alignment question

[[an...]]

hello everyone!

quick question on alignments.
kind of a hypothetical scenario for me but I would like to know how to "solve" this problem if ever faced with the task.

so over the weekend I had a little time to basically mess around on our duramax cmm just checking features I don't normally check.
typically our fixtures are pretty solid and most of the jobs we run are repetitive so I don't have to manually alignment every part I put on the fixture.

so I decided create issues by adding a .02" shim on the base of my tool on one side or even shift the fixture .050"-.1" in the Y axis
obviously measurements would change

but how would I correct this if this was actually an issue
instead of manually aligning the part again what are my options?

is there anything I can add to my characteristics to the beginning of the run to realign its actual position
or a plane shift correction???
I saw there is a loop alignment or the true position feature not sure if that would actually fix the problem

I'm no wizard with the calypso system by any means I'm just trying to learn the correct way to tackle any scenario thrown my way!

thank you in advance to anyone with any info!

[[Je...]]

These small amounts would not typically effect your measurement unless you have very very tight clearances for styli entering bores or something similar in terms of navigation. The CMM/CALYPSO use the part itself to define its navigation and measurement values, not your fixturing or machine coordinate system (this is being over simplified). That is unless your measurement plan includes the fixture in its measurement or alignment. This is not typical and, in most situations, not advised.

Adjusting the retract distance and/or the "probing before/after nominal" settings in the Features Settings Editor is enough to mitigate the small amounts you are mentioning if you do encounter a problem.

If the shifts were something closer to >.250" then I would advise a Start Alignment that has increased clearance/retract distances and "probing before/after nominal" settings to allow the CMM to "find" the part before starting the Base Alignment.

Do not make the mistake that many programmers make of using the Base Alignment to "roughly" find the part then use a Secondary alignment to define it closer for the rest of the program. Your Base Alignment should be robust and fully constrain the part in 3D space (all 6 D.O.F.) wherever possible. If you require a method to "roughly" find the part prior to measurement due to fixturing abnormalities or inconsistencies, the "Start Alignment" is the proper method.

[[Ni...]]

Wouldn't the start alignment be used to solve this issue?
You create your base alignment and then add a base alignment with a big retract distance so if the part did shift over in one direction, it should the base alignment with it.
That is my understanding but i could be wrong.

[[Ro...]]

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I would expect that moving the part around a little bit, that your measurement would not change.
Obviously i don't know your company or the kind of parts you measure so i cant be for sure, but if the retract on your base alignment features is bigger than the amount that you moved the part, i would expect Calypso to align and measure the same every time.
I dont work in a production setting, most of what we check is 1-5 parts, so maximum efficiency and speed isn't really an issue with us. I typically set my base alignment feature retract to .250" (6mm) and the remainder to .100" (2.5mm). Inside the box speed set to 30. I do use 1-2-1 loop fairly often.

Jeffrey, i'm sorry to say that i use secondary alignments all the time 🙂
Just today i finished a program where Datum A is a long slice of a cone, and i have 2 flat planes to use that are not perpendicular to each other as base alignment features. So i create a simple 3-2-1 situation, loop it a couple times and let the cmm find the rest.
I do however fill in all the boxes in my secondary alignments, always. I don't leave anything empty to default. its one instance where the 20 seconds i spend adding in features is well spent for knowing it is exactly how i want it.Its just outer space stuff.

[[No...]]

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Just to make sure we're on the same page here: Do you have "Clear existing results" checked when you run a part? Do you select an existing base alignment or do you leave it on "Current Alignment"?

[[an...]]

yes I have "clear existing results" selected

I use an existing base alignment. I just select the job file and do "change current base alignment" and manually touch off the first part I make.

"current alignment" is going off of the last part ran correct?

[[No...]]

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Looks like the correct way of doing it. I asked because it wasn't clear from your first post.
If you do it that way and select the alignment without '(CNC)' extension for the run, your results shouldn't change significantly.
Of course there may be a tiny bit of deviation resulting from slightly different touch points of the alignment features. If that is still too much for your needs, base alignment loops would be the way to go.

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That is an interesting question. I never use this option and I don't remember what the Calypso instructor said 16 years ago 😃
The help file also has no useful information on this. Naturally, I would assume it uses the the last saved manual alignment (not the '(CNC)' version), but since there's already another option for both, maybe it only calculates the BA in memory from the currently stored actuals? I really don't know for sure 🫣

[[an...]]

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what is the difference with using the alignment with the CNC extension?
and how would I apply a loop alignment for normal QC production? ive honestly never used that feature before

[[Ma...]]

