I pulled my ski out of the press after 2.5 hours. To my suprise it was still about 120 degrees or so. After an hour I lost about half the camber. Is this due to not letting it completly cool?
BTW..I am using QCM 049 epoxy and 315 hardener.
Pulled ski out hot...lost camber
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Mine did the same thing. I think I'm using a little different epoxy than you are, (still QCM) After skiing them a few times they're reverse camber. I'm not sure how I'm going to solve this problem. Sound's like the Kam's are using a long cooldown to eleviate this problem. That will be my plan on my next pair. Hopefully I'll get on the ball & get a pair put together in the next few weeks.
That is interesting, since ours did the opposite. When we pulled them out hot (175f for 30 mins, cool down for 15 min), the skis came out with way too much camber. I could not get the skis to relax even elevating the tips and tails and jumping in the middle. Slower ramp up and cool down seems to help, but I've been using our 0 camber mold and the skis still end up with a little (~6mm) camber.
what temp and how long are you pressing? Is the epoxy curing completely?
-kelvin
what temp and how long are you pressing? Is the epoxy curing completely?
-kelvin
And here's a little different twist (I think I may have already mentioned this before... sorry if I'm being redundant)). As I've pointed out in other posts, my skis have come out of the press (too hot to hold on to) without any measurable gain or loss in camber after cooling, or after numerous trips up and down a mountain. But, I have been experimenting with different composite lay-up combinations (materials, axials, weights) in sample pressings, and they do sometimes come out a bit different. My conclusion, at least at this point, is that it may be the composite combinations we are using that may be partially causing the different camber losses/gains we are all getting. So, for comparison with what everyone else might be using, I used 22 oz. triax on the first pair, top and bottom, with no loss or gain in camber (or tip/tail curve), even after 30 +/- days on them. The second pair used 6 oz. uni carbon and 19 oz. biax glass on the bottom with 22 oz. triax on the top, again, no camber loss or gain. I'm not going to divuldge the third pair until I get a chance to do some more testing on it... sorry. The test pieces that have produced camber variations have been one's where I've used a stiffer/heavier glass or carbon on the bottom versus the top. One example is a piece where I used a 12 oz. uni glass and a 19 oz. biax glass on the bottom, with a 20 oz. triax glass on top (trying to get a stiffer flex without increasing the overall weight too much). I did another sample the same as above, except that I lightened up the bottom uni glass layer to 6 oz. Both of these samples came out with more camber than intended, the first, more so than the second. But, I have yet had a situation where I have lost camber, either initally, or over time.
It's so interesting that we are all getting such varied camber results. Of course, there is a rational reason for this, but the influences are certainly varied and many. Only by comparing the many variables will we be able to identify the causes and then come up with the remedies. I don't know if it is possible to do this as a group, or if we will just all have to find the solution basically on our own. Since there are so many influencing variables, I think that process consistency is the key to a predictable camber. As long as the process is consistant, the mold camber can be adjusted to achieve the desired end camber result. I would imagine that it is also possible that, because we are all using different woods for building our cores, the wood species could also be a big influencing factor.
My two cents worth.
G-man
It's so interesting that we are all getting such varied camber results. Of course, there is a rational reason for this, but the influences are certainly varied and many. Only by comparing the many variables will we be able to identify the causes and then come up with the remedies. I don't know if it is possible to do this as a group, or if we will just all have to find the solution basically on our own. Since there are so many influencing variables, I think that process consistency is the key to a predictable camber. As long as the process is consistant, the mold camber can be adjusted to achieve the desired end camber result. I would imagine that it is also possible that, because we are all using different woods for building our cores, the wood species could also be a big influencing factor.
My two cents worth.
G-man
The temp got a little out of control and I ended up at about 220 degrees F for approximatly 2 hours. The epoxy seemed completely cured upon removing it from the mouldkelvin wrote:That is interesting, since ours did the opposite. When we pulled them out hot (175f for 30 mins, cool down for 15 min), the skis came out with way too much camber. I could not get the skis to relax even elevating the tips and tails and jumping in the middle. Slower ramp up and cool down seems to help, but I've been using our 0 camber mold and the skis still end up with a little (~6mm) camber.
what temp and how long are you pressing? Is the epoxy curing completely?
-kelvin
Wow, 100 degrees is pretty hot with that much humidity! I just finished pressing my 7th pair of skis in my single ski press. So far, I have only had one pair of skis that lost their camber or tip height (the bremallows) but that was my first pair and there were lots of other problems with those skis.
I press at just over 105 degrees F using the QCM epoxy I mentioned in the "better rockets" article and I usually press for about 12 to 14 hours. The epoxy feels pretty hard after 2 to 3 hours usually, but the extra time in the press really seems to help cure the ski a little better. Plus, I typically press over a weekend so that I put a ski in on friday evening, pull it out saturday morning, reset the press, and put another ski in late saturday afternoon or saturday evening, pulling ig out sunday.
