Ski Builders Forum

Ok, so here is my design for the press frame. I'm using two pairs of 80x40x3mm steel beams. My gut feeling says this should do.
Anyone here with more steel (bending) experience care to comment?



Thanks!

JVV

Your link doesn't work, and I perused your Picasa albums and couldn't find a press sketch anywhere?

I made it available now, sorry about that. The link still doesn't work.
The design is quite light weight, I know.
Stupid question: are I-beams stronger than tubes, by weight?

yes I-beams are stronger by weight,

if this is your first press i would recommend having a complete steel base and top so that you reduce the variables if you get uneven pressing. also you want to think about keeping it square. with just those 2 steel strips i would imagine that you might get some movement side to side once you have the mold and everything in it

it looks like you have some kind of cad program i would try and run it through the simulation software, i use a factor of safety of 3 for mine. if u want me to run a simulation for u i can just pm me

I fixed your link for you.

That press alone will not work, unfortunately. You will get some serious deflection in the middle, and with the bars unsupported laterally I think you'd get some pretty serious buckling. Unsafe!

If you add some supports in the middle to stop the deflection you'll be ok, you just need a way to load the press. My press is built of 2x4 steel beams (roughly the same size as yours), 3 on top , 3 on bottom (two laying flat, middle one vertical) and they're all welded together. They are supported on the ends, but then I have 3 sets of vertical supports in the middle as well. Without those I had a LOT of deflection.

Remember the forces you'll be dealing with, they're huge. On my press every 10psi equates to about 10,000lb of total force on the press frame. I press at 60psi, so that's 60,000lb of very real force. Don't take that lightly!

As for i-beams vs tubes - you can't just say I beams are stronger for the weight, cause that is not necessarily true. It all depends on wall thickness and dimensions. Bending stiffness is equal to the area moment of inertia multiplied by the modulus of elasticity. If an i beam and a tube beam have the same moment of inertia (if the wall thicknesses are the same and the outside dimensions are the same, they'll be damn close), then the stiffness will be the same.

http://en.wikipedia.org/wiki/Area_moment_of_inertia

Here is a picture of my press - it is by no means impressive, but I've pressed about 20 skis in it with no issues. There are 3 supports welded on the back side, on the front those supports are pinned in place. By removing the top pins the whole thing swings down and turns into a nice platform that helps when loading the press.



I have been planning on building a new I-beam press for a long time, the beauty of an I-beam press (with sufficiently large I-beams), is that you don't need vertical supports in the middle. Just makes loading the press that much easier/quicker.

Thanks gardner and twizzstyle, excelent advice from both of you! I'm using SW2011 and did not realize I have a simple FEA tool hidden in there... I found out quickly the first design was seriously light. I've never had to design stuff like this so the forces were kind of a surprise.
After a bunch of models and analyses I came up with a model quite like Twizz's, although mine will be loaded from the end, with the bottom mold sliding out of the press to make loadin easy.
This seems to be the lightest way to do it. I got the FOS to a minimum of 3, but I had to make an assumption for the rigidy of the mold. I figure it's easy to weld more beam if it still deflects, the thing should atleast be safe by now.
I'll post a pic, drawing or the analysis later. I promise I will post results even if it self destructs, so put some beer outside and get ready to ROFLYAO

Nice work!

We've loaded our press by sliding things in from the ends before too, it's a little trickier, but not too bad at all. I think you're all set.