Heat affecting camber

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gozaimaas
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Location: Nagano Japan

Post by gozaimaas »

Damn Im geting dead flat bases on a 300mm+ wide snowboard, skis should be a walk in the park to get flat.
I heat mine to 100°c on the bottom and 80°c on the top then I let it cool for 20 mins. The bottom will drop to about 80°c andvthe top only drops to about 75°c. Pull it out and stand it on edge until room temp. Dead flat every time.
MadRussian
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Post by MadRussian »

MontuckyMadman wrote:Cook the skis at 180 on the bottom and 155 on top for most of the cycle and finish it off at 180. You will get camber.
by mistake I done that and it didn't work. By time problem got noticed it was too late. Top got as high as 200° F bottom about 160° F total cook time 30 min. With difference of almost 40° skis came out zero camber from zero camber mold. Glad it didn't work because I didn't want any camber
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
gozaimaas
Posts: 663
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

MadRussian wrote:
MontuckyMadman wrote:Cook the skis at 180 on the bottom and 155 on top for most of the cycle and finish it off at 180. You will get camber.
by mistake I done that and it didn't work. By time problem got noticed it was too late. Top got as high as 200° F bottom about 160° F total cook time 30 min. With difference of almost 40° skis came out zero camber from zero camber mold. Glad it didn't work because I didn't want any camber
Did you ramp them up seperately or together?
I start my bottom heat first and when it reaches 20°c above ambient I turn on the top mat. That 20°c differential is maintained the entire time with very consistent results
MadRussian
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Post by MadRussian »

gozaimaas wrote: Did you ramp them up seperately or together?
I start my bottom heat first and when it reaches 20°c above ambient I turn on the top mat. That 20°c differential is maintained the entire time with very consistent results
yes ramp up together. It happened unintentionally because I misplaced TC for the top blankets on the bottom cassette and TC for the bottom blanket on the top.
For now I'm making skis with zero camber and quite happy that temperature differential did not produce any camber/rocker. Because of my mistake top running 40°f higher I could've get a reverse camber or banana skis
I'm not trying to determine what went wrong simply stating my experience.
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
gozaimaas
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Location: Nagano Japan

Post by gozaimaas »

Well thats why you didnt get camber.
MadRussian
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Post by MadRussian »

gozaimaas wrote:Well thats why you didnt get camber.
so because ramp up both blankets together I didn't get any camber/reverse camber?
I like final results and want to continue doing same way maybe not so much differential like 40°f maybe sums and 25° to 30°f
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
gozaimaas
Posts: 663
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

MadRussian wrote:
gozaimaas wrote:Well thats why you didnt get camber.
so because ramp up both blankets together I didn't get any camber/reverse camber?
I like final results and want to continue doing same way maybe not so much differential like 40°f maybe sums and 25° to 30°f
Yes.
By ramping both up at the same time it kicks the epoxy at the same time top and bottom. By the time you get to max temp the work is done so having a differential at the top end will have less or in your case no effect.

To get camber start the bottom heat first and maintain the difference as the heat increases.
pavelbozak
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Post by pavelbozak »

hi, this is interesting and very familiar topic....

What about heat and all the variables affecting full rocker construction?

my experience is only with doing camber with tip and tail rocker. I always got less camber and tips with tails increased a bit according to a bottom mold. The stiffest construction is, the more camber decreases. In fact my camber was now set in mold to 12 mm and I ended in real with cca 7 mm of camber.

I have also tried flat camber and I got once full rocker shape (symetrical layup) and once slight camber cca 2 mm (there was some carbon layer extra on the top...

I am going to try to built full rocker ski, but I am not sure how to set my bottom mold. Construction will be symetrical with carbon and fiberglass. I want to make quite a stiff setup, so I could count with huge decreasing of my full rocker shape? Am I right? I d like to get something about 40 - 45 m radius of rocker underfoot. So I would set my bottom form to 30-35 m and if the shape decreases it could reach something around aimed radius... ?

on the other side what if rocker increases more? :D That would be quite bad such a banana skis.

