Heksu

[MontuckyMadman]

Aspen is noticeably softer than poplar. The numbers are close but in practice they are diffferent.
Uni carbon wont really increase the tortional stiffness. You need to read allot more on here.

[twizzstyle]

I didn't find anything about asymmetric fibers could you please give me link or short explanation.

Here is a very short basic explanation: all of the materials in your skis expand/contract with changes in temperature. If you have different materials above and below your core, you may have drastic changes in camber with changes in temperature. This is especially true if you are heating your skis as the epoxy cures. Having a symmetric layup means any expansion/contraction will be even on both sides, and the camber will not change with temperature. (fun fact: not all materials expand with heat)

Some other quickies: fibers running longitudinally down your skis do nothing for torsional stiffness. Diagonal fibers must be used to increase torsional stiffness. The thickness of your core can have a larger impact on overall stiffness than what composites you use. You could use a boatload of CF, but have a core profile that is too thin, and you'll have a noodle. It took me about 10 pairs before I had a profile I really liked.

[skidesmond]

Thank you all.
I didn't find anything about asymmetric fibers could you please give me link or short explanation.

With CF I'm looking for more edge grip..torsion or what is correct word? I can live with out using CF😊. What about using 400 g and 760 g triax glass to have more torsion. Or 400 g triax in the middle of ski? Katana has race ski feeling it is slow to turn from edge to edge but even on ice edge grips well if edges are sharp.
Wood core will be 11 mm in middle. Made of aspen, it is like poplar.
It has been very cold this year..today -27C.

Either the Katana or Kendo had a layer of Titanal, I believe. I demoed a pair before but I forget which model it was, but it had a layer of Titanal. That would attribute that grip you feel. It's feels slow edge to edge because it's 111mm wide.

Triax will give torsional stiffness, Uni-CF won't. Read more. See Twizz
s comments.

[heke]

Yes..i will just go with Glass fibre. Just finish the Wood work and cut the base. I start to bend edges tomorrow. I need to modify my bending tool but I think it will work well.

What would be easy and practical way to test the vacuum. I have build some surf &kite boards but no experience using vacuum. Do you use valve between vacuum pump and bag? By using heat vacuum time should be around 4 hours. My pump is model with oil..maybe not the best possible.

[heke]

I'm making the ski so that the core is cut to final dimession before laminating, so there will be GF and veneer side wall's. It this this will give some additional torsion as it is like small box?

There is rounding on top of the core app. R=10 mm ( 0,3" ..slightly more) to be able to bend the veneer.

I made template of half of the bottom using plywood and mirror it with same template to final template. It seems to work well and the plastic parts are identical even when putting on top of each others.

The wood core planing went also quite well; parts are almost the same even when using a cheap Chinees plane, there is less than 0.1 mm height difference. Tail part could have been app. 0.3 mm thinner. I think I will use sand paper to remove some material.

I have been making quite a lot of wood works and I'm interested to have a full wood ski some day. We have long tradioins in my country to make skies.

[Akiwi]

Yes..i will just go with Glass fibre. Just finish the Wood work and cut the base. I start to bend edges tomorrow. I need to modify my bending tool but I think it will work well.

What would be easy and practical way to test the vacuum. I have build some surf &kite boards but no experience using vacuum. Do you use valve between vacuum pump and bag? By using heat vacuum time should be around 4 hours. My pump is model with oil..maybe not the best possible.

Hi Heke, Sounds like your skis will be similar to mine.
I don't have a valve between the pump and bag, and leave the vacuum pump running for the 24 hours it takes for my epoxy to harden.
I agree that the cap construction should give more torsional rigidity, but I haven't made any tests to that effect.

A few things to think about when using the vacuum.
1. make a test before you put your ski in to make sure everything is air tight.
2. Before putting everything into the bag, make sure all sharp edges / corners are covered so you don't puncture your bag.
3. Make sure there is a way for the air to get out from the far end of the bag. Up till now I lay a piece of plastic netting like material (Sort of like onion or potatoe bags) either down one side, or between skis.
One board I pressed, I noticed the vacuum was next to nothing at the end as the bag sucks itsself together and seals off. The fleece layer wasn't enough. Yesterday I ordered a length of spiral hose to use for this.
4. When sucking the air out, try to smoothen out any wrinkles..
5. Use a roller over the skis when in the bag to help push excess epoxy around to a good flat surface.
6. If you press 2 skis at the same time, make sure that the materials between the 2 skis have enough room to be pressed down flat and not to form a bridge between the skis.
On my first pair the top layer triax was one piece, and I noticed the side walls didn't press as flat in the middle as on the outsides... Now I cut the fiberglass out for each ski.

Hope this helps. If you have any questions, feel free to ask.

