Concave Bases on early rise

monkeyshowpictures · Post by **monkeyshowpictures** » Tue Sep 20, 2011 1:31 pm

I am getting concave pockets in my bases in the early rise portion of the ski. I have a 20cm early rise tip block and a 40cm one and it happens on both. Bases are flat through the middle of the ski. I have top and bottom heat and top cat track. I used to let skis cool in the press but following Black Sheep's advice stopped doing that. No improvement. I cut a cross section of the ski at the concave portion and found that the glass is far more compressed in the concave area than elsewhere. I have tried pressure every where between 30 and 90 psi with the same result. Many skis are too concave to grind flat. Very Frustrating. Has anyone had this problem and solved it?

Thanks,
Morgan

vinman · Post by **vinman** » Tue Sep 20, 2011 2:07 pm

Is the space between the curve on the top mold too close to the material creating too much pressure? I suspect this is the cause of the top sheet denting I get sometimes.

Brazen · Post by **Brazen** » Tue Sep 20, 2011 3:48 pm

Pre-bend.

monkeyshowpictures · Post by **monkeyshowpictures** » Tue Sep 20, 2011 5:26 pm

That is an interesting idea Vinman, I do not have different top molds for use with my early rise tip blocks. I have tried a lot of different pressures though so it would have to be the progressively increasing pressure into the tip not the amount of pressure itself.

Brazen do you prebend the early rise curve or just the tip curve itself? The early rise curve seems to subtle to make much difference (2cm rise over 20cm run and 3cm rise over 40cm run). Not that that rules it out as the cause, strange things seem to happen inside the press. I prebend the tip curve some, just by hand, so that it will sit in my pre bent cassette.

Brazen · Post by **Brazen** » Tue Sep 20, 2011 5:30 pm

The concavity is being caused by a non-compliance under pressure in your press. Whatever you need to do to sort that. But that's it.

skiercaleb · Post by **skiercaleb** » Tue Sep 20, 2011 6:24 pm

Brazen wrote:The concavity is being caused by a non-compliance under pressure in your press. Whatever you need to do to sort that. But that's it.

Are you trying to be helpful or show off your big vocabulary? If you actually would like to help this guy and you know how please say so because I would like to know the answer to this problem also. Thank you for any suggestions on how to really solve this issue.

Brazen · Post by **Brazen** » Tue Sep 20, 2011 6:36 pm

Great. See what you've done here? If I WAS going to re-explain the simple concept that was proffered with problem specific details, even though none were specified, now that I know it might help you it's never gonna happen. Way to step up on your first post. Anything else?

twizzstyle · Post by **twizzstyle** » Tue Sep 20, 2011 7:10 pm

Since when is non-compliance a big word?

sammer · Post by **sammer** » Tue Sep 20, 2011 7:16 pm

twizzstyle wrote:Since when is non-compliance a big word?

Probably get you a pretty good scrabble score

sam

monkeyshowpictures · Post by **monkeyshowpictures** » Tue Sep 20, 2011 7:21 pm

Ok everyone take a deep breath. Brazen, I understand the concept of non compliance and have actually done experiments where I forced only the base (with edge attached) into the tip shape by hand. This produced a concave base. What I want to know is if the problem can be solved by actualy pre bending the base and edge in a slip roll type device like twizz's. This seems like it could relieve some of the tension in the system. I will try rolling in the tip curve in the slip roll tommorow and see if that helps. I wonder if it is necessary to roll in the early rise curve as well, doing this would make for a tricky lay up, I think.

sammer · Post by **sammer** » Tue Sep 20, 2011 7:41 pm

Is your concavity like this?

sam

monkeyshowpictures · Post by **monkeyshowpictures** » Tue Sep 20, 2011 7:53 pm

Sammer, yes I get some of that, but it continues back through the early rise (20cm or 40cm). Did you have more concavity further back on the ski and ground it off or was it pretty flat after the tip? I actually made some skis with a extra patch of glass cloth in the early rise portion to take up volume and keep the skis from being railed. it worked, but made the tips stiffer than I wanted and it is not really solving the problem.

Twizz and others who have been pre-bending your tips, what prompted you to start doing this? Were you having any concavity problem like mine? Did pre-bending solve them?

MontuckyMadman · Post by **MontuckyMadman** » Tue Sep 20, 2011 9:04 pm

grind it dawg.
there is no hyphen in scrabble.

twizzstyle · Post by **twizzstyle** » Wed Sep 21, 2011 6:50 am

monkeyshowpictures wrote: Twizz and others who have been pre-bending your tips, what prompted you to start doing this? Were you having any concavity problem like mine? Did pre-bending solve them?

The only reason I started pre-bending (I've only done it on one pair so far) is because I do my layup in the mold, and it was becoming a huge pain in the ass laying everything on the stiff/flat base/edges. With the pre-bent base/edges it all lays nicely in the mold and layup is a breeze.

I've never really had concavity issues, if anything I have convexity issues, but some of that is because I'm only heating from the top

Richuk · Post by **Richuk** » Wed Sep 21, 2011 9:30 am

I think Brazen was saying that you need a more holistic view on this:

We rebate the core to allow the edge set to nest properly during lay-up. If the rebate is too deep, the pressure applied by the cat-track (assuming one is being used) is reduced and the epoxy pools in the area below (below means near to the seam created between the edge set and the base material). It follows that you may well rebate correctly, but the mold is nominally inaccurate, then the same result.

We don't rebate the tip-spacer, so you have to ask what is happening within that area. What causes the pressure to be different, as you can't just force everything together and expect compliance (well not strictly true).

So what are the options?

Re-bate tip-spacers - which requires full or partial cassette? Or, maybe depending on the material used as a tip spacer (thermo-plastic) and the heat applied, force is an option. Iggy - feel free to jump in at this point : ) Anyway, does the Black diamond video offer anything - why the black epoxy and why is it so thick? Is it Thixotropic?. Does it form a seal? If so, is this sufficient for the standard you want? Maybe it adds value when QA testing? Clearly it reduces clean up time. Other options ...

Have a think about all the transition between the core and the tip-spacer, the material you are using and how you control the epoxy within the press and you'll find a solution that works for you. Pre-bending could be considered important, depending on how you are treating you edges. Relieving the tension etc. It's a QA issue too.

Oh, the other point, no, you don't need to pre-bend the early riser.

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Concave Bases on early rise

Concave Bases on early rise