I have had really good luck with this method and once you get used to pressing, and get used to setting everything up, you will get pretty comfortable leaving the press running for extended time periods. The only problem is that the compressor can be a little loud, but that is a minor inconvenience for the joy of homebuilt skis!
I press at just over 105 degrees F using the QCM epoxy I mentioned in the "better rockets" article and I usually press for about 12 to 14 hours. The epoxy feels pretty hard after 2 to 3 hours usually, but the extra time in the press really seems to help cure the ski a little better. Plus, I typically press over a weekend so that I put a ski in on friday evening, pull it out saturday morning, reset the press, and put another ski in late saturday afternoon or saturday evening, pulling ig out sunday.
I have had really good luck with this method and once you get used to pressing, and get used to setting everything up, you will get pretty comfortable leaving the press running for extended time periods. The only problem is that the compressor can be a little loud, but that is a minor inconvenience for the joy of homebuilt skis!
Okay, the correlation I see here is that MLReed and I are the ones losing camber. We both use a exterior heat source for the press rather than a heat blanket. We both are impatient & press the ski just long enough & then pull it out hot.
I'm thinking that I'll be springing for a heat blanket here soon.
Those of you who use a heat blanke system. Are you using a top & bottom heater, or just a bottom heater?
I'm thinking that I'll be springing for a heat blanket here soon.
Those of you who use a heat blanke system. Are you using a top & bottom heater, or just a bottom heater?
Just the bottom for me. I thought about installing a top heater, but since my camber results have been good with just the bottom heater, I didn't want to risk messing things up. A top heater would speed up the pressing process because, now, I have to wait long enough to be sure that the ski is heated through and through... about 30 minutes for my temp sensor to get up to 170F, then another 60 minutes holding at that temperature. With just a bottom heater, I'm sure that the bottom portion of the ski is expanding and curing before the top, thicker portion has become fully heated and expanded. It seems like this would have some kind of effect on the final camber, but I just can't get my mind around it enough to predict what that effect would be... increased camber???, decreased camber??? Maybe someday I'll install a top heater and see what happens.
I figure that the addition of a top heater would save about 30 minutes of pressing time... certainly not a big deal for me at the present time. Also, the addition of a top heater would increase the electrical current load on the solid state relay, so I'd want to be sure that I wasn't exceeding the relay's rating. Most SSR's are rated at 10 or 20 amps. A 10 amp probably wouldn't handle both top and bottom heaters, but a 20 amp should be okay. Also, the heat blanket "watt per square inch" rating could be reduced from 5 watts to 2 or 3 watts /sq.in. because the heat generating surface area would essentially be doubled. 2 watt heaters are a lot cheaper than 5 watt heaters.
G-man
I figure that the addition of a top heater would save about 30 minutes of pressing time... certainly not a big deal for me at the present time. Also, the addition of a top heater would increase the electrical current load on the solid state relay, so I'd want to be sure that I wasn't exceeding the relay's rating. Most SSR's are rated at 10 or 20 amps. A 10 amp probably wouldn't handle both top and bottom heaters, but a 20 amp should be okay. Also, the heat blanket "watt per square inch" rating could be reduced from 5 watts to 2 or 3 watts /sq.in. because the heat generating surface area would essentially be doubled. 2 watt heaters are a lot cheaper than 5 watt heaters.
G-man
the gain/loss of camber is interesting to me, but at the same time it's somewhat frustrating. i'd like to get to the bottom of it like everyone else... maybe we need to create some sort of matrix to see if we can spot patterns...
but here's an observation between the significant gain in camber that Kelvin and i noted and the loss experienced by MLReed05:
when we experienced the huge camber gain, we pulled out the skis while they were hot and the air temp was rather cool -- Seattle cool. in MLReed05's case, it seems like he's living in a sweatbox (i.e., really hot and humid). i wonder if the rate at which the skis cool down has an affect? after our initial experience, Kelvin started slowing down the cooling process by letting the skis cool in the press...
but here's an observation between the significant gain in camber that Kelvin and i noted and the loss experienced by MLReed05:
when we experienced the huge camber gain, we pulled out the skis while they were hot and the air temp was rather cool -- Seattle cool. in MLReed05's case, it seems like he's living in a sweatbox (i.e., really hot and humid). i wonder if the rate at which the skis cool down has an affect? after our initial experience, Kelvin started slowing down the cooling process by letting the skis cool in the press...
