Formula For Estimating Steel Of Different Lengths?

[Frank Pizzo]

I was searching through old posts on this site and other sites but I couldn't find exactly what I was looking for.

If I know what a particular piece of steel rates at a certain length how do I estimate the rating for a different length of the same steel. I'm wondering how to figure this both ways i.e. shorter or longer.

My next question is does the accuracy of the estimation change much as you get further from the original length.

Example: If I know a piece of steel rates 400 lbs at 7" is the accuracy for conversion to 6.5" higher than say 5.5"

Thanks for any info guys.

[EJ Livesey]

For every .5" taken off multiply by 10-15% I estimate high so I'm not surprised by the steel.

500 @ 7

550-575 @ 6.5 etc etc

[Andrew P]

I have a chart that I can't get formated right here. I'll email it to you.

Edited September 12, 2014 by Andrew P

[EJ Livesey]

Andrew P

That's not what he was asking. Yield strength isn't important to us. According to your calculations the gold has a yield strength at 5450lbs. When we calibrate using Mike k or Eric M' s method he get a value of 585-600lbs to kink to 30 degrees. Yield and tensile strength are pretty much useless numbers to us. We need to calibrate to 30 degrees and based on that, it's the amount of strength we need to apply to bend that piece of steel.

[Tim71]

Frank,

If you look in the FBBC calibration thread pinned, Eric talks about this some as well. Pretty much as EJ said unless you start going much longer then instead of 1/2 inch, you'd actually have to use a percentage length of the bar. If you'll look at Eric's first post, you'll see he calibrates bastards at 3 different lengths to show the difference. From 7 inches down to 6 inches, 15 percent is pretty accurate but if you start going up to the 8 plus inches then it's probably going to be closer to 10 percent as EJ said.

Now on a setup like Ivan's with the shorter chains then the percentages would almost certainly be different. They're measuring all their stuff at 7 inches which I'm starting to believe is the best way to do the majority of it.

[acorn]

From what I remember of what Eric and I discussed and worked out years back when I was still bending and also rating bars. It worked out to a pretty consistent 15% per 1/2" change in bar length in the normal length range that we unbraced bend in. Say 5-7", possibly even down to 4.5". but I cannot remember for sure on that one. This only accounts for estimating the rating of the steel that you would get if you tested it with a rating rig. It is not directly comparable to a different length bar rating if you are trying to determine which bar will feel tougher to bend. For that what I used to estimate cross length comparable toughness numbers was a 10% per 1/2" rating and it felt pretty accurate as long as the lengths were not too much different. Here is an example of that. Lets say you just bent a 440# Red nail at 7" and you want to know what the comparable 6.5 or 6" bar rating would be so that you can try for something a little harder the next time.

440 @ 7" x 110% = 484# @ 6.5" , or 440 @ 7" x 110% x 110% = 532# @ 6" would be about equivalent challenge to bend. Whereas if you just cut the 1/2" off another of those Red Nails it would be 440 @ 7" x 115% = 506# rating.

Hope that makes sense

- Aaron

Edited September 12, 2014 by acorn

[Frank Pizzo]

Thank you to everyone for the well thought out and informative responses!

[Andrew P]

Andrew P

That's not what he was asking. Yield strength isn't important to us. According to your calculations the gold has a yield strength at 5450lbs. When we calibrate using Mike k or Eric M' s method he get a value of 585-600lbs to kink to 30 degrees. Yield and tensile strength are pretty much useless numbers to us. We need to calibrate to 30 degrees and based on that, it's the amount of strength we need to apply to bend that piece of steel.

I agree. It helped me but it's one of those things I knew to take it with a grain of salt.