Mill, Drill, or what?

[TomWS]

I received a nice Kitchen Knife kit for Christmas where I need to add a handle (Knife Scale, I guess they're called). The kit includes some press together rivets to help hold the sides in place (the sides are also epoxied in place so the rivets may be entirely decorative). However, I'd like to use mosaic pins instead of the rivets. The pins are 6mm diameter, but the holes in the tang are oval, rounded slots ~5.7mmx3.7mm, so the holes need to be opened up.
Here's what the tang looks like, the two holes are shown with arrows:


I've have read that the tang is very hard metal and tough to drill. What is the recommendation for opening up these two holes to 6mm round? I have a LMS3990 Mini Mill that I can use to Drill, Mill, or ream these holes precisely in the center of each oval, but I'm not sure what the best method would be. It seems as if a twist drill would catch in the oval opening...

 

[compact8]

Plunging with carbide end mills should work. Carbide can cut into HSS so unless the material is harder, it should be OK. To minimize wandering, it will be better to do it in several steps, e.g. starting with 4 mm mill, then 5 mm and finally 6 mm.

 

[TomWS]

Thanks for the fast reply!
Should I care if it's 2 or 4 flute end mill? I'm going to have to acquire the mill in any case (I only have imperial HSS mills at the moment).

 

[compact8]

Should I care if it's 2 or 4 flute end mill?

4 flute should be better because the core is larger hence the tool is stiffer and wanders less.

 

[TomWS]

Rather than buying a bunch of small carbide end mills for this task, I wonder if I can use a tapered ball nose bit instead. I have these for CNC carving and I am thinking of using a Whiteside SC66 bit which is a 1/8" diameter at the tip and tapers up to a 1/4" diameter at the shank.

ISTM that if I slowly lower this into the center of the slot, lubricated with cutting oil, of course, that it should open up the slot to round, stop as soon as the opening is fully round, and then finish off the cut to 6mm using the suggested end mill.

Will this work or is there some hidden gotcha using this kind of bit?

 

[Mitch Alsup]

I think I would be tempted to alter the pins to fit the holes already present.

But realistically, you want the rivets not any harder than brass or straight copper.
This allows you to work the pin around the hole in the scale with a peening hammer.

 

[addertooth]

The decorative mosaic portion of the handle pins don't have to go all the way through. Go to the link below. Then drill out the center of them, put your decorative pins and epoxy in the "cup" you just made by drilling the center of the pins, then screw them in. You will notice the threaded portion is a MUCH smaller diameter than the big ends of these handle pins.

screw in handle pins with big heads

Here is a second source.

Screw in handle pins with big heads 2