:: View topic - frame overkill

Hey All:

I am, either fortunately or unfortunately, not a mechanical engineer. So when I look at the frame and hear about '40 to 50 PSI' required to press out a ski, I like to think that is the same sort of pressure that is in my mtn. bike tire. What am i missing?

I understand that its all about uniform pressure from tip to tail, but can't that be acheived (on a WAY less engineered-out frame) by a torque wrench and a home-made clamp press. Has that been tried yet? Seems to me that the cost and spirit of that is more in tune with the garage building scene.

Anyways, killer website and you guys are on it!

Endless Winter

Td

The frame needs to be very stong! While 40 psi does not sound like a lot, over the length of a ski it is quite a bit of force. (ie 5"x72" area at 40psi is 14,400 lbs of force pushing the frame rails apart, that's only for 1 ski, double that for a pair) While this is distributed along the rail, it is still a lot of force.

A clamp press will work, but it is hard to get even pressure along and across the whole ski.

-kelvin

Well, totally understand the PSI and how it adds up - thanks for the clarification. Have you (or anyone else) messed with a modified clamp scenario.. maybe still using drilled flat steel and a consistent pattern of clamping to acheive the same. Thoughts on a trial effort for that?

t dog

i really think a clamp press will work. it was actually my first option when i started to build skis. but when i began designing the frame i realized that you get much more out of a pneumatic press (uniform pressing and easy adjustability) than from a clamp press with almost the same amount of effort.

the thing with a clamp press is that it's difficult to get uniform pressure throughout the ski as Kelvin mentioned. but i think this can be achieved by using sand or water creatively. another drawback is that you may have to make a new top mold every time you change your bottom mold.

I have tryed clamping with a double mould. I got a lot of blisters in my hands, and compared to a pneumatic press there is not enough space for required amount of clamps (ca300kg/clamp=50-100 clamps.) and not enough time to tighten them. By the way you have done so it is time to untighten. bottlejacks would be a better option, but you would have to be very accurate when you build the molds. To even out the pressure you can use a cork mat (or even better a silicon/rubber mat if you can find one. ) If you want to experiment and develop your skills there is no good alternative to a pneumatic press.

I spent all day trying to make a jig for my router to cut out the tip/tail parts of the bottom mold. I cannot for the life of me figure it out. tigs/suggestions for making it, more specifically the curved section and how to fixture it?

1. First make a template of your tip/tail mold out of some scrap wood.

2. Secure wood template to a big piece of MDF (or whatever wood you plan on using for the tip/tail molds) with countersunk nails, double-sided tape, or hot glue. I use 3/8" thick wood or something similar. Your MDF should be large enough so that when your template is placed on it you can still clamp the MDF to your working table without getting in the way of your router.

3. Use your router with a either a template guide or a straight bit with a ball-bearing to follow the template and cut out the tip mold shape from the MDF.

4. Repeat for ____ number of pieces.

5. Glue pieces together using wood glue and clamp together.

6. Once the glue is cured, take your belt sander and sand away until the tip mold is nice and smooth.

I'm sure there are better ways of making a tip mold.

I made the mold using a turbocad printout of the tip, camber section and tail-> templates-> cut out and sand pieces->bolt together alternating pieces (tip/tail, then camber, then tip/tail again, etc.)

Has anyone ever tried using the discharge hose to a sump pump like this one http://www.contractors-depot.com/catalog/allitems-ss90.html

I can aquire a 4" thick one rather easily and was wondering if it would work in place of the fire hose.

PS... Just laminated the core last night. Used a maple/poplar mix. Will keep everyone posted with updates.