What is the best press to make for the least $?

[MontuckyMadman]

so I loaded up some proto bags I made in my 7" wide pnematic press.

Tried hard to break them and they did fail at about 60 PSI.
It was the stitching that failed and nor the material.

These proto bags I have been messing with for a while, making them different sizes, sewing and ripping out seams and sewing again.

This particular sew job only had one lengthwise single stitch holding these together. Usually it has 2 lengthwise stitches and a box stitch at each end.

Stitches started to pop at about 55psi and then the whole thing went pop at 60psi or so.
Flew open like a barn door in the wind and the firehose popped about 3 feet in the air and fell on the floor.

If you were standing directly over the press with your face down looking at it you could definitely be injured.

I think the only way to really test this is well, to test it.

I will sew these back together use some reinforced stitching and try and blow them up again.

I think the strength of this raw fabric is extreme. The weakest point is definitely the stitching.

Pradellach send me whatever the link is or put spaces in it and we can see it and visit.

[chrismp]

sounds good.
we'll see how it works out for our press.
as a safety measure we'll add some tension belts that will be wrapped around the press with a bit of slack to prevent the top mold from getting some airtime.

[nate]

This book has some interesting seams. Some even have efficiencies of over 100% (meaning the seam is stronger than the fabric. All in all fairly interesting material.
LINK[/url]

[MontuckyMadman]

I banged together the same material I have sewn probably 4 times with some new stitching from that parachute guide thing. Thanks for that. Some big box stitches almost all the way across. My compressor maxes out at 70 PSI output, I guess. I have a bit of a leak in the firehose. That shouldn't matter but the pic is at 60 PSI, 70 was fine with no sounds or sign of weakness.

These were badly sewn and have been perforated hundreds of times. Don't know how much the forces will differ across a double press but this seems pretty damn bomber.
Notice the center bubble. Probably a spot for mold deformation if your gap is to big in the middle.
That gap is about 9 inches.

[MontuckyMadman]

nevermind 2

[MontuckyMadman]

nevermind 3

[MontuckyMadman]

LINK

nevermind

[nate]

Now I'm curious what all that was about.

[MontuckyMadman]

somethin wrong with the edit button in my brain.

You would think by now I would understand the interweb.

[nate]

Very nice Montucky.

Something I've been thinking about concerning fabric ski presses. Techincally your top and bottom beams don't need any significant strength lengthwise if they're completely wrapped in fabric. This is a big advantage of the fabric press. However, if you make weak beams assuming they don't need any strength you can only count on the fabric directly around your top and bottom molds to provide the tensile strength.

Maybe that's not easy to understand.
To illustrate: If you have 8' beams (assuming beams with no significant lengthwise strength) wrapped entirely in fabric, but your hose is only pressurizing 6' of that, you can't do your strength calculations using all 8' of fabric. You can only count on the 6', since if that 6' fails the 1' of fabric either end isn't going to do you any good because your beams will also fail.

Not an issue (I hope) for me since I have fairly beefy beams (and your cordura looks like it's quite strong) , but something to keep in mind.


Another thing I've been thinking about is using Climbing webbing sewed into loops. 1" Climbing webbing is rated to 4,000 lb. Webbing doesn't have the advantage of not needing strong beams (like I discussed above), but it's readily available, cheap, and apparently super strong.

[Nanook]

That is the best idea that has come out of this subject. Nate, that seems like an awesome idea. Even if 1" can hold 4000lbs there are a ton of wider dimensions of that stuff too. PM me if you want to exchange some ideas. Great thinking!

[nate]

Something to consider, however, is breaking strength vs. working strength.
Climbing webbing doesn't have working strength listed as far as I can see, but I did find some more interesting stats for similar sizes of Tiedown Straps.

1"
1" Tie downs straps have breaking of 3,000lb, but a working of only 1,000lb.
2"
2" Breaking at 6,000lb and working at 2,000lb.
4"
4" breaking at 20,000lb and working at 6,666lb. Or a stronger 4" at 24,000lb and 8,000lb.

[chrismp]

we've considered using tiedown-straps as well, but wide straps to cover a good amount of the press would be way more expensive and a lot more hustle to wrap around the press.
then there's the problem of tightening all the straps at an equal level, which, if not achieved, could result in some areas not getting enough pressure.

[nate]

Can anyone confirm if you're allowed to count the fabric on both sides of the press into your calculations. Ie if you have a 8' long bag of cordura wrapping your press, and you say that cordura has a strength of 500lb/in of width(this isn't a true figure), is your strength 96x2x500 to account for the fabric on each side, or is it just 96x500.

[shopvac]

Nate - I think you multiply by 2. Can anyone else confirm this?

Montucky - awesome work with the cordura tests. This is very encouraging as I think a couple people on this forum will be using cloth ski presses here shortly. I feel confident pumping our bags up to 70psi (even though we usually press at 40-50psi). I thought I read in one of your posts (that now I can't find anymore ...) that you found some new stitches that were better. Is this true? I don't think we need new bags right now, but that would be good for the next generation we get.

I don't think using climbing webbing or tie down straps is necessary after Montucky's test. Is anyone building a cloth press considering pressing above 65psi anyways? That seems unnecessary in my mind.