CAD Origins

[Devaney]

I am interested to find how people are dealing with different/complex origins on their imported CAD model. I often import models where the origin is off in some far off place and to make things worse that print is not dimensioned to the origin.

Anyone have any tricks O' the trade to share on this topic?

Thanks,

[george frick]

CAD=PART

[dfiola66]

I've been doing some of this recently. Usually involves distances between holes and distances from one form to another (auto stampings). The way I've been doing it is to use the distance command and using the 3d option since it sounds like your model is in car position yet the print is dimensioned locally.

I've needed to take hits on the part, change the working plane, and dimension the distance between the points also. It's a bit tedious but it works. Good luck.

[kbotta]

A 'new' feature in 4.0 is an improved cad feature to change the location of the origin. Much less cumbersome than doing it the 'old' way.

If I need to cad=part, and the alignment is in body position, i'll select a few feature's to figure out the orientation of the modle, and rotations, then offset the alignement.
kb

[Devaney]

That would come in very handy!

[RussL]

Generally speaking:
We do a manual Iterative alignment to A/C coordinate system using any features we like (we never use CAD=PART).
We create DCC alignment(s) using features and zero our "customer" requests.
Actual customer: Generally leave it in aircraft coordinate system and do best fit and inspect target points OR use B/P datums.
Manufacturing Engineering: Zero and skew to their manufaturing datums.
Manufacturing: Zero to manufaturing datums, skew to fixture bank features on part.
If there are tight tolerances on print, we either dimension them using distance fuction, etc. OR create more alignments and re-dimension (if there are lots of dimensions).

[Matthew D. Hoedeman]

It does NOT matter in the least where the XYZ zero point is, AS LONG AS YOU KNOW what the relationship of the fixture base is to those values. Leave the data in car position, use the offsets in the alignment window (321) alignment or use an iterative alignment (yuck) on the fixture base or part. If you have dimensions on the print that you need to show in your report (like 231mm from hole to hole) do it with the distance dimension. You can also, at the end of the program (where I do it) create a new alignment using the first feature from the print, then dimensioning the second feature from the print. Usually you only need to set the XYZ origins (no offsets, no CAD=PART) to the 'first' print feature then you can dimension the second (3rd, 4th, etc.) features. Sometimes you WILL have to do a complete alignment, BUT, by putting them at the END of the program and having the actual measurements before the alternative alignments you don't have to worry about good/bad data, you just need to do the dimensions.

[rebeldude]

Sometimes, I have found that when are alot of dimensions coming from the Datums that are Not actually "0" on the cad, but the print calls it out as "0", that it is easier to just go ahead and move the cad or have design to do it for you. Like Kevin was saying, Version 4 has simplified this process right in the PCDMIS, so that will be how I do it for now on.

[Matthew D. Hoedeman]

Well, there is also another way, just to show that there are MANY ways to do it, I have not done this. You can leave everything in car position, measure all the features in car position, then get the distance or location, or what ever and use assignments to 'subtract' the 'origin distance' out of the answer. Sure, it would be a pain in the rump, but it IS another way of doing this.

[kbotta]

Just like Pcdmis. 20 ways to do one thing...

[Devaney]

Sometimes, I have found that when are alot of dimensions coming from the Datums that are Not actually "0" on the cad, but the print calls it out as "0", that it is easier to just go ahead and move the cad or have design to do it for you. Like Kevin was saying, Version 4 has simplified this process right in the PCDMIS, so that will be how I do it for now on.

Well said, this is much like the situations I am running into. I'm getting files from the customer many time and I am unable to move the origin. Wish I had version 4.0

Many great insights, thanks

[Bill **********]

It amazes me how often this question comes up.

If your origin is out in space, move your cursor before ANY alignment, find your 4 way locator on your CAD model, dimension it, and watch what your Axis alignments are. Now you do your 3-2-1 or tooling ball or whatever alignment you want, make sure your aligmant axis directions are the same as the CAD model and do offsets to make your 4 way read what it was in the design before any alignment.

If you need a local alignment on the part for some dimension simply create that alignment on the part and make your measurements and dimension them out. Now here is where a problem can occur. Make certain that you RECALL your CAR or whatever your primary alignment is named before creating a third or fourth etc alignment. If you don't, you can get stacking errors. Alignment stacking is not a good way to program.

Bill

[Bill **********]

I don't understand why anyone needs to move an origin?

[kbotta]

For ease of cad=part...

[Matthew D. Hoedeman]

Well, you can offset the alignment (part of the alignment) or by moving the cad data the same amount. Most automotive people want the XYZ data to match car postion, thus NOT allowing the cad to be moved. Which is easier? Move the cad (hopefully the right way) or type in a value for the axis offset? Once you've done it once or twice, it is just plain easier to use the alignment offset. Also, if you are using a fixture, and you move the cad based on the values stamped on the fixture, then start checking the fixture, and find that some yahoo stamped the X value as 2312.35 instead of 2321.35, then you have to go back and move the cad (AGAIN) or you can just type in the correct value for the X offset in the alignment, do CAD=PART again and keep going.