This issue comes up at work fairly frequently. I usually just grin and bear it, but thought I might save myself a great deal of time and frustration by summarizing some of the more common issues I deal with in taking customer models and designs.
Sam,
Just a couple notes on these files.
When specifying feature locations in the flat, you are opening yourself up to a lot of potetial problems. The material allowance you use would have to match ours or the finished part will not meet your requirements. Material allowance is determined by a combination of factors: Material type, thickness and inside bend radius(IBR) are a few of the main factors. Any deviation in the model from what will actually occur with the part will translate into problems with the finished part. It is far safer to dimension the finished part, rather than the flat pattern. If we were fabricating the blanks for your shop to bend, flats would be no problem. In short, convey what you want, not how to fabricate it.
Ordinate dimensions are fast, clean and easy, but you can't convey design intent with them. Parts that are made to print and are within tolerance can actually be bad be bad parts. I'd be happy to provide some examples of this if you like. Any deviation in any of the factors determining material allowance will result in a tolerance stack-up across bends.
Locating features in the flat with ordinate dimensions compounds the potential for producing parts that will not work as intended. Parts dimensioned in such a way that mate to other parts dimensioned in the same manner is almost assuring that there will be problems.
Inside bend radii should be as near to or greater than material thickness in aluminum. The specified .030 IBR in .100 material you have request will likely result in stress cracks. Standard IBR for aluminum are: .030, .060, .090, .125, .25. We can achieve virtually any IBR if we 'cap' our punch, but bend consitency can become an issue, so it is best to use these standard IBR.
When conveying profile dimensions, the most practical approach is to dimension legs from outside intersecting faces. These dimensions are clear and will not change if the IBR should deviate from nominal. It provides an abslolute dimension without the abiguity that can result from dimensioning tangency, flat run or radius centers.
I'll forward copies of the drawings after I modify them for your appoval and as a means of illustrating what I'm attempting to convey here. If I can be of assistance or answer any questions, don't hesitate to call.