Need help with math on bending project

[finsruskw]

I need to cold bend in my press brake, two 90* X 1" stubs on each end a piece of round 1/2" HRS and wind up with 32" center to center on the stubs.

I have already discovered that a .8125" bend point on both ends of 6" blank will produce the 1" stub on the ends of a scrap piece and result in a 4" center to center measurement.

I could probably keep practicing and come up with the answer but really don't want to waste a bunch of material doing so.
Am hoping there is a "rule of thumb" that covers this??

Or do I just add the 2 x .8125" to 32" to get 33.625" and bend accordingly??
Or am I "all wet" in this assumption??

 

[DavidR8]

Is this helpful?

Calculating Bend Allowance, Bend Deduction, and K-Factor

When calculating Bend Allowance, Bend Deduction, and K-Factor there are tests that involve bending some samples and carrying out measurements/calculations.

www.javelin-tech.com

Or this?

Bend Allowance Calculator

Calculate the bend allowance, bend deduction, and setback for a bent piece of sheet metal, or use this information to determine the K-factor.

www.custompartnet.com

 

[Tim9]

maybe welding a stub would be easier. Weld and then clean up on the mill.

 

[DavidR8]

Unless I needed the radius on the corners I would do what @Tim9 suggested.
The ends of the long section could be radiused to accept the 1/2" stubs. That would help ensure a 90 deg corner.

 

[finsruskw]

Radius is not an issue here.
Just need a quick solution so I can crank out a few of these in a hurry for a fellow.
Math was not my strongpoint some 60 years ago!!

 

[Aukai]

Two tape measures, one out flat, the 2nd with your desired dimensions. You should be able to find the measurement at the 2nd 1" stub allowing for the radius of the bend. It might cut down on the material use. If you have a sample measure outside dimensions, and see where the center of the radius is. I admit I'm a hack.....

 

[Flyinfool]

To figure out what your bending apparatus will do you have to run a test coupon.

Simply take a piece of your half inch rod long enough to grip both ends for making the bend, and face both ends.
Accurately measure its length.
Make a mark exactly 1 inch from one end.
Now bend it exactly at that mark.
You can now measure the bent part to determine exactly how much material was used in each direction and will know how long you need for the straight length and where to start your bends.

Above I said to start with a mark at one inch, depending on your setup that may be to short to grab for bending, In which case you will need to make the ears longer and then trim to 1 inch after bending.

You kind of did this but did not do the first steps to be able to get all of the information that you need.

The method you are using to make the bend, the radius of the bend have a big impact on the amount of material consumed by the bend. That is why you have to test your setup. There are all kinds of formulas and tricks that will get you close, but only the coupon test will get you right on.

 

[finsruskw]

I made an adjustable stop for the anvil on the brake to get the 2"
The anvil is 4 x 4" and I'm using the widest VEE which is 2" so had to go bigger than 1"

Here are the results.
Test piece 6" long

6" test piece wound up being 4.383" on the long, outside end
and 2.344 on the short outside end
So, the overall length grew by .724"
The long end (outside) grew by .383" and the short end (outside) grew by .344

The long (inside end) became 3-7/8"
The short end became 1-7/8" approx.

My short lagged 'U' needs to be 33" outside to outside in order to get 32" center to center?

My head hurts!!

 

[Flyinfool]

OK so take a piece of bar, face the ends to measure its length, use you brake to make the 1 inch bend and then you can measure the remaining leg center to end so that you know how long to make the bar before bending to end up with your needed center to center distance.

For instance, If you start with exactly a 4 inch bar, make your 1 inch bend and have 2.5 inches from the center of the one inch leg to the tag end of the bar, then you know the bend used 1.5 inches of material. Add 1.5 to each end of your needed center to center distance and you know the blank length needed for your setup.