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Mounted Points and Burs: Shapes, Shanks and Safe Speeds
Mounted points are the smallest abrasive tools in the workshop and the ones most often used incorrectly. A point is a bonded abrasive on a steel shank, held in a die grinder or a rotary tool, and its shape, grain and shank diameter decide whether it grinds a surface cleanly or burns it. This guide covers the mounted points and burs we stock and how to use them without damaging the work or the tool.
What a mounted point is
- Bonded abrasive head. Vitrified or resin-bonded grain on a spindle. It wears down as it cuts, so it conforms to the shape it is working.
- Shank. The steel spindle that goes into the collet, most commonly 2.35 mm or 3 mm for rotary tools, with larger shanks for die grinders. The collet must match the shank exactly.
- Shape. Flame, round nose, cylinder and tapered shapes each reach different features. The shape is chosen for access, not for cutting power.
- Grain. Aluminium oxide for steel, silicon carbide for cast iron and stone, diamond for hardened material and glass.
Shapes and their jobs
| Shape | Reaches | Typical use |
|---|---|---|
| Flame | Curved surfaces and tight radii | Blending a weld into a fillet |
| Round nose | Flat faces and shallow depressions | Cleaning a surface without digging in |
| Cylinder | Straight walls and slots | Deburring an edge or a bore |
| Taper | Corners and internal angles | Reaching a shoulder |
Ceramic and alumina points
A ceramic mounted point on a shank in brown fused alumina is the general-purpose point for grinding metal, and ceramic grain is worth the premium where the point has to keep cutting under pressure instead of glazing over. A round nose mounted point in alloy covers flat faces and shallow work where a pointed shape would dig in. Both are consumables: as the head wears, the effective diameter changes, so a point that has lost its shape should be replaced rather than forced.
Diamond points and polishing burs
A diamond flame mounted point from 80 to 2000 grit on 2.35 and 3 mm shanks holds its shape and cuts hardened material, glass and ceramics that would destroy an alumina point. Because diamond does not wear into shape, it is the tool for detail that must stay crisp. A polishing burr set for carving and mirror finishing goes a step further and is used for refining a surface rather than removing material, which is where a hard point stops being useful and a soft burr takes over.
Speed, pressure and the two failure modes
A mounted point fails in one of two ways, and both are caused by the operator rather than the tool.
- Glazing. Too much speed and pressure melt the bond and smear the grain, and the point skates across the surface. The cure is a lighter touch and a slower speed.
- Breakdown. The point sheds grain and loses its shape. On a small point this is normal wear, but a point that crumbles immediately is being run far above its rated speed.
The maximum speed marked on a point is a limit, not a target. A small head on a fast die grinder is the classic overload, and the failure mode of an overspeed point is that the head separates from the shank, which is why eye protection and the correct guard are not optional.
Holding the work and holding the tool
A mounted point is a small tool used on a small area, so control comes from bracing the tool and clamping the work. Hold the grinder with both hands where possible, rest a hand or the tool body against the workpiece or the bench, and start the point on the surface before applying load. Keep the shank as short as the job allows, because a long overhang amplifies vibration and bends the shank, and a bent shank runs out of true and chatters. Insert the shank fully into the collet and tighten it properly: a partly inserted shank is the most common cause of a point being thrown, and a thrown point travels fast.
Grain and grit selection
Match the grain to the material first and the grit to the finish second. Coarse grit removes material and leaves a scratched surface, fine grit refines. On hardened steel and carbide, only diamond will cut at all, and on aluminium the point will load almost immediately, so use a coarse open grain and a lubricant rather than pressing harder. Where the job is polishing rather than grinding, change to a burr or a felt bob with a compound: continuing with an abrasive point simply cuts deeper grooves that then have to be removed. Keep points separate by material, because a point contaminated with steel will mark stainless steel with rust spots.
Frequently asked questions
What shank size do I need?
It depends on the tool collet, most commonly 2.35 mm or 3 mm for rotary tools and 6 mm for die grinders. The collet must match the shank exactly; an undersized shank will slip and an oversized one will not fit.
Why does my mounted point burn the work?
Too much speed, too much pressure, or the wrong grain for the material. Reduce both speed and pressure, and use a grain suited to what you are grinding.
Can I use a mounted point on aluminium?
Only with a coarse, open grain and a lubricant, because aluminium clads the abrasive and stops it cutting almost immediately.
How do I stop a point loading up?
Use a coarser grain, reduce pressure, and dress the point on a dressing stick. Loading is a sign of too fine a grain for the material.
Are mounted points safe at any speed?
No. Every point has a maximum speed and it must not be exceeded. An overspeed point can shed its head, which is why a guard and eye protection are mandatory.
Where to start
Browse the full Mounted Points range, or the wider Abrasives category if you also need discs, belts or polishing wheels. Tell us the material, the access you have and the finish you need, and we will point you at the shape, grain and shank that fit.
