CNC Router Bits: Which Bit for Which Cut

A CNC router bit is the cutting tool held in the router or spindle collet; on a CNC machine most of them are end mills, meaning they cut on both the tip and the sides so they can plunge, pocket and profile. Which bit you choose sets the finish, the speed and whether the job works at all, so most beginners get better results from four well-chosen bits than from a 30-piece set.

This guide matches bit types to jobs, using bit specifications and October 2026 prices from Carbide 3D’s store, the Techno CNC Systems chipload chart and Makita’s RT0701C product page. We did not run cutting tests. For the machine side, see our CNC router guide.

Which CNC router bit should you use for each cut?

Use a flat end mill for pockets and cutouts, a V-bit for lettering, a ball nose for 3D shapes and a surfacing bit for flattening. The table maps the common hobby bits to their jobs.

A drag bit scratches a line rather than cutting a groove; our engraving machine types guide compares drag, rotary and laser engraving.

Upcut, downcut or compression: which spiral bit fits?

An upcut lifts chips out of the cut and leaves the top edge fuzzier, a downcut pushes chips down and leaves a clean top edge, and a compression bit combines both to leave clean top and bottom faces on sheet goods. The choice is about where you need the clean face and how well chips can escape.

• Upcut: best chip evacuation, so it clears pockets and deep profiles fastest. In plywood the top veneer tears out; on solid wood that matters less.
• Downcut: Carbide 3D describes its #251 downcut as ideal for laminates and wood without tearing out the top side, and warns that chip evacuation needs care. Use it for shallow pockets and visible faces.
• Compression: a short upcut section at the tip with downcut flutes above it. It only works as intended when the first pass is deeper than the upcut section, so the downcut part reaches the top face. That makes it a tool for rigid machines cutting full sheets, not a light 3018.

On a typical hobby machine, an upcut for roughing plus a downcut for the final pass on show faces covers most plywood work.

What V-bit angle should you use for signs?

A 60 degree V-bit carves deeper, crisper-looking letters for the same width; a 90 degree V-bit carves shallower and handles wider strokes faster. The math is simple geometry: depth = half the line width / tan(half the bit angle).

Deeper cuts catch more shadow, which is why fine script often reads better with 60 degrees. The trade-off is that a 60 degree bit needs more depth for wide strokes, more passes on a light machine, and thicker stock. Carbide 3D sells both angles as 1/2 in V-bits with two flutes and an HSS core with brazed carbide edges. V-carve toolpaths are where CAM software matters most; our CNC router software comparison notes which programs include V-carving on their free tiers.

How many flutes should a hobby CNC bit have?

On most hobby routers, one or two flutes beat three or more, because fewer flutes let the machine reach a real chipload at a feed rate it can handle. Feed (in/min) = rpm x flutes x chipload (in), so every extra flute raises the feed the frame must sustain.

Worked examples with the Techno CNC Systems chipload chart:

• 1/4 in bit in hardwood (chart 0.008 to 0.010 in): at 10,000 rpm, a 2-flute needs 10,000 x 2 x 0.008 = 160 in/min; a 3-flute needs 240 in/min.
• 1/8 in bit in MDF (chart 0.004 to 0.007 in): at 18,000 rpm, a 2-flute needs 144 in/min; a single flute needs 72 in/min.
• 1/4 in single-flute in aluminum (chart 0.005 to 0.007 in): at 10,000 rpm, 50 to 70 in/min.

If your machine cannot reach the feed, the chip gets thinner, the bit rubs, and heat dulls it. Carbide 3D’s #201 1/4 in flat end mill has three flutes, while its Essentials #205E is a two-flute 1/4 in, which suits slower frames. Our CNC feeds and speeds calculator runs this math for your bit, material and machine class.

Which bits cut aluminum and acrylic?

Use single-flute (O-flute) carbide bits for acrylic and HDPE, and single- or two-flute carbide bits made for aluminum. The large flute space clears chips before they melt and weld back onto the edge, which is the main way plastics and aluminum fail on a router. If acrylic is your main material, a CO2 laser is the other route; see our laser cutter for acrylic guide.

Carbide 3D’s #278Z is a 1/4 in single-flute solid carbide end mill with a ZrN coating, sold for $40 in October 2026, and its #274Z is the 1/8 in version at $30. The coating reduces aluminum sticking to the edge. For aluminum on a hobby router, take shallow depths, keep the chips clearing (air blast or vacuum), and expect slow progress: frame rigidity limits aluminum more than the bit does. If aluminum parts are your main goal, a desktop CNC mill is the stiffer tool.

Steel, stainless and titanium are out of scope for hobby routers whatever bit you buy.

What shank size fits your router or spindle?

Buy bits with the shank your collet holds exactly: usually 1/4 in or 1/8 in on hobby routers. Makita’s RT0701C trim router, the common spindle on hobby machines, includes a 1/4 in collet, and Makita lists a 3/8 in collet as a separate accessory.

Never mix metric and imperial: a 1/4 in shank is 6.35 mm, so a 6 mm collet will not take it and a 6 mm bit slips in a 1/4 in collet. Carbide 3D sells its McFly surfacing cutter in both a 1/4 in shank and an 8 mm shank for ER16 and ER20 spindles for that reason. Insert the shank deep enough for full collet grip, but do not bottom it out. Our guide to using a CNC machine walks through installing a bit step by step.

What should a CNC starter bit set include?

A useful starter set is seven bits that cover profiles, clean faces, lettering, 3D work, plastics and flattening. Prices below are from Carbide 3D’s US store in October 2026; most packs contain two bits.

Add the McFly surfacing cutter ($90, 1 in cutting diameter, four carbide inserts) when you first flatten a spoilboard. Two ready-made alternatives: Carbide 3D’s Shapeoko Endmill Starter Pack ($195, eight bits including two #201, a #251 downcut and both V-bits) and the Amana AMS-119 three-piece pack ($125.59, a 60 degree insert V-bit and two downcuts). Budget for bits as a running cost; our CNC machine cost breakdown includes them.

Solid carbide or HSS: does bit material matter?

Solid carbide is the standard for CNC end mills because it stays sharp far longer than high-speed steel (HSS) at router speeds. Carbide 3D’s flat, ball and single-flute end mills listed above are solid carbide; its V-bits use an HSS core with brazed carbide edges, a common construction for larger-diameter carving bits.

Coatings are a smaller decision. A ZrN coating, as on Carbide 3D’s “Z” bits, helps in aluminum by reducing sticking; for wood, uncoated carbide is the norm. Cheap unbranded multi-packs exist at a fraction of these prices; their geometry and runout vary by batch, so treat them as experiments rather than your baseline bits.

When is a bit dull, and when should you replace it?

Replace a bit when cuts burn at feeds that used to run clean, edges fuzz more than before, or the machine sounds strained at familiar settings. Burning in wood is the earliest and most common sign, but it can also mean the feed is too slow for the rpm, so check the chipload math before you blame the bit.

Bit life depends on material (MDF glue and plywood glue lines wear edges faster than solid softwood), on chipload (rubbing dulls carbide quickly) and on chip clearing. A simple log of which bit ran which jobs, kept next to the bit numbers in your CAM tool library, is the easiest way to see when a bit is near the end.

Who is this guide not for?

This guide is for hobby routers cutting wood, plastics and some aluminum. It is not for metal machinists choosing carbide end mills for steel, stainless or titanium on a mill, where coatings, helix angles and flute counts follow different rules and much stiffer machines.

If you are still choosing the machine that will hold these bits, our best CNC router for hobbyists page compares frames and spindles by budget.