View Full Version : Breaking cutters machining aluminium

14-08-2011, 08:52 PM
I'm running a job machining badges on my Emach cnc router and am breaking cutters frequently. Wasn't too bad on the original stock that I had -duraluminium I think -but now I'm using 5251H22 cutter life is dire.
Details are:
Cutting tool speed 21000 rpm
Cutter travel speed .25m/ min
Cutter pas depth .3mm
Tool = 2mm single flute carbide cutter from ITC Ltd
Coolant = ITC coolant via mister

I can't increase the cutter size due to the small radius on some of the letters. Am I better using a softer grade of aluminium or will I then get chip clogging?

Any thoughts where I'm going wrong? It's getting a bit pricey at 20+ per cutter

Robin Hewitt
15-08-2011, 09:43 AM
Find a cheaper cutter :naughty:

You want about 250-350 ft/min for aluminium. 432 ft/min is pushing it.

I suspect you have clag building up on the tool edge, some alloys are worse than others. Get your magnifying glass out, does the finish become progressively icky before the tool break?

John S
15-08-2011, 10:04 AM
Find a cheaper cutter :naughty:

Try these


Robin Hewitt
15-08-2011, 10:16 AM
Try these

I think I'd go for a stub length slot drill to engrave text. Anything to reduce flex in the system.

John S
15-08-2011, 11:13 AM
Personally I'd go for a Vee cutter, far stronger, only the very tip is small

15-08-2011, 12:58 PM
Im with john on that one! but if you manage break a vee cutter then you doing something wrong.

15-08-2011, 06:48 PM
Personally I'd go for a Vee cutter, far stronger

As long as you don't get one with a very acute angle...

John S
15-08-2011, 08:15 PM
To be honest I have found that most of these carbide engraving cutter take the tip off far to easily, makes sense when you think about it as carbide is a sintered powder and has no grain as such.

Recently I have been grinding my own up from 6mm HSS drill blanks, don't last as long as carbide but once you have the D shape they cam be resharpened in about 2 minutes. Plus bit is you don't scrap a job because it takes the tip off 1 hour into a 3 hour job.


8" x 3/4" all done with HSS tool.

15-08-2011, 08:21 PM
Think I've seen that photo before somewhere ...

I'll have to try the drill regrinding suggestion. I've kept any drills I have snapped (thankfully few) to regrind into spot drills. They seem ideal for that.
Oh just noticed you said drill blanks, not drills. Just a D shape?

John S
15-08-2011, 09:27 PM
or the broken shanks of HSS end mills and slot drills

16-08-2011, 08:23 AM
Thanks for the advice. I'm going to try a 2 flute cutter instead of the single flute, perhaps better balanced? I've ordered a batch of the cheap EBay cutters. At a tenth the price of those I'm currently using it'll be interesting to see what the tool life is. I'll look at the stub drill option. V cutter won't work as I'm cutting 2mm into the stock with multiple passes and need a vertical edge. Thanks Peter.