Goat-Ham-Ah project

Document your personal work here. Show photos, movies, and share your secrets.

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skidesmond
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Post by skidesmond »

Very nice! Let us know how they ski. I found the skis I've been making are very firm also compared to my commercial skis. But they turn very smooth and track awesome. It seems now matter how hard or far I lean on the edge I can stay upright. I would definitely fall over on my commercial ski. It must be the side cut that allows me to do that?? Not sure, but after my last day of skiing on my home made skis I see no reason to go back to commercial skis.

Most of the snow conditions I ski on are hard pack, loose granular, etc.... , typical east coast stuff.

SKI ON!
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falls
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Post by falls »

ben. I was looking at your pictures where you measured your rocker and loss of rocker. I don't doubt that you are not getting quite as much rocker as you intended, but wonder if it right to measure the rocker with the camber at its highest. If you have a camber mold then place your rockered tips on it the initial part of the rocker is actually heading downwards/tangent to camber before it has time to curl up and produce the rocker. I think it is more fair for you to compress the camber til the running length is flat. This will bring the tip and tail up a little and show how much rocker you actually have from your contact points.
Does this make sense or am I off the mark?
Don't wait up, I'm off to kill Summer....
ben_mtl
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Post by ben_mtl »

Falls -> yes I understand exactly what you mean but the rocker I forecsted on my molds was considering the camber... well... cambered, not flat on the snow.
Anyway it's no big deal, at least this made me improve my setup as I bought a few thermocouples from Omega.

I'm just back from the ski hill, cold spring conditions with corn on ice. The skis are pretty nice but wayyyyyy too stiff for a ski this wide (at least for me).
The tip shape is nice, the mini-early-rise makes it easy to go through ice, then a soft corn mogul, the soft snow, mogul again, then hardpack... That's great.
Another thing : skis seems to be on rails, when edged they keep the direction with no chatter, very stable even at high speed. I think it comes from the added stiffness.
Only drawback is it's so stiff that I can't load them enough to make tight carved turns, when carving it's like if I have a 50+m radius ! (it's only 17m).
I tried moving the bindings back and forth, seems a bit easier when moved 1in backwards but still it's not the fun I was expecting on the groomers.

For next year I'll prepare 2 new versions of this shape : one with only a 1in carbon strip, nothing else changes. The other one with carbon (1in also) but only in the bindings area (10in fwd and aft), thus keeping the tips soft -> easier to bend for carving.

If you have any suggestion or question feel free to ask !

Ben
A bad day skiing is always better than a good one at work...
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falls
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Post by falls »

Ok.
Sounds like the latest pair require concentration at all times. The early rise tip, camber then normal tail seems to be a good shape for all round performance. This is what the pm gear bro models are like and my friends think they are great for everyday use and touring.
Don't wait up, I'm off to kill Summer....
ben_mtl
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Post by ben_mtl »

Second test ride yesterday with skiing conditions pretty different from the day before : cloudy but quite warm, no crowd at all, soft snow (corn), soft moguls, sometimes a patch of more icy snow (leftovers for the day before I guess...).
I started the day on my ol' Goat-Ham-Ahs while a friend of mine (who's a ski instructor, he should give me some tips that would help) was riding the new white skis. I called them "Slim Fats", cause basically I took the "fat" shape of Goat-Ham-Ahs (105 underfoot is fat for the average east coast skier I am) but put them on a diet and reduced the waist to 98 while tip and tail are unchanged.

Me riding the ol' Goats : That was fun but the ski is not that responsive, pretty soft, long turn radius. Definitely not my everyday ski but I enjoyed myself. Anyway I only took it so I can compare with the new Slim Fats.
My friend on the Slim Fats : It's stiff ! very stiff @ 150lbs (the rider) but it's so fun and powerful. He really liked it excepts in the moguls. Was in love with the tip profile/rocker. I noticed the tail to be a bit catchy sometimes I guess that comes from the added stiffness : the carbon stips go almost up to the end of the tail, thus always having the tail pushing firmly on the snow. He also noticed the ski is great when you find the correct "balance" on it (where you put your weight), he told me the "sweet spot" it pretty narrow, unlike on Rossignols skis. I'm no good skier enough to feel all that, I'm wondering how I could make this sweet spot larger.

