Rotary Burr Shapes Explained

Three Names for Every Burr Shape

A rotary burr shape can be described three ways. Machinists use a plain name: ball burr, cylinder burr, tree burr, cone burr, flame burr. Most catalogs print an industry code from SA through SN. Severance uses a single shape letter, A through X plus BI and FL, that was in place before the SA to SN convention existed, which is why the two letter systems do not line up. Industry SD is a ball; Severance Shape D is a cylinder with a corner radius.

This guide maps all three so you can cross a competitor's part number or a customer drawing to the right Midget Mill® shape page and EDP number. It also covers what each shape does best, the cut patterns Severance grinds, the three shank sizes, and how to read a tool number such as CJA-EC-W.

Cylinders: A, A-EC, C, D

A cylinder cuts on its side and leaves a flat wall. Shape A is the general-purpose burr for edge breaking on flat stock, slot walls, and keyways. The end-cutting A-EC adds flutes across the face for plunging and flat-bottomed pockets. Shape C rounds the end so it can run a fillet where a wall meets a floor without digging a corner. Shape D puts a smaller radius on the corner only, for a cleaner blend than A with full straight-wall cutting.

Ball, olive and pear: B, Q, P

A ball burr cuts the same in every direction, so it is the tool for inside radii, concave surfaces, and contour blending in die cavities. Smaller balls also open up and deburr cross-drilled holes. The olive (Shape Q) is an elongated ball whose continuous curve blends compound surfaces and radiused grooves without sharp transitions. The pear (Shape P) tapers smoothly to its full diameter for irregular cavities.

Trees: R, S, T

A tree burr has a tapered body that reaches into a cavity while the nose does the finishing. Choose Shape R (round nose) for die and mold blending without gouging, Shape S when the cavity needs a smaller nose radius, and Shape T (pointed) for tight corners and sharp internal angles a rounded nose cannot enter.

Cones: E through M

Severance grinds nine cone tapers so you can match the chamfer or tapered hole on the print. Shape E at 20° per side is the widest and suits broad chamfers; Shape M at 5° per side is the slimmest and reaches deep, narrow openings. In between, Shape G handles V-groove deburring and tapered bores, Shape L is the SL industry cone, and Shape J is the SM pointed cone. Angles are listed per side; double them for the included angle.

Inverted cone and double angle: N, X

Shape N widens toward the end, so it reaches through a hole to deburr the far side, undercuts behind a shoulder, or back-chamfers without turning the part over. It comes in multiple head angles. Shape X is a diamond, two angled faces meeting at the maximum diameter, for V-grooves and thread forms.

Concave, convex, radius end, bi-convex and flame: U, V, W, BI, FL

Shape U is waisted, so running it along an edge leaves a convex radius on the part. Shape V is the opposite, a barrel that finishes concave surfaces. Shape W carries flutes only on its radius end, for end-only cutting where the side must not touch the work. Shape BI is a lens for contour finishing. The flame burr pairs a pointed tip with a curved body for tight-access deburring, carving, and die sinking.

The same shape letters carry across three shank sizes, so a Shape B ball is a Shape B on a 1/4 inch Midget Mill or a 3/32 inch Lab Mill. Pick the shank by the grinder and the size of the feature.

Every Midget Mill® shape is ground in M2 high-speed steel hardened to Rockwell C 63-65 and in a tungsten-cobalt carbide blend. HSS is the tougher material: it absorbs the shock of interrupted cuts and side loads in a hand-held die grinder, so it suits cold and hot rolled steel, annealed tool steel, aluminum, brass, bronze, and cast iron. Carbide holds its edge at higher speed and temperature, lasts 10 to 20 times longer in hard materials, and is the choice for hardened steel, stainless, titanium, and production deburring.

Run an HSS burr at roughly half the RPM of a carbide burr of the same diameter. The speed and feed page gives RPM by head size for both, and the HSS vs carbide guide works through cost per part. For shape, size, material, and cut in one walkthrough, read how to choose the right rotary file.

When either material dulls, the Severance regrind service restores the original ground geometry on burrs of any brand, 1/16 to 3 inch diameter, with a 1-3 week turnaround.