards: (http://www.grafsnowboards.com/phpBB2/vi ... 0717ce7f57)
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/st ... _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
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
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 doesn’t require much effort to cut, thus reducing the amount it can stretch the p-tex?
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 doesn’t 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...
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...
-
hendryxskis
Warping ski base!
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
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...
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...
-
hendryxskis
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
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