[JuicyBurger]

Hi Guys;

I'm currently making a part for someone that has 1mm wide .1" deep channels milled into aluminum. I have a homemade CNC machine including the spindle.

I ran a few tests before setting on 7000 RPM (max) at 6 ipm feed .005 DOC (so 20 passes to get it as deep as needed). After about 45 minutes of cutting smoothly with air as chip removal / coolant (.070 deep) the endmill decide to snap.

I thought I'd ask before I broke my last 1mm endmill (more on the way) doing something wrong... What would you change? Is it just a function of run out breaking the tool in such a deep slot or are my numbers wrong? I noticed some welding of chips in the channel, is this my fault (too fast, not great enough chip removal)?

Thanks,

Cody

[JuicyBurger]

1mm 2 flute HSS endmill

[riche543]

If your cnc isn't rigid enough (flex) you can get chatter which can lead to snapping bits, this is just Expierience I've had as I have homemade mdf machine,
Riche.


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[JuicyBurger]

My machine is rigid enough to do light steel machining, no issues with aluminum, even with larger endmills. A 1mm endmill should provide no issues with respect to rigidity..

[underthetire]

6 ipm at that low of rpm might be pushing it. Smaller tools like that require a lot of finesse. We would be in the 14-20k rpm range ourselves. Are you using just air or air/mist ?

[JuicyBurger]

Just using compressed air. What would you recommend I knock it down to?

[underthetire]

I would drop it by 30% of the feed once you get down that far in the slot. Spray mist would help on this as well.

[bebob1]

You said home-made spindle and machine? Most important part is the spindle I suppose. Did you measure your runout? I think its possible runout is contributing to your tool breaking.

Maybe chip evacuation too could be a problem. You might need some really high pressure flows blowing directly at your cutting location to remove the chips successfully. Plus 6ipm is quite fast and the 1mm channels not really wide enough for good chip evacuation. For milling channel slots, i find a flooding of the cutting area with cutting fluid and a slow feed rate works great. For example using cutting oil to completely flood the cutting area in a sea of cutting fluid, where the chips generated get carried up the flutes and settle or flow away caused by the circulating flow generated around the rotating end mill.

I do a bit of 1mm diameter channel milling into Al too. I usually run at a much lower RPM due to spindle limit, but I also use slower speed. My DOC is only 0.004". I have cut as deep as 0.08" (max flute and cutting depth of tool).

[HorridHenry]

The cutter is sticking to the Aluminium so a slower speed and the use of proper coolant would greatly help instead of a blow from air which is far from satisfactory in cooling the endmill down and coolant would also minimise sticking.

What you have is metal bonding to metal,can you imagine a cars pistons without lubrication,.

[JuicyBurger]

Thanks for the awesome responses. I showed the part to the guy who drew it up and he said wow those channels are too small! -.- so I re-made the part with a 1.6mm endmill , lowered the feedrate to 4 ipm and increased the pressure on the compressed air for better chip evacuation. I think welding chips was a problem previously by the increased pressure really did the trick. Also, working with a 1.6mm endmill is infinitely easier than a 1mm endmill...