Is My Press Design Dangerous?

J. Keeton

J. Keeton

Joined
Nov 15, 2005
Messages
1,209
Original Press Thread - https://www.bladeforums.com/threads/homemade-hydraulic-press-recap-plans-parts.1805864/

So I got this comment today on my press build YouTube Video and it got me thinking:



What do yall think? Is this a valid concern? Seems like enlarging these to 1/2 grade 8 bolts would be a simple thing to do. (or upgrade the 7/16 bolts I have to grade 8...)





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Since responding to his post; I've found some conflicting results on the strength of grade 8 bolts... Does this table imply a tensile strength of 60 tons for that whole size range!? Doesn't seem right





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If Edward sees this thread, thank you sir for brining this to my attention. It's something I didn't think about.
 
I also found some grade 9 bolts at McMaster:




edit: I'm thinking of replacing my current bolts with these grade 9 bolts and possibly adding two more
 
Looking at Mr Ron's design again. I'm guessing he welded the front guide and bolted the back guide.

I think I should be good to upgrade to Grade 9 bolts and possibly go up to 6 per side instead of 4 per side.

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With some rough math here on 7/16ths G9 bolts:

Bolt Diameter = 0.4375 in
Tensile Area = 0.106 in2
Ultimate Tensile Strength Grade 9 = 180,000 psi
Safety Factor = 1.25
Constant= 0.6

Single Shear Capacity = (0.6*180,000*0.106)/1.25 = 9158 lbs for one bolt



I'm not sure if it's additive... but If I have 6 bolts per side that would be 54,948 pounds (27 tons) of shear capacity per side and 54 tons total capacity?
 
What if you welded on 90 degree steel angle as a "shield" to keep them flying off into the users face?

Seems faster/easier than taking everything apart and redrilling....
And Still being unsure
 
I don t think that you need to do any change to your press.They are guide plate , even in that scenario there would be not enough force to make some damage , far away that it will snap those bolts !
It is possible that should you ever press something that cants or goes off center, you could send those bolts flying like bullets if the stress fractures them. Worst case scenario, you want the guide plates to bend, not snap off those bolts. What you have now is a bit dangerous.
Click to expand...
 
Yes, tensile strength is psi, per square inch of bolt diameter.

7/16" is such an odd size and so close to 1/2" I"d never use that size.

You gain much more area by going up in diameter (because of the squared in pi r squared.) than the linear increase of adding more of them.
Nothing wrong with adding more of them too.
Looking at the photo of your press, there is room, go up to 6x 3/4" s and just use normal grade 8
I would do 6x 1" screws, but you run into practical limits on being able to drill those holes.

shear off and fly like bullets ?
Presses do have large potential energy, but that's Chicken Little ish

The guideway slides on the inside of the tubing keep it straight and from being canted.
Make sure you're not cheaping out and going too short on those.

There is huge room beside the cylinder on each side.
If you're looking for changes, I'd make the inner slideway guides go up as far as possible on each side and clad them with HDPE, or nylon- long wearing slippery, glide bearing surface


The pressure relief valve on the press is set to relieve pressure far before it builds that much tension.
Forging presses aren't ever used like a shop press on a stuck shaft, less stress, no sudden impacts, no stored energy bombs.
It's all gentle shoving.

I'd be more worried about guarding the hoses against accident hot steel.

If I was worried about bolt bullets, I'd put a plate on that retains the bolts.- make that an option for that guy
but who actually knows anyone who had that failure ?


Folks are going to use your design, but then change every detail about it to suit themselves (cheap out) then claim it's fault of bad design.
Expensive grade nine bolts that they have to order ? No they are going to use cheap by the pound grade 5 from the TSC they can get off the shelf.
( look at baking recipe and reviews, no one can follow a recipe as written.)
 
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Good points above.

I feel like a failure like this is unlikely. Especially considering that the 1-1/4'' pin in the clevis would need to have a lot of play for this tilting motion (That is tilting towards or away from the user).


I will order and install the 7/16 grade 9 bolts just to feel good about it. And consider adding 4 more in the future...



1 12345678910 - I agree on the traveling block. When I rebuilt this press I left it as is, but if I ever upgrade it, I'll make the traveling block come high up the sides of the cylinder. No reason not to.
 
J. Keeton said:
With some rough math here on 7/16ths G9 bolts:

Bolt Diameter = 0.4375 in
Tensile Area = 0.106 in2
Ultimate Tensile Strength Grade 9 = 180,000 psi
Safety Factor = 1.25
Constant= 0.6

Single Shear Capacity = (0.6*180,000*0.106)/1.25 = 9,158 lbs for one bolt



I'm not sure if it's additive... but If I have 6 bolts per side that would be 54,948 pounds (27 tons) of shear capacity per side and 54 tons total capacity?
Click to expand...

