DANE

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twizzstyle
Posts: 2203
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle » Fri Jun 24, 2016 9:31 am

Those diagonal braces on the top and bottom aren't doing much more than holding your mold in place. It looks nice though. A "car or two" is maybe 6000lb. If you press at 60psi, you might have upwards of 60,000lb of total force in your press.

I beams work well because they have very large shear walls. That's why large cross section beams work well too. You get a lot of bending stiffness from shear walls. My press is made with 2x4 1/8 wall steel beams, two oriented horizontally, one vertically. With no supports in the middle, at ~30psi, it deflected about 3/4" in the middle. No bueno. I ended up adding a bunch of vertical supports. If your back side is entirely open, the thing may pretzel itself. Pump it up slowly and stand back!

dane
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Joined: Thu Mar 29, 2012 10:09 am
Location: Portland, OR

Post by dane » Fri Jun 24, 2016 11:09 am

Thanks for clarifying Twizz. I am following now. More welding to come!

gav wa
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Location: Perth

Post by gav wa » Fri Jun 24, 2016 4:20 pm

You also need to look at where the load will be held. Those two verticals at each end will take all the load at the moment. They will flex easily and quite possibly tear away at the weld. The reality is that the load at the end is being held by 2 sheets of 3mm steel, the thickness of your tube.
Increase your vertical load bearing pieces.

gav wa
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Location: Perth

Post by gav wa » Fri Jun 24, 2016 4:28 pm

Also change those gate latches. You want something strong like a basic pin through a hole. With that design I would run 5 not 3 too, same with the hinges, at the moment only the middle hinge will do 90% of the work. If you add some fit them so they are straight vertical when you close the gate, the weld will be stronger as it will be more a shear load rather than tearing load like on your current hinges.
It's only small and easy changes we are talking about so don't get disheartened. In less than a day you could make that a safe solid, sweet press.

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falls
Posts: 1455
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Location: Wangaratta, Australia

Post by falls » Sat Jun 25, 2016 12:12 am

You need to make the back and front symmetrical. With the gate just on one side that side won't deflect as much but the other unsupported side will deflect a lot. That will mean weird warping in any boards you build.
I agree with the others. The only thing stopping deflection on one side is 3 thin hoops of steel and 3 narrow hinge pins.
My press has 24 x 1/2 inch grade 8 bolts to counter the shearing force created when the press wants to deflect.
At present your press is going to deflect majorly and assymmetrically. No good for pressing something you want to come out flat and true. I think it is likely the hinges and clips will bend and eventually break too, if not on the first inflation. Definitely stand behind something solid.
Remember that it is only as strong as the weakest part and right now your weakest parts are the hinges, clips and welds between the top and bottom forms and the end pieces.
It's all about how you stop deflection. Look up mongo press on benmtl. They have used similar materials to you, but in a much stronger way.
Don't wait up, I'm off to kill Summer....

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falls
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Location: Wangaratta, Australia

Post by falls » Sat Jun 25, 2016 12:19 am

Looking at the gate side again it is actually not going to stop deflection at all. The clips are 90 degrees off where they should be. All they are doing is stopping the gate from swinging down away from the press. When you pump it up the top and bottom forms will move away from each other and the loop of the clip will just rotate in its hole as the top form moves up. You would need to orient the clip in a vertical fashion to even begin to counter the deflection force.
Don't wait up, I'm off to kill Summer....

MadRussian
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Location: USA

Post by MadRussian » Sat Jun 25, 2016 4:52 pm

I think you need seriously rework the press construction.in current form outright scary. not designed to take a lot of pressure
Also in one of the pictures you have five bolts holding two firehose?????????????? where only one bolt in the middle of each fire hose imo this is not enough
I have not failed. I've just found 10,000 ways that won't work.
Thomas A. Edison

twizzstyle
Posts: 2203
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle » Sat Jun 25, 2016 9:39 pm

MadRussian wrote: Also in one of the pictures you have five bolts holding two firehose?????????????? where only one bolt in the middle of each fire hose imo this is not enough
That shouldn't be a big deal, looks like he's using angle iron, it won't flex much. If you do get any tiny leaks you can spooge some silicone in there, but I bet the angle iron alone will keep it leak-free.

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