Alignment methods on a fir tree root

[Liambo734]

I have to align a blade using the fir tree root, there are no basic points or basic dimensions to locate points on the root. There is just a line struck through the root with a Datum A symbol attached. I have a cad model of the final ground blade with the root geometry. I was wanting to get some opinions on the best way to align a blade root, best fit points on the flanks, scan sections and insert rollers tangent to the scanned lines, Iterative alignment? TIA

[dwade]

An iterative alignment is the only logical method of aligning the part.

[neil.challinor]

Iterative alignment and the target points / alignment method should definitely be defined clearly on the drawing. Generally when aligning to fir tree roots you will be trying to simulate rollers fitting into the flanks at various positions. And iterate to minimise any alignment error. I've done this in the past using a variety of methods depending upon what CMM the program will be run on...

1) Touch trigger vector / surface points on each flank, offset back along the vector by the roller radius, construct lines perpendicular to the vector, intersect the lines to simulate roller centres
2) Scan across root flanks from top to bottom then construct scan minimum circles (fit a given diameter into the scan) to simulate the roller centres.
3) If the roller Ø is the same as the probe tip Ø and I have a scanning head, use a basic center scan (or equivalent vector point adaptive scan strategy on newer versions) to simulate roller centres.