Why a router bit burns or chips the wood, and how to fix it

01What causes a router bit to burn or chip wood?

Burning comes from friction heat, mainly a feed that is too slow or a bit that has lost its edge. Chipping and tear-out come from the way the cutter meets the fibres: a dull edge, too much in one pass, or a bit whose flutes lift the surface you need clean. Feed direction belongs on the same checklist for control. Router manuals from Bosch, DeWalt and Milwaukee and bit makers' guides name the same short list. Speed set too high for the feed is a further cause named by one bit retailer, covered in the speed section below. The table pairs each symptom with its cause and fix.

02Does a slow feed rate make router bits burn?

Yes. Feeding too slowly leaves friction burns, and router manuals tell users to feed smoothly and steadily. The common belief that a slow feed gives the cleanest cut is the main reason people get scorch marks: the bit keeps rubbing the same wood instead of cutting fresh chips. Pausing at a corner, at the end of a board or to reposition your hands has the same effect.

How do you confirm it?

Burns that appear where you slowed down, such as at corners, starts and ends, point to feed rate. Burning along the whole length at a normal pace points instead to a dull bit or a pass that is too heavy.

How do you fix it?

Plan the cut so you can move through it in one steady motion, with hands and cord clear, and keep the stock moving past the bit on a router table rather than stopping to regrip. The same friction logic applies to saw blades; our page on fixing scorched cuts covers the blade version of the problem.

03How do you tell if the router bit is dull?

A dull bit makes the motor labour and needs more push to move through the cut, and manufacturers warn that the extra force can break the bit. The rule in router manuals is simple: never use dull or damaged bits. Look at the carbide edges under good light for rounding, chips or missing pieces.

When a correctly set-up bit still labours at a normal feed, it needs sharpening or replacement. The fact base behind this page holds no wear limit in hours or feet, so judge by how the bit cuts.

04Can taking too deep a cut cause burning and chipping?

Yes. A single heavy pass overloads the motor, slows the bit and invites both burning and rough, chipped edges. Router manuals tell users to take deep cuts in several passes of increasing depth instead.

For profiles, the same applies: rout a large round-over or ogee in two or three passes, raising the bit each time, rather than in one, so no single pass loads the motor heavily. Our guide to edge-profile router bits explains how each profile cuts and what it is used for.

05Does feed direction matter when a router burns or chips?

Yes, for control. Feeding the router the wrong way, called climb cutting, lets the bit pull the router along, and an uncontrolled cut is hard to keep at a steady feed. Seen from above, a hand-held router bit turns clockwise, so on an edge in front of you the router moves left to right. Go counterclockwise around the outside of a workpiece and clockwise around the inside.

Bosch, DeWalt and Milwaukee all tell users to avoid climb cutting because of the control risk. On a router table, feed the work against the bit's rotation as your table's manual specifies.

06Which spiral bit stops chipping on the top face?

A down-cut or compression spiral. Up-cut spirals lift chips up and out of the cut, which suits deep cuts and mortises, but they leave more tear-out on the face nearest the router. Down-cut spirals push chips down and leave the cleanest edge on that near face, which suits shallow grooves, dadoes and inlays, though they clear chips more slowly. Compression spirals combine both flute directions to leave clean edges on both faces of sheet material.

A common misconception is that any spiral bit gives a clean top edge. It depends on the flute direction, so match it to the face that will show. In veneered plywood, where chipping on the top face is the usual complaint, the down-cut version is the one makers list for clean top edges. For raised panels and other large profiles, Freud's Quadra-Cut design uses shearing cutters to reduce splintering on panel faces.

07Is router speed causing the burning?

It can be. ToolsToday, a router bit retailer, says running the bit too fast for the feed rate causes burning: each cutting edge takes a thinner chip, rubs instead of cutting and builds heat, so lowering the speed while keeping the same feed can reduce burning. That is one source's explanation, and it fits Freud's note that a bit making dust instead of chips dulls early because fine chips carry little heat away. Router manuals and bit makers also say to use lower speeds for larger-diameter bits and higher speeds for small bits.

In practice, check feed and sharpness first, because those are the causes the router manuals name. If the feed is already steady and the bit is sharp, try a lower dial setting at the same feed rate. CMT, a bit maker, adds that a bit's maximum speed depends on its diameter and application, that its chart's maximum falls as diameter rises, and that the speed marked on the bit or its packaging governs, so any change stays within that marking.

