I built a couple of rubber press formers for my wing ribs, and thought I'd relate my experience and advice concerning them.
When I first priced out the metal and rubber for building one, it was far too expensive. Then I found a 6'x3' roll of 1/4" thick rubber at the hackerspace, and the drop rack at Metal Supermarkets near me had 2 pieces of 3/16" C channel the correct length and a 3/16 angle the correct length to fit inside for 65 cents a pound. So I built two forming boxes, one for the nose ribs, and one for the rear ribs. I dusted off my decade-old stick welding skills using some old, moisture laden 6010 rods and made some ugly looking but strong welds. Total cost was somewhere around $50-$75, I think, but I was buying a bunch of metal at the time.
I cut my ribs out on the Shopbot CNC, and also made forms from 3/4" MDF with flanged angles for the lightening holes. I also put a stiffening bead groove on the forms.
I cut and layered 6 pieces of the rubber to fill the smaller nose rib box, and went to press it, only to find the hackerspace's Harbor Freight 12 ton press' jack was leaking fluid badly. Bought a new jack, got everything in place and started pressing, only to find the rubber wasn't compressing the flanges nearly enough. I modified 3 layers of the rubber to match the shape of the form, then pressed again, only to hear a loud bang as the press ram bent and the tip shoved up back into the tube - it is a press no more. It formed most of the rib including the flutes pretty well, the back lightening hole flange wasn't complete and it did not even start the stiffening bead.
Score: .020" aluminum 1, press 0.
I thought I'd try the rear ribs on a 20 ton press. Made the same type of rubber setup, press slowly until my weight was no longer enough to move the jack handle, then my more gravitationally abundant friend compressed it a few more pulls. The side flanges bent some, but not enough to form any flutes, the bend from the fluting pliers was the only one evident. It pressed the middle two flanges on the lightening holes, but nothing on the other two. No stiffening beads were evident.
Score .020" aluminum 2, presses 0.
So I decided to form the rear ribs by hand and the front ribs in the 20 ton press. Forming 24 rear ribs the "slow way" instead of pressing them took all of 2 hours, excluding the stiffening beads and lightening hole flanges. I did put the flanges and stiffening beads on one rib by putting a piece of the rubber over the rib on the form and hammering in the approximate locations, it took about 1 minute, worked fine.
My personal opinion is that rubber press forming makes no sense unless you are going into production. You'll spend far, far, far more time building the boxes than it takes to press the ribs. If you already had the boxes, I'm not sure forming a rib with the rubber press would be any faster than forming one with a hammer. Also, it's only good for nose ribs unless you have a greater than 20 ton press, and I'm not even positive about that as I haven't gotten back to the 20 ton press with the nose ribs yet.
I decided to do a few things with this project that I knew would be slower, as I wanted to learn some new techniques (CAD, CNC, etc). This was one of those things, and, although I'm glad I went through the process, it doesn't seem to be worth the time and expense (~$300, if using new steel and rubber) for a home builder.
When I first priced out the metal and rubber for building one, it was far too expensive. Then I found a 6'x3' roll of 1/4" thick rubber at the hackerspace, and the drop rack at Metal Supermarkets near me had 2 pieces of 3/16" C channel the correct length and a 3/16 angle the correct length to fit inside for 65 cents a pound. So I built two forming boxes, one for the nose ribs, and one for the rear ribs. I dusted off my decade-old stick welding skills using some old, moisture laden 6010 rods and made some ugly looking but strong welds. Total cost was somewhere around $50-$75, I think, but I was buying a bunch of metal at the time.
I cut my ribs out on the Shopbot CNC, and also made forms from 3/4" MDF with flanged angles for the lightening holes. I also put a stiffening bead groove on the forms.
I cut and layered 6 pieces of the rubber to fill the smaller nose rib box, and went to press it, only to find the hackerspace's Harbor Freight 12 ton press' jack was leaking fluid badly. Bought a new jack, got everything in place and started pressing, only to find the rubber wasn't compressing the flanges nearly enough. I modified 3 layers of the rubber to match the shape of the form, then pressed again, only to hear a loud bang as the press ram bent and the tip shoved up back into the tube - it is a press no more. It formed most of the rib including the flutes pretty well, the back lightening hole flange wasn't complete and it did not even start the stiffening bead.
Score: .020" aluminum 1, press 0.
I thought I'd try the rear ribs on a 20 ton press. Made the same type of rubber setup, press slowly until my weight was no longer enough to move the jack handle, then my more gravitationally abundant friend compressed it a few more pulls. The side flanges bent some, but not enough to form any flutes, the bend from the fluting pliers was the only one evident. It pressed the middle two flanges on the lightening holes, but nothing on the other two. No stiffening beads were evident.
Score .020" aluminum 2, presses 0.
So I decided to form the rear ribs by hand and the front ribs in the 20 ton press. Forming 24 rear ribs the "slow way" instead of pressing them took all of 2 hours, excluding the stiffening beads and lightening hole flanges. I did put the flanges and stiffening beads on one rib by putting a piece of the rubber over the rib on the form and hammering in the approximate locations, it took about 1 minute, worked fine.
My personal opinion is that rubber press forming makes no sense unless you are going into production. You'll spend far, far, far more time building the boxes than it takes to press the ribs. If you already had the boxes, I'm not sure forming a rib with the rubber press would be any faster than forming one with a hammer. Also, it's only good for nose ribs unless you have a greater than 20 ton press, and I'm not even positive about that as I haven't gotten back to the 20 ton press with the nose ribs yet.
I decided to do a few things with this project that I knew would be slower, as I wanted to learn some new techniques (CAD, CNC, etc). This was one of those things, and, although I'm glad I went through the process, it doesn't seem to be worth the time and expense (~$300, if using new steel and rubber) for a home builder.
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