Base Alignment vs. Start Alignment

[[La...]]

Hello, I am new to CMM programming and I am having trouble with understanding alignments. More specifically base and start alignments and the difference between the two. Could someone break this down for me?

Thanks!

[[Cl...]]

Start Alignment simply locates (tells) the software, where in the volume of the measuring space the part is.

So, now the software knows the parts XYZ location relative to MCS (machine coordinate system), and it can now measure the Base alignment.

[[Du...]]

start alignment are generally much simpler alignments than the base alignments, usually easier to reach features or features that are quicker to manually probe. in the attached screenshots my base alignment and start are similar but in the start alignment i use a single circle.

[[Ke...]]

Base Alignment: Foundation of your program, this tells the system exactly where the part is and how it is located, and is the starting point of every measurement in a program (depending on the programming style, some people use this more directly than others)

Start Alignment: A rougher locating, can be used for an approximate find in order to allow the base alignment to run more consistently if part locating on the cmm is a bit less precise. It is also useful to create a simple way to manually teach a part location manually on the cmm, particularly in the case of complex base alignments. 

These are also both part of the hierarchy of inheritance for alignments, with the order being CMM System->Start Alignment->Base Alignment->Secondary Alignment with Base as parent->Secondary alignment with Secondary as parent. Calypso will work its way up that chain referencing back until all degrees of freedom are fully defined

[[Sv...]]

If it’s still the way calypso works, while programming you have to define the base alignment fist (its the base of the calculation in the software) and after that all other alignments. But then in cnc mode he will proceed as mentioned above: start -> base -> ….

Edited August 7

[[Ma...]]

As mentioned create your base alignment first. Then you can select several features to roughly locate your part as your Start Alignment. Calypso will then display the distance from your start alignment is from the base alignment. It is important to note that your Start Alignment doesn’t not have to be the same features that make up the Base Alignment. That is the beauty of this method. Choose features that define X, Y, Z. It could be just three simple points. Also the Start does not necessarily need to have the Rotation in Space or the Planner filled out, only if applicable.

The intent is to quickly locate a part:

• if fixturing is not repeatable 
• you need to move the part around the table occasionally 

 

[[Je...]]

Base alignment should robustly define your part in the measurement volume (strive to achieve a robust definition for 6 DOF).  Start Alignment is a "locator" for the Base Alignment to start.  It can be as simple as a single point to define a single DOF.  IE - you have a fixture that is often moved laterally on your CMM but the Y and Z location is repeatable (as is the rotational constraints) as if it were slide against a rail.  A single point on the -X or +X side of a feature would be enough to inform CALYPSO on where to look for the part and conduct a Base Alignment.  Using a Start Alignment is a highly preferable method to reducing the quantity of "loops" and improved break conditions needed for Base Alignment calculation/repeatability.  
Important note: Start Alignment features are intended to be REAL features, not theoretical/calculations (with a few simple exceptions).  It is meant to be significantly simpler in its structure as to make the start-up task for an operator much easier.  Even in full CNC mode, this is still advised to improve your repeatability.  I STRONGLY advise the use of a Start Alignment for any part that will see any quantity of production type measurement.  Even with fantastic fixturing, you will see an improvement in Base Alignment break conditions (hint: I use a CNC Start Alignment and no Base Alignment looping/break condition in 99% of cases and still pass GRR without issue)