Mike,
I cut and pasted the following from another thread that I contributed to a few weeks ago (cut and pasted because I don't know how to do that page linking thing that some of you guys do). I edited it just a bit to better fit this thread and to (hopefully) make it more clear than it was written before:
I got my flexible silicon heaters from www.hiheat.com. (click on 'catalog heaters'). They offer a number of off-the-shelf units for 40 or 50 bucks. Only problem is that the longest of-the-shelf size is 40 inches. I tried to get a longer and more expensive custom made unit from a couple of other companies (Michael's was one of them), but they just never came through. I got tired of waiting and just ordered a couple of units from Hi Heat. I got the 3 x 36 incher's for about $50 each. I routed a 1/16 inch deep recess into my mold base, placed the heaters in the recess (with lead wires sticking out both ends of the press), then placed two layers of .040 aluminum sheet (7 inches wide) over the top. I left a 2 inch gap between the heaters at the center of the mold and attached my temp sensor to the aluminum sheet at that gap. Basically, the heaters heat up the aluminum sheets (great heat conductors), which, in turn, heat up the ski. The 3 inch wide heating units work so well that I'm quite sure that the 2 inch units would work just fine... and for about $30 each off the shelf. If a heater should go bad for some reason, you can just call up Hi Heat and order another one. It just takes about 3 days to get them. Keep in mind, though, that even though these heaters are pretty cheap, the electonics could run you a couple hundred bucks by the time that you're up and running. All I do is button up my press, inflate the bladder, flip a switch, and walk away for an hour. The electronics bring the heat up to 170 F +/- 2 degrees and keep it there... very nice.
Like the K's, I also got my PID controller and solid state relay off of e-bay. In fact, I got two of each, one set for my ski press and one set for my test press.
G-man
I cut and pasted the following from another thread that I contributed to a few weeks ago (cut and pasted because I don't know how to do that page linking thing that some of you guys do). I edited it just a bit to better fit this thread and to (hopefully) make it more clear than it was written before:
I got my flexible silicon heaters from www.hiheat.com. (click on 'catalog heaters'). They offer a number of off-the-shelf units for 40 or 50 bucks. Only problem is that the longest of-the-shelf size is 40 inches. I tried to get a longer and more expensive custom made unit from a couple of other companies (Michael's was one of them), but they just never came through. I got tired of waiting and just ordered a couple of units from Hi Heat. I got the 3 x 36 incher's for about $50 each. I routed a 1/16 inch deep recess into my mold base, placed the heaters in the recess (with lead wires sticking out both ends of the press), then placed two layers of .040 aluminum sheet (7 inches wide) over the top. I left a 2 inch gap between the heaters at the center of the mold and attached my temp sensor to the aluminum sheet at that gap. Basically, the heaters heat up the aluminum sheets (great heat conductors), which, in turn, heat up the ski. The 3 inch wide heating units work so well that I'm quite sure that the 2 inch units would work just fine... and for about $30 each off the shelf. If a heater should go bad for some reason, you can just call up Hi Heat and order another one. It just takes about 3 days to get them. Keep in mind, though, that even though these heaters are pretty cheap, the electonics could run you a couple hundred bucks by the time that you're up and running. All I do is button up my press, inflate the bladder, flip a switch, and walk away for an hour. The electronics bring the heat up to 170 F +/- 2 degrees and keep it there... very nice.
Like the K's, I also got my PID controller and solid state relay off of e-bay. In fact, I got two of each, one set for my ski press and one set for my test press.
G-man
Thanks for the info. I will look into that.G-man wrote:Mike,
I cut and pasted the following from another thread that I contributed to a few weeks ago (cut and pasted because I don't know how to do that page linking thing that some of you guys do). I edited it just a bit to better fit this thread and to (hopefully) make it more clear than it was written before:
I got my flexible silicon heaters from www.hiheat.com. (click on 'catalog heaters'). They offer a number of off-the-shelf units for 40 or 50 bucks. Only problem is that the longest of-the-shelf size is 40 inches. I tried to get a longer and more expensive custom made unit from a couple of other companies (Michael's was one of them), but they just never came through. I got tired of waiting and just ordered a couple of units from Hi Heat. I got the 3 x 36 incher's for about $50 each. I routed a 1/16 inch deep recess into my mold base, placed the heaters in the recess (with lead wires sticking out both ends of the press), then placed two layers of .040 aluminum sheet (7 inches wide) over the top. I left a 2 inch gap between the heaters at the center of the mold and attached my temp sensor to the aluminum sheet at that gap. Basically, the heaters heat up the aluminum sheets (great heat conductors), which, in turn, heat up the ski. The 3 inch wide heating units work so well that I'm quite sure that the 2 inch units would work just fine... and for about $30 each off the shelf. If a heater should go bad for some reason, you can just call up Hi Heat and order another one. It just takes about 3 days to get them. Keep in mind, though, that even though these heaters are pretty cheap, the electonics could run you a couple hundred bucks by the time that you're up and running. All I do is button up my press, inflate the bladder, flip a switch, and walk away for an hour. The electronics bring the heat up to 170 F +/- 2 degrees and keep it there... very nice.
Like the K's, I also got my PID controller and solid state relay off of e-bay. In fact, I got two of each, one set for my ski press and one set for my test press.
G-man