Snapped bit cutting 0.080 aluminum with 1/8" bit


Gwizard seems to be telling me I need speeds greater than 100 ipm to cut 5052-H32 aluminum with any of my bits. I have Amana Tool HSS1622 (2 flute up-cut 1/4″). I had the HSS1620 1/8″ bit but it snapped at 16000 rpm at 100ipm.

The spec sheet from Amana Tool says 0.004-0.006″ chip load per tooth and that SFM = 0.262 * diameter * rpm. Max RPM is 18000. My router goes from 12000 to 24000 rpm. If put in SFM = 0.262 * 0.25 * 12000 = 786. Does that sound right? I put that in gwizard along with the chipload of 0.006ipt.

I don’t see in gwizard where it tells me the depth of cut? I’m nervous to try the 1/4″ bit now seeing as how the 1/8 bit snapped pretty quickly. Am I not going to be able to cut 0.080″ aluminum because my machine is limited to 100 IPM?

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There could be a lot of things going on with this cut that would break the cutter.  Ideally, email me a screen shot of the settings used.

Some thoughts based on the information in the question:

Feeding too slowly is not a problem unless the tool is rubbing, and G-Wizard will warn you about that in the Tips dropdown if it’s a problem.  It doesn’t look to me like it is.

The most likely culprits for tool break I see are:

  1.  Lack of lubrication.  Aluminum has a chemical affinity for your tools and will try to weld itself to the cutter which leads to breakage shortly thereafter.  Even just a light spritz with WD40 during the cut will help tremendously.  See my post on cutting aluminum with a CNC Router for more info:
  2. Excess Tool Deflection.  This is usually due to too much stickout.  I don’t know how far your cutter was extended from the collet, but less is better.
  3. Excess Runout.  If you have a bad collet or other problem, you’ll have excess runout.

Runout and Tool Deflection are additive.  For a good discussion of deflection and a chart that shows what the combined runout and tool deflection will do to tool life, try this article:

What Every CNC’er Ought to Know About Tool Deflection

Last thought is that the default numbers in G-Wizard are close to Amana’s but more conservative.  I would just run with those unless all-out cutting speed is important.

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