Why does my end mill break in aluminium?

Nearly always too many flutes, too deep a pass, or a chipload so low that the tool rubbed itself hot before it broke. Single flute, shallow, fast, and some lubricant fixes most of it.

Should I use a feeds and speeds calculator?

Yes, as a starting point, then reduce the depth of cut for a desktop machine and keep the feed. Record what worked; your machine and your material are the authority, not the calculator.

What is trochoidal milling?

A toolpath that keeps the cutter engaged over a small, constant arc rather than plunging into a full-width slot. It suits light machines particularly well because the load never spikes.

desktop CNC machines, tooling and upgrade parts / Buying guide

Feeds and speeds on a desktop machine

Feeds-and-speeds calculators assume a machine that does not flex. Desktop machines flex, so the numbers they produce are a starting point that needs an adjustment the calculator cannot make for you.

The underlying idea is simple: each tooth should take a chip of a certain thickness. Everything else is arithmetic around that.

In this guide

Chipload is the number that matters

Chipload is how thick a chip each cutting edge removes per revolution. Too thin and the cutter rubs rather than cuts, which generates heat and dulls the edge — the commonest desktop mistake, and it feels like being careful.

Feed rate = RPM x number of flutes x chipload. That is the whole formula. Everything else is choosing sensible values for the three inputs.

Starting points by material

Softwood and MDF — high RPM, generous chipload, deep passes. The machine is rarely the limit here.
Hardwood and plywood — similar, with a downcut or compression cutter if the top edge matters.
Acrylic — moderate RPM, single flute, and enough feed that the chip carries the heat away rather than melting back into the cut.
Aluminium — high RPM, single or two flute, shallow depth of cut, and a feed fast enough to make a real chip. Lubrication helps more than any other single change.
Steel — low RPM, low feed, and a machine that can take it. If your machine chatters in aluminium, it will not do steel.

Adjusting for a machine that flexes

Take the calculator's depth of cut and reduce it; keep the feed. A shallower, faster pass loads the frame less than a deep, slow one, and the tool lasts longer because it is cutting rather than rubbing.

Adaptive or trochoidal toolpaths are the other half of this. They keep the tool engagement constant and low, which is exactly what a light machine needs, and modern CAM generates them without ceremony.

Listening to the cut

A good cut has a steady tone. Chatter is a rough, irregular sound and a visible ripple on the wall of the cut; the fix is usually less depth, not less feed. A high-pitched squeal usually means the chipload is too low and the tool is rubbing.

Chips tell you too. In aluminium you want small comma-shaped chips that come off warm, not dust and not a welded lump on the flute.

Questions & answers

Common questions

Why does my end mill break in aluminium?: Nearly always too many flutes, too deep a pass, or a chipload so low that the tool rubbed itself hot before it broke. Single flute, shallow, fast, and some lubricant fixes most of it.
Should I use a feeds and speeds calculator?: Yes, as a starting point, then reduce the depth of cut for a desktop machine and keep the feed. Record what worked; your machine and your material are the authority, not the calculator.
What is trochoidal milling?: A toolpath that keeps the cutter engaged over a small, constant arc rather than plunging into a full-width slot. It suits light machines particularly well because the load never spikes.

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