So, seems like people that are using bolts all recommend to go with grade 8, from what I remember. After looking at the actual numbers though, i think i should be fine with grade 5.
my press design is nearly identical to the kingswood one.
there will be 14 bolts, top and bottom holding the thing together.
1/2 inch grade 5 fasteners are rated with a shear strength of 14730lbs. same diameter grade 8 are 17870lbs.
surface area is at maximum 1400 square inches (this is the area of the entire bottom surface of the press cavity, which is much larger than the contact area of the hoses). at 75psi, this would result in 105 000 total pounds of pressure on the frame. spread this out over 14 fasteners and you end up with only just over 7500lbs on each one.
just over 50% of the rated strength seems like a pretty safe margin to me. any significant errors in my thinking here?
bolts
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I am not positive on your design but I believe you need to look at tensile strength not shear strength. If the load on the two pieces being held together is trying to seperate the pieces(stretch the bolt) as opposed to the load trying to slide one piece on the other in a way that would mis-align the holes. The former would require to know the tensile strength(resist stretching) and the latter shear strength(resist cutting/shearing)
Maybe someone else will comment on this off hand I couldnt tell you what to use. I know on my press at 45psi I had more creeking and groaning along with beam deflection than I anticipated and went up from 5/8 grade 8 to 3/4 just to feel better.
Maybe someone else will comment on this off hand I couldnt tell you what to use. I know on my press at 45psi I had more creeking and groaning along with beam deflection than I anticipated and went up from 5/8 grade 8 to 3/4 just to feel better.
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Grizzly Adams
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If your design places the bolts in shear (picture cutting them in half with a pair of scissors (shears)), use the shear strength in your calculations, if your design places the bolts in tension (picture stretching them like a spring) use the tensile strength in your calculations. I would agree that most designs I've seen employ bolts that undergo almost entirely shear stress.
Whoa, I think my engineering education was just put to effective use... Wild.
Whoa, I think my engineering education was just put to effective use... Wild.
Its a good thing cold smoke doesn't give you cancer.
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knightsofnii
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how much are you saving on bolts vs. how much you'd have to spend rebuilding your failed press, or rebuilding your severed car/shop/body, if the thing blows up on you?
grade 8's are "bridge bolts", right?
but if you're going to go with the weaker ones, just make sure you use more of them, and check the torque on them periodically, which should be done anyway.
grade 8's are "bridge bolts", right?
but if you're going to go with the weaker ones, just make sure you use more of them, and check the torque on them periodically, which should be done anyway.
Doug
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doughboyshredder
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My understanding is that grade 8 bolts, while stronger are actually more brittle. In other words failure is more catastrophic. They snap instead of bend. I went with grade 5 bolts. I am using them in a shear situation and the numbers work. I would rather have a failure be evident by a bent bolt, instead of a snapped bolt. camhard, my calculations were similar to yours.
For my airbag closures I am using grade 8 bolts because that is a situation where you need tensile strength and the increased cost of grade 8 bolts is insignificant for the increase in tensile strength.
For my airbag closures I am using grade 8 bolts because that is a situation where you need tensile strength and the increased cost of grade 8 bolts is insignificant for the increase in tensile strength.
thanks for the replies. I positive that I am using the correct type of force here (Im pretty sure the sheer is generally about 60% or so of tensile anyways). I am just finding it more difficult to find grade 8 bolts. im sure if i put some effort in i could find some though. i also thought they were much more expensive; this is probably only in terms of large scale projects though (my friends in engineering thought the price difference was quite large).
I believe grade 8 are the standard for bridges and such, though it's also important to consider diameter. grade 8 bolts aren't all the same (e.g. they wouldn't use 3/8" ones for a bridge). It seems as though I am already on the lower end of things size wise though, so if i can get some grade 8 ones i probably will, just to be extra cautious, but i won't put a lot of effort/extra money into it as i think i am well within a safe range).
regarding the brittleness: yes, they are more brittle, officially, no, i don't think it would noticeably effect the way in which they fail. they both soft enough that they wont 'shatter'. i can't remember at what point, but if metal is too brittle, it will essentially become more dangerous/weaker in certain ways, though grade 8 bolts are not affected by this.
hope this all makes sense; I just spent the day breaking trail through waist-deep (no skis as I didn't expect there to be enough snow) at points going up 70 degree slopes, in -12 C, with a 40lb pack. it was pretty fun, but tiring.
I believe grade 8 are the standard for bridges and such, though it's also important to consider diameter. grade 8 bolts aren't all the same (e.g. they wouldn't use 3/8" ones for a bridge). It seems as though I am already on the lower end of things size wise though, so if i can get some grade 8 ones i probably will, just to be extra cautious, but i won't put a lot of effort/extra money into it as i think i am well within a safe range).
regarding the brittleness: yes, they are more brittle, officially, no, i don't think it would noticeably effect the way in which they fail. they both soft enough that they wont 'shatter'. i can't remember at what point, but if metal is too brittle, it will essentially become more dangerous/weaker in certain ways, though grade 8 bolts are not affected by this.
hope this all makes sense; I just spent the day breaking trail through waist-deep (no skis as I didn't expect there to be enough snow) at points going up 70 degree slopes, in -12 C, with a 40lb pack. it was pretty fun, but tiring.
camhard, I live in a small town and my local hardware store carries grade 8 bolts (ace hardware). There are also lots of places online to order from such as mcmastercarr.com, which can be a great place to get many things for skibuilding and other projects. Good luck. I think that type of press design is a great way to go.