no one wants to grind my skis!

MontuckyMadman · Post by **MontuckyMadman** » Sun Dec 25, 2011 10:02 am

skibum wrote: I bring it up to temp over 8 min and bake for 30 min then put it in the snow.

In the snow. crazy.

twizzstyle · Post by **twizzstyle** » Sun Dec 25, 2011 10:29 am

I believe that's called blanching.

skibum · Post by **skibum** » Sun Dec 25, 2011 11:55 am

Ya still experimenting with it for now but the idea is to get everything down quickly. It made super flat skis on the last pair so I'll try it again over the next couple days and compare. I found otherwise the middle (underfoot of the ski) stays warm a lot longer. I had the opposite issue however, my edges were going up (convex base). I'm guessing the shop didn't want to touch a ski with 1mm variation between edges (concave from what I understand) because bases are only 1.3mm think generally and thats a pretty fine line between hitting fibreglass.
We will see how the next ones turn out

sir.orange · Post by **sir.orange** » Sun Dec 25, 2011 12:49 pm

just to throw in how i pressed these skis, maybe you lll find the critical point:

im tempering the resin 24h - 20°C and 16h - 60°C these are specific temerature cycles given by the manufactors. im pretty accurate with this, im using a pid controller, and do not increase the temperature more than 10°C per hour (manufactors suggestion) after that i switched the heating off and put skis immediatly out of the press (12°C ambient air temperature) and started cutting them out...

sir.orange · Post by **sir.orange** » Sun Dec 25, 2011 12:50 pm

skibum wrote: I'm guessing the shop didn't want to touch a ski with 1mm variation between edges (concave from what I understand) because bases are only 1.3mm think generally and thats a pretty fine line between hitting fibreglass.
We will see how the next ones turn out

yes, concave (edges went down, base up)

Richuk · Post by **Richuk** » Sun Dec 25, 2011 1:51 pm

The speed of layup isn't the issue ... otherwise I'd have all sorts of funny shapes. Skibum what does your core cross section look like?

Not sure how it can be the speed of cooling ... DBS pulls them out hot and leaves them to cool naturally, but if Brazen is thinking this is the issue, I'd look hard at this.

The only other thing to consider, if its not the cross section, is thickness of the cassette. At only 1mm, is the ski a little more sensitive to the heat map created within the heat blanket - never used the silicone one, so not sure, does the temperature vary much across the width? It may explain different result from same materials, but it doesn't sound very likely ...

I'm just glad that its nothing you can't fix - at least a temporary fix

Here are a couple of additional links: http://www.matweb.com/reference/compres ... ength.aspx , http://www.matbase.com/material/wood/cl ... properties

It would be interesting to know where the areas of convexity are appearing?

skibum · Post by **skibum** » Wed Dec 28, 2011 7:34 pm

Richuk I'm guessing you are asking if I cut a step for the edges and yes I do. If I am misreading let me know.

Richuk · Post by **Richuk** » Thu Dec 29, 2011 4:25 am

Hi skibum, I was thinking more about the materials being used for the core and the sidewall - if you don't mind sharing this info )

skibum · Post by **skibum** » Thu Dec 29, 2011 5:27 pm

Bamboo core, bamboo sidewalls. Ya I'm totally happy to share info.

Richuk · Post by **Richuk** » Tue Jan 03, 2012 3:03 am

bit thrown by this skibum ... I wonder, how do you lay up. Do you fully wet out the fabric in advance or do you let the press do some of the work. I think this is what OAC was pointing at.

Might this explain the squirely nature of the problem? Tri-axial glass, different layer not fully wetting out, therefore, sometimes convex/ concave and in different areas.

skibum · Post by **skibum** » Tue Jan 03, 2012 8:36 am

I wet everything out as I am laying up. I use 22oz tri-axial above and below with a carbon strip on top and mat(t) glass on top for binding retention. I tend to get a slight amount of convex in the transition between tips and tails. Talking to the shop I go to most big manufacturers have this as well, especially Black Diamond. It could possibly be contact of the bladder in the transition which I will look into. It is very minor in my case though and a belt takes it out in a couple passes.

Richuk · Post by **Richuk** » Tue Jan 03, 2012 11:53 am

Thanks skibum - all good to know. Around the tip and tail sounds like the fibre and I could see how cooling could play a big part.

Shout if the fibre I'm using sounds interesting.

EDIT - sorry, I mentioned in the other thread that it is nominally quad-axial.

sir.orange · Post by **sir.orange** » Tue Jan 03, 2012 3:59 pm

just measured the concave skis: the biggest arc is under the binding section, the arc gets flater towards tip and tail but remains with something like 0,2-0,4mm.

BLOODTYPEZX10R · Post by **BLOODTYPEZX10R** » Sun Feb 19, 2012 12:48 pm

I have been having the same problems and has raised some questions for sure.
1. I cook my boards according to the epoxy specs.
2. I use QCM emv004 eca324
3. Ramping of the cure temp will cause incomplete cross-link during curing process. Low temp ramp cure may be causing a bond to occur at lower temp and increase temp ramp is just finishing off the cure and not gaining the advantage of full temp cross-link at full temp cure. Cure temps 160-180f specified by resin manf.
result: 1.5-2mm+ concavity of base. Not just the base but the entire core-excluding tip and tail curvature areas.

I am not sure what type of bases that some of you are using, but I use Isospeed 7200. I have placed the base cassette in press (just lying in press) while I have been prepping some materials and within a few minuites have a wavy base due to thermal expansion of base material; and of course the metal edged will not have the same thermal expansion rate.
As I have stated on this forum before I do not construct my snowboards like anyone I have found yet. I have never had this problem before I began heating my press. Carbon fiber like fiberglass are choice materials because the have very low thermal expansion rates-even compared to wood, the plastic expands much, much more. Have you ever seen the body work of a Corvette warp or deflect?
Conclusion: Resin in its uncured state allows slip of of base to core/composite-whatever, base expands, board cures and everything is set-at 180f. Cool board, base shrinks to original ambient temp size and draws all components with it. Now I suppose there is a possibility that some base material cannot contend with the strength of core and will stretch. Use of VDS foil between base and core covering aprox. 50% of core width will allow give.
Now if board is placed again in press and raise temp again to near full temp cure the concavity is gone-base has expanded again to cure temp size and all is flat. If temp is raise to say 140f-has less concavity, not as much as room temp-not as flat as at full temp. I do not subscribe to the thought that resin is shrinking-that is one of the main reasons we use resin. It does not shrink from its uncured volume. Atleast the shrinkage is so minimal-so minimal it is not a concern. Besides if this were a factor I would see this happen in the construction of my cores or for that matter the making of my core blocks.

OnDeck · Post by **OnDeck** » Thu Apr 05, 2012 6:24 am

falls wrote:did you rebate the sidewalls for edge teeth?
I think not doing the rebate leads to concave bases (at least in my experience).

Like he said, this was my first thought. My stuff was coming out concaved until someone here kindly pointed out the error of my ways. Shoulder your sidewalls!

And the grinder is correct, he could really mess up a stone with a non-true base, and the way those things cost gridners are rarely ready to take a risk.

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no one wants to grind my skis!

It is happening to me too.