CNC Boring Bar vs. Interpolation?

[txcncman]

drills wander , reamers follow
some machining practices are hand downs which have been used for years and are still practiced because they are proven to work .
boring technology isn't a thing of the past and some of the boring heads that are being manufactured are the best that have ever been , and in a few years they will be even better .
I'm not by any means saying that reamers are not a good tool to use but there is a time and place for them and in my opinion this isn't one of those times .
I do not agree with " the magic of cnc " statement in this case , and I disagree with interpolating the holes out and hoping that they would be good enough as well
take it for what it's worth or not , I'm just trying to be helpful and pass along some worth while knowledge

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Do you know what a head plate for a diesel is even for or how important the tolerances really are? If it is what I remember a head plate to be, it is a plate that is bolted into place on the cylinder block to hold the cylinder sleeves in place and to mimic the stresses of having a head bolted into place while boring the cylinders. I am willing to bet if the plate is 1/16" off location or size, it would still work. The call out for the 0.6325" dimension is so the holes will have a slip fit/running fit over 0.625" dowel pins.

[RICHARD ZASTROW]

Could be a closer fit to a 16mm pin. A jig borer reamer doesn't follow a reasonably drilled hole.

Dick Z

[Boots]

I can't beleave these holes are for a .625 or 5/8 dowell pin. That's just plain dumb. Interpolated holes are only as good as the machine they are cut on. In all the 4 quadrants there will be a line where the axes change direction and backlash occurs and shows up on the finish and the hole will be out of round. A bore Bar may be a better tool here to get position and finish. Rapid to whith-in 1/8 in. on the x and y and feed into position for hole location before boring. Use the proper G-Code for a Bore Bar canned cycle so it stops and moves off center before retracting so as not to hit the finish with the insert. CNC's are Magic but you have to know how to perform the trick.

[txcncman]

I can't beleave these holes are for a .625 or 5/8 dowell pin. That's just plain dumb. Interpolated holes are only as good as the machine they are cut on. In all the 4 quadrants there will be a line where the axes change direction and backlash occurs and shows up on the finish and the hole will be out of round. A bore Bar may be a better tool here to get position and finish. Rapid to whith-in 1/8 in. on the x and y and feed into position for hole location before boring. Use the proper G-Code for a Bore Bar canned cycle so it stops and moves off center before retracting so as not to hit the finish with the insert. CNC's are Magic but you have to know how to perform the trick.

What size hole would you call out for a slip fit/running fit on a 5/8" diameter dowel pin?

How much out of round will it be?