[Jim27]

Just learning machining and used a 3/8 HSS end mill to bore (spiral down) about a 1.5" hole in 0.5" 6061 plate on a CNC. Ended up with lots of burs on the top side and some on the bottom. I am thinking I would have a lot less of this if I bored the hole undersize and then cleaned up the hole with more depth per pass. I could chamfer the edge but didn't set up for that operation or have the tool for that - that is a fairly obvious solution and not really my question. Looking for suggestions to get less burrs.

[coherent]

Most important is your feeds and speeds. Without knowing more it's hard to say exactly what would help. Most CAM software especially the more recent HSM and Inventor HSM Cam allow for a finishing pass with a very light last pass/cut that will help clean things up. Generally speaking though it you're getting burrs with 6061 aluminum using a HSS end mill, your feeds and speeds/rpm need adjusting or your end mill is dull. A high helix end mill made specifically for aluminum will also give a better finish and cleaner cut.

[CNCMAN172]

Switch to Solid Carbide when working with aluminum and you will be much happier with the finish.

[Jim Dawson]

Climb cutting at least the finish pass will help. Razor sharp tools and kerosene or WD40 coolant is a big help also.