climbing webbing in a press frame

[brianmwaters]

Hi everyone, I'm new to this forum, and want to start building a ski press (as cheaply as possible).

It seems like most of the press frame designs on this site use a "top brace" and a "bottom brace," held together by a "support structure" (usually steel rods or square tubing) with the mold and bladder sandwiched in the middle.



Well here is my brilliant idea:
I was thinking that I would build the sandwich of bottom brace, mold/bladder, and top brace and then wrap the whole thing many times around with 1 or 2 inch tubular climbing webbing.

This stuff is really cheap (something like 50 cents a foot) and has a high tensile strength around 20 kN. you could make the frame's support structure as strong as you want just by adding more wraps.



Has anybody tried anything like this before? Engineers, and expreienced press builders, what do you think?


- BW

[plywood]

i did it!
as you wrote, my press had to be as cheap as possible too. so i took some very strong cloth, wrapped it around the press once and sewed the borders together. you can find pictures in the middle of following post:

viewtopic.php?t=474&postdays=0&postorder=asc&start=15

so it worked for...5 pairs up to now which means about 16times of pressing. i normally press with about 2,5bar , highest pressure on my system were 5 bar.

your idea could work - just keep in mind that it needs some time to wrap the whole press with the webbing. and if you want to use a wider mold for building 2 skis at once you probabely had to reinforce the mold that it doesn`t crack in half lenghtwise...but if you did 2 skis at once you really had to hurry to get everything done in time.

i just can tell you...my system works, but it`s a bit bitchy to operate. needs quite some time to get the "cloth tube" over the mold because it fits more or less tightly.

[scottychop]

Climbing webbing is also just a bit stretchy. You'd also have to make sure there were no twists at all , and have a really slow epoxy.

[Steevner]

So carbon fiber or fibreglass would work super well then?because fibreglass cloth is very cheap (compared to lets say... steel)
I can get +20m long by 1m wide cloth for about $8/square metre.
The only problem would be attaching it to itself once it's wrapped...

[dante]

plywood: "i did it!"

Wow Plywood! That was pretty innovative. I hadn't seen that thread before. Are you still using that method? I wonder how Kevlar fabric might work.

[plywood]

@dante: yes, it`s still up and running actually i`m thinking about sewing a second pressframe for my new mold. so as you see it works perfectly for me as i`m not using any higher pressures than 4,5 bar or so. such a "frame" is done quite quickly and easily and needs no room for storage. so my system is close to "portable"

@steevner: i`m not sure if i did get you right. do you want to use normal fibreglass for your pressframe? interesting idea. you`ve recognized the main problem: how to fix the two ends. furthermore you had to laminate the fibreglass with epoxy to protext it from any damage when sliding the mold into the fibreglass tunnel. so you had a pretty non flexible mold that needed some space to stand in...

a possible solution could be to wrap around the fibreglass 3-4 times. then the friction would take up a lot of forces and you could cover the whole thing with epoxy to get a bombproof mold. i think this could work. the only trouble i see there is that you had to be very careful when building it to get the needed accuracy. and you had to be careful whend putting the mold into the tunnel to align it properly because the fibreglass with epoxy cracks quite easily if you apply pressure to it in the wrong way.

so it could work - but it`s much easier to go with some proper cloth. some that can take up the load and is not that stretchy.

[Easy]

The problem with fibreglass is that it is quite brittle. The material functions well as a fibre within a composite material. As far as I know it is almost always used in composite materials (except ofcourse fibre optic cables, commonly used for data transfer). So (as plywood already stated) fibreglass would probably work, but you need to combine it with epoxy (or an other matrix material).

Please remain cautious and always put your safety first when experimenting with press setups. You don't want to end up winning the Darwin award!

[pau]

@ plywood
how did you sew the cloth together? do you use a special sewing technique because this is the weakest point of this construction.

climbing slings are alredy sewed together and are aviable in diverent lenght.
what do you think about that?

[plywood]

neow, no special technique. well, not really. i just let the cloth overlap for about 6cm and started to sew lenghtwise over the seam. just straicht stitches. there are about 25 rows of stitches on those 6cm, evenly distributed i`ll see if i can make a photo of the seam.

climbing slings would be an option. BUT: it would take you a load of slings i suppose. and you had to hurry up as you installed the frame. i`ve got 5 "slings" for my press, and it takes quite some time to pull them over the molds because they have to fit as tight as possible. so i wouldn`t recommend small climbing slings mainly because they take too much time to install. you may underestimate this, but it takes me about 10 minutes to install my 5 slings...

so i really have to hurry to get the whole layup and pressing done in 40min - otherwise my epoxy starts to cure.

[pau]

i thought to to put the sling around the mold- not pulling the mold through the sling - and connecting the two ends with a maillon ( somthing like a carabiner but much cheaper)
i hope you understand what i mean
with this method the slings should be able to hold out 30kN

my calculations: surface of the mold : 0,6m2 (30cm x 2000cm)
pressuer : up to 5 bar = 50 000kg/m2

0,6x50000=30000kg
so the pressframe has to hold 30t

-> 10 - 11 climbing slings

are this calculations correct or did i a mistake?

@plywood whats the diameter of your "slings" ?[/quote]