Frustration OR A reason to get drunk AND I need advice

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Hannes
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Location: NRW, Germany

Frustration OR A reason to get drunk AND I need advice

Post by Hannes »

After reading quite a bit in this forum I decided to give it a try.
During the last months I had built a core profiler and a mold. Then I made a longboard to test laminating and vacuumpressing. The mold for the longboard was made very easily: Two layers plywood with one strip of wood in between to get a camber. The foil for the vacuum was attached to the upper plywood, this way the vacuum was only between the underside of the upper plywood and the longboard. So far so good, everything was fine, longboard had the desired camber and was straight.
I planed doing it the same way with my first ski. The mold was made from 19mm MDF on the bottom, 19mm MDF on top (where the parts for tip and tail were attached to) with three strips of wood in between for camber. I made a testlayup to prevent any trouble and I found out that there were some leaks in the upper MDF from several screws holding everthing together (I hoped screws in 19mm MDF would be leakproof - MISTAKE!)
So what to do? Well,
1. Switch off your brain.
2. Forget every thought you had while building the mold 4 months ago.
3. Reach in the shelf an get your vacuumfoil and make a bag.
4. Test the bag. Leakproof.
5. Call your father-in-law to get him over to help the next day with the layup.
6. Make sure your brain is still switched of.
7. Layup.
8. Put the complete mold in the vacuumbag.
9.Throw the vacuumtube just across the ski (inside the bag).
10. Evacuate.
11. Have 1-5 beers and be so f..king incredibly proud of yourself.
12. Sleep.
13. Work.
14. Comehomeruninthebasementandcutthebagopen

So the first thing that struck my eyes: A ugly mogul just in the midle of the ski. OK, first ski. You learn. Its ugly but just under the binding (next MISTAKE: Don´t throw the tube on the topsheet).
So I take the ski out of the mold, turn it around and see a flat base with three cambers. (next MISTAKE: don´t put your weak mold in a vacuumbag). Hannes, you are such an idiot.

Since the vacuum was now pressing from under the lower MDF the whole mold was compressed. Three cambers from three distancepieces.

So what to do?
Its is my first ski. Since I had no idea what to built I just took my K2 World Piste and wanted to copy it. Just 10mm wider. It has just a few mm camber. The layup is: Base, 750g triax glas, birch 2,5mm - 12mm - 2,5mm, 750g triax, topsheet

I have a few different thoughts:
1. Get drunk (no solution, I know. Beer is empty anyways)
2. Build a really sturdy mold (expensive and time consuming)
3. Do it again, just the same but without any camber.
Will this be skiable? This is my question of the day.

Rideable ski without camber or rocker for telemarking with this layup?
I want it to be ready for X-mas. Not a lot of time to make a new mold from scratch.

Thanks for your oppinions!

Hannes

PS: What did my Girl say? "Nice color! Are you now able to build finaly our bathroomcabinet?"
pmg
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Location: Sonthofen

Post by pmg »

Hi Hannes,

that's why I wrote you to do a complete test layup including pressing :)

If you keep on using vacuum bags, you will need a strong mould, otherwise you won't be able to create camber skis. Also, the lower 19mm MDF is also bent by the vacuum (in your case, the top MDF and the lower 19mm MDF are bent the same amount as its the same material, The top one downwards, the bottom one upwards). This results in only having 50% of the planned camber :)

So a strong mould for vacuum bagging (when doing it your way with distance pieces to create the camber) consists of:
- A strong lower piece which has more than 10 times the bending resistance of the upper part. I would not use something solid here, but screw some e.g. 10cm high pieces of plywood below. But make sure the vacuum bag is big enough to fit it in.
- A strong upper part. MDF is too weak IMO. I am using a 15mm plywood plate. With distance pieces every 8cm or less I get a base without any uneventies. With an even thicker plywood less distance pieces would be needed.
- A lot of distances pieces in various thicknesses.
- And of course a tip (and maybe tail) mould part.

The need for a strong lower part made me built a proper vacuum press table...
pmg
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Location: Sonthofen

Post by pmg »

And, to answer your perhaps most important question:

flat skis can be quite skiable, especially off-piste. Völkl has recently created some full-rocker skis that are more or less flat. One of my first builds came out dead flat as well (was supposed to have 8mm camber), but also came out much harder than planned. I still ride it sometimes, very easy to turn thanks to the missing camber.
Hannes
Posts: 93
Joined: Wed Nov 09, 2011 2:20 am
Location: NRW, Germany

Post by Hannes »

I did the testlayup. With pressing. But I didn´t see any at that moment because I didn´t take a look at the mold from the side. Bummer...
Well, I will rethink it again. Either built a flat one fast (need success) or a sturdier mold. Or a sturdier mold fast. F..k the bathroomcabinet.
No matter which way: need to order new stuff:-)
MadRussian
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Post by MadRussian »

I don't use vacuum press so can't help you there.

as far camber in the skis. If you have a problem to make the camber forget about it and move on.
For first pair of skis I made mold with camber. Mold didn't came out perfect decided not to use it. For first pair I had zero expectations and continue without camber mold because zero camber mold much simpler to make. Now all skis I made after that from SAME zero camber mold and love performance of every one of them including the first one.

