Fast way to create bearing seats (holes w/ counterbore)

[cjjonesarmory]

My small business makes a product that requires us to cut a bore with counterbore to install an R8 ball bearing (.500" ID / 1.125" OD and .311" thick) into a .375" thick aluminum plate.

Long story short, I need to cut down the time it takes to make these plates and I have been looking for a cutting tool (combination drill/counterbore maybe) that could drill the center "through hole" for the shaft, as well as counterbore the hole to the proper diameter for the bearing. As of yet, I haven't found a tool for this purpose that is large enough, and has the proper diameter. More details are below:

The plate is a solid aluminum 6061 plate that is .375" thick. The bearing needs to have a slight interference fit (press fit) so that the outer race does not rotate in the seat during operation. That means boring a hole .311" deep with a diameter of 1.124" for an interference of 0.001". Tolerance is +/- 0.0005" (half a thousandth). The remainder of the depth is "bored through" at approximately .98" diameter to create the bearing seat for the outer race.

I currently use a CNC Bed Mill and a "jig plate" that mounts several of these parts on the machine at the same time. The CNC Mill is pretty basic and doesn't have a lot of advanced features like an auto-tool changer, etc. In fact it (originally anyway) was a Novakon NM-200 CNC mill. We run Mach3.

So far it has been faster to simply let the machine run a hole pocketing program (hole pocketing roughing operation followed by a finishing profiling operation) using .5" diameter HSS/TiN coated 4-flute end mill.

In the past, I predrilled the plate using a 15/16" (.9375") drill, then followed up with profiling operations to finish, but it was actually faster to let the machine just run the pocketing operation with the end mill rather than switching out and re-setting the tools in the CNC Machine between the drill and the end mill. It was still faster than drilling the plates by hand and then mounting them on the jig especially since I prefer to do all the hole-drilling (there are more holes and features than just the bearing hole) on the CNC machine without moving the part for maximum accuracy.

Just keep in mind, that this is a home-based business, and my resources are pretty limited as far as obtaining advanced products to do this the "best way" for a large high-production facility, although I DO consider this fairly high production for a home based business. So, I just have to do it the "best way I can". What I mean is, it would seem to me that a drill/counterbore tool as described above would be the best way to solve the problem rather than doing a complicated production process involving other machines. I just can't seem to find a tool of the proper size that can obtain the required press fit. Other suggestions are welcome!

I would love to attach a plasma cutter to my gantry machine and pre-cut the aluminum plates, but for now that exceeds my budget.

[levelzero]

True switching to a 2 flute end mill. You have to feed them half as fast but you can normally get away with 150%-200% more depth which ends up speeding up the whole process.

Outside of that you may have to have a cutter custom ground, and even then I don't know if you can consistently hit the tolerances with a single tool/operation.

Depending on your spindle speeds carbide 3 flute high helix cutter might also yield some nice gains.

[cjjonesarmory]

Thanks for the reply. I know it's been a while, but I was reviewing some old posts and realized I never saw this reply.