Calculate bends

[coykiesaol]

Hi all.
Was just after some help in how to calculate bends into a piece of sheet.
If I cut a sheet of 5mm plate which will have 6 bends ( all the same direction to end up with a bull blade face) at 12.5 deg and each segment is 125mm, how can I calculate the size of the sheet I have to cut first, if I want the end part after bending to be 700mm . Any help would be really appreciated.
Thanks

[neilw20]

Try using set back. It is the easiest (IMHO)
Cut a small piece of the same material, say 60mm long.
Bend through the middle, and measure each leg.
The total will be over 60mm, the excess material being what was gained in the bend.

That extra amount is the set back.

Now after marking the first section, move back by the setback and start the next panel from that line, and so on.

The bend line for the blade is central between the lines, but with a folder, it won't be evenly between them.

Do a few test bends first, and it must be with the same material you will use.

[fatal-exception]

If you have a CAD program, you can draw the exact bent profile of your part, then put a center line through it (by offsetting one of the sides). The length of the center line is the length of sheet that you will need to start with. Works for us...

Solidworks also does sheet metal bend calculations very well in my experience.

[Frantic Fab]

if your going to do all this by hand here is a very useful formula for calculating gain in bending applications.

start at the either end of your material but remember which end because you always have to measure in the same direction to avoid confusion. first pull a measurement from end to center of your first bend. mark the center. now from this center mark you are going to need to measure backwards (Xdistance) this mark represents your setback. then from your setback mark you need to measure foward (Ydistance) this distance is your advance. now you have 3 marks the two outter marks or you setback and advance, represent the beginning and end of your bend. to accurately measure the next bend and obtain the center to center distance for compound bends. very important step. 1.find the last ADVANCE mark from your LAST bend. 2. take the distance from the set back of THAT LAST bend you are on and subtract it from the total center to center measurement to your next bend. then mark this center. measure back (Xdistance) for your setback and foward from that mark (Ydistance) again you have just laid out the beginning and end for your next bend with the proper calculations made to keep the center to center measurement you are trying to obtain.

now for the formula to get your X(setback) and Y(advance) marks with respect to the RADIUS of your bend and the DEGREE. the radius and degree make or break this formula so be sure you calculate correctly and have the right radius and degree.

this formula works for all materials and any radius and degree combination possible
SETBACK= TAN(1/2 DEGREE OF BEND)*RADIUS
ADVANCE= TAN(1)*DEGREE OF BEND*RADIUS

so for your situation 125mm on center @ 12.5 degrees and lets say 10mm RADIUS
SETBACK=TAN(6.25)*10==== 1.095mm
ADVANCE=TAN(1)*12.5*10== 2.182mm
(these numbers are indicative to a 10mm radius now. just an example)

so working from one end to another you will measure out 125mm mark center. 2. from that center measure back 1.095mm mark setback. 3. from setback measure forward 2.182mm mark advance. 4. from your last advance mark measure forward 123.905mm (125mm-SETBACK from last bend) mark center. repeat this process untill you have all your marks laid out.

note: if your not using a roll type bender then you will want to find the exact center between all your setback and advance marks for each bend and line up your press bender on that mark!

hope this helps. i have used this formula for bending tube mostly. so far i am responsible for about 6.25 miles of 1/4''-316L EP SS @2.5'' radius with thousands of bends, rolling offsets, you name it i have bent it! if you need any clarification on any steps just ask!

Thanks!
Garrett

[KentC]

Garrett,
I see a lot of hand tube bender gain charts. For a 9/16 in radius bending 1/4 in. tube some charts say 1.4 in. and some say 5/16 in. Your calculation predicts 1/4 in. Am I missing something?

[neilw20]

bump. grr....

[neilw20]

a sixteenth of an inch. Run a test piece. Material stiffness -- elasticity -- characteristics cause variations.

[juergenwt]

Speaking from years of die making experience. Calculations and formulas will get you somewhat near. However before making the blanking die one builds the forming die and to do this you need to develop a blank. Start with a calculated length, do your bending and correct from there on until you come up with a good part. Keep record of what you are doing - record the dim's for all your bends.