The question was asked in our forum (www.SheetMetalGuy.com/forum), if any one could translate or figure out what the formula is in the Inventor Bend Table. I don’t know who created these formulas, but I will do my best.
First the formula in the Inventor Bend Table: =IF($B135>165,0,(IF($B135>90,(2*(E$118+$B$115)*TAN(((180-$B135)*PI()/180)/2)-PI()*((180-$B135)/180)*(E$118+($B$115/2)*(0.65+0.5*LOG(E$118/$B$115)))),(2*(E$118+$B$115)-PI()*((180-$B135)/180)*(E$118+($B$115/2)*(0.65+0.5*LOG(E$118/$B$115)))))))
Quite a mess isn’t it? Well the first step is to break down the three parts of the ‘IF’ statement. This shows that it is handling the bends three different ways based on the angle of bend.
I did some renaming of the variables and it looks like this:
=IF(angle>165
0
ELSE,(IF(angle >90,
(2*( radius+thick)*TAN(((180-angle)*PI()/180)/2)-PI()*((180- angle)/180)*( radius +( thick /2)*(0.65+0.5*LOG(radius / thick)))),
ELSE
(2*(radius+ thick)-PI()*((180- angle)/180)*( radius +( thick/2)*(0.65+0.5*LOG(radius / thick)))))))
But then I question why the author did some of it and is it incorrect or not?
It starts by saying any bend with an angle greater than 165 degrees will use a value of zero. I agree most bends in this range are things like hems. But specifying a zero will give incorrect results.
For the other two parts, angles greater than 90 and angles less than 90, the math is more complex than it needs to be and I am not certain about the resultant value. While many parts of the formula look familiar, they don’t add up. What is especially unique is the log function being used to calculate the k-factor. I have not seen this before and plan to do more testing to see just how good it is.
I made a test to compare the standard bend formula results to the table results. There is a statement in the table (The correction value X is applied as follows: L = A + B – x) which implies they are calculating the Outside Bend Compensation. However to get their value I had to use a k-factor of 2.03. Since a k-factor is a percentage of the material thickness, this is way out of range.
My best comments about these formulas are:
A) The note at the top of the file says - ; This is supplied as a sample only. Edit with your own data and formulas as required.
B) Try our standard formulas using the quick rule of thumb k-factor. That is when the inside radius is more than two times or more the material thickness, k-factor is .42. When the inside radius is equal to thickness, the k-factor is .3333. And when the inside radius is less than the thickness, the k-factor is .25
Again I don’t know where the formula in the Bend Table came from, but don’t use it. |
