Rb203a
Ballnose router bit with an ARC stop ring, for Zund cutting systems that run the RM-A QC ARC router and automatic bit changer. 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.
Onsrud 52-240BM geometry, ARC ready
The Rb203a has the same cutter as the Onsrud 52-240BM: 0.118 in (3.0 mm) cutting diameter, 0.472 in (12.0 mm) cutting length, and a 0.236 in (6.0 mm) shank. It adds a stop ring that sets the bit's depth in the collet, so the RM-A QC ARC automatic bit changer loads it at the same height every time. For a router without ARC, use the standard Rb203.
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.
Common questions
How do I know this fits my machine?
The Rb203a has a 0.236 in (6.0 mm) shank and a stop ring for the Zund RM-A QC ARC automatic bit changer. Not sure which router you have? Send us your machine model and we will confirm before you order.
What materials does it cut?
Onsrud lists the 52-240BM cutter 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.