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Help with calculations.


cracker72

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Can anyone point me in the right direction to find formulas for steel beam sizing? I'm looking at designing a 20t  c-frame press and would like to understand the relationships between load point spacing, depth of throat and beam length. Also, recommenced factor of safety would be helpful. I've searched log splitter info and the best I've found was "go as big as you can". I've also asked on another forum, and been told it's really complicated and to do a lot of reading...... 

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Call the steel supplier if they don't have the books as give aways they'll be able to tell you which ones to check out at the library. What you want to "understand" isn't to be found in calculations, there is a LOT more to engineering high energy/stress structures than finding the right numbers. You have a long way to go just on the jargon. Say, Moment and modulus of rebound or elasticity or deformation or . . . There are lot's of moduli of there to consider you know.

A C frame press is orders of magnitude different from a H frame press, it's one very good reason they're so rare.

Frosty The Lucky.

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Good Morning,

What books and other people can't prepare you for, is the noise. A 30 Ton or a 50 Ton C-frame, creaking and groaning. Can't explain the feeling, this thing is trying to come apart and I am standing right next to it. Spooky and not because it is Halloween!! The Flex is unimaginable!!

Neil

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I'd also be interested in finding out how to calculate the forces in c and h frame presses. Batson has his calculated factor of safety in his c frame presses. But nothing for the h frame. 

I'd like to know what happens as the width is increased. So as to be able to calculate what could work or what wouldn't.

I've found some calculations for beams under load but can't figure how these relate to press calculations 

Andrew

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Andrew,  hopefully someone who's successfully built one will be along to educate us. Looking at the log splitter sites it seems most diy builders just copied specs from professionally built machines.  I can't see why the forces generated in a log spitter would be any different to a forging press?

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Force divided by  distance= effective force   on inch one ton  two inches in half a ton  three inches  is 1/3 ton etc 

force in one direction must be resisted in the opposite direction.    C frames have a distressing habit of squirting parts out the press because the head cylinder support flexes in reaction to the pressure exerted by the cylinder.    In this example at 4 inches 15 tons pressure  would equal 60 tons bending force to be resisted. H frame presses take all that stress in tension not bend.  I've saw Batson's press when he introduced it in Alabama years ago.   I was not impressed. 

You would be well advised to use a well tested design rather than build your own.    When you start applying mechanical pressure to metals there are a host of gottcha  factors that you will not think about until something goes south.  

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Force divided by  distance= effective force   on inch one ton  two inches in half a ton  three inches  is 1/3 ton etc 

force in one direction must be resisted in the opposite direction.    C frames have a distressing habit of squirting parts out the press because the head cylinder support flexes in reaction to the pressure exerted by the cylinder.    In this example at 4 inches 15 tons pressure  would equal 60 tons bending force to be resisted. H frame presses take all that stress in tension not bend.  I've saw Batson's press when he introduced it in Alabama years ago.   I was not impressed. 

You would be well advised to use a well tested design rather than build your own.    When you start applying mechanical pressure to metals there are a host of gottcha  factors that you will not think about until something goes south.  

What I highlighted can not be stressed enough. Hydraulic presses can cause hurts that don't heal, if you know what I mean. As Charlotte posted above, find plans for a proven, safe design, and follow them. No offense meant, but a hydraulic press is not something one should just throw together without doing a good bit of learning on the forces being subjected to the framework. Even then, I still recommend following a known safe design.

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I understand the necessity of making the press correctly. What I want to do is understand "how" to calculate the forces and what beams are needed. Batson has his calculations of safety but doesn't explain how these are calculated, which is unfortunate as he shows his working for all the other parts. Though there are no calculations for the h frame.  So if I want a wider mouth in the h frame do I just search the web for someone else's build and hope there sums work?

Andrew

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Take an associate degree mechanical engineering at a junior college and you will have the needed information.    I don't want to be rude but short answer: " If you have to ask that question you would be unable to understand the answer."  Or precisely no one here is likely to risk suit by explaining it to you  because it would involve a liability that the site is probably not prepared to assume.  We all assume a Moral responsibility to promote safety in our chosen craft.

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I had built and sold mechanical power press even had repaired piles of them .

