4 ms·

I mean sure, things have bugs, right? I get that. Sometimes autocorrect messes up things I type. It's not really a bug per-se, more just a side-effect of how t

by rtpg 11y ago

I mean sure, things have bugs, right? I get that. Sometimes autocorrect messes up things I type. It's not really a bug per-se, more just a side-effect of how things like autocorrect work, right? But sometimes Chrome crashes, and that's a bug... The OP seems to say that the bend radius thing is more of the first case than the second, and I'm wondering how true that is. I'm not really sure of the science behind it (maybe it's an impossible constraints problem).

chris_wot 11y ago
Oh, no doubt. The issue is that the tools don't appear to document their limitations and constraints, and there is often no way of knowing until you get bitten. At least with OSS you can look at the code behind the program to work out how it calculates things like the bend radius. I'm no engineer, so I had to look it up (Wikipedia was no help whatsoever on this occasion) but I located this page which gives the formula and an explanation: "Calculating the correct flat pattern layout is crucial to getting a good quality finished part from your press brake. Yet, many CAD and CNC programmers have no idea how to calculate the required values. Years ago, the real experts created cheat sheets and tacked them to the wall. They only taught the new apprentice how to apply the results shown on the cheat sheet, not how to calculate the numbers. Well, now those experts have retired and it's time for a new generation to learn the right way to do the calculate the correct flat pattern layout." http://www.sheetmetalguy.com/bend-allowance.htm http://www.sheetmetalguy.com/bend-allowance.htm Now admittedly the guy does put the responsibility on the operator, but it appears CAD packages can indeed calculate this for you. So long as the right info was input into the program, the formula should be programmed correctly and the operator should be able to have confidence in the results!
- sammcf 11y ago
  >Now admittedly the guy does put the responsibility on the operator, but it appears CAD packages can indeed calculate this for you. So long as the right info was input into the program, the formula should be programmed correctly and the operator should be able to have confidence in the results! "Should" is the operative term. I can tell you with that having hand checked the automated results of several CAD packages at developing sheet metal flat patterns and finding unexplained variability and errors too many times to count that if you want confidence in the dimensional accuracy of a sheet metal part, you need to develop it by hand. Especially for anything over 5mm in sheet thickness. As far as I'm concerned you really can't engage in sheet metal design without being able to manually verify the development results, so in a sense it is up to the designer regardless of the capabilities of the CAD software. To be fair, I'm picking on one of the hardest physical manufacturing processes to actually get right - even CNC brake presses have a great amount of variance in calibration (e.g. the amount of bend allowance you need to make for various sheet thicknesses...) across different suppliers, materials, etc to produce physically identical parts. The valuable lesson for a fresh designer is don't trust your 3d representation of the part, don't trust the manufacturer specs on ANYTHING and always prototype. I'm guessing this is why people tolerate it - the world with 3d CAD is still a vastly nicer place to be an engineer than otherwise, so we just rationalise away the shitty parts as a reasonable price to pay.
  - chris_wot 11y ago
    I'm guessing this is why people tolerate it - the world with 3d CAD is still a vastly nicer place to be an engineer than otherwise, so we just rationalise away the shitty parts as a reasonable price to pay. Yeah, I know. In my experience, engineers are normally immensely pragmatic people. My dad was an engineer, so I have a lot of respect for the profession. It would just be nice if CAD would be more open.

by rtpg 11y ago

chris_wot 11y ago

Oh, no doubt. The issue is that the tools don't appear to document their limitations and constraints, and there is often no way of knowing until you get bitten. At least with OSS you can look at the code behind the program to work out how it calculates things like the bend radius. I'm no engineer, so I had to look it up (Wikipedia was no help whatsoever on this occasion) but I located this page which gives the formula and an explanation: "Calculating the correct flat pattern layout is crucial to getting a good quality finished part from your press brake. Yet, many CAD and CNC programmers have no idea how to calculate the required values. Years ago, the real experts created cheat sheets and tacked them to the wall. They only taught the new apprentice how to apply the results shown on the cheat sheet, not how to calculate the numbers. Well, now those experts have retired and it's time for a new generation to learn the right way to do the calculate the correct flat pattern layout." http://www.sheetmetalguy.com/bend-allowance.htm http://www.sheetmetalguy.com/bend-allowance.htm Now admittedly the guy does put the responsibility on the operator, but it appears CAD packages can indeed calculate this for you. So long as the right info was input into the program, the formula should be programmed correctly and the operator should be able to have confidence in the results!

sammcf 11y ago
>Now admittedly the guy does put the responsibility on the operator, but it appears CAD packages can indeed calculate this for you. So long as the right info was input into the program, the formula should be programmed correctly and the operator should be able to have confidence in the results! "Should" is the operative term. I can tell you with that having hand checked the automated results of several CAD packages at developing sheet metal flat patterns and finding unexplained variability and errors too many times to count that if you want confidence in the dimensional accuracy of a sheet metal part, you need to develop it by hand. Especially for anything over 5mm in sheet thickness. As far as I'm concerned you really can't engage in sheet metal design without being able to manually verify the development results, so in a sense it is up to the designer regardless of the capabilities of the CAD software. To be fair, I'm picking on one of the hardest physical manufacturing processes to actually get right - even CNC brake presses have a great amount of variance in calibration (e.g. the amount of bend allowance you need to make for various sheet thicknesses...) across different suppliers, materials, etc to produce physically identical parts. The valuable lesson for a fresh designer is don't trust your 3d representation of the part, don't trust the manufacturer specs on ANYTHING and always prototype. I'm guessing this is why people tolerate it - the world with 3d CAD is still a vastly nicer place to be an engineer than otherwise, so we just rationalise away the shitty parts as a reasonable price to pay.
- chris_wot 11y ago
  I'm guessing this is why people tolerate it - the world with 3d CAD is still a vastly nicer place to be an engineer than otherwise, so we just rationalise away the shitty parts as a reasonable price to pay. Yeah, I know. In my experience, engineers are normally immensely pragmatic people. My dad was an engineer, so I have a lot of respect for the profession. It would just be nice if CAD would be more open.