Ski Core Design & How am I doing?

[holmtech]

Hey Ski Builders. First of all let me say thanks to all of the big contributors to this site. It is a wealth of info. I've posted a few responses but this is my first thread and real request.

I'm looking for a little advice and reassurance on design of my ski cores.

Here's what I'm working with:

I-beam press nearly complete, 12" beams 15" wide:


Flat mold with early rise tip mold:


MEI Heater for heating bottom only at this point.

Entropy Resin, 19oz triax fiberglass (looking for a good price on some 22oz triax), I have some uni-directional carbon fiber that I am planning to cut into either 1-2" strips or pull apart into stringers (can I even do that), vertically laminated bamboo (I bought a 4'x8' sheet from Bamboo Hardwoods to cut down into cores)...

So I'm looking to design a mid-stiff, wide, Alpental ski for those of you around Seattle. Something that will be strong and stable but quick turning (I will probably be mounting them with Hammerhead Bindings).

So help me with my design/layup. Here's what I've got so far and I'm really looking for help with core thickness:
Length 182, running length 145 (early rise tip, not so much tail)
Tip, Mid, Tail at 142 - 110 - 134 which equates to about a 18.8 m radius. Tapered tip.
Core at 3mm tip for 10cm, taper to 10.5mm mid at 25cm before the middle, to 33cm behind the middle, taper to 5cm before the tail, 3mm tail.
19oz triax top and bottom, plus either the carbon stringers or a carbon strip, top and bottom.
vds Rubber over the edges.

Also I've heard differing opinions on heating from bottom, and in regards to pulling out hot or pulling out cold. My plan was to ramp up heat to say 130 for 30 minutes, then 180 for 60 minutes and leave them to cool under pressure over night. The two things to consider here are base flatness/concavity, and heat induced camber. I'd like to get 2-3mm of camber out of the boards this way.

Also, VDS Rubber... Does everyone on here use it? It seems like it. And if I'm only going over the edges all the way around, is this for adhesion only or is there a damping effect? I hop there is.

OK this was a long one. Thanks again for all of the monitors and creators of this site. You know who you are...[/img]

[twizzstyle]

VDS does a few things, but in my mind (and everyone probably has a different opinion) its just to provide a sheer layer between the steel and the fiberglass. Without it, the bond would brake and you'd have a delam/crack along the length of your ski. Cover up any exposed edge/metal with VDS.

I think what you've got in mind will be spot on. Best thing to do is just build it and see! I wouldnt' try to pull the CF apart into stringers, cut 2" wide strips and use that top and bottom. Sounds pretty similar to the skis I just made (although mine are much shorter).

I like to have dedicated skis for certain conditions, so my powder skis are 155/130/145, groomer skis are more on the order of 120/100/110 (those are just rough numbers, I can't remember the exact numbers). What you've got should be a good all-around ski.

How tall are you? I like my skis on the short side for getting around in the trees, it gets pretty tight at the bottom of Alpy , but I'm also only 5'5"

[holmtech]

Thanks Twizz. I'm 6' tall and around 195-200lbs. I was thinking about shortening it up a little, but with the early rise tip it should ski a little shorter for me.

Definitely props for the shorter, maneuverable skis. A while back I was skiing on a 175 Salomon Pocket Rocket. Unstable as heck at speeds but man were they fun in the tight spots. Not the most durable ski though. Didn't take long for them to gain some unintended rockered.

I'm hoping to layup next week some time. Probably towards the end of the week. I'll let you know when. If you're free maybe you can drop in and have a brew and entertain yourself by watching me nervously scramble through my first layup.

[twizzstyle]

Yeah let me know! It's always nerve-wracking the first time, but doesn't need to be. You've got loads of working time with the entropy resin, just mix it in a few small batches and you've got no worries!

Your photos are blocked at work, so I'll have to take a look when I get home.

[MontuckyMadman]

first off. I would like to commend you for actually reading the forum and comprehending the info you see here. Your post here should be an example to others as to what to learn before asking questions.

I suggest you move forward with your plan as stated.
You will most likely end up with concave bases heating bottom only until you figure out how your blankets ramp with temp and how it all works.
I would not let the laminate cool under pressure. In my experience this will exacerbate the problem with concavity.
I am 6'1" and 180lbs.
I dont really ski on anything smaller than 188cm. western snow pack.
192cm with rocker tip and tail.
If you have skied any rocked skis the key is contact length or running length to really get an idea of how easily the ski will turn in tighter conditions.
I would suggest demoing some new school skis and then base some rocker camber contact length numbers off of skis you enjoyed.
Don't forget the ski gets shorter when you press it because it curves up tip and tail so if you cut a 182cm and press with any tip and tail rise you will loose at least 2cm of total length.
Heat from the bottom only will also increase the camber from what your mold is and decrease the rise in tip and tail so be advised.
Depending on heating cycle you can expect a .5cm to 1cm increase in camber and about a 1cm-1.5cm decrease in tip rise with bottom only heat.
FYI.
Have fun. your are really on the right track.
Dont be skimpy with the rubber either.

