Question about measuring when bending steel.

[DJ_Schmo]

Thus is probably a stupid question but it’s my first go at making anything besides my work bench.

If I start with a sheet of 20 ga steel and do two 90° bends how much will I lose in length overall?

Essential I need a sheet that ends up being 15” on one end, 26.5” down the middle and 15” on the other end. Do I need a piece slightly longer than 56.5” to make up for the bends?


Sent from my iPhone using The Garage Journal mobile app

 

[OccupantRJ]

http://www.custompartnet.com/calculator/bend-allowance

 

[dogdog]

yea bend allowance formula, the only differences between material is the K factor, and some material have flex / spring back or something to that term if you wanted 90 deg you bend to 92 or 93 so it flex back to 90 (forgot that prper term)..........if you wanted super precision bends... I think this old tony had a YouTube video explains it as well but it is more of a overview and intro than explaining the formula....

This video is entertaining..

 

[DJ_Schmo]

Thanks so much! I’m thinking I don’t really need to worry about it much since this isn’t a precise project but it’s great info to have.

I’m buying a new toolbox at tax time and want to build my own power drawer. This sheet will cover three of the four interior walls of the drawer and my tool holsters will mount to it.


Sent from my iPhone using The Garage Journal mobile app

 

[dogdog]

that is a good knowledge to know if you are in any sort of fabrication trades.... but if it is not something critical...it's up to you. if you are learning it, I think it is better to learn it with paper and pencil than online calculator, that link posted earlier lead to another section that explains it well.... I don't remember it after so many years.... out of school and not working in that field.

if you click into that link posted this would lead you in to the learning more article...

http://www.custompartnet.com/wu/sheet-metal-forming#bending

 

[LXCam]

I'm sure that link points this out but totally dependent upon the radius of the brake, you'll gain the length. Even thought you can get 20ga to bend a really sharp angle it still will roll just a minor amount.

 

[matt_i]

I think more depends on where you put your layout line relative to the fingers.

The loss is going to be in the 1/16" range or less for 20ga I think.

 

[PugetDude]

The length of the part is measured through the neutral axis, irrespective of thickness or how may bends you make. The neutral axis is the centerline of the material thickness, it's easy to calculate developed length by adding straight lengths and radii. Obviously thicker material will have a different radius through the part centerline than thinner material when bent to the same outside radius.

 

[4 FN 27]

Thus is probably a stupid question but it’s my first go at making anything besides my work bench.

If I start with a sheet of 20 ga steel and do two 90° bends how much will I lose in length overall?

Essential I need a sheet that ends up being 15” on one end, 26.5” down the middle and 15” on the other end. Do I need a piece slightly longer than 56.5” to make up for the bends?


Sent from my iPhone using The Garage Journal mobile app

Your Blank length the should be 56.380 in the Flat using a 1/32 Inside Radius and .060 Bend Deduction per bend.

The Math: 15 +15+26.5 = 56.5 - (2x.060) = 56.380

Your Bend Lines would then be 14.970 in from each end. You should end up pretty close to 26.500 in the middle outside to outside assuming your bender can hold a .031 inside radii. If the Radii is bigger you would need to deduct more material.

 

[PugetDude]

Do I need a piece slightly longer than 56.5” to make up for the bends?

Your Blank length the should be 56.380 in the Flat using a 1/32 Inside Radius and .060 Bend Deduction per bend.

The Math: 15 +15+26.5 = 56.5 - (2x.060) = 56.380

Your Bend Lines would then be 14.970 in from each end. You should end up pretty close to 26.500 in the middle outside to outside assuming your bender can hold a .031 inside radii. If the Radii is bigger you would need to deduct more material.

As 4 FN 427 pointed out, you would actually need to make the blank shorter, as the path through the part centerline is shorter than the length around the outside of the part.

Think of it like making a 90 degree curve instead of a 90 degree corner when you're driving.

 

[DJ_Schmo]

These types of responses are what make GJ so awesome!

Thank you so much for all the info! I’m sad this new box is about 6 months away but I want to get a jump on having everything ready when it arrives. I’ll be sure to take photos and update.

Thanks again!


Sent from my iPhone using Tapatalk Pro

 

[Firstram]

For a layman's approach, start with a piece of the material you plan to work with and cut a 1" strip with square ends 10" long. Scribe a bend line 1" in from each end, which will give you 2 lines 8" apart, and bend both ends to 90°. Measure the resulting piece and layout a 2nd one adjusting the length for the bend take up and test bend it. When you can lay it out and get predictable finished dimensions, cut and bend your sheet with confidence.

Seeing the changes in length first hand and practicing before you commit can only lead to success the first time.

 

[toplessHO]

in bending this is called the "gain"
look at it as the radius of the bend isnt as sharp as 2 pieces butted together

 

[Firstram]

i called the "gain"

Term of the day, thanks. For some reason it's always been explained to me as "take up", gain makes more sense.