Ski Builders Forum

Hey all, I'm new around here so let me start off with saying thanks for the incredible content and expertise.

Some friends and I are looking to start building skis this summer and we are in the planning process for all the equipment and jigs. I've started to draw up plans for a 2x2 steel tube press and realized I was basically building a tube. So here is the meat of my question.

Has anyone tried using 12x12 steel tube with 3/8 ths thick walls as the press frame? Seams really simple to me although maybe a little narrow but probably workable.

Any thoughts?
Cheers.

I think it would deflect noticeably but without doing the math I have no idea.

I would recommend not using 2x2 steel tubing, it would require a fair amount of reinforcement. I did some stress analysis for ben_mtl on his 2x2 frame press, and he is choosing to add reinforcements to abate the deflection he's experiencing.

As for the 12x12, I would advise not making the mold wider than the 12" section, otherwise you'll run the risk of having your mold deflect in the unsupported areas, resulting in bases that aren't flat.

Am I right in thinking that you are planning on using the inside of the 12x12 as a press frame? in which case apart from being tight should work no problem

Idris wrote:Am I right in thinking that you are planning on using the inside of the 12x12 as a press frame? in which case apart from being tight should work no problem

Yup, just slide everything in.

Without some sort of bracing you will probably end up ballooning your tube and it will not be square anymore.
Depending on what its gonna cost for the tube it would be worth a try.
I'm a big fan of keeping it simple.

sam

I've thought about using the inside of a steel tube too. It is so clean and easy.
I wonder if these types of tubes are rated in terms of how much pressure they can withstand? I would not proceed unless I had some good numbers from an engineer or a manufacturer.

I don't think you will get good results with square 12 x 12. However, a 12" diameter pipe is another story.

you mean put the mold contents directly INSIDE the 12 x 12 tube?

it's worth a shot i suppose. I'd run it at low pressure at first. And put it in another room, hahaha.

I just ran a quick stress analysis for a 12"x12" x 1/4" wall thickness steel tube. At 40 psi the maximum deflection was 0.103" per side (total of .206"). Also, the maximum stress is 38.62ksi...which exceeds the yield strength of most carbon steels. In short, the tube has a high chance of breaking.

I have a picture ready but I don't have the time to figure out how to post it. The story would be quite different with a thicker walled tube (1/2" or better).[/img]

Jekul wrote:I just ran a quick stress analysis for a 12"x12" x 1/4" wall thickness steel tube. At 40 psi the maximum deflection was 0.103" per side (total of .206"). Also, the maximum stress is 38.62ksi...which exceeds the yield strength of most carbon steels. In short, the tube has a high chance of breaking.

I have a picture ready but I don't have the time to figure out how to post it. The story would be quite different with a thicker walled tube (1/2" or better).[/img]

Thanks for running the numbers Jekul. Would increasing the size tube to 14" or even 16" with 1/2" walls work?

Here's the quick run numbers. A 14"x14" x 1/2" wall tube will reduce the deflection to 0.025" per side (.05" total). That number is much more manageable. Max stress is 14.39ksi, well below yield strength for most carbon steels. I worked the numbers for a 12" tube with 1/2" walls and the deflection was reduced to 0.013" per side. If you can fit everything into that small of a package then you might have a cheap press. If you wanted to reduce deflection even more it would be easy to add/weld a piece of steel above and below that would increase the cross-sectional area of the 1/2" wall thickness tube.

Here are Jekel's FEA photos. Thanks for doing this for everyone. I believe he is using 40psi to do all of his analysis.

12" tubing with 1/4" wall thickness


12" tubing with 1/2" wall thickness


same 12" tubing with 1/2" wall thickness - stress in ksi

can you do the same analysis with round pipe?

I bet you'll be surprised at the numbers. I expect deflection to be very low, even with thin walled steel, and pipe is cheaper.

http://www.engineeringtoolbox.com/a106- ... d_370.html

900 psi anyone? 10" schedule 40 carbon steel pipe at 200 degrees.

Thanks for posting those shopvac.

doughboyshredder: I can run the analysis for you, but imagine trying to build up a mold to go into the round tube? It would take a unique idea to get everything even and squared up.