Calculating the Strength of a Pry Bar

I would use some spring steel, maybe get some from some old leaf springs at the junkyard....or just buy one...

Hello,

Perhaps I should mention that the specific reason why I wish to understand this calculation is that I want the pry bar to take to form of a balisong, and as such would like to keep the thickness of the "blade" around 1/8" while also using high-end materials, i.e. titanium alloys. So buying one is not an option, and I would prefer to work with a fresh billet of metal.

So it's a knife?

That would probably be 154CM stainless

https://www.knifecenter.com/info/knife-blade-materials

Bar stock...

https://www.knifemaking.com/category-s/199.htm

http://www.knifemaking.com/category-s/222.htm

It's not a knife. All knife enthusiasts, such as myself, know not to use knives as pry bars, as knife steels generally favor hardness over toughness, and as such are prone to brittle failure when used to pry. What I'm planning on building is a balisong that has a pry bar instead of a blade.

http://www.brownells.com/items/spring-steel.aspx

https://www.amazon.com/Ka-Bar-Becker-BK3-Fixed-Blade/dp/B001IPILMA

So this is for breaking and entering? If you are a Russian operative, the group you work for already has the tools of trade craft you need.

If you are a police officer, or other law enforcement type, you should know that it is illegal to break and enter unless you have a search warrant, in the United States, unless you have direct probable cause (you can see an injured or dead person lying on the floor inside, etc.)

I see from your name you are a pallindrome composed of Roman numerals?

Hmmm....Breaking into the Vatican could get you hurt.

Ah, yes, one of the exceptions to the rule. I probably won't use 1095, though, if only because it seems like 1/4" of it is required for it to stand up to prying, which far exceeds my ideal pry bar thickness.

I don't understand how a machinist can have so little knowledge of metals....

"... I probably won't use 1095, though, if only because it seems like 1/4" of it is required for it to stand up to prying, which far exceeds my ideal pry bar thickness....."

.

If 1095 would require too great a thickness for a prying type operation, something like even 6-4 titanium is going to exceed your thickness requirement by even greater amounts.

.

One thing seem to be missing is the fact that steel does not confer second rate. There are many tasks that steel is by far the best material. This is exactly on of those cases. Being able to be very hard (especially case hardened) and very tough is ideal for this application. You will be hard pressed to find other materials that can perform the job of prying as well as any of numerous types of tool steel.

Chances are I'll find a local heat treating service no matter which alloy I choose, so I think I'll stick with the CNC.

Your way over-engineering a tool (the lever) that's been around for thousands of years. If it isn't broke, don't fix it, unless you're going to "3D" print them. Even then, it wouldn't be cost effective than wrought iron (heat treated)

Out of curiosity, did you see the reply to SolarEagle mentioning the whole balisong thing? If not, it mentions a specific requirement that is the reason why I would like to know the math. Also, I just like knowing these kinds of calculations anyways.

I don't think there is any way to calculate the exact specifications of a metal that has been worked, other than testing it....and this is usually done in a lab as several test instruments are required...You can follow a formula though to approximate results....

https://www.amazon.com/Practical-Handbook-Blacksmithing-Metalworking-Blandford/dp/0830611797

http://www.azom.com/article.aspx?ArticleID=2598

They aren't calculated. They are forged, tested, and redeveloped.

On the basis of their purchase price in the retail market, all one needs to no is buy one these days. A mill is better deployed doing something more useful with its time.

They aren't calculated. They are forged, tested, and redeveloped

Drop forged give them toughness. The original poster stated that it doesnt matter which material he can choose, because he'll leave it up to the number of available heat treaters to make it work. That is a mistake and I'll tell him why.

You have to do some planning here. With all physical metallurgy, such as heat treating, it a balance of compromise. If you want something hard, you'll also increase fractorability. you want something tough, you may increase deformation/wear characteristics.

The original poster should think about this AND put more value on material selection.

Indeed, though it is the original poster that needs to do the planning.

I should mention that I have already considered the heat treated forms of different materials and understand some of the different tradeoffs involved.

Back to the original question, though: I want to understand which specific material properties (ultimate tensile strength, Young's modulus, etc.) are important, as well as how to calculate the strength of a theoretical design using said constants. After all, an equation exists to calculate the maximum flex of a part using Young's modulus, so it does not seem so unreasonable to believe that similar equations exist for the strength of a part.

