I am obviously new at measuring with a romer arm and sometimes i get an irregular part and do not know how i should position it to get the most accurate readings. i like to use our solid marble table as my reference plane, but sometimes i ahve to use planes on the part itself. I am currently working on an end for a steer axle. the part does not sit stable on the table very well and my first time through measuring the part i measured many unconformities. I am hoping it is the way i set the part up rather than the part being a piece of junk.
it could be your surface plate, marble is metamorphosed limestone which is much softer than granite and could be worn, it also reacts vigorously with acid.
it could be your surface plate, marble is metamorphosed limestone which is much softer than granite and could be worn, it also reacts vigorously with acid.