Me on the Slim Fats : Today there is no crowd so I feel more confident and am skiing more agressive. Now I understand what this sweet spot thing is about : when I'm charging I'm leaning more forward and I discover a very different ski than the day before. It's still stiff but I can handle it better. I had only 2 runs on them as the hill closed sooner yesterday but I really loved them. It's definitely a ski that need to be driven, you can't take it easy and let it go. I believe this comes from it being very stiff. Unlike the Goat-Ham-Ahs, this pair could easily be my everyday ski, and actually I think the next year version (softer) will be ! It's just crazy how good it was even on ice for a ski @98 underfoot !

One thing I'd like to have advises or comments on it this sweet spot thing : I understand the result (finding the point where the ski is the best) but I'm wondering how I could achieve a sweet "zone" instead of a sweet spot. That would allow to have the same ski behavior even if sometimes I'm more leaning backwards (as an average skier I have to say I'm not always agressive so I ski on my heels)


Falls-> I was expecting to have someting close to PMGear skis in terms of riding but with more sidecut so a bit easier to turn tight with less technique. I believe I'm not that far but still need some adjustments.
A bad day skiing is always better than a good one at work...
doughboyshredder
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Post by doughboyshredder »

I wonder if using a variable sidecut with a bigger radius underfoot would enhance this "sweet spot". IDK I don't ski, but I would guess this sweet spot is where the sidecut is being engaged evenly so having the larger radius underfoot would lessen the impact on the sidecut from fore aft weight shifts, maybe.
ben_mtl
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Post by ben_mtl »

Well this pair has actually 3 sidecuts... 16m in the tip, 18m underfoot and 16.5m in the tail... all 3 sections are almost the same length.
From what I just read on a website I can't recall the name, the sweet spot thing would have something to deal with the flex pattern... or not...

I never really thought a lot about the flex pattern, since I started building I just made the core thickness to be matching the tipspacer thickness in tip&tail (2mm), then I went with a 11.5mm thick flat area where the bindings are mounted (an average from what I've read here at this time), straight taper between those thicknesses... maybe I should investigate a bit more on this.

EDIT :
I just read another article where they talk about the sweet spot (of course I didn't kept the link for it...). Anyways from this article I understood that the sweet spot, technically speaking, would be the point on the ski where when you apply your weight the skis bends in a perfect (or so) circle. That would make sense... I'll try to use FEM on a CAD software tonight to see hoe my cores bend, depending on where I apply the weight.
Question is : considering my layup symetrical and on the full length of the ski, will the fiberglass, base and topsheet affect how the core bends (not how much but the shape of the deformation...) I'm no master with the composite workbench on my CAD software, if I could just study the core it would make thing easier.
A bad day skiing is always better than a good one at work...
skidesmond
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Post by skidesmond »

sweet spot/zone.... To me it's a subjective thing. You can design a ski that 'should' have the sweet spot but it may not work for everyone, depends on skiing ability as well as ski design, flex, firm vs soft.

On the last pair of skis I made (firm flex from tip/tail and firm torsionally also, 168cm 122-68-106 12M radius 12mm underfoot 3mm on tip/tail, all ash wood core) the sweet zone is when the shins are on the front of the boots, leaning forward and driving the ski down the hill fast and hard. They'll turn on a dime at high speed or turn great for long carving turns and I can practically have my hip touch the snow and they'll hold me up. To me that's perfect!

But when I'm just punzting around or going straight... not so much. The tail is firm so if I happen to get tossed back, the tails will hold me up and not wash out. I'm also 195lbs so if I gave them to a light weight they may not like them at all.

I tried that on a Volk 5 Stars 175cm and they washed out and down I went. And I like those skis too. The sweet spot on that ski (for me) is fast tight carving turns or long carving turns. Yet my friend who owns the skis isn't real keen on them.

