Ski Builders Forum

Cool man - good luck

J

All done with the frame!!!!!

Now onto the molds.

check out the pictures here:
http://community.webshots.com/album/416708061YxYdoH

i've never built a press before, but you could 'salvage' some staight pieces of steel from abandoned train tracks. just an idea...

that stuff is super heavy, but I did 'salvage' some perfectly sized i-beams from a DOT junk pile near my house.

haha well i guess i shoulda read all the posts before replying :P

melvs wrote:All done with the frame!!!!!

Now onto the molds.

check out the pictures here:
http://community.webshots.com/album/416708061YxYdoH

I was looking at your building frame and it looks like a nice job, I see a dangerous weak point though which will limit your pressure or cause failure. It might be that I was looking at an incomplete picture but I saw 8 bolts joining the upper and lower sections together. If you have 10*72" of clamping surface with a pressure at 60psi then the tension in each of those 8 bolts is 10800 lbs. I don't know the size of the bolts but if they are 1/2" bolts you would need 32 bolts joining each of the halves together to safely pressurize the frame. You could also work at lower pressure but your frame overall is quite strong so you probably want to work at higher pressures. email me if you want some recommendations

Tony

how serious of a problem do you forsee this being? are we talking the press blowing apart?

I was thinking about adding some clamps of some sort on it while testing it, do you think that would be a good solution to the problem as well?

Technically, those bolts should hold, but I would still tend to agree that you should use more bolts. Bolts are pretty cheap compared with the fresh pair of pants you will need if any of them blow apart. Some of the nuts I used on my press weren't of very good quality and they blew apart while I was pressing the first time. The press still held together because of the way it is designed, but when the nuts failed, there was enough energy released to lift the hole press frame off the ground about a half an inch. Not to mention the fact that it sounded like a gunshot.

melvs wrote:how serious of a problem do you forsee this being? are we talking the press blowing apart?

I was thinking about adding some clamps of some sort on it while testing it, do you think that would be a good solution to the problem as well?

Right now I would not go over 10psi until you add more bolts. The two halves will blow apart, they are not likely to go anywhere but if you have a pair of skiis in there you are going to have to do some mighty fast bolting. The clamps might help but the stresses on the clamps are difficult to predict so the more direct route of bolting has more predictable results.
Another alternative is to weld the two halves together. You have lots of bolts joining the long pieces to the transverse pieces, try and get the same number on the two halves so it will be of equal strength. If you tell me the number of bolts and the diameter and grade of bolt I can tell you the maximum pressures that you can use.

By the way, our press is wooden, and we have made 4 skis so far without any issues in that regaurd.

*ARMADA* wrote:By the way, our press is wooden, and we have made 4 skis so far without any issues in that regaurd.

Nothing wrong with wood at all its just a matter of using the materials in an effective manner. The comment on the bolts is just pointing out the weak link in the steel assembly, since the total forces on these presses is in the range of 20 to 40 tons the 8 small bolts will yield at about 18 tons so they are substantially undersized. Normally you don't want the bolts being stressed more than 1/2 their strength which is why I suggested that the number of bolts be increased to 32 whish is exactly how many bolts join the longitudinal sections to the transverse section. Have you got a picture of your wood frame, that is what I'm making.

I agree with the last post there, I got scared when my 32 M10 bolts started stretching at around 40tons (parallell press), so I drilled up the holes and changed them with M16, now I'm really on the safe side though..

Better safe than dead

origanally I had more bolts in the design, and all the holes are drilled for them, but I loose 3 inches of ski length if I do it, making the max length of the skis around a 178 or so. I guess that's fine and it will make the total bolts around 16 on each side ( a couple of the bolts can't go through because of how to steel is bent), so maybe that would be the best thing to do?

melvs wrote:origanally I had more bolts in the design, and all the holes are drilled for them, but I loose 3 inches of ski length if I do it, making the max length of the skis around a 178 or so. I guess that's fine and it will make the total bolts around 16 on each side ( a couple of the bolts can't go through because of how to steel is bent), so maybe that would be the best thing to do?

Pat that sounds good, I made the assumption that you were using 1/2"bolts when we last talked and 32 of those are perfect for all the pressures that you are talking about. If they are 3/8" bolts reduce the pressure a bit say aabout 35-40 max so you don't run into the situation that Endre described in the previous post. Like he says better safe than dead although I'd still test it with no ski inside and cover the whole thing with a blanket in case a bolt lets go. These are big loads we are dealing with.
Tony