Prebending tip and tail

ggardner90 · Post by **ggardner90** » Mon Nov 28, 2011 5:25 am

i am making some park skis and want them to be as durable as possible. on the last one i made it was somewhat easy to get the tip and tail to delam from the ski. i was thinking that it would help a lot to prebend the tips and tails so that they "want" to be pressed up against the core instead of "Wanting" to be flat.

is this true will it help, does anybody else do this

twizzstyle · Post by **twizzstyle** » Mon Nov 28, 2011 7:41 am

Yep. It will make your layup much easier too if you're doing it in the mold.

Do some searching, there is lots about this on here. Quite a few of us (myself included) made nice tip benders this year.

Dr. Delam · Post by **Dr. Delam** » Mon Nov 28, 2011 11:12 am

I don't think that it has much to do with why you are getting delams. There must be some other issues going on here.

Huck Pitueee · Post by **Huck Pitueee** » Mon Nov 28, 2011 2:30 pm

Plus one.

ggardner90 · Post by **ggardner90** » Mon Nov 28, 2011 2:33 pm

i was thinking about making a tip bender that is 1.5 the radius of the tip so that after it relaxes it will be the same radius of the mold

Richuk · Post by **Richuk** » Mon Nov 28, 2011 3:34 pm

Look for this thread in the equipment section: http://www.skibuilders.com/phpBB2/viewtopic.php?t=3199

twizzstyle · Post by **twizzstyle** » Mon Nov 28, 2011 5:29 pm

ggardner90 wrote:i was thinking about making a tip bender that is 1.5 the radius of the tip so that after it relaxes it will be the same radius of the mold

You've got it backwards, you want the bender radius to be smaller than your tip, but you've got the right idea. Don't overthink it, this is one thing that really does not need to be over engineered. Some radius smaller than your tip, but it doesn't need to be any specific value.

As others have said, you shouldn't be doing this to overcome delam issues... Yes it will make the skis less prone to come apart, but if you're getting delam you need to solve that separately. But this does reduce the "static stresses" if you will that the ski would have if it wasn't prebent. And again, it makes layup in the mold SO much nicer.

Video of mine...

ggardner90 · Post by **ggardner90** » Mon Nov 28, 2011 8:56 pm

i didnt have any delam till i started to test its durability. also thank you for pointing out that i want a smaller radius i was thinking smaller but said bigger but would .5 of the tip radius be good or overkill.

so u might think i am crazy but i am really trying to make a ski that is as durable as any of the line skis that i have ridden. so i was doing an extreme test of vibration dampening...and when the tip hit concrete at a decent rate of speed the edges blew out. but the base for the most part stayed attached. i had about 1.5in of delaming of base from core so that is good for the first ski ever i guess. (the core shifted during pressing and graphic was delaming so i wasn't going to get it base grinded and wanted to see what it could handle.

MontuckyMadman · Post by **MontuckyMadman** » Mon Nov 28, 2011 11:59 pm

I did some extreme concrete slap testing the other day and from what you are describing yuo are definitely having some bonding issues.
The edges shouldn't "blow out".
The tip will delam at the topsheet before any thing else in almost every type of wood core ski.
Did you use vds rubber over your edge?

twizzstyle · Post by **twizzstyle** » Tue Nov 29, 2011 9:34 am

ggardner90 wrote:i didnt have any delam till i started to test its durability. also thank you for pointing out that i want a smaller radius i was thinking smaller but said bigger but would .5 of the tip radius be good or overkill.

You're still overthinking it. No numbers!

Use a 5" diameter tube (2.5" radius). Good enough

(also, it's "you" not "u"... pet peeve of mine)

ggardner90 · Post by **ggardner90** » Tue Nov 29, 2011 11:10 am

sorry about the short hand u i will speak properly, its hard im only 21 and im language is really fast to type.

i am using VDS rubber, so to describe the test i grabbed the tail of the ski and lifted it over my head then smashed on concrete as hard as possible took 2 mashes to get the edge and base to delam i will post a pic.

when i pressed the ski i had a small leak in the bladder so it was kind of un even pressure and it didnt press for the whole amount of time i was hoping for.

also i am just using the numbers as a reference point so i know i can tell you how much of a difference i am thinking. i am not getting anything cnc'd for the tip bender.

could YOU guys post some pics of the tip bending settups YOU use

twizzstyle · Post by **twizzstyle** » Tue Nov 29, 2011 2:01 pm

Look at my youtube link above. That's me with my bender, that was easy to build and works great! I don't have any photos of it, but the video should suffice, and I've got some crappy MSPaint sketches in that other thread.

MontuckyMadman · Post by **MontuckyMadman** » Tue Nov 29, 2011 4:28 pm

I feel a better slap test is to bend the ski from a standing position and slap it down with your foot. Lands flatter than slinging it wildly and is more repeatable.

sammer · Post by **sammer** » Tue Nov 29, 2011 8:25 pm

It's here
http://www.skibuilders.com/phpBB2/viewtopic.php?t=3199

sam

ggardner90 · Post by **ggardner90** » Wed Nov 30, 2011 4:20 pm

i agree with you and do not ever anticipate repeating the smashing test. the core shifted during layup and the graphic is delaming so i kinda wanted to go extreme and see what it could take.

need to develop a slap test that is repeatable. i think i have an idea for the tip and tail bender so ill post a pic when its done.

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Prebending tip and tail

Prebending tip and tail