Turning brass

[RaisedByWolves]

If your cross slide has a lot of backlash, that will exacerbate your problem. Brass can self-feed with a positive-rake tool so it will act to pull the cross slide toward it, leading to excess material removal. +1 on suggestions for shortening the cutter length, reducing nose radius.

A standard nut and feedscrew have to have some mutual clearance so they don't exhibit excess friction. When moving the cross slide toward the work, the feedscrew threads push against the nut, reducing the clearance on the work-side to zero -- leaving a gap on the other side. When cutting materials like steel, the cutting forces push back against the carriage, but the zero clearance ensures accurate cutting -- the screw and nut act as a solid hunk of metal. If a material like brass "grabs" the cutter, the cutting force reverses, pulling the carriage forward -- and it can, because the threads on the opposite side have all the clearance. To test this, move your cross slide forward using the crank. Then push the carriage toward the work. If the backlash is large enough, you can feel the carriage move forward. If the backlash is fairly small, it might take a test indicator to reveal it -- but it WILL be there. Climb milling on a manual mill can exhibit self-feed related problems for the same reason.

A cross slide and compound lock will cure this.

I always lightly lock both whenever doing anything precise.

 

[homebrewed]

A cross slide and compound lock will cure this.

I always lightly lock both whenever doing anything precise.

Yes. But you have to be sure to repeat the same unlock/move/lock sequence each time you perform a cut. These days I do that on my mill out of force of habit, but it took some time to get there.