core design

[vinman]

SO now that I am done with building my shop. I'll be building my core profiler this weekend.

My plan for a profiler is basically 2 sheets of MDF for top and bottom with 10- 15 spacer blocks in the middle held in place by T-nuts and allen bolts.

So for core design I'm looking to make a fairly stiff ski. Other skis I have skied and liked are PM gear BRO model 188 cm (stiff) 1st year of production, black diamond verdict.

I hate soft skis. Being on the east you need a stiff ski to bust crud and hold on firm snow but also float pow. Yes we have pow on the EC...

My thought for core design is this 1.9 mm tip with linear taper to 11 or 11.5 binding mount area of 350 mm then linear taper down to 2.1 mm tail.

So in your opinion/experience will the 11.5 mm waist give me too stiff of a ski? Or since I am creating a flat mount area will that be too thick?

Will 1.9 mm be too soft in the tip?

I'll likely be using a maple-poplar core, with 19 or 22 oz triax glass, veneer topsheets. Not sure on the sidewalls yet.

I'm planning on building 2 sets of skis to start. With the likely scenario as the first ski being a test and the second being adjusted off the performance result of the first.

Thanks for the help.

[MontuckyMadman]

Your tip spacer will be 2mm so the Bro is in fact an aspen core and it is 2-12-2 on center. No flat area. He uses extra glass to stiffen the ski in the stiff.
With a flat area and maple/poplar yes it will be stiff. As stiff as anything on the market at the stiffest end of stiff. IMO.
With this plan I would go 19 oz.

[vinman]

OK so I'm at least in the ball park. What do you think of thinning the waist out to 10 or 10.5 mm.

I'm not a big guy I'm only 5'8 and 150ish so I'm not looking for the most burly ski out there, just stiff enough to perform the way I want it to.

I think I'll beef up the tip to 2mm to keep it from getting sloppy and to match up with the tip spacers better.

I won't be cutting spacers tomorrow but I will be cutting the MDF tops and planning out where to place my spacer blocks.

I'll likely drill and countersink the t-nuts and bolts Saturday and maybe start cutting spacers on Sat or Sun.

[skidesmond]

MM is right about the tip spacer. I have a flat area of 350mm as well. My planer crib makes a gentle bend into the flat area even though the crib itself has a flat area of 350mm.... trivia...

A 2-12-2 will be fairly stiff especially if they will be fat like the BRO 188 with 22oz triax. I just bought 19oz triax so I'm wondering how much difference they'll be.

Some day I'll post plans for an adjustable planer crib that will allow you to make different length cores as well as different thickness... once the idea is fully baked.

[vinman]

I'm going with a 185 cm fat ski 139-105-126, slight tail kick.I hate twin tips. Not sure about camber yet. For my first ski I think I'll stick with traditional camber. Future designs are definitely in the works for a reverse and or mixed camber ski, Rossi S7 like.

2-10-2 with a flat spot should be fairly stiff then with either 19 or 22oz triax.

Thanks guys. I appreciate the help. Keep the suggestions coming.

I need to get some decent calipers soon for cutting blocks and cores.

[MontuckyMadman]

I am almost ready to plane and layup some 2-10.5-2 with a 40cm flat area polar/maple at 105 mm underfoot with 22oz triax and SuperSap resin. Will report back in a few weeks maybe.

[Dr. Delam]

Once you get your calipers, double check your tip spacer thickness as well. I found mine from ski builders to be 2.2 mm. Not that .2 mm is that much but when your calipers measure in hundredths of a mm you start getting really picky. When your thicknesses are spot on, you won't see a transition from core to tip spacer.

I can't really contribute to your flex questions though. All my cores have not had any flat spot in the binding area. I think a continuous curve will allow for a rounder arc when flexed and less of a flat spot that a boot and binding creates already. I also based it on looking at lots of retail skis and didn't see any with flat profiles under foot.

[ruudsjoukes]

Just a little adding, can't reply on the core profile question.
A flat section underfoot is important if you're using bindings that request that. The smaller your arc will be, the more your centers of the 2 bindings (if you're using nose and rears) will be outlined and therefore less stable and more likely to pop out. It's just a little bit, but little bits in bindings can be crucial.

I'd go for at least a flat mount (like support under binding, e.g. rubber or a small thin piece of plastic) or go for a flat section on the binding mounts.