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(CNC) means that this alignment was performed by machine - not by manually touching points.
Everytime program finishes alignment then it's saved ( rewritten ). If you place measured part a few MM / INCH left, then next iteration / run of alignment will be moved to new location.
By using NON-CNC alignment program will be starting everytime on same place nomatter where was piece last placed.
For loops it's applied only on first run.

[[No...]]

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Like Martin said, the CNC version is the BA written by the last CNC run, so if your part has moved by a small amount, but the program can still probe the correct points for alignment, the CNC system will follow while the manual alignment won't.
But this is also potentially dangerous, especially with non-rigid parts like the plastc parts I have to deal with.

Because if you run an automated setup (Autorun) with untrained operators and all programs use the last CNC alignment, then if anything goes badly wrong in the alignment phase (while it still runs through), all subsequent parts won't run properly anymore, as the CNC alignment has moved unpredictably. With a manual alignment this can't happen as it always stays in place.

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Well, you basically just open the BA window and add a loop. If you are sure the possible movement of the part is rather small, it may be sufficient to add only two or three loop iterations and that's it. If you expect more variation, you can add more loops and enter an additional exit formula that exits the loop when the deviation between the current and the previous iteration falls below a certain value. I rarely use it, but I think the formula is baseSystem().valueA < .....

[[Mi...]]

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I want to say this again.

I have spent the last year rewriting hundreds of production programs that used an Incomplete Base Alignment as a "Rough" Alignment, then many.....many secondary alignments (50->300 in some cases) to "Refine" the Base Alignment. This practice made the programs incredibly difficult to diagnose and fix errors. Because if a given feature relies on 6 Secondary alignments, all with different features... how long do you think it takes to follow that back through the chain to find where the problem might be?

Looped Base Alignment that controls all 6 DoF is the only way to go. Then secondary alignments for special things to help you find small features that may move a lot. Or we find that we end up using correctly setup Secondary Alignments to help report things in specifically rotated coordinate systems as the Secondary Alignments rotate in a more predicable way than the Position Characteristic does.

Start Alignments for Rough Part Locations if you worry about poor loading, I actually tend to have many programs share a single Start Alignment, and I have the Start Alignment set to Automatic Measurement so it runs every time. That way 1 Start Alignment can set the Start for many programs, sometimes over 75 programs on a given CMM in the case of a part family. This took a bit of work to get right but now it's a huge time saver.

My point is the same as Jeffery's miss-loading the part in the way you suggest should not affect any of your results in the correctly setup program, as long as the CMM can still get to all the features with the part in it's slightly clocked state.

[[Je...]]

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Thank you Michael. You have hit the nail on the head and addressed the main and intended principle behind Start Alignments, Base Alignments and subsequent Secondary Alignments. I personally go as far as to say that with a well designed fixture set up, a proper Start Alignment and a robust Base Alignment, a loop is not typically necessary if using standard prismatic features.

[[Je...]]

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Some summary explanations of more common alignment types:
Start Alignment - Used to roughly define location of part prior to start of Base Alignment. Features are always measured data rather than constructions. Constructions are not allowed. This is best used to define the fixtured location of a part that may be dynamic relative to machine coordinates or if the Base Alignment uses several features in order to complete constructions used as Spatial/Planar/Origin
Current Alignment - Runs off previous part alignment without an update to the Base Alignment. It is rare that this should be selected. If you aren't sure, I do not advise use of this setting. Typically for something that may not need an alignment such as a qualification program. Usually "Load Alignment" is a better option in the event you want to use a fixture for your Base Alignment and it is hard-mounted to the machine.
Base Alignment (non-CNC) - Utilizes the coordinate system defined by the first alignment performed after a manual alignment. The Base Alignment features will always be probed in the location relative to the cmmSys (machine coordinates) or Start Alignment. This is best for parts using hard-mounted fixtures where locations are quite repeatable.
Base Alignment (CNC) - This utilizes the coordinate system defined by the LAST alignment performed. The alignment is updated after every part run and is defined by the CNC rather than the initial setup operator. This is best utilized for fixturing that may not be repeatable or is removed/reassembled after short runs and may slightly redefine locations.

The CNC option allows the alignment to "drift" from run to run as part locations vary. Non-CNC will never vary from its initial pickup position and orientation.

[[Mi...]]

Current Alignment is also useful to you as the programmer if you are testing a program for the first time. You can stop the program sometime after the base alignment, change a strategy, delete actuals, or whatever you need, then start it again to continue on without having to rerun everything that you didn't change.... As long as the part has not moved in any way