How the Strength of Steel is Determined in the Bending World
Wednesday, February 1st, 2012The Strength of Steel and Bending Stock
Over the years, lots of people have asked me questions about the strength of steel and bending stock. Because steel bending can be so obsessive, and the need to constantly bend more stuff can overtake an individual so intensely, it can be easy to understand why so many people are hungry for this knowledge.
Common Questions about Bending Stock Strength
Here are some of the types of questions I get most often:
“How Strong is my Steel?”
People will be bending a certain nail, bolt or piece of stock and want to know if it is a good bend or not. This is understandable, because people like to know where they stand.
“What nail/bolt/stock should I go to next if I am bending THIS and want to bend THAT?”
Most people want to ultimately be able to bend a certain bar, whether it is the Red Nail or some other high level bend like the Bastard from Fat Bastard Barbell or the Battle Bar from Benders Battlefield. Along the road to this goal it’s nice to know which bends to attempt along the way.
“How far am I from the Red Nail if I am bending this or that…”
Sometimes people are seeing progress by cutting what they can bend down to shorter lengths, or they have been moving up to harder graded bolts or slightly thicker stock, but they still want to know how far away they are from their goal.
And there are many, many more questions I receive about the strength of bending stock.
Comparing Strengths of Various Pieces of Bending Stock
There is a system that is used to rate the strength level of bars. This has proven to be quite useful in getting an idea of where different bars lie in relationship to one another, and it even works well for a variety of different stock, including Round Steel, Graded Bolts, Drill Rod, and even square and hex steel.
This system was innovated by Eric Milfeld and later Mike Krahling. These are just the guys that I am most aware of in the United States who are doing it. There may indeed be many more who are doing this.
This process involves special attachments that are put onto the bending stock being rated, followed by using the steel to pull against weight until it bends to the desired angle. Once the stock bends to that angle, it is assigned its strength level.
This process is often labeled “calibration,” although there has also been debate about whether that is the proper term. Perhaps a better term to describe it would be simply “rating the stock.”
Regardless of what you call this process, it has proven to be a fairly reliable method for a solid comparison tool, as well as something to base your progressions and purchases upon.
In the video below, Mike Krahling demonstrates the process of rating the strength of a steel bar.
Now, what you see here is just one bar being rated, but over the years, many bars have been rated and also logged for comparison at the AZ Grip website. You can see the strength comparison chart here: Steel Bending Progressions.
Now, there are limits to this process, and that needs to be understood from the beginning.
For instance, steel varies and it can vary quite a bit. Just because you bought a Red Nail back in 2004 does not mean that a Red Nail that you buy right now will rate out at the exact same number. New stock might have been selected to be used at some point. (Of course, the Red Nail is still a Beast to bend, so no disrespect to IronMind.)
Variance of Steel Strength
As I point out in this post, Strength Variations of Steel, it is possible to see strength variance within the same piece of steel. Remember that steel is created in long lengths and then cut down in order to bend in shorter lengths. There can be quite a bit of variation within one of those virgin bars pulled out at the factory. So in that regard, you have to understand that just because you buy a 7-inch by 5/16-inch length of Cold Rolled Steel, it does not guarantee that you are ready to certify on the Red Nail, even though the Red Nail, too, is 7 X 5/16 CRS.
Variance in Steel Strength & Differences by Length
Also, you have to remember that you must take the readings of bars of different lengths very carefully. For instance, if you look at that chart, it lists the Red Nail, 7 X 5/16 in length and diameter, at 420-lbs in order to bend. Also, that chart lists a Linear “S” Grade 5 Bolt 6 X 1/4 in length and diameter at 425. An assumption that has often been made is that if one can bend that Linear “S” Grade 5 Bolt, then they surely must be able to bend the Red Nail, which is rated at 5-lbs lighter.
Unfortunately, this assumption is completely wrong, because the Grade 5 bolt is only 6 inches long, meaning there is less leverage available to produce a bend using the testing device. In reality, if the Grade 5 in question were 7-inches long, it would feel like bending a coat-hanger.
Comparing Different Bars
So, as you utilize the chart, make sure that you remember that comparisons should be made between different pieces of stock of the same length only. Also remember that the way the calibrating set-up bends the bar is not completely the same as the way the bar bends when you bend it, so just because a piece of stock rates higher than another piece of stock using the device, does not necessarily mean it will feel harder to bend when you try it.
Solid Resource
Even with this handful of limitations, the “Steel Progression Chart” is a very good resource for you in your bending training. It has been an extremely helpful tool for both new benders looking for ways to progress in their bending, as well as seasoned veterans who are looking for stepping stones to their ultimate bending goal.
In fact, I reference this chart quite often with my coaching clients who are looking for progressions in their steel bending programs. And now, it is a tool you can place in your toolbox to reference whenever you need it.
All the best in your bending,
Jedd
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