[powderho]

So are you saying you have 58cm under-foot of essentially a flat profile of 10.5mm thick? If this is the case, these will literally ski like planks. I have around 6-8" of flat in my profile at 11mm thick and they feel very stiff underfoot. Don't be afraid to go thinner in the tips. You can have the core go all the way to 2mm and still have a surprisingly stiff tip depending on the rest of the profile. With the skis like you have designed you will want the tips to float a bit easier. This doesn't mean they will necessarily be flapping all over the place, but you just want a little initial give to them. I don't mind 3mm in the tails--that's fine in a lot of designs. It's more the area directly behind the rear binding that will be a too stiff in your design for my liking. You will soon learn that tweaking these numbers really is what most of the fun is all about in ski design. They are way more important than the shape to how the ski will actually perform.

Good luck and nice press!

[Sherpa Burns]

Good looking press.
I would second the thought of shrinking down the underfoot thickness length. I had the great idea to make a powder ski that I thought was going to the bees knees. I made the underfoot thickness 11.5mm for almost 22" which is very comparable to what you are thinking. Couldn't hardly turn them on hardpack. Powder didn't matter, but anything firm was almost unbearable. I am a pretty strong skier and I just got pissed by the end of the day. I had to slow wayyyy down on hardpack and skid turn with all I had. Probably didn't help there was an additional 4" of carbon over the core. They're beautiful, but they suck. Not sure what to do with them now. Need to find a monster capable of overpowering them.

[twizzstyle]

192cm with rocker tip and tail.

Ha, man... makes me feel inadequate! My powder skis are 160cm, and are basically completely reverse camber (there's about 40cm long of flat in the middle). Talk about no edge-contact, on groomers they are down right funny.

[holmtech]

first off. I would like to commend you for actually reading the forum and comprehending the info you see here. Your post here should be an example to others as to what to learn before asking questions.

I suggest you move forward with your plan as stated.
You will most likely end up with concave bases heating bottom only until you figure out how your blankets ramp with temp and how it all works.
I would not let the laminate cool under pressure. In my experience this will exacerbate the problem with concavity.

Thanks MM. I've been reading here on the forum for the past 5 months. Admittedly less time has been spent on ski layup than press design, but from actually talking with some folks (Kelvin from Blank Slate) and running into some custom ski builders in the lift line at Alpental I've gotten some mixed info. The advice is still well taken. The first few pair of skis will be a huge learning process for me.

If you have skied any rocked skis the key is contact length or running length to really get an idea of how easily the ski will turn in tighter conditions.

I've skied HellBents with Hammerheads to BlueHouse Radius with Hammerheads. Two total opposite ends of the spectrum. Selling the HellBents, Love the Radius. The Radius is more of an early rise than rocker ski... I'm shooting for a happy medium. I may go a touch longer but 192 is a bit long to work through the Alpental BC.

Depending on heating cycle you can expect a .5cm to 1cm increase in camber and about a 1cm-1.5cm decrease in tip rise with bottom only heat.

Thanks. I'm planning to ramp up slowly so hopefully I'll be closer to the .5 cm.

[holmtech]

So are you saying you have 58cm under-foot of essentially a flat profile of 10.5mm thick? If this is the case, these will literally ski like planks. I have around 6-8" of flat in my profile at 11mm thick and they feel very stiff underfoot. Don't be afraid to go thinner in the tips. You can have the core go all the way to 2mm and still have a surprisingly stiff tip depending on the rest of the profile. With the skis like you have designed you will want the tips to float a bit easier. This doesn't mean they will necessarily be flapping all over the place, but you just want a little initial give to them. I don't mind 3mm in the tails--that's fine in a lot of designs. It's more the area directly behind the rear binding that will be a too stiff in your design for my liking. You will soon learn that tweaking these numbers really is what most of the fun is all about in ski design. They are way more important than the shape to how the ski will actually perform.

Good luck and nice press!

Thanks! I think you're totally right on the thickness. For some reason I'm having a hard time letting it sink in that I need to go thinner.

Twizz said it too, I just need to build and see what I get. I'll be finishing the profiler today, so here goes nothing...

[doughboyshredder]

Thanks! I think you're totally right on the thickness. For some reason I'm having a hard time letting it sink in that I need to go thinner.

Twizz said it too, I just need to build and see what I get. I'll be finishing the profiler today, so here goes nothing...

10.5 is massively thinner than 11.5 and quite a bit thinner than 11.

.5mm makes a big difference.

I can't comment on the profile.

I would shoot for 2.5 on the tips.

[FrontierSkis]

We have been running with no VDS for the last few pairs of big powder skis, we have had no issues, but if you follow any of the big ski company layup videos they always use it... so to error on the safe side i would use it if you got it.... i just dont have any.

[holmtech]

MontuckyMadman, I am just about to print my ski base to use as a template and I just realized what you meant by the ski will shrink by a few cm due to the curve...

I'm actually at 188 for total length including the slight rise tail.

The cores came out pretty good. Not exactly what I was looking for but they're close. 10.3mm center and 3 tip and tail. I might thin the tip and tail a bit with a belt sander. I need to be more exact with the profiler with the next one. Also moved the mount area back and shortened to 33cm.

[twizzstyle]

I need to be more exact with the profiler with the next one.

With the next core, or the next pair? Whatever you do, make the two cores (for a given pair of skis) as close to identical as you can. Small changes in thickness, especially in the thinner parts, can make huge changes in stiffness! Stiff or soft - the two skis in a pair should at least be the same.

Bending stiffness is proportional to the core thickness cubed.

[twizzstyle]

Oh and I finally saw your pictures... and holy crap your press is a BEAST!


<<<< jealous!!!!!!