Frage Can't cut more them 10 mm

Hi guys,

I'm pretty new to this cnc thing. Although I've been able to complete some projects I keep having this issue of breaking bits when i go deeper than 10 mm.

This issue only happens when I’m performing a 2d contour (Fusion 360).

My configs:
Stepcraft 840
HF Spindle at 16k - 18k RPM
End Mill - 3 mm
Stepover - 1.5 mm
Feed rate - 1000 mm/min to 1500 mm/min

The thing is that, when I’m cutting MDF or in this last case pine (soft woods) at more or less 10 mm I start hearing this strange vibration and i notice that the bit touches the walls and breaks.

I've tried some different feeds and speeds but I never had successes with a thickness bigger then 3mm.

What’s annoying me is that when I do a pocket process this vibration happens on the first run and then stops and I can go deeper than 12 mm.


Please I could use some help here. Thank you for your time.

Hey,
do you cut the 10mm deep in one pass? Maybe choose more passes.
How long is the cutting edge of the milling cutter?
Note: a 3mm cutter may have a 1/8 "(3.175mm) shank, then you get the problem that the shank of the cutter is in the milling groove and therefore the cutter breaks.
Then you have to see if you can buy a cutter with a longer cutting edge, or at least a milling cutter, whose shank is the same thickness, or thinner than the cutting diameter.
Greetings Stefan

I had this as well if: x/y/z has some room to play. There should not be potential movement possible by hand.

The other reason I had was the cutter not having a sharp cut in that depth.

To avoid it you can run passes with max 5mm depth and amake a second cut outside the main cut with half a cutter size (1,8mm in case you use 1/8") .

In this case you broaden the cut and give the cutter in deeper areas more room .

Make sure that all the swarf is continually cleared from the slot, otherwise it will build into a solid mass and either stall the axis or break the cutter (or both!!).

Hi Stefan, thanks for your comments.

The tool I'm using is a 1/8" 2 Flute Square with the specs attached.

Hi Frank, thanks for your help.

At the beginning I notice some free room on the axis, but then I tuned the axis and there was no movement on any axis.

The depth I'm using is only 1/2 the diameter, in this case for the 3.175 mm I'm using a depth of 1.5 max.

By outside cut you mean I should run a pocket cut? I'm sure that it will work, but it will take twice the time. I don't believe that it is a solution.

I don't have this problems when I do pocket operation. Only when cutting. I believe that at some depth of the operation the starts to be to narrow and the upper parts of the end mill starting touching the upper edges, what causes the shakes.

Do you cut with a 3 mm end mill depth of 5 mm?

Thanks

Hi Peter, that you for your comment,

I almost never leave the machine working alone, and the main reason is to keep cleaning the swarf continuously.

Thanks

Hello,

maybe its possible, that the portal is not strong enough to lead the endmills without vibrations.
To compensate that problem, you have to "double" or "triple" the machine-desk with a rest of a kitchen-workbench. At my SC840, two of them lower the milling-depth to 60mms, wasteplate included.

Best regards
Maik