I design my skis some what typically, where the narrowest part of the ski will be under the ball of my foot. That's where you'll be steering the ski from.

One thing ski manufactures never told you is with a shape ski you have to change how you ski. If you're still skiing like you did on straight skis you're working to hard and missing out on a lot of fun.

I'm working on softening up my next set of skis by making a thinner core to make them easier to turn and a little bit more user friendly :)

So finding that sweet spot/zone can be difficult. Make a ski the way you like to ski.
skidesmond
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Post by skidesmond »

sweet spot/zone.... To me it's a subjective thing. You can design a ski that 'should' have the sweet spot but it may not work for everyone, depends on skiing ability as well as ski design, flex, firm vs soft.

On the last pair of skis I made (firm flex from tip/tail and firm torsionally also, 168cm 122-68-106 12M radius 12mm underfoot 3mm on tip/tail, all ash wood core) the sweet zone is when the shins are on the front of the boots, leaning forward and driving the ski down the hill fast and hard. They'll turn on a dime at high speed or turn great for long carving turns and I can practically have my hip touch the snow and they'll hold me up. To me that's perfect!

But when I'm just punzting around or going straight... not so much. The tail is firm so if I happen to get tossed back, the tails will hold me up and not wash out. I'm also 195lbs so if I gave them to a light weight they may not like them at all.

I tried that on a Volk 5 Stars 175cm and they washed out and down I went. And I like those skis too. The sweet spot on that ski (for me) is fast tight carving turns or long carving turns. Yet my friend who owns the skis isn't real keen on them.

I design my skis some what typically, where the narrowest part of the ski will be under the ball of my foot. That's where you'll be steering the ski from.

One thing ski manufactures never told you is with a shape ski you have to change how you ski. If you're still skiing like you did on straight skis you're working to hard and missing out on a lot of fun.

I'm working on softening up my next set of skis by making a thinner core to make them easier to turn and a little bit more user friendly :)

So finding that sweet spot/zone can be difficult. Make a ski the way you like to ski.
ben_mtl
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Post by ben_mtl »

Yeah I do agree that ths sweet spot thing is very subjective.
What I felt on the last pair of skis is when I let it go it's OK but not great and I have a hard time carving (relatively short) turns. When I'm going faster and lean more forward though, I push harder on my feet and the ski is really fun to carve ! The thing is neither my technique or my confidence allow me to push on the ski in all conditions. That's why I'd like to keep this great feeling when pushed hard but would love to add some fun/carve factor when riding "easy" and [ashamed mode] "on the heels"...

So.. I've been investigating the last 2 days about the G-... hum sweet-spot, sorry and ski stiffness and all that and I noticed 2 interesting things.

I checked the PDF file that Endre made a few year ago about ski stiffness. The I remembered that my friend (who tested the skis) told me that Rossignol skis, in his opinion have a pretty "large sweet-spot", so in the PD file I only activated the Rossignol skis. Here is what I found :

Image

Basically the tendency with Rossignol skis (and It's not necessarily the case with other manufacturers) is a quite large zone of constant stiffness in the middle of the ski.
For other manufacturer in the PDF, I sometimes see the same pattern but the other common cases are a "rounded peak" of stiffness in the graph. This peak can be exactly at the binding position, slightly FWD or slightly AFT... I'm wondering what does that changes on the skiing.


This made me think about how my skis are done. Basically, and I believe that's how most home builders do, I have a taper from 2mm to my desired thickness (11,5mm) from tip to slightly before the binding area; then it's flat where the binding mounts, and finally it tapers down to 2mm from behind the binding to the tail. Both tapers are straight.
When you think about it in the binding area the thickness is constant, but the with is decreasing when you get closer to the narrowest point (mounting point in my case), thus the stiffness in the binding area is no constant !
In a nutshell, from tip to tail my stiffness increases 'till just FWD of the binding, then slightly decreases to the mounting point, then slightly increases again and finally decreases with that back taper... The curve as shown for the Rossignol skis would be shaped like a "M".
It might not be that much be I'm wondering how it affects the feeling on my skis.. for next year I might try a more "constant stiffness" or "peak stiffness" in th binding area to see the difference.
A bad day skiing is always better than a good one at work...
skidesmond
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Post by skidesmond »