I had always made presses by what i can actually find in workshop or i could get from scrapyard

But let me tell you for this you need quite bigger machines and many special attachments only if you can manage those or contract it outside will be good

Depending on which machines you do have in your workshop

Many of parts needed to be cast or fabricated if you do have any casting supplier then only try to build it

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Calculations on the structure of a C frame press are seriously complicated as people have said.  You are not just dealing with material strength but you have to deal with deflections and deflection is not linear, it's exponential.  Twice the distance, 4 times the deflection to worry about while "strength" remains linear to fool the calculator.  It becomes a dance between strength and deflection to get it right.  The dance can be so complicated without software evaluation solutions that most people simply grossly over-build.

We have a 100 ton ship built C frame hydraulic in the shop and it is a monster-- multiple 1-1/4" thick solid side plates of some very expensive certified material.  Makes a hell of a noise when punching holes in thick stuff and the whole world shakes when the slug breaks free.

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On 11/1/2015, 8:32:22, cracker72 said:

Right, that's me convinced.  H frame it is. Thanks for that. 

I would concur with that opinion,

Many years ago I was involved in making these, Mainly used for straightening shafts or pressing on interference parts in assemblies.  Smaller capacity ones are available and many other similar types, but most are not as robust as these.

 

563d196cba26e_Laycockpress.jpg.88ffbe632 563d1c0b5af88_Laycock60tonpress.jpg.333c

They were that well made there are plenty still around and come up for sale regularly, Google in Laycock hydraulic press for sale 

No need to reinvent the wheel, just use these as a basis for your design,and adapt. If you only want a small throat, then you don't even need the adjustable table.

Convert the hydrauilics to powered instead of manual,

The throat on these presses is adjusted by moving the handwheel on the Right hand side which raises the table to the desired height, using the four threaded bars, I would not think you require this facilty.

If you want a chat, pop into Westpoint Forge on a course day, next one is Basic Blacksmiths Skills course on 13,14,15 November, or the members day forge in on December 19th, or I can arrange a date to suit.

 
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On Fri Nov 06 2015 21:38:21 GMT+0000, John B said:

I would concur with that opinion,

Many years ago I was involved in making these, Mainly used for straightening shafts or pressing on interference parts in assemblies.  Smaller capacity ones are available and many other similar types, but most are not as robust as these.

 

563d196cba26e_Laycockpress.jpg.88ffbe632 563d1c0b5af88_Laycock60tonpress.jpg.333c

They were that well made there are plenty still around and come up for sale regularly, Google in Laycock hydraulic press for sale 

No need to reinvent the wheel, just use these as a basis for your design,and adapt. If you only want a small throat, then you don't even need the adjustable table.

Convert the hydrauilics to powered instead of manual,

The throat on these presses is adjusted by moving the handwheel on the Right hand side which raises the table to the desired height, using the four threaded bars, I would not think you require this facilty.

If you want a chat, pop into Westpoint Forge on a course day, next one is Basic Blacksmiths Skills course on 13,14,15 November, or the members day forge in on December 19th, or I can arrange a date to suit.

 

Thanks John.

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Thanks for the replies. The common answer I get is, "if you need to ask, you shouldn't be building one!"

However, I did get an answer from an engineer and it's not rocket science. 

So I have stopped asking now but I did ask a lot of people who have built presses for themselves and for sale to the public! The remaining question I have is did these people just guess? I know some of them did because, by their own admission,  they had to modify their design after the frame flexed on trial run. What is really amusing, one of these people gave me the "if you need to ask..." reply. 

 

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You asked how the calculation was done.   You still don't have an answer.   I'm sure you got an answer from the engineer.  No it is not rocket science but it basic mechanical engineering.  The calculations for an H frame are MUCH simpler than for a C frame.   One of the characteristics of home built rather than engineered designs is that they are typically over built in some areas and weak in others. 

Did your engineer friend even bother to point out that there are tables for the strength of each grade of steel.  The required dimensions change depending on the loading and direction and methods of attachment. 

The bottom line here is what ever you build on his advise is his liability not IFI

btw are you planning on welding any part of it?   What welding certificates do you hold??

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Yes he did point that out. 

I did city&guilds in welding over twenty years ago when was an apprentice mechanic. However,  I've been welding in the real world for over two decades. 

I didn't think any liability was given or implied on an Internet forum?

I'm not building a c frame press now, for a number of reasons. The main one being the cost of my time. It would be cheaper to buy a suitable press second hand. 

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Thank you Cracker 72 for the respect you have shown here.  It is hard sometimes to access the skill and experience level of correspondents here. I apologize if I have been a little rude in my responses.   There is a moral responsibility if not a legal one.   Since this forum is international in scope it is hard say where any answer would be liable,   Good luck with your purchase.

Charlotte

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