Speed also decides how soon an edge goes dull enough to burn. A 2016 Journal of Wood Science study milling melamine-faced particleboard ran an HSS cutter to a 1 mm flank-wear limit and recorded about 290 vs 1,000 m of cut at 18,000 rpm against 6,000 rpm. That is one lab setup in one sheet material, not a router-bit life rating, and it remains the most recent open-access speed-and-wear figure of its kind we found, but it shows why a bit run faster than the job needs can start scorching sooner. Once an edge has dulled, it also works the motor harder: in a 2024 BioResources test on a CNC router at 18,000 rpm, a blunt 16 mm carbide cutter needed about 51.6% more cutting power than a sharp one, so a bit that has started to burn may simply need sharpening or replacing.

Speed dials give a guide. On the Bosch 1617EVS, settings at the low end are listed for larger bits and the upper settings for smaller bits and softwoods; DeWalt's DWP611 manual groups its dial the same way. The table below shows the dial settings with their approximate speeds, from each maker's manual.

08Is it safe to run a large bit at full router speed?

No. A bit run above its rated speed can break and fly apart, and Bosch, Makita and Freud state that a bit's rated speed must be at least the router's maximum speed. Whiteside's published ratings fall as cutting diameter rises, and large raised-panel bits are meant for router-table use at the reduced speed rated for the bit. Compact routers in our data run up to 27000 rpm (DeWalt DWP611) and 30000 rpm (Makita RT0701C), which is why the rating on the bit or its packaging must be read before fitting it. Compact routers also carry their own maximum bit diameter in the manual, so check that before fitting a large profile.

09Can the collet cause chatter, burning or chipping?

Yes, indirectly: a bit that is not held properly does not run true, and a mismatched collet may fail to grip or even break. Use a collet whose bore matches the shank exactly. An inch shank and the nearest metric shank are different sizes and are not interchangeable in the same collet, which corrects the idea that the two are close enough.

Bosch, DeWalt and Milwaukee all say to insert the bit fully and then back it out slightly so it does not bottom out, and Milwaukee adds that the collet must not clamp on the fluted part of the bit. Where the router accepts it, use a 1/2 in shank bit: larger shanks give more stability and less vibration than small ones. Compact routers from DeWalt, Milwaukee and Makita ship with a 1/4 in collet, while the Bosch 1617 family lists both inch and metric capacities. The router collet sizes guide lists the collets supplied with each model.

10How do you prevent burning and tear-out?

Most burning and chipping is prevented by a sharp bit, a steady feed in the right direction and passes light enough for the motor.

• Inspect bits before each job and retire any that are dull, chipped or damaged.
• Feed steadily; plan the cut so you do not stop partway.
• Rout against the rotation: left to right on an edge facing you, counterclockwise around outside edges.
• Take deep cuts and large profiles in several passes.
• Lower the speed for large-diameter bits, within the bit's rating.
• Pick spiral direction by the face that must stay clean.
• Use the matching collet and seat the shank correctly.

11When should you replace the router bit?

Replace a bit when its carbide is chipped, cracked or missing, when it still labours and burns after you have corrected feed, depth and direction, or when it is the wrong design for the face you need clean. Damaged bits are not worth nursing along: they can snap or throw carbide.

The bits below cover the common jobs behind burn and chipping complaints: a straight bit for grooves, a round-over for edges, and an up-cut and down-cut spiral pair for choosing the clean face. Specs come from Freud's and Whiteside's product pages. Whiteside's speed figures for the up-cut spiral are confirmed by a second listing and shown below; for the other three bits, read the rating from the bit or its packaging. A starter set is another route, and our guide to router bit sets for beginners compares those.

13What related routing problems appear alongside burning?

Burning often appears with chatter, a router that pulls, and stalling, because slow or uneven feed, climb cutting and heavy passes share the same root. Chatter and vibration also point to the bit holding: a small shank on a large cutter, or a shank seated wrongly in the collet. Tear-out on the exit edge of a board is a related but separate problem from top-face chipping.

For bit types and shank choices, the router bits explained hub groups every router guide. For other accessories, the accessory problems and fixes index lists each fault by tool, and the tool accessory lookup shows which bits and collets your router accepts.

14Questions readers ask