Probably the number one issue for hobbyists is clearing chips. If you’re already close to the “edge”, you’ll break the cutter just as surely as dialing up more chip load by any other means would.ģ. Hence, a lot of runout, as a % of tool diameter, is increasing your chip load by that same %. Runout places most of the work on just a few or even one flute depending on how the flute is oriented relative to the direction of the runout. I mentioned it is too much chip load that breaks cutters. It’s pretty hard to accurately measure your runout on tiny endmills, but it is important to keep this source of trouble in mind. Replacing it immediately improved my results. I was convinced my cheap collet chuck was at fault, but I eventually tracked it down to the brand new collet. It looked perfect, but I was breaking 1/8″ cutters in it right and left. I had a brand new ER32 collet one time that turned out to be bad. Runout can also be made worse by your tool holder. Even pro-grade CNC machines can run into this problem over time as bearings start to fail. Hence a small cutter tolerates very little runout, and the smaller the cutter, the less runout that can be tolerated. This is a real problem when micro-milling because you should think of runout as a % of the cutter’s diameter. Small hobby machines typically have more spindle runout than expensive pro-CNC’s. Reducing the rpms balloons the chip load, and it is chip load that breaks cutters. Never reduce the spindle rpms much without reducing feedrate first. Here are a few thoughts of where to look for problems when you’re breaking small cutters:ġ. Our G-Wizard feeds and speeds software takes all this into account, and is well-suited to providing feeds and speeds for your tiny cutters.įor best results though, you have to go beyond the feeds and speeds. For example, the geometry at these scales is such that the rake on the cutters is almost always negative. The feeds and speeds formulas and calculations that work reasonably well for larger cutters need quite a bit of adjustment for smaller cutters to account for these changing conditions. Cutters smaller than 1/8″ or about 3mm live in a different world than most of our cutters are used to. First thing is first, you need to have proper feeds and speeds for these cutters. Over time certain questions and queries start to stand out, and one I hear a lot about is that machinists are breaking their delicate micro-mills and other tiny cutters too often, and they’d like some pointers on how to avoid it.
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