[Winspear]

Hey all. New here, been lurking and learning for a while and have had fairly good results with my first week on CNC with some plastics and wood. I tried to do some brass today in an attempt to finish up a gift for my girlfriend for Christmas. No luck due to tool breakage. Would really like to be able to get it done in time!

The pieces I am cutting are from 3mm brass. Mostly ground down to result in 1mm sheets with 2mm pegs sticking out. I broke my only 2mm end mill and two 1.1mm carbides. I believe I had the feedrate set too high at first on the 2mm, at 50mm/s. I went down to a tiny 4mm/s on the 1.1mm end mills but they still broke almost instantly. RPM was maxed at 20,000 and I was using pass depths and stepover of just 0.2mm. All bits broke on the very first stroke. Any suggestions?
Cheers

[Winspear]

P.S. Should this be in woodworking machines due to my CNC, or..?

[BarryB]

I have a woodworking mill that I've cut metal several times. The smallest bit I've used was 1/8 inch but my depth was still only about .2mm each pass. It worked fine for that, no breakage, but I did have problems with deeper cuts. I'm thinking a .2mm cut is too deep for a 1.1 mm bits. Oh, mine was air-cooled too. I understand you can cut deeper/faster with oil/mister cooled, but I don't have that option here yet.

[tanvon]

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[MonoNeuron]

Brass can be a real bugger to cut if you have a positive rake angle on your cutters. You need a zero rake angle to stop the cutter from digging into the metal. Are you using a spiral end mill? Try a straight sided milling cutter like the one below and if you can just hone a flat along the cutting edge to make it zero angle ( I would try it without doing that first though ). Try a wood router bit if you have to. You also need a fast spindle speed.
Hope this helps a bit.
Rich.Attachment 266474