If you want to make skis before Christmas keep moving forward and don't worry about "small" stuff
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison
twizzstyle
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Re: Frustration OR A reason to get drunk AND I need advice

Post by twizzstyle »

Hannes wrote: 2. Build a really sturdy mold (expensive and time consuming)
This is not a hobby to be skipping necessary steps because they are expensive or time consuming. If you try to go cheap/fast, you'll set yourself up to build unusable stuff (an even bigger waste of time/money!). My advice is always take the time to do things right, the end results are better and more satisfying.
Hannes
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Joined: Wed Nov 09, 2011 2:20 am
Location: NRW, Germany

Post by Hannes »

Well I now I will not save any money compared to buying skis :D

Was the thought wrong to seal the the vaccum foil against the top of the mold? This way the lower side of the upper board of the mold would have been at the "fresh air", top side in vacuum.

Well need to get to work now.
Thanks for your answers.
skidesmond
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Post by skidesmond »

Excellent thread. Step 14 is so true no matter how many skis you've made
:-)

Now that you've been baptized with your first ski you've learned a lot! If you already have a full time job, awesome! Get another part time job to finance ski building :-)

Somethings you can't skimp on like the mold. Since that gives the shape of the ski you have to make sure it's solid. Any imperfections will transfer to the ski.

Lots of people use a vacuum setup so I'll them chime in since I have a pneumatic setup.

Keep it simple until you get something that looks and skis well. Then start branching.
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falls
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Post by falls »

I don't think a solid vacuum mold needs to be that expensive.
Cut one rib from MDF or ply and use it as a template for the other ribs. Don't make it solid. Use a spacer between every second rib and then skin the top with ply or MDF.
Right?
Don't wait up, I'm off to kill Summer....
pmg
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Location: Sonthofen

Post by pmg »

Well, 2 ways are common for a mold:

1) A mold with fully adjustable camber with lots of distance pieces. Have a look here:
http://www.skibuilders.com/phpBB2/viewt ... 4936#44936

Pros: Once its built you can create any camber for any ski length you want - perfect if you do not have an exact idea what skis you want to build or if you want to build lots of different skis.
Cons: Some testing needed to get perfect results.

2) Create lots of stripes that have the shape of the camber (+ some height centimeters to make it solid) and put them together. Thats what falls suggested. I do not find a picture at the moment, but you surely have seen some of them here.
Pros: If the shape is created properly, hardly anything can go wrong as its really solid.
Cons: Limited to one camber. If you want to build a ski with a different camber, you have to build another mould. Also limited length adjustability.

I would take into consideration what you plan to build:
- If only skis for you and more or less the same model, 2) should be easier, and has less space for mistakes.
- If you want to go for a lot of different ski types, you will have more options with 1)
Hannes
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Location: NRW, Germany

Post by Hannes »

Thats just the point:

I had built version 1. I wanted to attach the vacuum foil to the top. The problem was that the mold was to short and I had leaks at the top- and tailend. I don´t think that there would have been any trouble with compression of the mold because the air was able to press under the upper board (I hope you know what I mean. It´s kind of difficult to explain for me in english).
Since there were these leaks I came up with the sutip idea to put the whole mold in a vacuumbag. So ist got compressed and I got a ski with three cambers:-) I just didn´t realize it while doing the testlayup. IDIOT! But afterwards it was clearly visible on the pic I took with my cellphone.

So what I did today: I bought two boards of plywood, 50cm longer than the mold. I hope this will solve the leakageproblem. I will set it up the way I planed before, make a testlayup and measure the camber under vacuum. If it works out I will layup my second attempt. If not: get some structual lumber and screw it underneath the whole mold and use a vacuumbag.
pmg
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Post by pmg »

Hi,

I would take plywood (Multiplex schimpft sichs im Baumarkt) when trying to reinforce the mould. With normal wood there is always the trouble that it moves a bit with temperatures, humidity etc, making the results unprecise again. With plywood this effect is very very small only.
Hannes
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Joined: Wed Nov 09, 2011 2:20 am
Location: NRW, Germany

Post by Hannes »

I thought about using 3 or 4 "Leimbinder" beams screwed in between 2 panels of Multiplex plywood. So it would be like a row of I-beams.

But first I will try my old construction firmly clamped down on my workbench (40mm beech).
rnordell
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Post by rnordell »

Attaching the vacuum bag to only the top surface of a mold is a perfectly acceptable method. You have balanced pressure on the mold and you are not crushing the tool under 14.7 psi. In fact you can vacuum bag a part to a wine glass but, if you put the wine glass inside a bag, the pressure will crush the glass.

The problem with MDF is it is not airtight. In fact many, myself included, use MDF as the sacrificial surface on a CNC vacuum table since even without holes in it you can draw air through it. You need to put something airtight on top of the MDF if you want to vacuum bag to it, ie a sheet of aluminum or thick plastic.

You can see in this photo the adjustable ski mold that I use in my autoclave. The tool surface is only 0.250" thick but because I only vacuum bag to the top surface, not enclosing the entire tool, I can apply any amount of pressure to the bag and ski, but the force on the top and bottom of the tool face is completely balanced and the camber unaffected.

https://fbcdn-sphotos-a-a.akamaihd.net/ ... ab4bc662c8
[/img]
Hannes
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Location: NRW, Germany

Post by Hannes »

I just did another testlayup. I attached the vaccumbag only to the top of the mold and it worked fine.
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