Yes the calculation is arrived at by testing the metal....

https://en.wikipedia.org/wiki/Tool_steel

http://www.engineersedge.com/manufacturing_spec/properties_of_metals_strength.htm

http://www.eatonsteel.com/steel-bar-products.html?_vsrefdom=ppcgoogle&ex=1sgl7ju-20htem6-mie6t5&pmc=AW-1&gclid=Cj0KCQjwgtTJBRDRARIsADsXL6FYoUlAoCIYSpgdXO9SyTGH54J96BU15_Qrm9c_HlrinI_4WytSvQAaAhnUEALw_wcB

Your really aren't prepared for an answer.

There are not equations... here is empirical knowledge that you may find in charts derived from empirical testing.

such as effects on carbon on the shape of a transitions curve or the effects of manganese on a Charpy V-Notch with a 0.30% carbon.

effects of nickel content on the resistance to low temperature embrittlement.

You read it off a chart, understand what you are looking at and choose.

This was a valued book for me.

Alright. I suppose I should say thanks anyways. However, I want to mention that I don't wish to calculate, say, the ultimate tensile strength of a material itself, but instead the strength of, say, a 1/8" by 1 1/2" bar made of a certain material with known properites. Are there equations for that, or am I basically left to guesswork?

Alright. I suppose I should say thanks anyways. ? actually you don't have to say anything because we are not tell you what you 'expect'.

The answer is No, anyways,... equations are calculations...

empirical informationderived from testing in a metallurgy lab to get a base understanding of the properties of materials.

Its well documented that using a known base material, the heat treats can use this, and get results one requires.

Your problem is you need to start working with one of your heat treater, it a lot more direct.

Start off with telling them the properties you desire as an end result, they will suggest the raw material.

Alright. I'll assume that you mean that besides looking at the quantified properties of the material, it's mostly guesswork and experience. In that case, which property should I consider if I'm placing something under bending force? Is it still yield and tensile strength, or are there other properties I should be aware of?

Force? is that all we have to go on.

you have very little information on what you're trying to accomplish.

My goal is to find a material that can be used in a relatively thin pry bar - maybe between 1/8" and 1/4" - that can perform as well as thicker pry bars. I'm interested in determining the force at which the pry bar will break, given the known properties of a material and a shape determined by yours truly. From what you have asserted so far, I have concluded that calculating the exact force at which the pry bar will undergo plastic deformation or catastrophic failure is not possible or practical. However, I would like to know which material properties are related to a material's resistance to failure while bending.

Being pry bars have been around for thousands of years I am pretty sure by now the technology and metallurgy has advanced the point where the higher end pry bars most likely have the best material to do their job.

Pick one and go with that and be done with it.

Indeed. What is the OP trying to lever? Weight, fulcrum point, lever length etc. would be helpful. As for equations for stress and deflection, there are those, the same as those used in any structural design. CISC or American Institute of Steel Construction have those formulas in them. Probably can be found on line as well. All you need to know or find out are the properties of the materials you may want to select.

He wants a Filipino Butterfly knife, known as a Balisong, for prying into the secrets and rich treasures of others, and is not a tradesman, as is clear as if I were spouting on the virtues of this or that alloy for a given application (without reading the spec sheet on it).

I think he should be forced to go to Wal-Mart and buy whatever pry bar they have, test it, and, if it fails, start over and explain how he is going to fix it so it will work.

Move the world with a single lever, OK, but what will you use to withstand the force at the business end?

I don't know if I would use Walmart stuff for testing. Most everything they sell is made in China and, as you are probably aware, the quality of goods from that land are not the greatest. May want to step up to a recognized brand name that should have better QA in their processes.

Well, nobody said I had to make it easy for this prying genius to get into places he clearly does not belong.

OR, he could just order one from an American made online tool supplier and get it over with.

1/8"×1-1/4"× ???

Make and break regardless of equations.

Your talking about a pry bar not a jet engine.

Make and break... It's what you would do after equations to test the numbers.

Right? Right? Right?

"Your talking about a pry bar not a jet engine."

Damn, even Jet engines are made and broke during R&D

I knew of a guy that would break a steel ball. Also not the sharpest tool in the shed.

That would have been the sponge he used to break that steel ball.

Equations? What Blacksmith uses equations?

http://www.screwfix.com/p/roughneck-utility-bar-1-x-15/58202

(usual disclaimer)

I'm a machinist, not a blacksmith.

we are not being stark with you. As your are finding out, one can expect a simple answer to such as material sciences that are filled with variables such as application.

The forum is not here to solve that problem.

'..I'm a machinist...'

That is no small claim....especially as 'machinist' is not preceded by a modifier such as 'aspiring', 'novice', 'hobby', or 'neophyte'.

