Controlling Burr Formation within Small Intersecting Holes

A reader recently used the “Ask an Expert” feature of our Micromachining Zone to ask about a challenge in milling with a relatively small tool on one of his existing machines.

Question

At the junction of a 1 mm hole and a 0.3 mm hole, we struggle with burr formation. How can we reduce this? We use three drills, for center, pre- and finish drilling.

Response from John Bradford, micromachining R&D team leader for Makino

This is an area where much time and research has been spent. At this time, my only recommended process countermeasures might be:

● Support material—After machining the first hole, is there a means to plug or fill the cavity void, thus creating a "backing" material for the intersecting hole to meet? This helps reduce or eliminate the chip formation as the tool is breaking out, or the chip pushing away when the drill breaks through.

● Altering workpiece temperature—Generally speaking, burr formation characteristics change as the temperature of the material changes.

● Feeds and speeds—Burr formation can be minimized (but not eliminated) by increasing spindle speed and slowing feed rate. However, higher tool wear may occur.

I have also seen several related published papers from UC Berkeley, from Professor David Dornfeld. You can find him here: http://www.me.berkeley.edu/faculty/dornfeld.html.