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Krahling Rating Rig 3.0


Squeezus

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So, a month or so ago, I endeavored to build a rig to rate steel. In the process I built a version of the 2.0 rig that used a winch and a crane scale attached to two fixed points on a squat rack to rate steel, but after trying to rate a few bars I decided something had to be changed. With that system, after bending a bar to the requisite 30 degrees, the strain (stretch or deformation) of the bar caused the rating to drop precipitously as soon as I stopped cranking on the winch, making it very difficult for me to maintain consistent ratings. So, I had to figure out a way to eliminate the factor of the strain.

This brought me back to the original rating method of using weight on a barbell. Since the weight is hanging, it doesn't matter if the bar stretches a little bit. The weight below (and force exerted by that weight) stays the same. So the question was, how can I use a hanging weight with the crane scale and still have some adjustability without shuffling a bunch of plates around?

Answer: Leverage.

By using a beam attached to a pivot, I can use a small amount of weight on the end of the beam to create a very large amount of downward force closer to the pivot, and if I make it adjustable, I don't have to vary the weight at all. Also, this allows me to still use a crane scale, which means I don't have to worry about doing any math with the beam or weight, just watch the crane scale. To make it adjustable, I used a piece of unistrut with a special unistrut trolley with a nut welded to it so it can be driven back and forth in the channel using a drill or wrench. I can hang whatever weight I need from the trolley and start rating.

So, here are some averages that I came up with on 7" stock (I didn't rate any 6") after doing some rating:

CRS:

  • Red Nail - 437
  • 5/16" Batch #1 - 445
  • 5/16" Batch #2 - 485
  • 5/16" Batch #3 - 505
  • 5/16" Batch #4 - 540

Bolts:

  • 5/16" G2 (307A LB Head) - 390

Nails:

  • 70d Big Head (McMaster) - 410
  • 70d Small Head (McMaster) - 430

O1 Drill Rod:

  • 0.25 (McMaster) - 300
  • 0.281 (Speedy Metals) - 310
  • 0.281 (McMaster) - 410
  • 0.290 (McMaster) - 400
  • 0.295 (Speedy Metals) - 430
  • 0.295 (McMaster) - 465

And here's a video of the Krahling 3.0 rig:

@Stanley sallee @wobbler

Edited by Squeezus
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Engineering at it's finest. I bet this same technique could be used to rate grippers too. I don't have a crane scale so when I rate grippers I end up shuffling weights back and forth to my ground scale to weigh them, which is kind of a pain. This rig is more extensive to build, but I'm sure would be easier to operate. Neat-o.

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Awesome!

I bet there wouldn't be much additional work to use that for rating grippers too.

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I love that due to the scale placement you can replace that 50lb weight with any weight at all and it will still work. I have a tiny concern with how much force you might unintentionally be applying with the drill, and also I would try to make the strap holding the weight as short as possible to reduce oscillations that would alter the force. 

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5 minutes ago, Climber028 said:

I love that due to the scale placement you can replace that 50lb weight with any weight at all and it will still work. I have a tiny concern with how much force you might unintentionally be applying with the drill, and also I would try to make the strap holding the weight as short as possible to reduce oscillations that would alter the force. 

You're correct, care has to be taken with the drill to make sure that it isn't acting like a wobbly "finger on the scale". After a couple practice nails, I was able to get a feel for how to hold the drill so as to minimize any force imparted to the end of the beam. In addition, I set the drill on the floor several times throughout the process, like when I am measuring the nail angle, which removes any human element from the scale number.

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Use a corded drill, physically attach it to the arm, and then actuate it remotely with a kill switch to the power. Then you don't have to touch the arm at all. Or heck even a small motor and whatever type of controller you want would work great. 

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This machine will be the new way to bend. We have reverse, du,  do, and now MAB. Machine assistance bend. The equivalent of geared powerlifting lol

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Yeah might as well make it remote control at this point (even if that just means pulling the battery, zip tie on the trigger, and manually short wires to the battery, or be fancy and add a switch)

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11 minutes ago, king crusher said:

This machine will be the new way to bend. We have reverse, du,  do, and now MAB. Machine assistance bend. The equivalent of geared powerlifting lol

Still not as strong as humans, at least not until it can kink a railroad spike of course. 

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Machine is badass. It would be more badass with large wheel (bonus points gained with real or stylized skull in the center of wheel) which can be used instead of machine screwdriver to manually rotate it. You can go full pirate if you casually spin the wheel with one hand between some important conversation and it keeps on swinging doing its job.

Edited by Goran Paulinič
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Just to be clear, I built this so I have the option of getting the Krahling rating on some nails. I have another completely different rating device in the works that will become my primary rating system. I'll share details once I'm happy with the prototype.

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Great one and even that you get the same numbers as in the past is really impressive. Hats off!

Looking forward to your own rating system and how it works.

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2 hours ago, king crusher said:

This machine will be the new way to bend. We have reverse, du,  do, and now MAB. Machine assistance bend. The equivalent of geared powerlifting lol

Brb getting my edgins

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I kind of dig it.

small side note to add to comments on the drill. I don’t think the drill, or the weight of it rather, will have any meaningful effect on the rating. The poundage is still measured on the scale that’s chained directly to the steel. So whatever dead weight on the arm doesn’t matter. As long as it’s heavy enough to do the job. The weight on the lever is only used to amplify the leverage at the chains- where the actual measurement takes place.

Edited by Tommy J.
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