round press idea

[scottychop]

Just to get the engineers upset, I decided to tinker with a round press idea. Besides the obvious alignment issues, any thoughts? Could make for an inexpensive option using large diameter, high pressure PVC or ABS?

http://picasaweb.google.com/scottychop/ ... 6509261042

[doughboyshredder]

Funny, I thought about the same thing when I was trying to design my press. I was thinking about using steel pipe though. You can get used steel pipe cheap. I figured you could design a mold assembly the same as normal (with the air bags between the top mold and the board), and then slide (roll) the assembly in to the pipe. It could work pretty good and be a much less expensive option than a steel framed press.

[plywood]

i like the idea, it`s somehow similar to what i did. i just took cloth instead of a steel pipe.

i`d recommend you to put the bladders as always between the molds, as doughboy said. roll your setub into the pipe and then you maybe have to but some support pieces at the top and bottom of your mold, some halfside round, other side flat wooden blocks in to evenly distribute the pressure over your whole molds. if you don`t to so you may got too much pressure on the edges of your mold which may result in deflection or something like that.

alignment of the molds should be no problem as you`re going to have plenty of space at both sides of the mold. so you could construct some sort of guides on the side of the mold, connecting the top with the bottom mold and fixing everything a little for the roll in into the press...

[Greg]

I think that is a really excellent idea. Especially when you consider that most piping is rated to relatively high pressures (over 100 psi). Good luck with it.

The only thing I could see causing troubles is if the epoxy leaks out of the ski during pressing and glues everything together. But that is an easy problem to prevent. Just make sure you have a wrap of plastic around the ski to catch the extra epoxy.

[jono]

This is a very elegant idea. Why assemble a creaking contraption when you can contain all of the pressure with a simple steel cylinder? I look forward to seeing someone try this approach.
I would be leery of pvc or abs. Even if they have a high pressure rating they seem like they could be weak or brittle from focused concussive forces in a way that steel pipes are not.
What are the pressure ratings and weight per foot for various wall thicknesses? Steel pipe is really heavy, I wonder what the thinnest wall is that you could get away with?
Rectangular steel tubing could operate in the same manner as a cylinder with some weight savings. This stuff comes in a 12" by 16" size. This is just big enough for a two ski press.
This type of tubing is probably not made for pressure in the way a pipe is but it would be pretty slick if it could work. Are cylindrical tubes inherently stronger than rectangular tubes or is the strength derived mostly from the thickness of the steel?

[doughboyshredder]

I couldn't find the page, but it's out there in google land somewhere.

I seem to remember that a 20" diameter pipe of .065 wall steel was rated to withold much higher pressure than what we generate. I would worry about deflection if the mold isn't shaped the same as the inner diameter of the pipe, though.

I still really like the idea.

[scottychop]

I am now thinking, that round tube would distort too much, even in steel. IF the bladder were in the middle, and molds top and bottom form fitting, the sides of the tube would tend to straighten due to the vertical pressure. I'm certain the wall thickness would be a =/- factor but too risky. Besides, Large diameter steel and PVC are extremely expensive right now.

I ended up making a simple single ski press this weekend out of some rectangular tubing.
Cheers,
Scott