I've been looking for a drafting standard to show how to properly dimension a sheet metal jog's leg length for the purpose of calculating bend deductions and haven't found one. I have always dimensioned to outside control points and aligned the dimension to the jog leg as shown below. This seems to produce the right number for calculating the flat dimension knowing the bend deductions, but I'd like to verify that I'm using the proper method. Anyone know a good reference?
Agree with Frederick here. The tools that are available will drive how that should be modeled/dimensioned. We are going thru growing pains here since we bought a new laser/brake-press and are now trying to make parts we previously bought. We are finding many of our sheet metal designs require tools we do not have.
If you're not forming heavy gauge material, tools can be 3D print.
just give the offset. indicate allowable limits for the rest. otherwise they will price it based on making a tool.
Let me clarify what I'm asking. We are the fabricator. I'm wanting to make sure that I'm calculating bend deductions and flat dimensions based on the proper dimensions on my formed views that include a jog. Here is my bent part:
Here is the flat vertical dimension for this part produced by SolidWorks:
Maybe this is a dumb question because the math does seem to work the way I'm doing it. Just want to make sure that I'm doing this properly to verify that I can use this same method of dimensioning for other parts. If I add the leg dimensions: 1.650+.267+3.250, and then subtract the bend deduction from our company's bend deduction chart for each of the 45 degree bends: -2*.070, the answer comes to 5.027, which is the flat dimension as produced by SolidWorks. Here is a closeup of how I'm dimensioning the 45 degree jog:
My .267 dimension is from outside sharp to outside sharp and aligned with the straight line between the bends.
Is this the correct way to measure the jog leg as a part of the bend deduction calculation? I think it is, I just wanted to verify and if possible find an authoritative reference that will tell me if this is the right way to measure/calculate this kind of geometry.
Barry Watkins wrote:
We are the fabricator.
Since you're the fabricator, you tell the designer, us, what bend allowance to use.
Not the other way around.
The is only one way to find accurate bend allowance: measure, test bend and measure.
Bend allowance is require on the bend area where material deform and stretch.
Does your forming tool stretch the leg?
This is what I'd do and then give it to you. First of all, nothing is three places and I do care about the offset dim of .28 (.277 modeled) and I also care about overall length but only 2 places.
Steve C
Are you planning to make a tool for the jog?
If not, you might want to contact fabricator and see what tooling they've got.
Usually important part is the offset. Radius and other dimensions depends on the tool.