Also to bring this a little further... Canting of the traveling block towards or away from the user I think would result in an "uplift force" or "pull force" more so than a "shearing force"....

From the internet.... the formula is:

Max Uplift Force (pull force) = (0.9 x Tensile Strength x Tensile Area ) / Safety Factor

For a Grade 9 - 7/16 bolt:
Bolt Diameter = 0.4375 in
Tensile Area = 0.106 in2 (at threads)
Ultimate Tensile Strength Grade 9 = 180,000 psi
Safety Factor = 1.25

Max Uplift Force / Pull = (0.9 x 180,000 x 0.106 ) / 1.25 = 13,738 lbs per bolt ~6.8 tons


Since all 8 bolts will be resisting the motion, that would be around 54 tons of pull strength... The same 8 bolts would give you 36.6 tons of shear.

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As it sits now my press has a 11GPM pump on it capable of around 2,500 psi. With my 5'' cylinder and 2'' rod this can produce around 24.5 tons of force. If I upgrade the pump to a 3,000 psi pump down the road, I'll be able to get 29.45 tons.

24.5 tons is 67% of the shear and 45% of the pull. This feels pretty good to me... but I'm no design pro. Yall agree?
 
J. Keeton said:
24.5 tons is 67% of the shear and 45% of the pull. This feels pretty good to me... but I'm no design pro. Yall agree?
Click to expand...
I don't know what the forces on the bolts might be, but they are not necessarily limited by the maximum force your press is rated. Imagine you used the 24.5 tons to drive a shallow wedge between the plate and the frame... How you could generate such a situation in practical use is a bit difficult for me to imagine.

If you are at all concerned, you could weld the bolts in place on the front side where you stand, or add an L-bracket cover like Crag suggested. I would increase the bolt size to 5/8" and add an extra one or two bolts on each side.
 
Safety Sally is never in short supply on YouTube.

Reminds me of a conversation I had with an supervisor at one of the steel mills I used to work at. He had recently taken some RCFA training or something similar, where the "what could go wrong" turned into "what could have a .01% chance of happening, and how can we prevent it?".

He pointed to an open Pepsi can on his desk and joked that somebody somewhere could come up with a scenario where accidentally tipping over that soda can could potentially kill everybody in the entire steel mill. Granted, the odds might be 1 in 100000000000000000000, but if you introduce enough variables and freak coincidences....

The point was, to some people, everything is a potential danger or failure waiting to happen. Some have a high chance of happening, while some have almost no chance of happening. Even still, there's always gonna be "that guy" who says "but what if...."

Adding more or bigger bolts certainly wouldn't hurt anything, but I really don't envision any practical scenario where it'd be absolutely necessary. Plenty of other hazards to worry about when using a multi-ton forging press though... :D
 
Natlek said:
Why don't you post some pictures here so we can see what you did ? You expect me to click on that video clip and listen you for five minutes talking about the several bolts you changed?
Click to expand...

1.) No one is forcing or expecting you to do anything here. I'm sorry you feel like your time was wasted.

2.) If you want to speed up the videos on YouTube in the future; click the gear on the bottom right of the video viewer to configure playback speed:



 
J. Keeton said:
If a picture is worth 1,000 words then a 4:46 video at 30 fps is worth 8,580,000 words? 🤔
Click to expand...
Your math is correct if each image provides entirely new information and is indeed each worth 1000 words. However, at 30 fps, many successive images are nearly identical and only provide a smaller amount of new information. I claim that your video is worth roughly 40,000 words.
Still greatly appreciated!
 
James, you always make a really good video - took me less than a minute to go thru and see what you did. I do 100% agree with the spacers used to remove the slack from the top of cylinder. Upgrading to grade 9 bolts doesn't hurt anything, not at all sure it's actually needed. I do admire your press - it's impressive :)
 
Natlek said:
Why don't you post some pictures here so we can see what you did ? You expect me to click on that video clip and listen you for five minutes talking about the several bolts you changed?
Click to expand...
Cmon man. Really?

J. Keeton said:
1.) No one is forcing or expecting you to do anything here. I'm sorry you feel like your time was wasted.

2.) If you want to speed up the videos on YouTube in the future; click the gear on the bottom right of the video viewer to configure playback speed:



Click to expand...
For what Its worth. I love the videos man. I'll put them on when I'm bored, or sometimes listen to them in the background while I work. Theres always something good to be learned in them.
 
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