Finding The Center Of A Boss On A Small Casting

benmychree said:
I agree, there is also the hermaphrodite caliper for this sort of work, it has one leg like a inside caliper and the other with a scribing point; bear the caliper leg against the boss diameter, adjust the scriber to approximate center, scribe a line and move the caliper leg around the part in 4 positions and scribe lines; their junction will be the center.
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I have seen these, but did not know their purpose. Thank you!
 
The Co Ax indicator is worth its weight in gold; it preforms internal and external indicating plus indicating from prick punch marks; it also is expensive! There are knock offs to be had at a cheap price, but you get what you pay for ---
 
Will the Coax Indicator work in the example given by the OP? What I am concerned about is that the outside edge of the boss may be the rough surface of the casting and I think the Coax indicator needs a smooth surface.
 
You are correct in that the Co Ax would not work for that application very well; If I were doing the job, I would layout the center lines, trying to center the bosses as best as can be possibly done to make them ALL as close to centered as possible. One has to realize that this is not a perfect world and bosses may not always be at proper centers due to the foundry process being an imperfect art; that is what the layout process is for, to divide up the imperfect into something that is a compromise and allows a part that will serve its intended purpose. This is quite a simple casting, so it should not be hard to accomplish as opposed to larger complex castings. In the shop I apprenticed in back in the 1960s, we had a full time layout man, always busy, saving the machinists much grief and lots of spoiled work ----
 
Also, CoAx indicators don't really fit well in my Sherline mill. This makes me sad (sad emoticon here, or not), as I have one. I am thinking of getting the longer column just for that reason.

I really like my Sherline stuff, but the vertical travel on the mill can be quite limiting.

Cheers,

Tom (the OP)
 
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