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Workpiece Offset Machine Coordinate vs Manual Alignment

Nicholas Norton

Hey all, 

We've got some bright Machinists here that are tired of having the CMM programmer manual align their parts every few months. We get a few repeat jobs once every 6 months or so, and by that time either probe calibration, machine settling or by some other factor I'm not aware of our programs will need a new manual alignment. Afterwards, we unmark these features and let the job run in DCC mode. (sidenote, my hunch is that the manual alignment feature's measured coordinates are married to the previous probe alignment, so after a new alignment they don't 'match' the expected coordinates for DCC mode)


Anyways here is my question/discussion; What are the pros/cons of using a manual alignment vs a know x,y,z position for part programs?
I don't have a good answer for rebuttal to our machinists, and I'm starting to wonder if some of our programs would be better off with hard-coded workpiece offsets. We use an Erowa chuck with custom fixturing for 70% of our jobs, so these parts are highly repeatable. 

What are your thoughts?

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  • If you're using an Erowa chuck that is permanently bolted to the CMM bed and never moves, then it might be better to have a program that aligns that chuck and saves an external alignment.  Then, instead of having a manual alignment that gets unmarked in each of your programs, you would just recall the external fixture alignment.  That way, whenever the fixture position needs updating, you just run the fixture alignment program and it's position is updated for all programs, negating the need to redo the manual alignment in every program you need to run.

  • in reply to Neil Challinor

    I was thinking of this, but our custom fixturing vary in height and holding location for the parts, despite being welded to erowa blocks. So then I would need some xyz offset from the erowa alignment to keep everything in agreement. Correct? Here is an image of one of the fixtures. We have 3 part styles for this job, 3 corresponding fixtures which have different heights. We have give or take 15 different vices and fixturings to choose from for all our jobs...lots of small, complicated parts. 

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  • in reply to Neil Challinor

    I was thinking of this, but our custom fixturing vary in height and holding location for the parts, despite being welded to erowa blocks. So then I would need some xyz offset from the erowa alignment to keep everything in agreement. Correct? Here is an image of one of the fixtures. We have 3 part styles for this job, 3 corresponding fixtures which have different heights. We have give or take 15 different vices and fixturings to choose from for all our jobs...lots of small, complicated parts. 

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  • in reply to Nicholas Norton

    I prefer both readpoint and external alignment. Based on the picture you provided, I plan to add slot locations with pictures and notes (e.g., X10 Y10 U10 with M8 bolts) to improve fixture location accuracy. This will help operators follow the setup more effectively.

    For readpoint alignment, it works better with progress alignment, offering improved efficiency and convergence.

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