Just all I know on this.

[powderho]

Well I thought I liked soft skis but...........my cores are quite a bit thicker. A few pair of skis last year were around 2-2.5 tip, 10.5-11 waist, 3-3.5mm tail, and everyone thought they were too soft--but me. I've always been a fan of a softer, more forgiving tip and tail, but stiff under foot. This summer we made some ash/maple cores that were 2.8-12-3.5, with about 5 inches of flat under foot. I'm worried about them being too stiff, but everyone else thinks otherwise. We'll see. I think my ski design needs a stiffer core in a way. They are 135 -120 - 130 early rise style with 2 layers of 22oz glass. My last pair has a bamboo core at 2.7-11.7-3.5 with about 5 inches of flat under foot. I'm really liking the way they flex; at least in my living room.

The more I think about these numbers, the more worthless I think they are. The first pair I ever built was way too stiff. They were still skiable, but weird to say the least. The poplar/ash cores were 2-10.5-2 with about 7 inches of flat under foot.

[doughboyshredder]

I'm going with a 185 cm fat ski 139-105-126, slight tail kick.I hate twin tips. Not sure about camber yet. For my first ski I think I'll stick with traditional camber. Future designs are definitely in the works for a reverse and or mixed camber ski, Rossi S7 like.

2-10-2 with a flat spot should be fairly stiff then with either 19 or 22oz triax.

Thanks guys. I appreciate the help. Keep the suggestions coming.

I need to get some decent calipers soon for cutting blocks and cores.

2-10-2 is a whole lot softer than 2 -12 -2.

[Idris]

Vin

Beware your design looks like quite a noodle

The Bro model 188 was 12.8mm underfoot (triangle core) and 2 tip and tail

The Stiff had 22oz each side + 19 oz biax

The Extra Stiff had 3 layers (1 below 2 above) of 22 oz tri

The aspen cores were relatively soft though.

[vinman]

I realize that even .1mm make a difference on stiffness. But with all of that thickness right under the foot I was thinking it would make things very stiff. especially for a guy my size.

I guess I'll split the difference and go with 11 mm and adjust from there.

I like this thread though, please keep going with core design pearls.

[skidesmond]

You won't really know till you try them. But 2-11-2 maple/poplar is a good place to start. Ski design is very subjective with a few good facts thrown in. Very much an art form. If you think it may be soft use all maple or ash, but the ski will be heavier. Want it lighter and a bit softer, use all poplar. Lots of ways to change flex and firmness even when the skis have the same dimensions. It's endless.

I would pay attention to the details of the build, ie, how to keep the core from moving, make sure the bases are symmetrical, edge fit, proper placement onto the cassette and press, etc, etc.

[vinman]

I'm likely going to put maple under the edges and binding mounts and the rest poplar.

as for the layup I have a tecnical advisor so to speak with many years experience in the snowboard industry. I'll be hitting him up for some assistance on the big day. But I get your point on having a good clean layup procedure to prevent slippage and delams.

[ben_mtl]

I made my skis last year almost all on the same principle : 2mm tip and tail with flat area for bindings at 11.5 / 11.7mm depending on the model. The flat section was 450mm long !
The skis were a good stiffness IMO, a bit soft on icy terrain especially at 100-110 underfoot.
On my last pair I tried to add some carbon to add stiffness for on-piste use : a 2" UNI carbon 9Oz full length top and bottom -> very stiff ! At 5'11, 150ish it's hard to ski !

Another thing some friends noticed with my skis is the "sweet spot" is kinda hard to find (but once you got it it's amazing according to them) From some researches I did, this sweet spot notion would have to deal with the flex pattern. So this year I changes the way I profile cores : 2mm-12mm-2mm with only a 120mm flat area. the profile is more "rounded" as I use Sammer's idea for my bridge rails. It makes smoother transitions between flats an tapers.
I hope with this new profile I'll achieve a more "round" flex pattern and by adding a 1.5" or 2" UNI Carbon strip top and bottom I'll be just in-between the 2 stiffness I had so far.
I'm also gathering a lot more data on this year's builts : weight of everything, I kinda measure the flex of the core VS finished ski... some stuff like that. Hopefully it will give me some more accurate guidelines for the future.