The issues I'm having with centering are when trying to set the work offsets before running a program on parts that don't have any clear defining edges to reference.
For example, I got a split 65 tooth 219 sprocket from Azusa and wanted to open up it's bore, drill some bolt holes, and some lightening holes. The sprocket isn't split exactly through the center, and the split isn't a straight line. They cut the sprocket as one piece then just crudely shear it in half. I have a little laser alignment tool that makes a tiny dot at the center and concentric circles but my mill doesn't have enough z travel to make the circles bigger than an inch or so. For this part, optimally, I would have widened the laser circle to the tooth root diameter but it would just barely go big enough to pick up the one inch center halfish bore. I set the center the best I could this way but with the z height one part thickness above the part. I let the program run and paused it for measurement as it went around on the bottom pass, just over the part and it was off-center by a millimeter. I know at that point I could have just gone back to home, bumped the y back a hair, reset it, and run the program but I really wanted to figure out a quicker way to find center for the next seventy odd shaped parts that I have to machine from scratch or modify. My next idea, I thought was a good one. I taped a sheet of stiff paper to the sprocket half and used my drafting tools to locate a dot perfectly in the center. This process took a few minutes. Then I used the dot on the laser to pick up the center, ran the program at non cutting z height, and it was off by 2mm on the -y. Then I thought, maybe the laser isn't that accurate so I switched to a broken drill bit that I cut to a tiny point on the lathe and it lined up with the laser mark. Ran the program again, still off. So then I went back to cad, checked the dimensions, went to cam checked dimensions, regenerated code, repeated entire process above and it's still off. My next thought was that I was tired, possibly psyching myself out and over thinking things so I set z and hit run. It flew through the part but when it got to the apex of the arc, it was obviously off. I'll be cutting a fresh one from scratch out of a rectangular plate today!
So to solve the centering issue, I designed a little tool with a center degree wheel with cross hairs and a tiny hole in the center, and four graduated arms that can pivot around the center that indicate on the degree wheel. The idea is to be able to clamp the arms to a piece of stock at known measurements and angles, then just pointing the origin to the center of the tool, removing the tool, and running the program. I have it all drawn up in CAD and the profiles worked out on cambam but am stumbling around on the engraving part. Cambam imports it but doesn't recognize the origin for the engraving from the dxf. It puts it off to the side??? Anyway, what I'm doing today is trying to figure out if I'm about to waste my time building a tool that's already available,......or worse, isn't necessary at all because I'm missing something obvious.
So on that part in the second picture you posted, if you had bought that from someone else and wanted to write some code and mill some modifications into it, how would you locate the origin? That's a beautiful part by the way! What is it?
I really appreciate any pointers you may have!
