Genmitsu
Genmitsu 10pc Nano Blue Flat Nose End Mills
Ten identical flat-nose cutters. Buying one geometry in bulk is how you stop treating bits as precious and start running the feed rate the chart actually recommends.
$34.19
at Amazon
CNC Router Bits: How to Choose + 9 Compared (2026)
End mills, V-bits and profile cutters — the thing you replace most often.
How to choose
The decision is made in a fixed order, and getting it out of order is what leads to a drawer of bits you never use. Shank size comes first because it is decided by your machine, not by preference - the collet in your spindle accepts one diameter and no adapter runs the wrong way. Geometry comes second, decided by the material and the finish you need. Coating and flute count come last, and matter far less than either of the first two.
The single most common mistake is buying a large assortment early. A forty-piece set looks like value and is mostly an education in which five geometries you actually reach for. Once you know that, buying those five in quantity costs less per cut and means you stop treating cutters as precious - which matters, because a cutter you are afraid to break is a cutter you will run too slowly, and running too slowly is what burns the work.
The geometries explained
- Upcut spiral
- The default, and the geometry the published chip-load charts assume. The helix lifts chips up and out of the cut, which keeps heat out of the workpiece and the slot clear. The cost is the top surface: lifting chips also lifts fibres, so the top edge tears. Use it where the cut face matters more than the top face, and anywhere heat is the problem - deep slots, hardwood, most metal.
- Downcut spiral
- The mirror image. It presses the top fibres down for a genuinely clean top edge, and packs the chips into the slot rather than clearing them. That packing is why the effective chip load has to come down about 30% - the cutter is partly recutting its own swarf. Use it for shallow work where the visible face is the top one, and never for deep slots in anything that scorches.
- Compression
- Upcut at the tip, downcut above it, so both faces of a sheet stay intact. This is the correct and only real answer to plywood veneer tear-out, and the price is justified in a single sheet of birch ply. It needs a first pass deep enough to bring the downcut section into the material - a shallow first pass leaves you cutting on the upcut tip alone and you get exactly the tear-out you paid to avoid.
- V-bit
- For carved lettering and chamfers. The thing to understand is that a V-bit's effective cutting diameter changes continuously with depth, so any single chip-load figure is an approximation - treat calculator output as an upper bound and start below it. The point is also the most fragile part of any cutter you own.
- Ball-nose
- For 3D finishing passes, where the stepover rather than the feed decides the surface. The effective diameter at the very tip approaches zero, so the tip is cutting at almost no surface speed however fast the spindle turns - which is why ball-nose finishing is slow and why nobody roughs with one.
- Straight flute
- No helix means no chip-clearing action at all. Evacuation depends entirely on the cut being shallow or open. Cheap, fine for through-cuts in thin stock, and out of its depth in anything else.
Each geometry carries its own chip-load penalty - the feed & speed calculator applies them and shows the factor separately.
Matching them to your machine
Shank diameter is set by the collet in your spindle, and the two common sizes - 1/8-inch (3.175mm) and 1/4-inch (6.35mm) - are not interchangeable. A 1/4-inch shank is meaningfully stiffer and deflects less on a deep pass, which is why larger machines standardise on it, but it will not physically enter a smaller collet. Machines with an ER11 collet nut can usually take both by swapping the collet itself, which is a five-dollar part rather than a new spindle.
Cutting diameter is a separate figure from shank diameter and the two are frequently different on the same bit - a 1/8-inch cutting diameter on a 1/4-inch shank is a common and useful combination, giving you fine detail with a stiff shank. Read both numbers before ordering.
Every product below lists the machines it fits; machine pages list the consumables matched to their collet. Browse the machine database to check yours.
How many you actually need
The honest answer for a first purchase is one assortment, then quantity. Buy a modest set to find out which geometries your work actually needs, then re-buy those in multiples. Ten identical cutters of the geometry you use daily is a better inventory than forty singles, because it removes the temptation to nurse a dull bit through one more job.
Budget for cutters as a running cost rather than a one-off. Abrasive materials - MDF, and anything with glass fibre in it - consume edges far faster than hardwood, and a dull cutter does not announce itself. It shows up as a fuzzy edge on a job that was cutting cleanly an hour earlier.
9 router bits we track
In stock
Genmitsu
Genmitsu 5pc 4-Flute Carbide End Mill Set
Four flutes put twice the cutting edges of a 2-flute into the same rotation, so the feed rate has to double to hold the same chip load. Use the calculator before you run these - a 4-flute at 2-flute feeds will rub and burn.
Price unavailable
Out of stockat Amazon
This listing was out of stock at the last check. The link is kept so you can see whether it has returned.
Genmitsu
Genmitsu 8pc End Mill Set, 1/4in Shank
Eight cutters rather than forty, chosen rather than assorted. The better buy once you know which three bits you actually reach for.
$94.99
at Amazon
Genmitsu
Genmitsu MC10A General Purpose Collection
A 1/4-inch shank collection for machines that have outgrown 1/8-inch tooling. The larger shank is stiffer, deflects less and survives the deeper passes a rigid machine can actually take.
$113.99
at Amazon
Genmitsu
Genmitsu MC40A 40pc End Mill Set
The default first bit purchase for anyone on a 1/8-inch machine. Forty cutters means you can afford to snap a few while you learn what a chip load actually feels like, which you will.
$64.99
at Amazon
Genmitsu
Genmitsu VG03A V-Groove Bit Set
Two angles, and the cheapest possible entry into V-carved lettering. Remember that a V-bit's effective diameter changes with depth, so treat any single chip-load figure as an upper bound.
$17.09
at Amazon
Genmitsu
Genmitsu WC04A Wood Carving Bit Set
Profile and V-carving geometry rather than end mills. This is the set that turns a machine that cuts shapes into one that carves relief work.
$37.99
at Amazon
SpeTool
SpeTool 5pc Carbide Spiral Downcut Set
Downcut geometry presses the top fibres down for a clean edge, at the cost of packing chips into the slot. Drop the feed about 30% against an upcut - the calculator does this for you.
$33.99
at Amazon
SpeTool
SpeTool Up & Down Compression Bit, 1/4in Shank
Upcut at the tip and downcut above it, so plywood comes off the machine with both veneers intact. The one bit that solves sheet-goods tear-out outright - provided your first pass is deep enough to reach the compression zone.
$26.99
at Amazon
Router Bits - common questions
- What size router bits do I need for my CNC?
- Whatever your collet accepts - usually 1/8-inch or 1/4-inch shank on a desktop machine. The collet decides this, not the bit, so check the spindle before ordering. Many ER11 spindles take both sizes with a collet swap, which is a cheap part.
- Upcut or downcut for CNC router bits?
- Upcut clears chips and keeps heat out of the cut but tears the top edge; downcut gives a clean top edge and packs chips into the slot, so its feed has to drop about 30%. If both faces of a sheet need to be clean, a compression bit is the only geometry that does both.
- Why do my router bits keep breaking?
- Usually the chip load is wrong in one direction or the other. Too small and the cutter rubs, overheats and dulls until it snaps; too large and it is simply overloaded. Work backwards from the feed rate and RPM you actually ran using the chip load calculator - that will tell you which of the two happened.
- Are expensive router bits worth it?
- The premium buys edge life rather than a better cut on the first pass, so it pays back on long jobs in abrasive material and not much on occasional work in softwood. While you are learning, cheap cutters are the better purchase because you will break some regardless.
Feeds and speeds by material
Chip-load ranges differ per material - pick yours before the first cut.