Ski Builders Forum

that last design is looking really good!
using full wood for the archs is deinitely the way to go. i guess you could do well even without choosing hardwood.
for our base layers (the pink boards) we use 27mm formboard, which basically is a three layer plywood.

Thanks chrismp!

I made a joke about using concrete a few posts ago, but that got me thinking...



I wonder how viable this would be:



What you are looking at here is a concrete form instead of a the actual press frame. It's based around the blue arch I started with. Inside that you see white styrofoam which is there to create voids in order to keep the weight down. I would also suspend steel reinforcement in the spaces to strengthen the concrete as well as keep the styrofoam in position. In this drawing there is 25mm space everywhere around the styrofoam, but that was just pulled out of thin air, I have no idea how thick this would need to be. Also, as a weight saver, the flat side would be made out of something like chrismp suggests above. I do need to calculate the volume so I can try to figure out what the weight would come to.

Not to throw off all you guys who are here offering help and insight by straying too far off the mark, but I seriously think there might be some potential in using concrete. Not to mention that this would actually be pretty easy/fun/interesting to do. Probably significantly cheaper than all wood as well. Thoughts?

Addicted to Sketchup today!

In case the last post was not clear, here's the idea with the concrete mold. Left side is the mold, right side is 1/2 of the press body in concrete. It's been modified a bit since I thought it would be nice to use readily available 100mm Styrofoam (extruded polystyrene.)



Edit: If my calculations are correct, (based on a cubic yard of concrete weighing 3300 lbs,) then as drawn here, this should weigh about 142 pounds / 64 kilos. The total weight of the press frame would then be around 300 lbs or so. Not too bad. :P

Hi webboy,

Yes that was what I was suggesting. It would probably work, but I don't know if I'd recommend it, though purely because I haven't tested it myself. I would test it if I were going down the path you are, however for your sake (especially if you're short on $) I would go with the vertical supports. Those last pics on Page 2 look good! You could avoid hardwood with a design like that I'm sure.

The concrete would also probably work. One thing to remember, concrete is extremely strong in compression but very very weak in torsion and shear. I don't think there'd be a lot of torsional/shear forces in that design though just by looking at it, but it depends on the gaps in between each cordura "band" along the press. The other downside is weight, if you're ever going to try to shift it. For a cordura type press I'd be leaning towards as light a weight as possible while remaining structurally sound.

Maybe now is a good time to do a test. Concrete is heavy and your in danger of re-designing your base support to take the weight ...

I'm assuming weight is a factor - you have to move it around, so have you thought about putting a layer of fibreglass on or between the base plate (pink) - thus reducing any deflection within the cells that you may be concerned about.

I think you solved a lot of your problems with the first design - you just need to increase the number of arc supports (green), reducing the size of the cells and focus on choosing the right materials - arcs (green) and (blue), may be pine can be a little soft to be put under compression.

With the top section, I think you might have forgotten that the mold for the top of the ski is structural and will contain any deflection to your pink layer. If these forces are contained, then the next area of stress in the ends. Your ends are supported by ensuring the condura reachs the end of each mold, top and bottom. You can see this in Plywoods design and provided the bottom tip mold does not go all the way to the very end, then all you are seeking to contain is the force of the hose trying to make itself straight.

I'm thinking that the issue you are concerned about within the video is contained by arcs you have running the length of the mold, provided you use the right materials (blue) and add a few more arcs (green) in the right places. You don't have to provide a gap that allows the hose to fully inflate. The right gap size will give you a flat'ish hose - you're not loading from the side. Excluding the spine will save you time, as this is not another new piece to create. I would discount the idea that these arcs placed at 90 degrees will move - provided they are slotted into green sections and they are attached to your blue layer. I am assuming everything is bonded together in addition to any nails or screws.

Sorry to chime in so late and cut across a few lines, but if you slim everything down to the least number of parts and make them work together, you will have a quicker build .

The only other thing to add strength - if your not happy and really want to pull it all together, would be to corrugate a piece of fibreglass as you add the each blue section. Cheap epoxy and bi-ax. Alternatively, varnish will help pull it all together.

