Bolt Circle Evaluation Help

[[Za...]]

What evaluation method is best for a bolt circle Dia of threaded holes? We have been using LSQ but just noticed that the number changed quite a bit when switching to GX (Outer Tang.) I would think that it wouldn't matter since it is just going off the center of the 4 holes.

[[Jo...]]

How are you constructing the BHC ? Recall features, NOT feature points. That would give lsq of pattern from individual centers.

[[De...]]

In my opinion, the best bet is to use true position on the holes independently as it gives you a lot more relevant information to work with.

A check on the center of the bolt circle will not give an accurate idea of the location of any of the holes because it is by nature a result which is created based on the combination of the actual results for the centers of all of the holes. So it will always leave you with additional questions if the results are unexpected - ie bad location / size of bolt circle.

You have to measure all of the holes anyhow so you should already have the data you need to check true position individually.

That said, if you use LSQ and one hole is out, the error will be averaged between all the holes, if you are using Outer Tangential then your circle will be fitted between the three points which will create the smallest circle and will simply ignore any hole center that falls outside the smallest circle created from the other three points. With only four points being used, it is almost certain that you will always have one point thrown out altogether. I am pretty sure the only time one point would not be ignored in the final result would be when all four points fell on a geometrically perfect circle.

[[Za...]]

I am using Recall Feature (not feature points).
The print has a BC Dia callout on it so I have to report that. I could use the TP for my own piece of mind and reference it on the report.

[[Jo...]]

Derek's method will also let you report the angle, which typically is in conjunction with BHC Dia.