CAD=Part Question

[keith]

When creating an alignment with CAD data imported, the message box states that CAD=PART cannot be undone. Please explain this.

When I import the CAD data, measure my features for each datum, and create the alignments, I do NOT click on CAD=PART until my final alignment when in DCC mode. Then I program the part. After running the first part, I replace the part with another. The program measures those datum features, adjusting for manufacturing differences. Does the CAD adjust then to the new part features?

Is there a way to unload the CAD data and read in new data? I want to change the alignment to offset the X,Y,Z origin point so the points I'm checking will be closer to 0 instead of + stock on one side and - stock on the other.

Thanks,
Keith

[keith]

oops! using 3.7 mr3

[Paul Sarrach]

Read these threads. As I state if you are using CAD, use Iteritive alignment, you never USE CAD = PART

http://pcdmisforum.com/showthread.php?t=2400

Also do a search on CAD = PART, this subject has been addressed many times. Its good reading.

[Farmer]

The DMIS people at our other divisions have told me not to use CAD=PART. I have never received an explanation though. Could somebody please explain?


*uses CAD=PART all of the while*

[\v/inston]

it can't be undone but it can be done again.

[ag162]

Hello,
Cad=Part is a bad feature. It can not be undone and the model along with the part have been known to skew the alignment and many attampts to realign just make it worse. Therefore I always promote the iterative alignment.

VP A.Gore

[Schrocknroll]

Even without iterative alignment, if you pick the initial features for your alignment from the CAD model they will always be linked together. The relationship between CAD and part alignment is all about the theoretical values. As long as the theoretical values of the features used for the initial alignment match the values of the same features on the CAD model, then all will be good.

I'm pretty sure that's all in the world CAD=PART does is correct the therotical values of the features used in the 1st alignment. I say this because I clicked on CAD=PART and watched them change.

HTH

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

The broad statement that CAD=PART is a bad feature is totally misleading. I build gages and the ONLY way to pull CAD and the gage together in the build stage is CAD=PART. Align to the tooling balls, rotate to the proper axis direction, set your offsets, and CAD=PART. This way I can bump tooling ball numbers around to bring in as much of the gage as possible without sending it back to CNC to be recut.

If all you're doing is running parts then I might agree within some limits. When done properly CAD=PART is a very stable and repeatable method of aligning your part. When I do second party gage cerst, part layouts, and final gage certs I use iterative alignments because the part will see the datums and not tooling balls, but there are times when an iteritive doesn't work nearly as well as CAD=PART. I suggest learning to use BOTH methods and becoming familiar enough with them to decide which will work best for you in a given situation.

Bill

[Matthew D. Hoedeman]

The broad statement that CAD=PART is a bad feature is totally misleading. I build gages and the ONLY way to pull CAD and the gage together in the build stage is CAD=PART. Align to the tooling balls, rotate to the proper axis direction, set your offsets, and CAD=PART. This way I can bump tooling ball numbers around to bring in as much of the gage as possible without sending it back to CNC to be recut.

If all you're doing is running parts then I might agree within some limits. When done properly CAD=PART is a very stable and repeatable method of aligning your part. When I do second party gage cerst, part layouts, and final gage certs I use iterative alignments because the part will see the datums and not tooling balls, but there are times when an iteritive doesn't work nearly as well as CAD=PART. I suggest learning to use BOTH methods and becoming familiar enough with them to decide which will work best for you in a given situation.

Bill

HEAR! HEAR!

I use CAD=PART 100% of the time (even with the rare iterative alignment!) and I NEVER have any problems with it. You can NOT un-do it, but you can RE-DO it as many times as you like.

[ag162]

In ref to Bill,
When I was certifying gauges or check fistures, I would do an iterative to the datums and after locking them into place for accuracy, I then would check the tooling spheres for verification of their location. Then delete that prg and do a new prg using cad=part with the correct tooling locations. Manipulation is easier with cad=part, but allows for mistakes if you are unfamiliar with the process. It is all in the programmer and how he/she wants to do it. Both ways are repeatable and accurate if done correctly. As for free state parts, resting on magnets, I personally like the iterative better.

VP A.Gore

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

Al,

That's fine for a gage thats already built, in fact I use it myself, but one thats is BEING built this doesn't work because the locators and nets always come in full and as a smaller qualifying hole. You tell the gage maker how much to take off to bring the nets in tolerence, and what direction and how far to move the holes to bring the locators in tolerence. An iteritive doesn't work here at all because every thing needed to align to is known to be off location and out of tolerence for size.

Bill

[ag162]

Wow,,,,,I haven't had to deal with that in almost 8 yrs. We built check fixtures in Atlanta and I had to work with tooling on these items. But, the datums were in first and we moved the rest accordingly ( stab pins, surfaces etc ).

VP

[keith]

I used an iterative alignment and found the points to be MUCH closer to CAD than when using a CAD=PART. Rather than having most of my points +/- .005", they're now showing +/- .0007". Now the question becomes which one is right!

HAHA

This QC work doesn't seem to be very precise...

[\v/inston]

i wish i had a PART = CAD button.

[Mike N.]

CAD=Part and Iterative are two separate "TOOLS" to get to a common goal....inspect the part. It is totally up to the programmer as to which one to use. They both have equal use in creating a useable alignment to continue to measure the part. CAD=PART will exactly match the CAD origin and rotation to the part origin when it is pressed. Iterative will exactly match the measured hits on the part to the same points on the CAD model, and when using more than six points to do this could create a "best fit" condition that will not be exactly what some people are looking to do.

I use CAD=PART most often for "simple" alignments using the 6pt method (3pln,2lin,1pt) on straight forward parts.

I use Iterative on complex non-conventional surfaces like a computer mouse or something that doesn't have ANY straight features.

Both methods are good for different parts!!
It isn't necessary to say that one is DEFINITELY the way to go

lets not start an pcdmis myth here folks

Mike N