[jblowsef]

Hello,

I just got a small "hobbyist" grade desktop CNC with a 500w spindle motor. Its mostly going to be for wood/plastic, but it is supposedly capable of working aluminum (obviously only slow, shallow cuts).

Question is, for working with aluminum what type and size of end-mill bit should I order? The machine comes with a 1/8" E11 collet, but I think I can order a 1/4" collet.

So would a 1/8" or 1/4" tool work better? It seems obvious that for a small lower power machine a smaller bit would be best, but I'm wondering if the 1/4" bit would be more rigid and less likely to chatter.

Thanks!

[awerby]

It's probably not going to work too well, no matter what bit you use. I'd say try it with the one you've got, and see if it's worth getting another bigger one. If the spindle motor's underpowered, as they tend to be on those machines, a larger tool is more likely to bog it down.

[fc60]

Greetings,

My CNC mill is not very rigid. As a result, I take lots of "finishing cuts". Fortunately, my machine repeats well and going over the same tool path is not a problem.

I would suggest a stubby 2-flute endmill to play with.

Run the Spindle RPM near maximum and experiment with the feed rate.

Look for a combination that cuts clean, no chatter, the chips get evacuated, use air if needed, and monitor the accuracy of the cut.

Would not hurt to spray some cutting lubricant on the tool while contouring to keep chips from welding to the cutter.

Cheers,

Dave

[6061billet]

Start off with 1/8" bits. That is all your machine is rigid enough to handle. While you can run 3/16" and 1/4" you simply can't run them in an optimum range.

A lot of people will say that we need to know the type of machine that you have and more about your setup. Based on "500w motor" and "desktop", I'm assuming that you have a cnc router built with extrusions.
A 1/4" endmill is probably more rigid than your entire machine and you would just break the endmill (assuming carbide) from chatter.
If your endmill is properly sized then you should be able to crash it into the work on a horizontal cut with the spindle off and the carbide endmill should break without your machine flexing or causing any damage to the machine.
If you have a small extrusion based CNC then a 1/4" bit is just going to be a longer and more rigid lever to break your spindle. And, larger endmills require more horizontal force to take the chipload they are designed for. Using an oversized endmill and then babying it with tiny cuts because the machine isn't rigid enough just creates extra heat and decreases tool life. Your best MMR will be in the 1/8 to 3/16" range. 1/4" is for specialty applications or when your really figured out the limits of your setup.

Also,side note, the larger the cutter, the stronger your workholding needs to be.

I have an 1,100 pound 2hp mill and 3/8" is the top end for an efficient cut. 1/2" is really pushing the machine hard.

Ballpark recommended largest end mill diameter based on machine weight.
100lbs and under stick with 1/8" to 3/16"
500lb machine 1/4"
750lb machine 3/8"
1,100lb machine 1/2"

Now, this is just a ballpark assuming typical cuts. There are special case where it makes sense to go outside these limits.
i.e. if you might be able to get away with 1/4" if it was an extra short / stub bit. That reduces the level arm and greatly increases the rigidity of the system.

I often use an 3/4" x 4" extra long end mill, but I have to use it carefully. I only use it for very light profile passes where I want to cleanup a side without any stepdown marks.