# Slightly OT: K-Factor?

• posted

Okay.

I'm trying to calculate a K-factor for use with my bent part. Here's what I know:

-bend angle (BA) is 90 degrees

-material thickness (T) is .0625

-Flat length (FL) is 4 inches

-Bent leg outside length 1 (OL1) is 2.0625 inches

-Bent leg outside length 2 (OL2) is 2.0625 inches

Here's the formula I use to reverse engineer the K-factor:

Bend Deduction (BD) = OL1 + OL2 - FL Outside Setback (OS) = (Tan(BA/2))* )T + BR) Bend Allowance (BA) = (2 * OS) - BD K-Factor = (-BR + (BA / (pi * BA / 180)))/T

When I input all of my values into this mess, I get a K-Factor of

1.320303226. I'm pretty sure that's not right, as the K-factor can't be over 1 (right)?

Using a small program called Plus-Bend to do the same thing, I get a value of .14 (the program rounds it). I believe that value to be correct.

Can anybody help me figure out where I'm going wrong--is it the formula, my math, or something else? I basically want to be able to use the known variables given above to calculate the K factors for the various materials I'll be bending. I'm new to this so it's a little confusing. Please let me know if you need more info than I've given here. Thanks!

Brian

• posted

I did a quick figure on it and got K=.1366, so you are correct there. But, I don't have time right at this moment to go through your formulas. I will when I get a chance. Sorry.

WT

• posted

Hi Brian,

K-factor cannot actualy be over .5 under any circumstances that I know as it is the location of the "neutral axis" on a bend. .5 represents an extremely gradual bend. It's effective low limit is something like .2

You might find this useful:

Regards,

SMA

• posted

Hi Brian, My little calculator comes up with 0.136620310097753 whn it doe the reverse engineer K facto calculation. If it's of any use to you, it's a downalodable at:

Olaf

• posted

This is a very tight bend so there should be a lot of plasticity and the small K factor might be expected as the neutral axis moves toward the inside face.

• posted

I know several people have led you to the proper answer, but it's good to see what actually went wrong for the learning value, so I worked through what you had. There were a few things I found. It looks like you really probably had it ok except fo rthe Radians thing.

1. You have 2 variables called BA - bend angle & bend allowance. I changed the second to AL for arc length.
2. OS - you have to convert the bend angle to radians to use the Tan function.
3. In the OS line you had *)T, and should have been *(T - probably a typo in the message.
4. On the K-factor line, PI must be followed by ().

-bend angle (BA) is 90 degrees

-material thickness (T) is .0625

-Flat length (FL) is 4 inches

-Bent leg outside length 1 (OL1) is 2.0625 inches

-Bent leg outside length 2 (OL2) is 2.0625 inches

Here's the formula I use to reverse engineer the K-factor:

Bend Deduction (BD) = OL1 + OL2 - FL Outside Setback (OS) = (Tan(RADIANS(BA/2)))* (T + BR) Arc length (AL) = (2 * OS) - BD K-Factor = (-BR + (AL / (PI ()* BA / 180)))/T

WT

• posted

Olaf -

Nice PDF file on your site as well describing the many bending circumstances. This should help a lot.

Nice stuff mate.

Later,

SMA

• posted

Wayne--thanks! It *is* important to me to know where I went wrong--I need to know how to do this properly going forward. Most of what you pointed out is due to me hurriedly typing this message--what I did not know was that I need to convert the angle to radians.

Thanks again...

Brian

• posted

Brian

• posted

Thanks to all for your help.

We bend not only sheet metal, but plastics and paper stock (cardboard) as well. For those materials, you can throw many of the standards for sheet metal out the window. Being able to reverse engineer the K factor will allow me to figure out what K Factor I need to use for each material based on our bending experience. I'm hoping to set everything up in a table, one for each material & thickness.

I'm looking at the table template "kfactor base bend table.xls" that comes with 2005 in the lang\english\Sheetmetal Bend Tables directory. It's fairly obvious how it works, except that there seems to be no place to put radius AND thickness, which would both be necessary (right?). Maybe this isn't the right table for what I want to do?

The easiest thing for me would be for someone to send me a sample of a table which contains K-Factor values for a given material thickness and bend radius, at a number of different angles. I don't want to copy anybody's work--rather I would like to see the proper way to set it up.

So, does anybody have a table that they'd be willing to share? It would be a huge help. Thanks again for all of the help, and let me know if there's more information that you need to give a better response.

Brian

• posted

As I recall, some people use K-factors >.5 when they model cardboard boxes.

Jerry Steiger Tripod Data Systems "take the garbage out, dear"

• posted

Indeed Jerry - I would not argue with anyone who is getting good results. I have often wondered about about how hot polycarbonate would be behave, another use of this type modeling. A true philadelphia lawyer would have appeneded my statement with "when forming sheet metal". Again, I have this nasty fixation with that stuff . . .

:)

Later,

SMA

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