Ski Builders Forum

so i used the above link and came out with this.

img809<dot>imageshack<dot>us/img809/1202/frame.jpg

how does this look? i will be welding the 84" c channels together

whats up with this 2 post thing too. sorry for the <dot>

fa wrote:no, i didn't know that, interesting link

MM, if the 5x5s are cold-rolled, might be safe to cage them with frames to prevent skewing. (lower sketch)
Also, for the middle vertical supports, you might want to use flat bars instead of the tubular 2x2, as it will be easier to tide fit the pin through. (solid profiles are good when bolting or drilling & these members will only resist tension so no need to be hollowed). Flat bars match nice with L 's
just my thoughts, good luck with it!

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I really appreciate the help. Most of what I see here is similar to chinese in my understanding. I do not speak or read chinese.
Japanese I have a rudimentary knowledge and can read but have no idea what the sounds I am making mean. very odd.

I was not planning to cage the center span, only the ends like in teh pictures I made. The beams will be stitch welded and I was hoping it would cause these to act as a single unit and by trussing the front and rear like whiteroom's press then I would be good, more points however. You recommend 4 additional supports and caged?

Thanks.

MM, I'm planning on testing my press under progressive loads and measure deflection. I'll start with 20 psi and work up to see what happens.

I'll add additional posts if things deflect too much.

What is thought of as an acceptable deflection range for safety and for not losing camber? In my head I was thinking less that 1/8 inch.

V

I found 1/8 to be too much. My press deflected 1/8 on the bottom, I'm assuming it deflected 1/8 on top also but never measured the top. I also press at room temp which in past posts, folks have said you can lose up to 50% of camber. I ended up supporting the middle of my press. I retested at 40 psi and have near 0 deflection. I haven't pressed any skis yet since updating the press. So I'm hoping by supporting the middle will retain more camber.

I know, sorry, my english doesn’t help me much either. Let me try in Korean.
If you re bored to read it all, just read the bolt letters:

In a beam that is resting in supports at its both ends (first diagram, called “free standing” in Chinese and “simply supported” in korean) for a uniform load Q, the maximum deflection (in the middle of the span) is 5QL^4/384Ei, where L is the span.
If you extend that beam both ways and place multiple supports at equal distances keeping all spans =L, then the deflection for that same span will be QL^4/384Ei, that is 5 times less than in the previous case. (The load in the neighboring spans act as a counter weight reducing the deflection. You can see in the first diagram, that just beyond the supports, the beam is deflecting upwards. In an arrangement with multiple supports that upward distortion is reducing the deflection in the middle of the neighboring span. I called that “a continuous beam” in Chinese and in korean.


In the past the Chinese have tried to build a continuous wall around the earth, but not a infinite beam around it. Not yet. So all beams, even the “continuous”, have ends. At the end spans of you design the counter weight effect comes only from one side. So there the deflection it will be less than what is in a “simply supported” beam with equal span, but increased (~doubled) compared to the typical middle span of a “continuous” beam.
That’s why in an optimized arrangement of multiple supports, the end spans should be sorter.



In both beams (simply supported & continuous) deflection is proportional to L^4. That means that if the span (L) is doubled the deflection (f) is expected to grow 2^4=16 times.
In your second drawing you have a design with 3 extra pairs of vertical supports. Alex calculated the maximum deflection with out them. By reducing the span with these supports to 1/4rth of what it was, the deflection would be decreased 4^4=256 times. More reduction (>2*256=512) is expected, as the beam is now “continuous” and not just “simply supported at it ends”.

About what I wrote in perfect Chinese for skewing and caging:
I missed that you were talking imperial (god, That is Chinese) and thought that the tubular 5x5 are 2,5mm thick. My mistake. Since they re 6mm thick, probably welding them together is enough to transfer loads from the the middle SHS to the outer's SHS’s walls where the extra supports will be joined. Still, it might be easier to use cages for the xtra supports, instead of stitch weld the three 5x5 together.

Usually flat bars are cheaper than tubular sections for the same weight. Plus, pushing a pin through a tide-fitting hole is easier than through 2 tide-fitting holes (no laughs pls). So making the extra vertical supports with flat bars instead of making it with hollowed 2x2s might be more convenient.

Hope it made some sense,
fa

edited/ in the kingswood video @~4:50 there s a press with multipl twins flat supports

fa, that is one big math brain you have there. Just like MM the numbers might as well be hieroglyphics to me.

But the pictures make perfect sense to me and after looking at those diagrams I think my press is going to perform well and if not I know that adding additional vertical posts will fix any deflection problem I might run into.

Do you think welding 2 inch flat bars, in several locations on the span, to the top and bottom of 2 stitch welded beams would create less chance the sections might twist independently? Or does it really have to be caged to prevent any sort of twist?

Vinman wrote:...one big math brain...

Vinman, not quite. In highscool maths i scored 8.5 out of 20. Maths give me big headache

Do you think welding 2 inch flat bars, in several locations on the span, to the top and bottom of 2 stitch welded beams would create less chance the sections might twist independently? Or does it really have to be caged to prevent any sort of twist?

I dont know what sections you used for the top & bottom beams. In MM's design there are 3 beams, so the midle one isn't directly conected with the extra supports. Plus i got wrong the thickness of his SHSs. (I know that cold formed steel sections are not that good in resisting torsion & twisting and usually thin walled hollowed steel is cold formed.)
In your press i see you 've used 2 beams, so it's different. Caging where the supports are is probanly the sure way to keep everything in place, but it s probably not needed in you press. An engineer can tell that for sure. I hope i could help, but it takes more than i know.
I like these press designs with the midle supports, because they can be made significantlly lighter. But I suppose with them one should go for even less tolerence, as the deflection becomes wavy (down and then up again wher the midle support is) and i guess this is the less wanted.
By the way I saw the pic of the shop you have build. Great job!

The site www.efunda.com might be usefull for calculating beams etc.

Buuk