Milling bits for brass?

[Shopgeezer]

I have heard this suggestion for brass for drilling and milling but have no idea what it means in terms of tool geometry. In practical terms, how do you modify mills drills and lathe tools for brass? Looking at diagrams of rake angles on tools makes no sense to me in terms of negative angles.

 

[alan.crawley1]

Been busy in my workshop today making parts for a lathe and my mill. I tried to mill some brass bar for a lathe part but kept running into problems with the mill digging in and either stalling or jerking the part out of the fixture.

I've tried slow feeds, made sure to not be 'climb milling' and have very sharp high quality tooling.

Am I forgetting the chicken giblets or something else? (Sorry Zee, no tan M&M's to offer the machine Gods.)

Been cutting steel and aluminum all day without a hitch...

So, what am I doing wrong?

For the best part of a century I have used HSS in a fly cutter successfully.

 

[stanstocker]

Just take a small stone and stone a narrow flat on the cutting edge. This will give a zero rake cutting edge. Perfect for brass, worthless for steel or aluminum. Mark the tool in some way, such as a paint pen band so it doesn't get used for the wrong application. If you do a lot of brass, it's worth having a dedicated box for zero rake tools in the tool chest, saves looking around for the one you know you have somewhere

The flat only needs to be a few thou (US thou as in 0.001 inches) wide, just as with drills.

 

[Shopgeezer]

When you say a "narrow flat" what angle are you holding the stone in relation to the cutting edge? Are you trying to increase the angle of the existing cutting edge, or make it dull? Having trouble visualizing this.

 

[stanstocker]

You would stone the acute angle so the edge is on the axis of the tool. You don't touch the clearance angles at all. If you hold the tool in your right hand, with the cutting end facing your left hand, the stone in your left hand moves towards your right hand.

If you do a search on "modify drill bit for brass" there are several youtube videos that will help.

 

[johwen]

I have heard this suggestion for brass for drilling and milling but have no idea what it means in terms of tool geometry. In practical terms, how do you modify mills drills and lathe tools for brass? Looking at diagrams of rake angles on tools makes no sense to me in terms of negative angles.

Instead of a positive cutting rake on the cutting edge of the say lathe tool you have a zero or maybe a 1 degree negative rake on a drill or a slot drill/ end mill cutter the leading g edge is reduce to a zero rake or a slightly negative rake. This stops the digging in when machining brass. Hope this helps Johwen