The lack of appreciation of the merits of tool steel certainly suggests a preceding modifier was probably needed. Owning or having access to a machine tool does not a machinist make.

You could buy a few of these, test them, then start modifying it. A bit of grinding should do it!

excellent suggestion ... even though he may not know the recipe or prior heat treating.

THat's what I would do . Find out hat it takes to bend/break one and then just assume that the forces are proportional to the relevant dimensions.

That, or just make one and beak it the you know for sure what the limits of the design will be for the second one you build!

I would have to 'amen' that suggestion as well! Assuming he had settled on purchasing his desire material in bulk, taking a test piece straight to the Rockwell Hardness tester, is standard protocol, to make certain it had the desired fail limit; and, that the manufacturer sent the 'right stuff' regardless of how it is labeled. .

Still, safety precautions should always err on the far side side of caution, because You could still get hold of one with a micro-fracture, which had been overlooked by the manufacture.

Status update:

I was able to get my hands on a copy of Autodesk Fusion 360, which can perform the simulations that I was looking for. However, I wanted a benchmark to compare my designs to and have decided on the pry bay/knife that SolarEagle mentioned. My question now is, does anybody know the properties of 1095 carbon steel when tempered to 56-58 HRC? I've been able to find the properties of the steel when it is treated at a higher temperature, but not anywhere close to the approximately 260 degrees Celsius required to achieve around 58 RC.

You have a lot to learn about heat treating.

Well you're not being precise enough.....It's not just 1095, it's 1095 cro-van....and it's probably already at 56-58 HRC....

For AISI 1095 carbon steel...

http://www.azom.com/article.aspx?ArticleID=6561

Thank you for clarifying that weird cro-van bit . . . however, that does not really answer my question about the properties of that knife blade.

A pry bar can be considered a beam, so of course you can calculate a theoretical yield point using published properties of the chosen material in its treated state and the geometry of your part. Your results will be useful for comparison, but nothing beats a practical test.

https://skyciv.com/tutorials/calculate-bending-stress-of-a-beam-section

FYI -

SPECIFICATION
Since Enderes® Bars are forged only from domestic high carbon tool steel, heat treated and polished, they will resist excessive wear more effectively than any other bar. They conform to all applicable ANSI and ASTM steel standards for materials, physical properties and testing, including A-29-79, A332-80, A331-79, A576-79, and A681-76. All styles fall within the appropriate Rockwell hardness ranges recommended by ANSI and ASTM for their intended applications.

http://cr4.globalspec.com/blogentry/28374/Stress-Cracks-in-Steel-Bar-Products

sigma=(M*y)/(E*I)

E=60,000,000psi for steel

M=P*L

I=(B*H^3)/12 for a rectangle

y=1/2 material thickness

Sigma = stress on steel at material surface

L= distance from the fulcrum of the tool to the point the load is placed on the tool.

For spring steel hardened to Rc 57, sigma should be less than 60,000 psi

So figure out how much pry force you want to apply (P)

determine how far from the fulcrum you want to apply the load (L)

mess around with the stock width (B) and thickness (H) until you end up with a sigma in the right range and make the darn thing.

That is actually a really good answer. I might not use it right now, as I have access to simulation software, but I think it could be really useful during next FRC season as way to check if aluminum beams are being made too thin/should be replaced with steel.

So you're building a fighting robot, is that it?

http://www.botmag.com/how-to-pick-the-best-fighting-robot-design/

. . . not right now, and probably not for a few years.

Depends on the yield and tensile of the pry bar material, the radius (if any)and the distance from mid radius point to the end load.

I'd just machine one out of a chunk of old forklift fork! Can't say I have ever seen anyone break one of those!

I've seen one bent (72" pair from a 10K machine bent ~10" off square) and even acquired the pair for free from it but the guys who did it impress the heck out of me in how it was done.

10K# off road forklift would not pick up big pump unit so they gave it an assist with a payloader that could lift double that. 30K# lifting capability is what it took to find out the huge pump unit was still bolted to the concrete slab it sat on at the far end

Moral of the story is sometimes that one big bolt that doesn't look like it goes all the way through the frame and anchors the machine to the concrete base actually does. (really, looking at the design I would not have guessed it either. )

Wow.. that had to be pretty funny... Afterwards.

I've been taught the moral of that story repeatedly.. but on on a much smaller scale.

As for the off road forklift? If I could have a vehicle cab mounted on one of those and after a few mechanical modifications​ were able to have a good daily driver?

I just want something that can hit the highway with passengers and a loaded pallet

You could really do your part to unjam traffic and get vehicles moving....