A 17m radius would be difficult to do short carving turns (ie railroad tracks), unless you slid the turn. You can do it but you'd have to be driving the ski fairly hard. You could try making a ski with a smaller radius or if you want to keep the 17m radius adjust the shape to make it more narrow. If you took your dimensions and adjusted downward by 10% so the ski is 178cm 121-86-109 you still keep the 17m radius but I bet it would be easier to turn because the waist is more narrow, less material to flex/bend. Well, that's what I think..... I'm still learning too.

You could also soften the ski by not using carbon or maybe have the core 10mm instead of 11.5mm and keep the carbon.

So many variables!

The profile of my skis generally are as follows, for a 168cm the tip is 3mm for a length of 140mm, then tapers up to 12mm for a length of 570mm, then 12 mm for a length of 350mm (binding area), then tapers down for a length of 560mm to 3mm, then the tail is 60mm in length at 3mm in thickness. I haven't tried tip/tail spacers yet, so this is a full wood core.

For me, I decided to play around with the core thickness and ski shape as my variables and stick with a static basic layup of full ash wood core and triax fiberglass. Limit my variables and see what works well or not so well.
ben_mtl
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Post by ben_mtl »

Cross-post from other topics, here starts the 2010-2011 collection !

3 cores + edges:
Image

Screen-printed topsheets (small logo just to test the process and ink):
Image

A surprise on its way for the GF : splitboard !
Image

Need to let the ink cure on the topsheets for 4 days, hopefully I'll press the first ski of the season early next week ! I'll use black epoxy to have a white logo on black background. The surprise will be to see if the white is really opaque and also if the black epoxy is opaque enough to hide the core...
A bad day skiing is always better than a good one at work...
ben_mtl
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Post by ben_mtl »

I'm just back from the workshop !

Here is my work of today :

I prepared all the materials : cut the bases and glued edges, pre-weighted epoxy, cut different composite materials and VDS... well you know the list.

All the material for the new pair are ready :
Image

cores with my usual locating pins :
Image

Bases attached to the cassette :
Image

1 hour later :
Image

It was a try at screen printing the topsheet and using black epoxy as a background color.
The white logo came out pretty neat. The black epoxy turned out kinda deep blue because of the P-Tex material and the fiberglass cloth appears through the topsheet. It's not that bad but I'll try to screen-print the black background for next pair.

One thing that went not that great is I felt like the resin was kinda "greasy", it was like when you put oil in a hot pan, it didn't want to stick to anything... kinda weird wen you put resin on the edges and you actually see it flowing and not staying where you wanted ! On the VDS it was also a strange feeling.
I don't know if it's because of the black pigment (it's a gel you have to mix with the resin). It's also a new batch of resin and I didn't have this feeling last year... maybe I just didn't saw it...
The ski looks OK, I'll see if I have any delam issue while flashing... Meanwhile I'll write an e-mail to the resin supplier...
And I'll make a little test with non-tinted resin just to see how it reacts (should have done this beforehand but didn't thought adding color could be a problem, especially when the dye is supplied by the resin manufacturer.
A bad day skiing is always better than a good one at work...
ben_mtl
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Post by ben_mtl »

And here are the finished skis :

Image

Image

Image

I'm very happy with the result, still need the final touches on finishing + prepare the bases but I already can't wait to try them !

Those are 168cm long, early rise tip and almost flat tail. Lots of camber due to my stupidity with heating blankets controls. Dimensions are 120-66-96, don't remember the radius but it might carve pretty good !

Made everything myself including custom graphics ! awesome !

It's a good start for the 2011 collection :)
A bad day skiing is always better than a good one at work...
skidesmond
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Post by skidesmond »

Great looking skis! Should be able to carve anything with those. Camber is a good thing if you're going to be doing carving. Should be great release from each turn. Sweet!
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