Thanks for the latest (both of you.) OK, so I'll let the concrete idea go- it was intended as more of an interesting study than anything else. If the weight were not such a factor, then I think it would have had promise.

Moving back to the all wood design, I'm perhaps a little unclear on a few things you said Richuk:

Richuk wrote:I'm assuming weight is a factor - you have to move it around, so have you thought about putting a layer of fibreglass on or between the base plate (pink) - thus reducing any deflection you may be concerned about.

You mean since it should be rather mobile and lightweight, then adding fiberglass is a good way to stiffen without having to add weight to the supporting structure, correct? I like that idea a lot- That just got added to the design! Thanks.

Richuk wrote:I think you solved a lot of your problems with the first design - you just need to increase the number of arc supports (green) and focus on choosing the right materials - arcs (green) and (blue), may be pine can be a little soft to be put under compression.

Right- I do plan to add more arc supports. I'll have to see what other types of wood I can get my hands on that isn't too expensive.

Richuk wrote:With the top section, I think you might have forgotten that the mold for the top of the ski is structural and will contain any deflection to your pink layer. If these forces are contained, then the next area of stress in the ends. Your ends are supported by ensuring the condura reachs the end of each mold, top and bottom. You can see this in Plywoods design and provided the bottom tip mold does not go all the way to the very end, then all you are seeking to contain is the force of the hose trying to make itself straight.

Actually I had thought of that when it was pointed out to be a potential weak point, but I decided that it wouldn't hurt to try and address that anyway. Seems like you are saying the design will be fine as long as I factor in running the Cordura all the way to the ends of the press, correct?

Richuk wrote:I'm thinking that the issue you are concerned about within the video is contained by arcs you have running the length of the mold? Provided you use the right materials (blue) and add a few more arcs (green) in the right places. This will save you time, as this is not another new piece to create. I would discount the idea that these arcs placed at 90 degrees will move - provided they are slotted into green sections and they are attached to your blue layer. I am assuming is bonded together in addition to any nails or screws.

Totally on the same page.

Richuk wrote:Sorry to chime in so late, but if you slim everything down to the least number of parts and make them work together, you will have a quicker build .

No worries at all- much appreciated and I am not in a big hurry.

Richuk wrote:The only other thing to add strength - if your not happy and really want to pull it all together, would be to corrugate a piece of fibreglass as you add the each blue section. Cheap epoxy and bi-ax. Alternatively, varnish will help pull it all together.

Would you mind explaining that a bit more? I'm not sure what you mean by "corrugate." I mean, I get the concept of corrugation, but I don't see how you mean to apply it here. And isn't varnish basically just paint?

You understand all the points I was making : )

The idea of corrugation sounds a bit odd, corrugation - thin material made strong (sorry to butcher the explanation). Imagine what it would look like if you'd nailed a piece of corrugated sheet fitted across the arch. It would be fitted so that the wood slats continued to run the length and they fitted within the corrugation of the sheet. The corrugated sheet would restraint the slate when put under pressure. Now imagine if you did this with fibreglass - it would bond each piece of the arch and reinforce at the same time.

Does this make sense now - not easy to do.

PU varnish - in my experience the varnish will toughen up the wood and make it stronger. not by a lot, but it will be helpful to your design. Again, I'm just thinking about the arch you are constructing and its a matter of what you have hanging around in you garage. Paint won't do this for you.

Looking forward to seeing the final result.

OK- now I get the corrugation idea. Very clever, and it seems obvious that it would also strengthen things a lot without adding much weight. I'll have to consider how to actually implement that and then decide if it would be worth the effort. Thanks again!

p.s. Suddenly staples come to mind.

Updated- now with even more backbone!

Webboy - How is this project coming? I'm curious to see how it turned out.

Thanks for the interest. I'm taking a bit of a break during the winter. I plan to continue working on this when springtime rolls around. I will definitely post here once I get this moving again.

how much would this type of design cost? And is it as flawless as the Pneumatic press?

14costurm wrote:how much would this type of design cost? And is it as flawless as the Pneumatic press?

im interested in this as well.