I was thinking about setting the form to a flat camber and adding one carbon tape stringer under a wood core to get reverse result to my skis with carbon layer on top. But I would be grateful for some experience with making controled full rocker shape :)

oh and, important notice - my heating is "spartan style hotbox" - hot air ventilator from bottom (temperature is slowly increasing from 20 °C to 40 - 50°C) and I left skis in my press for full 24h (my epoxy is 90 % curred after 24 h at room temp - 25 °C and after 20 min at 80 °C)
MadRussian
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Post by MadRussian »

if I understand correctly you are using a room temperature curing epoxy. Even hotboxed I don't think it's relevant to general subject of the discussion because people used heat cure epoxy where skis done in 20 – 40 min.
imo you should keep hotbox at 70° F for entire duration of the pressing and try to get camber/rocker from mold. also air cure epoxy even after 24 hours might be very soft and pliable you might want to experiment with time in the press. Maybe no heat but longer. it all depends on the manufacturer and their recommendations for cure time
sorry can't help you with your problems since never had any of those.
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
pavelbozak
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Location: Europe

Post by pavelbozak »

My epoxy system is originaly made for building skis/snowboards and is used in many factories (5M Letoxitt LH176, Czech product). It is designed to fully cure at the temp of 80°C in 20 min.... But the same result you can get at room temp (25 °C) after 24 h (48h maximal strenght). I have chosen this epoxy because I do not have to care so much about temperature and I can be sure that it fully cure even at lower temperature. It is not cheap but other systems in here need mostly an exact temperation and at this moment it is nothing for me - as I don t have heating blankets with PID controller yet and my cassettes are not aluminium, so the heat in press acumulates quite slowly.

But am I right that full rocker will behave similairly as camber and its height will decrease acording to the bottom mold?
gozaimaas
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Post by gozaimaas »

You will get some spring back, how much depends on how thick the core is.
pavelbozak
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Location: Europe

Post by pavelbozak »

Well. After first "building" season I have done the second. I had some experience from the first and tried to implement it this summer.

I wanted to get as flat bases as possible and to get cca 5-8 mm camber in my skis. So I made mold with 10 mm camber end expected decreasing of camber like previously.

I let all cure for 24h at room temp, maybe a bit more (it was quite hot this summer). Result was quite nice. Camber was a bit higher then I expected (7-8 mm). Lastly it decreased 50 % against mold. And all the skis were nicely flat.

BUT

now temperatures are like 5-10 °C and ale the cambers are HUGE !!! :D and some skis are quite convex (railed). I tried to put skis into infra sauna and heat them. result was that it got back. I wouldn´t expect that temperature could affect camber so much when ski is already cured!

Well maybe I should write some numbers... Camber at room temp: 7-8 mm, camber at 5-10 °C: 16-18 mm !!!! really HUGE (something like nordic ski). I am afraid what about temps like -10 °C :D

Some things that could support this problem:

- Wooden veneer on top - wood is dead against UHMW plastic base

- Fat bases - the more heat reactive material the more spring

- or something else?

Has someone also noticed that problem?


It is a pitty there was not oportunity to put the skis into fridge during summer. I would decrease the amount of camber mold...


Maybe I will have to make some heating system for my skis to decrease camber or maybe I could make some thermoregulating system to set any camber/rocker shape :D

I discussed that problem with ski manufacturing company (Sporten) and they told me they struggle with something similliar. They solve it with setting huge top heating temparature (20-30-40 ° more then bottom) and they just count with some heat affecting issues.

Similiar problem is also for example with racing skis. There is a titanal and the ski springs into flat camber or even full rocker shape at low temperatures :)

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gozaimaas
Posts: 663
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

I get consistently beautiful camber with and without veneer, so I would not assume that is your problem.
I use sicomin epoxy and heat to 100°c/bottom 80°c/top for 10 mins, the whole process takes 25 mins. I pull it 30 mins later and cool it on its side.
Personally I think the short sharp heat cycle I use has something to do with my success rate.
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