Barrel / Cylinder alignment

[borne2fly]

I just fit a new cylinder to my 62 Police and found the same misalignment with the edge of the hammer face and two nipple ports in the cylinder. My remedy was to Dremel grind out the sides of the two offending nipple ports to accommodate the hammer nose. Little touch up blue and all is well.
Now both cylinders are fit to the frame.
I did have to do some ratchet filing on both to make them work smoothly which I'm told is common with this five shooter model.

I have to wonder how things like this happen assuming all the parts are made on modern CNC machines, which can often hold accuracies down to a few tenths. One would think the same error would appear in all five locations or not at all.
But if this were machined manually it’s a little easier to understand.
I use an index head for work where precise angular displacements are required, but this old index head only has templates for specific angles. Unfortunately, 72 degrees (divide by 5) is not a common one, and I would need to use a rotary table or the digital display, both of which would be manual operations. If *this* is how they made it, then maybe I can understand.

 

[M. De Land]

I have to wonder how things like this happen assuming all the parts are made on modern CNC machines, which can often hold accuracies down to a few tenths. One would think the same error would appear in all five locations or not at all.
But if this were machined manually it’s a little easier to understand.
I use an index head for work where precise angular displacements are required, but this old index head only has templates for specific angles. Unfortunately, 72 degrees (divide by 5) is not a common one, and I would need to use a rotary table or the digital display, both of which would be manual operations. If *this* is how they made it, then maybe I can understand.

I think probably the cylinders start life as investment castings and the chambers and nipple ports are finish gang reamed and CNC multiple milled simultaneously. My guess is the ratchet star is milled first indexing both the chamber boring/reaming and bolt notch cuts.
The chamber reamers and milling tools have a plus and minus tolerance spec as they are sharpened periodically and the spindle head bearings wear over time also computer numerated control (CNC) (the wonder of mass production driven equipment) is only as accurate as it's calibration to the machine it is serving so there are many places along the production schedule for tolerance mishap even in modern manufacture.

 

[borne2fly]

I think probably the cylinders start life as investment castings and the chambers and nipple ports are finish gang reamed and CNC multiple milled simultaneously. My guess is the ratchet star is milled first indexing both the chamber boring/reaming and bolt notch cuts.
The chamber reamers and milling tools have a plus and minus tolerance spec as they are sharpened periodically and the spindle head bearings wear over time also computer numerated control (CNC) (the wonder of mass production driven equipment) is only as accurate as it's calibration to the machine it is serving so there are many places along the production schedule for tolerance mishap even in modern manufacture.

Indeed, tool wear and spindle/collet runout will erode tolerances. I would expect these things to impact the workpiece fairly uniformly. Machine wear (Ways and Gibbs) however can introduce errors that are very position dependent. And if this is responsible for prod your-of-spec parts then it needs to be pulled offline. Then again, who knows what the specs are on these guns?