What Size I Beams
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What Size I Beams
Could you reply on which weight i beams you used with building your presses. And also how did you deiced which weight suited your press the best. thanks
The biggest ones possible.
Here's a link to a beam calculator. Of course, the force in a ski press isn't a nice simple point load, but this should help.
I didn't actually end up building mine out of I-beams, simply because after like 4 months of calculating, researching and designing, I couldn't justify the enormous size necessary (it would be too hard to move, and pretty expensive too, unless I could get scrap, which I now know I could have).
http://www.engineersedge.com/beam_bendi ... nding2.htm
Here's a link to a beam calculator. Of course, the force in a ski press isn't a nice simple point load, but this should help.
I didn't actually end up building mine out of I-beams, simply because after like 4 months of calculating, researching and designing, I couldn't justify the enormous size necessary (it would be too hard to move, and pretty expensive too, unless I could get scrap, which I now know I could have).
http://www.engineersedge.com/beam_bendi ... nding2.htm
I built mine with (4) 7' long scrap I-beams that I got for free. The top (2) beams are W16x36's and the bottom (2) are W18x40 somethings (forgot the exact weight). I did the deflection calcs on them once and I think bottom came out to have less than 1/16th of an inch of deflection in the center for a double wide mold at 70 psi. Don't quote me on that though - its been a while since I did the math.
The funny thing is though - even though I put all the time and effort into building a press with a super stiff bottom section, I still had skis come out with camber that didn't match the mold because of heat ramp rates. With just bottom heat, I have been able to get 5mm + of rocker with a fast heat ramp rate, and have had added regular camber to a ski with a very slow heat ramp. Getting that down can be tricky.
I'm not going to tell you what size beams you should use because that is all dependent on your design and building method - well, that and I don't have a PE Stamp or insurance. But you can find some simple equations that will tell you how much a beam will elastically deform under an applied load, and that will let you know the approximate size beam you should use to have a desired amount (or less than an undesired amount) of deflection (see web site on camhards reply).
If and when you do finally build a press, be careful. Ive seen press frames on here that have had the I-beam flange rip off the web, and have heard of presses designed by people with graduate engineering degrees have bolts shear. You don't want to be in the wrong place when that happens, and for that reason, I don't want to assume any liability and tell you how to build your press.
Point being, even if you understand the mechanics, you may want to do the math. But even if you've done the math, if you don't understand the mechanics, your math may not be valid.
In the end if you do want to understand what size beams you should use, the best advice I can give you is to go find a statics and mechanics of materials book and do a little (or a lot of) reading.
I don't think that was any help was it????
The funny thing is though - even though I put all the time and effort into building a press with a super stiff bottom section, I still had skis come out with camber that didn't match the mold because of heat ramp rates. With just bottom heat, I have been able to get 5mm + of rocker with a fast heat ramp rate, and have had added regular camber to a ski with a very slow heat ramp. Getting that down can be tricky.
I'm not going to tell you what size beams you should use because that is all dependent on your design and building method - well, that and I don't have a PE Stamp or insurance. But you can find some simple equations that will tell you how much a beam will elastically deform under an applied load, and that will let you know the approximate size beam you should use to have a desired amount (or less than an undesired amount) of deflection (see web site on camhards reply).
If and when you do finally build a press, be careful. Ive seen press frames on here that have had the I-beam flange rip off the web, and have heard of presses designed by people with graduate engineering degrees have bolts shear. You don't want to be in the wrong place when that happens, and for that reason, I don't want to assume any liability and tell you how to build your press.
Point being, even if you understand the mechanics, you may want to do the math. But even if you've done the math, if you don't understand the mechanics, your math may not be valid.
In the end if you do want to understand what size beams you should use, the best advice I can give you is to go find a statics and mechanics of materials book and do a little (or a lot of) reading.
I don't think that was any help was it????
Brian