[heke]

Thank you Akiwi,

I have bought vacuum tube with some vacuum tape, so there is only two openings.
I have https://www.skibaumarkt.de/produkt/saugvlies/ and https://www.skibaumarkt.de/produkt/abreissgewebe/ I don't know if this is enough.

I have also this. https://www.skibaumarkt.de/produkt/lochfolie/

I will make one ski at time. What type of spriral pipe did you order?

Thanks for tip for rolling.

I will have my mould bolt connected but I will build a cover over each bolt.

When I made boards, I use abreissgewebe and Saugvlies, it works well to get nice surface.

I need to make a heated cabinet for lamination, we have currently very cold weather -29,9 C at morning => it is only +10--15 C in my workshop.

[Akiwi]

I bought this.
Haven't tried it yet to see if it works.

http://shop.hp-textiles.com/shop/Vakuum ... 60-05.html

I am not sure what you mean by this "I will have my mould bolt connected but I will build a cover over each bolt. "

For a heat cabinet, if you want to go cheap (Ghetto)
Just go to your hardware store and buy some polystyrene sheets (50 x 100)
I think mine are 1.5 cm thick
If you get 7 of them, you can build a rough box over your skis, and put a fan heater at one end blowing through.
Cut the last sheet in 2 to cover the ends, but cut a hole for the heater to let air in, and leave a gap at the bottom at the other end to let air out.

Idealy you should get something like this thermostat with an external sensor to be able to set your temperature.


http://www.elv.de/universal-thermostat-ut-300.html

[heke]

I was planing to use insulation wool. App. 100 mm or 4" thick it's quite cheap. I have a heating gun that is adjustable from 55C->.. I can use the insulation wool in our house roof. I have two digital termometer that can be push thought the wool. I have use same system when building bamboo rods.


Btw.. I bend edges today, I bought some pre bended edges. I find it more easy to bend the tail that was not pre bend. Is it a problem if the edge turns to bottom side. It is bended somehow side ways not much..

This termostat looks good; I need to find out if I can get it here locally. The heat gun is not so simple to use, normally temperature must be adjusted about double what I want to have and some times the temperature will be too much. It works but needs control.

I also found spriral from local shop

[Akiwi]

Try to get the edges flat.

On my last skis there was a bit of a twist in the edges and I hoped it would get flattened out by the press. It flattened a bit, but you can still see it. So invest the time now, and you won't regrett it.

I haven't tried the spiral tube.. just thought it might be a good idea.

[heke]

I have seen here some pictures where the tip/ tai of the bottom with edge is bended to mould before laminating. Someone has just roll with pipe. I was thinking to use same method as I don't know how much my vacuum pump can press. I think that pre bending would also give better result.

Making the planing jig was the most difficult work until now. I build the jig and notice that to ply wood pieces under the top plate were not in 90 deg angle; ie. it was 19 mm on other side and 19.8 mm on other side. So I made new parts.. then I made 3 pcs test pieces & 3 adjustments with planing jigi before the result was good enough..the height did not mach with calculation and I need to put some shimming plates under the top plate. Well next time it might work easier.

The planing was easy I use a hot glued wood piece to prevent core moving.

After first ski I marked height position of the adjustment with tape to planer, worked well.

[pmg]

I have seen here some pictures where the tip/ tai of the bottom with edge is bended to mould before laminating. Someone has just roll with pipe.

That was me, the pipe-rolling. Works also well just bending by hand. This definitely prevents delamination. If you leave the edges flat, they do not get completely the shape of the mould only by pressing. The metal flexes a lot...
So when the edges are flat before pressing, they are mostly held in the ski shape by the epoxy but want to get back in a more flat state. Thats why pre-bending them vertically is important. More work, but a better result.

[sammer]

I have seen here some pictures where the tip/ tai of the bottom with edge is bended to mould before laminating. Someone has just roll with pipe. I was thinking to use same method as I don't know how much my vacuum pump can press. I think that pre bending would also give better result.

There is a pretty good discussion here.
I still haven't rebuilt my tip bender and it's still working fine.

http://www.skibuilders.com/phpBB2/viewtopic.php?t=3199

sam

[heke]

Today I try to finalize the mould. Bending 2.5 mm mdf plate on top is not so easy. I put some mould wax on mdf and put some tension on it. Lets see if it bends..i have heard that polycarbon plastic is good. But I had that mdf at home.

[Akiwi]

I built a bender using a couple of rolling pins and scraps of wood.
I welded the handle together.

It doesn't bend the edges enough to fit in my mould exactly...

Looks like this. Here I was using it to bend my mould.


I think you might be better off clamping your skis in the curve of the tip / tail and using g clamps or something to hold them tight into the mould.
I haven't tried that myself, but will probably do it for my next build.