First Pair - Layup Critique

[nfaust]

Well it's approaching 90*F today here in NJ, so that can only mean one thing: time to start working on some skis! I'm slowly working towards laying up my first pair and could use some critique on my shape before I start cutting a mold, ordering material, etc.

Some quick info:

• Pintail powder skis (based on an existing design from an existing mfg)
• 5'10", 150 lbs, east coast (read: variable) conditions
• Will be vacuum pressing these and most likely bamboo core, profiled in a planer, without sidewalls
• Hoping to press without heat, unless it's absolutely critical (comments/recommendations on this are welcome)

Here's where I'm at so far:

Overall Shape


Camber Profile


Core Profile - Relations are not shown, but I was thinking just a linear taper from the binding mount to the front/rear contact patches (316mm tip, 110mm tail)

Specifically, I could use some suggestions on:

1. Core profile - does the core require a completely flat space for the binding mount, or do cores start tapering underfoot?
2. Additionally, I'm shooting in the dark here for dimensions. Seems like most are in the 2 - 4mm range for tips/tails and 10-15mm range underfoot. I'm assuming I should be on the lower end of those ranges, but just guessing here.
3. Layup - again, this will be my first pair, so I don't have much of a baseline. Is one layer of 19oz triax on each side of the core a good starting point?

[sammer]

Specifically, I could use some suggestions on:

1. Core profile - does the core require a completely flat space for the binding mount, or do cores start tapering underfoot?
2. Additionally, I'm shooting in the dark here for dimensions. Seems like most are in the 2 - 4mm range for tips/tails and 10-15mm range underfoot. I'm assuming I should be on the lower end of those ranges, but just guessing here.
3. Layup - again, this will be my first pair, so I don't have much of a baseline. Is one layer of 19oz triax on each side of the core a good starting point?

1. No your core does not need a flat spot.
   I've used either, most have been thickest at center of running length and tapered to the ends from there.
2. Stick with 10-12 underfoot and 2 or so at tips and tails.
   If your using tip spacer anything other than 2mm will give you an odd transition area.
   1/2mm makes a very noticeable difference in stiffness.
   If your going to leave a flat spot underfoot you should probably go 10-11mm
3. One layer of triax on either side will be just fine.
   You might want to add something in the binding mount area.

sam

[nfaust]

Thanks for the info, Sam. Probably going to forego the tip/tail spacers to keep things simple for the first go, but I'll stick with the 2mm regardless.

I've read/seen recommendations for the reinforcement in the binding mount area - is this just another layer of the 19oz triax only under the binding mount, on top of the core?

[twizzstyle]

The bamboo is going to be hard to bend to the tip shape, especially if you're just doing vacuum. Might want to re-consider tip-spacer for that reason alone.

Your profile seems to be very biased towards the rear. Those are going to be some noodly tips with STIFF tails!

[skidesmond]

I'm an east coast skier also. Tip height seems a bit high (78.5mm = 3.1 in) to me, mine are about 2.25-2.5in or so. I agree with Twizz, the boot center seems a bit far back. Based on the dims you have, I would make the boot center (i.e. center of the ski) at 682mm (1364/2), I add another 50mm to push it back to 732mm. Adding the 50mm is up to you, but a lot of DIY builders do that. Then the height of the camber s/b at the boot center or close to it. Draw that out and see how it looks.

[nfaust]

Thanks for the help so far guys.

The bamboo is going to be hard to bend to the tip shape, especially if you're just doing vacuum. Might want to re-consider tip-spacer for that reason alone.

Noted, thanks. Does the core typically extend into the tip at all? Or is it all tip-spacer?

Your profile seems to be very biased towards the rear. Those are going to be some noodly tips with STIFF tails!

Yeah, after posting I was looking at it some more and realized that as well. I think I messed something up there.

Tip height seems a bit high (78.5mm = 3.1 in) to me, mine are about 2.25-2.5in or so.

Was going for a relatively high tip for the powder. Maybe the 2.5" - 2.75" would be a good compromise?

Thanks for the recommendations on positioning the boot center. Here's where I'm at now:


One other question:
Does the core profile typically extend linearly from the thickest point to the tips? Or are the tips constant thickness (2mm) to the contact patch, and then start their taper?
A quick sketch to highlight:

[skidesmond]

To answer the tip question, the tip is a constant thickness usually 2-3mm is normal.

[MontuckyMadman]

you can do it either way and you can use 3 veneers for tip spacer if you dont want to do plastic.

[nfaust]

Thanks for the help, guys.

Not so worried about the plastic, but moreso making sure I have tight interface between the core and the spacer. Figured since it'll be my first build, the fewer variables the better.

[twizzstyle]

Everybody does tip spacers a little differently.

Some people cut their core to a point, and cut a matching shape in the tip spacer. This is what K2 does, I used to do this. Some people cut a circular arc with matching tip spacer.

Now, I'm lazy, I just cut my core straight across. I use as much tip spacer as I can from one of the squares I buy from BlankSlate, which ends up being about 6" of tip spacer (4 spacers per square, for one pair of twin tips)

As for how you do the taper, that can also vary, but I would have the taper end at your contact point. The ski effectively doesn't flex past that point, and if you move the end of the taper up into the tip, you will have a stiffer ski.

If your core and tip spacer aren't exactly the same, you'll only have a small step in your topsheet, it's not the end of the world (on one of my pairs I had 3mm cores at the tail with 2mm tip spacer, I didn't do anything to make them match, and the step is hard to see unless you look. The gap just filled with epoxy.

[MontuckyMadman]

another thing to keep in mind is the rabbet for the edge. If you make you cores 2mm thick at the end when you rabbet your .8mm or whatever the sidewall is 1.2mm thick and it looks crappy. so leave the core at like 2.6-2.8 so when you rabbet the sidewall will match the tip spacer and the .6 or .8mm will be compressed. Trust me. Fit and finish is much better at this area doing it like this. Of course you need to compensate and make the total thickness less otherwise it will be a 2x4.
THis is my experience so YMMV, I would like to here how others deal with his rabbet/sidewall interface.

[vinman]

MM so you are asking about the sidewall and tip spacer joint and the difference in thickness between the end of the profiled sidewall and the thickness of the tip spacer?

I do an interlock type of tip spacer. This leaves me lots of wood out in the tip that measures 2.2mm to match the tip spacer. I usually sand this by hand to match the tip spacer to the core. then by the time the core thickens back near the start of the sidewall they are nearly matched up even with the rabbet.

[MontuckyMadman]

Yeah Vin, I dont feel that belt sanding the tips of my cores is very accurate and an extra step I try and avoid.
I have done it that way and I dont find that I need to extend the core into my tips for the skis I make. The 22oz triax and resin is sufficient in that area. If I ram my ski into a tree or rock head on and it breaks at the interface, so be it.
Good info though thanks.

[vinman]

The biggest thing I try to do is match the wood in the tip to the thickness of the spacer to keep my base and top sheet nice and flat. If this is not right things get convex on the base for me.

The rest of it I don't really care about, such as any height difference between the sidewall and tip spacer. I like the interlock tip for exactly what you mention, I don't want that weak spot at the core-spacer interface.

[sammer]

I've always been worried about the straight across tip space so cut at a 90 from the center.
Bought a little skillsaw attachment for my dremel. Works slick.
Easy to see in the pics in my log.

http://www.skibuilders.com/phpBB2/viewt ... 3&start=33

With vacuum a little difference in thickness will be OK.

sam