Rb203

Direct replacement for the Onsrud 52-240BM, for Zund router modules with a 0.236 in (6.0 mm) collet. 2-flute upcut ballnose bit with a 0.118 in (3.0 mm) cutting diameter on a 0.236 in (6.0 mm) shank.

Sold individually.

Direct replacement

The Rb203 matches the Onsrud 52-240BM: 0.236 in (6.0 mm) shank, 0.118 in (3.0 mm) cutting diameter, 0.472 in (12.0 mm) cutting length, and 1.969 in (50.0 mm) overall length. If you run the 52-240BM now, the Rb203 drops straight in. Not sure? Contact us before you order.

What a ballnose bit does

A ballnose bit has a rounded tip instead of a flat end. It cuts rounded-bottom grooves and smooth 3D contours, which makes it the right tool for carving, sign lettering with a soft profile, and shaped surfaces where a flat-end bit would leave steps.

Two flutes, upcut

Two cutting edges split the work, which leaves a smoother surface than a single flute. The upcut spiral pulls chips up and out of the cut.

Common questions

How do I know this fits my machine?

The Rb203 has a 0.236 in (6.0 mm) shank and fits Zund router modules that take 6 mm bits. For the RM-A QC ARC automatic bit changer, use the Rb203a with the stop ring. Not sure? Send us your machine model and we will confirm before you order.

What materials does it cut?

Onsrud lists the 52-240BM for soft and hard wood, wood composites, soft and hard plastics, and aluminum. Reach out if you are not sure it fits your job.

How do I know when to replace it?

Watch the surface finish. Tool marks, burning, or a rough contour where it used to cut smooth all mean it is time for a fresh bit.

Getting the most from your cutting table

A fresh bit is a good start. But if you are going through bits faster than expected, or edge quality has become inconsistent, the bit is rarely the whole story. Spindle speed, feed rate, depth per pass, material hold-down, and machine condition all affect how long a bit lasts and how clean it cuts.

It is worth asking: When was your machine last serviced? Are your parameters dialed in for this material? Is this the right bit for what you are cutting? Could your operators use time with someone who runs these machines every day?

Flatbed Tools offers machine service, preventive maintenance, operator training, and workflow consulting. If something is not cutting right, reach out. We have probably seen it before.