Accuracy Of Holes

[chips&more]

When I am working on separate pieces requiring accurate positioning of with the CNC, I spot the holes with a countersink, drill and undersize hole, run a circular pocket routine to the diameter required for reaming and finish with the ream. The circular pocket routine eliminates any backlash considerations and the ream will follow the hole defined by the pocket.

I put a 3 x 4 grid of 3/16 reamed holes on my CNC mill table for mounting a sub plate. When I have work that exceeds the work envelope of the mill, I can shift the sub plate and appropriately redefine my coordinates and continue machining. I have not had any problem with mis-registration for these light press fits.

CNC definitely has its advantages! I only have manual, so I’m forced to use an undersized end mill then ream to size for any critical hole locating work. If you use a drill bit, you’re asking for trouble…Good Luck, Dave.

 

[RJSakowski]

CNC definitely has its advantages! I only have manual, so I’m forced to use an undersized end mill then ream to size for any critical hole locating work. If you use a drill bit, you’re asking for trouble…Good Luck, Dave.

Nothing wrong with the manual approach. As long as you are careful about moving to your location from the same direction each time.

I use the pocket routine because I can go slightly undersized for the finish hole without having a huge inventory of end mills. Having a DRO will also aid in eliminating lash issue to the resolution capability of the DRO.