Fully adjustable vacuum press mould - howto

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pmg
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Fully adjustable vacuum press mould - howto

Post by pmg » Mon Nov 28, 2016 12:20 pm

Hi,

this will become a bit of a journal, but not building a ski but a mould.
Over the last few years I have been using an adjustable mould in my vacuum press, but it has some disadvantages. So now I am going to improve it and will document it here in case you want to build something similar.

How should the mould be like?
Very much adjustable! I build several models for my own use, one model for my girlfriend, and the number of different models will keep on growing. I do not have much space in my workshop and also don't want to use that much material for skibuilding, so I want to be able to press all the different models with as little materials as possible. And I will rebuild the models over the years with small improvements, hence also changing the mould a bit.
That is not possible when using a full mould for each ski.

Some things I found out during the last years:
- Adjustable Tip and Tail moulds don't work, at least not for me. So I will use tip and tail moulds and need to build different ones if I want different tips/tails.
- The only way of building different camber/full rocker setups without building a complete mould is to take a solid plate (e.g. plywood) and put different distance pieces under it. In my press creating a pressure of 85g/cm² the max distance between the single distance pieces was around 10cm with a 15mm birch plywood plate.
- If everything is build of wood its very easy to position tip/tail moulds, a hardboard plate with the skis drawn on, the base etc -> just use screws. Thats why I will keep on building the mould nearly completely wooden. Then different temperature behaviour of different materials won't be an issue.

Ok, so the basic plan is:
- Take a 22mm plywood plate as mould base
- use 0.5mm and 1.5mm plastic pieces below to create the full length camber/rocker
- put Tip/Tail moulds on top of the plywood

Tonight I started with the 22mm plywood plate. Its 2m long and 40cm wide. This will hopefully fit all skis I am going to build.

Pictures and further progress explanation will follow!

Cheers

pmg
Posts: 435
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Location: Sonthofen

Post by pmg » Tue Nov 29, 2016 12:26 pm

Ok, time to start building camber/rocker profile:

I bought some platic sheets, they are available in 0.5mm, 0.75mm and so on. I have 0.5, 0.75 and 1.5mm sheets. With these I can build pretty much any camber /rocker profile I want.

So, the setup for the camber/rocker profile is:

- 22mm plywood plate
- plastic sheets in various thicknesses
- 3mm hardboard as bottom

So, time for some pictures:
Image
In the front you can see the plastic sheets (white) and the 3mm hardboard base below.

Image
A closeup of the plastic sheets. Its obvious that any profile can be made using this method. What I am looking forward to is changing the mould shape a bit when building the same ski model again: Just change the plastic sheet setup a bit, everything else stays the same.

Image
The plastic sheets are fixed by using thin tape, in my case the tape painters use. Do not try packing tape! When removing it the sticky part sticks to the plastic and its an ugly work to get it off again.

Image
At the moment, the 22mm plate pulls up the hardboard bottom, but when its put in the press, the 22mm plate is pressed down making a nice even camber profile.


So everything below the 22mm plate is done, Next step is to put tip and tail moulds on top of it - coming soon.

skidesmond
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Post by skidesmond » Wed Nov 30, 2016 6:04 am

Interesting... I basically have a planer crib that is built in the opposite way. The middle is lower and the ends are higher. I have the layers so they can slide to make different length cores, from 150cm - 190cm. Once I have the layers adjusted I lock them in place and place another 3mm full length layer of the crib to smooth out the transitions, and then the wood core. I have a post about it in the forum.

pmg
Posts: 435
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Location: Sonthofen

Post by pmg » Wed Nov 30, 2016 10:28 am

Same here, my planer crib is exactly the same system. Its a shame my planer is not wide enough, so I can't use the same plastic sheets - that would be perfect. However, the plastic isn't expensive and easy to work with- just cut it with a knife to the dimensions you need.

