Press doesn't work quite right.
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Press doesn't work quite right.
Hi, so tonight we tried to do the first dry run on my ski press and we ran into a few issues. The pins we had holding the side bars in bent under pressure approximately 40lbs psi. Since the pins were 1/4inch cold roll steel I'm thinking re-drill the holes in the frame to 3/8 and use bolts instead.
The other issue Was that at the curve towards the tips it didnt look like the hoses were pressing down enough. I'm thinking about adding material to the curve on the top mold. I was talking with the guy who was helping me and he said that we should add pressure to get them to fill the cavity but I'm concerned about the frame and the hoses. The hoses I have are only rated to 70 psi max. I'm not exactly sure what pressure I want to press at either. I'm using the QCM emv-0043.
The other issue Was that at the curve towards the tips it didnt look like the hoses were pressing down enough. I'm thinking about adding material to the curve on the top mold. I was talking with the guy who was helping me and he said that we should add pressure to get them to fill the cavity but I'm concerned about the frame and the hoses. The hoses I have are only rated to 70 psi max. I'm not exactly sure what pressure I want to press at either. I'm using the QCM emv-0043.
- MontuckyMadman
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Yeah we winged it, slowly applied pressure. This is about what I was thinking we would do pressure wise before we started and I don't want to go too much past it if at all. You do make a good point about the length on the top mold, I think it may be possible to re-cut it so its a bit shorter and matches to the bottom mold better.
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Just cut the top mold in half, and take an inch out or so. You don't need to fix the two halves together either, since once its under pressure it'll hold itself togetherUnderdog wrote:Yeah we winged it, slowly applied pressure. This is about what I was thinking we would do pressure wise before we started and I don't want to go too much past it if at all. You do make a good point about the length on the top mold, I think it may be possible to re-cut it so its a bit shorter and matches to the bottom mold better.
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I think the steel bent like that because since the pins had freedom of movement the steel slipped on them as it was pulling. Bolts should fix that movement and be stronger. I really like your idea of just cutting the mold in the middle to make it shorter. Here's the best picture of the complete frame I have at the moment. There are 4 of these hoops on it. One side is pinned(bolted soon) for side access.
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How we did ours was two flanges, on on other side of the vertical supports, with a pin through them. That way the vertical support can't go side-to-side.
Bolts are certainly easier, just a bit more work during the layup to get it all closed up (and then again to open it back up).
Here's the best picture I can find showing the flanges on our press
Bolts are certainly easier, just a bit more work during the layup to get it all closed up (and then again to open it back up).
Here's the best picture I can find showing the flanges on our press
This, and 1/2" Pins/grade 8 bolts.twizzstyle wrote:
Unless your press is perfectly square and aligned it will twist slightly when you apply pressure, and your supports will be loaded in all sorts of weird ways rather then in pure tension. A bolt would likely take care of that, but then you have an odd loading situation on the head of the bolt, shear and tension in some unkoen combination.
Weld on some tabs like twizzstyle did to keep everything in alignment, then pick up a few of these:
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I had the same problem with the hose not bending into the tip area. My problem was the the tip block was too tall so I cut about an inch off and the bottom mold needed to be raised. However your tip block looks ok, as far as I can tell from the pic. Also your opening looks much smaller than mine so I'm sure you don't need to raise the bottom mold. As far as the top mold goes, you got good advice already.
Definitely use a cat track.
If you're going to use pins or bolts use hardened steel #8, and bigger than 1/4 if you can.
Definitely use a cat track.
If you're going to use pins or bolts use hardened steel #8, and bigger than 1/4 if you can.
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I don't ever remember coming across that while studying fastened joints. I'd look it up but my book is packed away somewhere.doughboyshredder wrote:DO NOT USE GRADE 8 BOLTS
If a grade 8 bolt fails it snaps. Grade 8 bolts should not be used for an application where they are subjected to shearing forces.
The guy who wrote this article works for Lockhead BTW:
http://www.rockcrawler.com/techreports/ ... /index.asp
He does a grade 5 vs 8 1/4" shear calculation, and there is a table for a bunch of fasteners. Long story short, use grade 8 over 5 if using bolts.
Grade 8 might "snap" during a shear failure, but if it gives you an extra 1/3 ton capacity and brings your factor of safety (F.S.) into the correct range then who cares? For a press you want at least a F.S. of 2, or the press should be capable of holding 2x the amount of pressure that you intend on running at.
Is the threaded portion of the bolt being subjected to the shear? IIRC bolts are not rated for a shear load on the threaded portion. 3/8 is kinda small as well.Underdog wrote:Well I re-drilled all the holes last night to 3/8 and put grade 8 bolts in. I do realize that they are designed for tensile forces primarily but I don't think in this application there is nearly enough force being generated to shear them especially since each bolt is running through 4 holes.
Plus, I still think you have some weird loading due to either the bladder sticking out the side or just because the vertical support is only held on one side. I hope it works out for your, but honestly you wouldn't catch me near that thing while it is under pressure...
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