pic: sheet metal 6WD

[AdamHeard]

Originally Posted by Chris is me

How much is "much"?

The moment of intertia of the cross section is directly related to it's stiffness.

If you google, you'll see for a rectangle, the moment of inertia is 1/12bh^3 (base and height). Base being the side parallel to the axis the beam is being bent around.

So, a 5" tall .050" thick plate has an I = 1/12(5in)(.050in)^3 ~ 5x10^-5.

The same beam with two 1" flanges is that I plus the I of the two flanges. I = 1/12(.050)(1)^3= .004

So the beam with the two flanges has a total I of .004+.004+5x10^-5 ~.084.

.084 / (5x10^-5) ~150:1.

Even if I made a mistake in the math somewhere, this demonstrates the difference flanges make in design. I could go on for pages elaborating this, but it'd better to google and look yourself (key terms being beam, cross section, moment of inertia, etc...). You'll also then understand why I-beams are shaped the way they are.

[Chris is me]

Originally Posted by AdamHeard

The moment of intertia of the cross section is directly related to it's stiffness.

If you google, you'll see for a rectangle, the moment of inertia is 1/12bh^3 (base and height). Base being the side parallel to the axis the beam is being bent around.

So, a 5" tall .050" thick plate has an I = 1/12(5in)(.050in)^3 ~ 5x10^-5.

The same beam with two 1" flanges is that I plus the I of the two flanges. I = 1/12(.050)(1)^3= .004

So the beam with the two flanges has a total I of .004+.004+5x10^-5 ~.084.

.084 / (5x10^-5) ~150:1.

Even if I made a mistake in the math somewhere, this demonstrates the difference flanges make in design. I could go on for pages elaborating this, but it'd better to google and look yourself (key terms being beam, cross section, moment of inertia, etc...). You'll also then understand why I-beams are shaped the way they are.

I meant how much of a strength difference does cutting part of the flange out for the gearbox make? A poster said that it would be much stronger, and I wanted to know how much.

[AdamHeard]

Originally Posted by Chris is me

I meant how much of a strength difference does cutting part of the flange out for the gearbox make? A poster said that it would be much stronger, and I wanted to know how much.

I totally misread your question then.

Similar concepts apply, just inverse. The beam is substantially weaker due to that flange removal. Depending on how the gearbox is attached, the gearbox itself could add a lot of support to the beam where material is removed.

[548swimmer]

Originally Posted by AdamHeard

I totally misread your question then.

Similar concepts apply, just inverse. The beam is substantially weaker due to that flange removal. Depending on how the gearbox is attached, the gearbox itself could add a lot of support to the beam where material is removed.

Great explanation

The loss of a continual flange will not only decrease the second moment of area, but will also "chase" the stresses to the ends of the flange.

[Chris is me]

Originally Posted by 548swimmer

Great explanation

The loss of a continual flange will no only decrease the second moment of area, but also "chase" the stresses to the ends of the flange.

If that's the case, what's your basis for saying it'd be okay to remove the bottom flange entirely?

[548swimmer]

Originally Posted by Chris is me

If that's the case, what's your basis for saying it'd be okay to remove the bottom flange entirely?

Different design. The flange I said would be okay to remove was the bottom external flange. The top external flange used to mount bumpers will working in tandem with a properly mounted plate should, depending on material thickness, provide more than adequate structural integrity. That's why I said you could most likely remove that flange.