I have been using this mould method with distance pieces for quite a while, and I found the plastic sheets to be the easiest method. Had aluminium distance pieces before, but positioning them perfectly and keeping them in place was a mess. Screwing works, but theres soon lots of holes in the wood and you cannot position the stuff exactly where you want. And as I calculate the camber, I want to be able to have the distance pieces within +/-1mm of the calculated position.

skidesmond
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Post by skidesmond » Wed Nov 30, 2016 11:53 am

So what you can do to make it truly adjustable is to cut slots in the plastic for machine screws to ride in. In the top piece of plastic drill a counter sink hole for the machine screw to sit in. The machine screw will slide through the bottom layers of plastic. Use a nut on the bottom to keep the plastic in place. Does this make sense?

pmg
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Post by pmg » Wed Nov 30, 2016 12:24 pm

Yes, totally understand it and thougt about it. But: If I move the plastic the slots might not be aligned to the screw holes any more, and then I have to cut more slots and so on. Also thougt about making the platic about 4cm smaller than the rest so I can have screws on both sides of the plastic. But (again but): I am afaid the lack of support on the sides of the plywood might deflect it when pressure is applied, and I'd have to use a thicker, more stable board below, making the mould higher and heavier.

I am quite happy with the simple tape solution. And if I am worried the thickness of the tape (less than 0.1mm) might be an issue, I just use tape everywhere :) Its cheap, easy to apply an remove.

skidesmond
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Post by skidesmond » Wed Nov 30, 2016 1:55 pm

Hey as long as it works that's all that matters.

pmg
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Post by pmg » Sat Dec 03, 2016 1:32 pm

Ok, the next step is to add tip and tail moulds on top.
Here a change is going to come:
At the moment my tip and tail moulds have a minimum height of 15mm, hence I have to add 15mm plate(s) in between to match the height. For future builds, I will rout the tip and tail moulds down to 5mm min height, saving 10mm. (5mm MDF is available here and 5mm MDF is 5mm. 6mm poplar plywood is from 5.7-6.3mm, not precise enough). But as the way I built the moulds is.... ah, lets face it: It'll be a lot of work to thin them by 10mm and winter is coming and I wanna ski so I'll do this when season is over - for now I work with 15mm.

Ok, lets have a look:

Image
Tip and Tail mould attached to the plate, and 15mm thick scrap put in between. In future, this will only be 5mm, saving weight and height. The white tape is there to keep the fillers in place, its in the middle far enough away from the skis, hence not influencing the skis (duct tape is about 0.3mm thick, a thickness to worry about when in the wrong place).

Ok, this looks ok, but far from nice. A bit scrappy. Lets add another layer:


Image
This is the top layer of the mould. The skis are drawn in it, and some helplines as well: Middle markings, markings for the reinforcement fibres to align them perfectly (and later the border between wood core and tip/tail spacers, added that later).

Ok, lets put it on the mould:


Image
Now it looks much nicer, doesn't it? Aligning everything is now really easy. Tomorrow I will skp the red wine and won't forget to make the pics correctly :)

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Akiwi
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Post by Akiwi » Sun Dec 04, 2016 12:34 am

Looks great. What plastic are you using, and where did you get it from?
I am nobody. Nobody's perfect, so I must be perfect.

pmg
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Post by pmg » Sun Dec 04, 2016 6:39 am

Hi,

is Polypropylen from modulor.de. They have it in a lot of different thicknesses. Very easy to work with, just cut it with a cutter.

pmg
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Post by pmg » Sun Dec 04, 2016 2:14 pm

Ok, this mould here is finished, hope it helps some people.

What I really like about this system is that the tip and tail moulds can be tilted. e.g. if I decide to build a full rocker, I rocker the whole 22mm plate, and don't have to build extra tip/tail moulds (in case they are the way I want for that ski of course). Or if I ever decide to build a very agressive piste ski (not likely to happen soon), I camber the complete plate giving my normal tip/tail moulds a very defined contact point (the point where the unloaded ski is on the ground).

Here you can see the further progress, the base is screwed onto to mould:
Image

If you like to follow the complete build, have a look here:
http://www.skibuilders.com/phpBB2/viewt ... 9669#49669

mammuth
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Post by mammuth » Thu Dec 22, 2016 11:39 am

pmg wrote:Hi,

is Polypropylen from modulor.de. They have it in a lot of different thicknesses. Very easy to work with, just cut it with a cutter.
Polystrene!?

https://www.modulor.de/en/polystyrene-white-matte.html

Didnt find PP sheets on their site
Tom

pmg
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Post by pmg » Thu Dec 22, 2016 11:50 am

Thats exactly the stuff I've been using.

mammuth
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Post by mammuth » Thu Dec 22, 2016 1:19 pm

cool, thanks
Tom

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