core profile

[fouldsys]

ive decided to go with the planer profiling method to profile my cores. i was wondering what were your thoughts on the advantages/disadvantages on having flat areas in the tip and tail of the core vs having no flat areas because having no flat areas would be easier to make in my opinion. also, my skis will be 127-95-127 and im looking for a medium-soft ski, what thicknesses do you recomend?

any help is appreciated

[fouldsys]

heres a pic if ive confused anyone

[ben_mtl]

well, actually I got another question about profiling core with a planer : do you guys use a "2 sides crib" (to profile tip and tail in one operation) or do you profile one end at a time ?
If the 2nd choice, do you feed the planner with the tip of the ski or with the middle ski ?

To answer you question fouldsys, I plan on profiling in 2 steps : first no flat areas and then the tips will be softer so I'll be able to bend them on another crib to profile the flat tip and tail.
My skis will be 133-105-124, thickness will be 2-11-2, it's my first attempt I hope the ski no to be too soft (maple/poplar core, maple sidewalls).

Ben

[dsmith3232]

I also have been wondering how people do this with a thickness planer.
Because of the flats at the tail and tip.
I decided to do the profiling with a hand router and crib.
Good picture examples!

[Idris]

My crib was very simple. 2 planks of chipboard. Screwed together in the middle (thickest core point). Then wedges under the ramp and end parts. With a few more screws through the end parts to keep it all together. A strip of griptape on top keeps the core in place.

[fouldsys]

thanks for your input guys but noone has really answered my question yet. do you think it makes a difference having flat ends?

[sammer]

I haven't pressed my skis yet but
my thinking is that the flats at tip and tail will bend easier.
My taper only goes to the end of my running length,
then flat for easier bending.

sam

[G-man]

do you think it makes a difference having flat ends?

It kinda depends on what you are doing for tip spacers. If you are using solid tip spacers that start at the point where the tip starts to bend upwards, then your core doesn't need to have flat ends. If, however, your core extends into the area of the upward bend, having flats at the ends of the core make a huge difference in getting the tips and tails to bend into you mold without breaking. I've found that any tip thickness over 3mm will likely break rather than bend, so I start my flat sections just back a bit from where my tip and tail curves start.

If your skis are designed with flat tails (rather than twin tip), whether or not you have flat or tapered tails will affect how the tail section of the ski performs, especially when exiting turns. I've discovered lately that a stiffer tail performs much better than a softer one when skiing really steep, somewhat frozen early morning corn (less chatter and better hold at the end of the turn), but that as the corn softens up, I like a softer tail (allows the ski to release and come around faster in short turns). But, because I can't change skis as conditions change on the bigger peaks that I ski in the spring, I've found that it works best to start the day with a bit stiffer ski for the frozen corn, then just open up the turns a bit as the snow softens... that way, having a tail that releases a bit later isn't such an issue. If, however, I get a late morning start on a corn day, I'd probably rather start out with a ski that is a bit softer in the tail for the softer corn that I'll be skiing on.

So, what I'm saying is that I personally think that flats at the tips and tails (and how they're designed) are pretty important because how and where the core tapers into the flats will determine a lot about how your finished ski will perform. At the same time, maybe you shouldn't get too wrapped up in the finite details of your core on your first pair or two because, on your first couple of pressings, you're really just trying to get an end product that looks like a ski and stays together reasonable well. If you're like many of the rest of us, you'll be working on the finer points for a few years to come.

G-man

[fouldsys]

G-man

thanks for clearing that up for me. another thing i wanted to know is how long the flat part in the middle should be. should it be as long as where the screws for my bindings will go in? longer? shorter?

[G-man]

For my stiffer skis, I go with about 18 to 20 cm for the center flat. On my softer skis, however, I shorten it up to about 10 cm, which seems to maintain a more uniform and consistent flex curve over the entire length of the ski. I have a quite accurate fixture that allows me to assess the overall flex arc of a finished ski, so after building and testing each ski, I adjust my core dimensions to give me a smoother flex arc on the next ski. After building and testing quite a few skis, I kind of know empirically how to design the core profile to get pretty much the end result, in terms of ski performance, that I want. If I change anything about the materials that I use, though, the empirical stuff goes out the window, and I have to kinda start over in terms of fine tuning the core profile. So, because we all use different approaches to ski building, what works for any one of us (in terms of core dimensions), may not work real well for any of the rest of us. It's a bit of trial and error, just like much of the rest of life... mine, anyway.

Oh, I ski tele, so there may be reason to design the center flat a bit different for alpine/alpine touring. Never been there/done that, so someone else may be able to provide thoughts on an alpine mount.

G-man

[jono]

I have used both a wedge and a flexible crib to plane cores. I like the flexible crib because of the flat ends it yields. I get less ripped out end pieces than I got with the wedge system. I then use tapered sections of fiberglass to round out the flex.
You don't really need a flat area in the middle of your ski. I remember one of Idris's posts about not having any flat area. After reading that post I noticed my Volkl Explosiv skis did not have any flat area underfoot. They have a " rounded off peak" under my heel. I think if you go without a flat section the "peak" has to be under your foot (or maybe behind your foot) but probably not in front of your foot.

I find it useful to imagine core stiffness in terms of volume. I think core volume, or the area of an infinitely thin slice, at any point along the length of a core would give you a basic stiffness value. With this in mind a flat area that contains the narrowest point of the ski would be the least stiff at that narrow point and would be the stiffest at the wide ends of the flat area. Getting rid of the flat area and having the thickest point of the core coincide with the narrowest point of the ski would a yield more solid feel underfoot in terms of stiffness because the basic stiffness value would be more constant underfoot. Having a flat area towards the tip, where the ski gets wider, creates a different problem. The ski gets stiffer as you approach the tip (right where I want it to get a little softer) because the added width contributes volume to the core. I have found these issues to be pretty subtle. Composite choices also trump subtle core thickness issues.
Overall, I think that having less of a flat area makes it easier to get a consistent flex pattern. I generally limit my flat area to the length between binding screws. If there is a soft flex underfoot it is strengthened by the stiffness of my boot/bindings combination.