Top & Bottom Cutters for Double-Edge Radius Routing

Carbitool Rad Cutters are 4-flute, carbide-tipped top & bottom cutters for the Carbitool Double Edge Radius system, giving woodworking shops a precise way to configure 3mm, 5mm or 8mm radiused edges. The current Industrial Shed collection contains six individual cutters: three right-hand top cutters plus three left-hand bottom cutters.

For the complete two-edge routing concept, Carbitool Bull Nose Radius Bit provides a related approach to shaping both sides of a board. Where the required edge is a larger, sweeping curve across wider timber, Carbitool Half Bull Nose Radius Bits moves into 45mm, 60mm & 75mm radius profiles.

The crucial distinction on this page is position + rotation + radius. A 5mm top cutter is not interchangeable with a 5mm bottom cutter simply because their radius matches.

What Are Carbitool Rad Cutters?

Carbitool Rad Cutters are the individual cutting components associated with the manufacturer's 4 Flute Double Edge Radius Bit system.

The complete Carbitool R670 assembly is designed to round the top & bottom edges of timber at the same time.

Its configuration combines:

• Top/right-hand radius cutter

• Bottom/left-hand radius cutter

• Bearing

• Spacer

• Washers

• Arbor

Industrial Shed currently lists the six individual radius cutters rather than the complete TDA assembly:

Carbitool specifies these individual cutters as 4-flute, carbide-tipped components.

That makes terms such as radius cutter, double-edge radius cutter, top radius cutter & bottom radius cutter useful descriptions of the range without forcing repetitive wording into every paragraph.

Why Choose Carbitool Rad Cutters?

The clever part of this system is not simply that it makes a radius—it coordinates what happens above & below the timber.

Carbitool's complete Double Edge Radius assembly positions separate cutters around the workpiece so both edges can be rounded during the same operation.

That makes the individual Rad Cutters particularly relevant for workshops maintaining, replacing or configuring the manufacturer's R670 system.

Three Radius Sizes Create Three Different Edge Treatments

The range offers 3mm, 5mm & 8mm radii.

A 3mm radius creates the smallest edge treatment.

Moving to 5mm increases the curve.

The 8mm cutter creates the largest radius in this particular family.

Those sizes should be compared against the material thickness & required finished cross-section rather than viewed as small, medium & large versions of an otherwise identical job.

Top & Bottom Cutters Have Different Rotations

Carbitool distinguishes the cutters explicitly.

Top cutters are RH.

Bottom cutters are LH.

That directional relationship is fundamental to the assembly.

A buyer replacing one component should therefore identify its radius + position + rotation before ordering.

Four Flutes Distinguish This Family

Carbitool uses four-flute cutters in the Double Edge Radius system & states that the four-flute design is intended for longer cutting life.

That is another reason these individual cutters should not be described as ordinary two-flute round-over router bits.

They belong to a specific multi-component radius-cutting system.

Common Applications

Rounding Two Timber Edges Together

One pass across the component can address two corners when the complete assembly is configured correctly.

Carbitool's R670 system is designed specifically for rounding the top & bottom edges of timber simultaneously.

That makes it relevant where the required component cross-section calls for matching radii on opposing edges.

For another Carbitool approach to two-sided rounded profiles, Carbitool Rounding Fillet Bits provides the third direct profile comparison, although its geometry & operating concept differ from this stacked double-edge system.

Repetitive Timber Components

Repeated components expose setup inconsistencies quickly.

Once the correct radius, cutter pair & spacing have been established, preserving that configuration can reduce unnecessary interpretation between batches.

Accurate stock dimensions matter as well. Measuring & Layout Tools supports dimensional checking before the material reaches the radius-cutting setup.

Furniture & Joinery Components

Rails, furniture parts, trim & other timber components can require corresponding rounded edges.

The appropriate radius depends on the finished cross-section.

Rather than describing every application as generic “edge shaping”, compare 3mm, 5mm & 8mm against the actual timber thickness & visual requirement.

Replacement Cutter Requirements

This collection has a particularly strong replacement-tool intent.

A workshop may already own the R670 assembly but need only one worn or damaged cutter.

In that situation, identifying T 194-5 M RH rather than merely searching for a “5mm radius cutter” prevents ambiguity about whether the required component belongs above or below the timber.

For workshops managing cutters, setup components & job-specific tooling together, Tool Storage provides a relevant cross-sell pathway into broader workshop organisation.

Material Thickness Changes the Assembly Setup

Carbitool documents the complete Double Edge Radius assembly for material up to 30mm thick.

The bearing, spacer & washers alter the spacing between the cutters for different timber thicknesses.

That means the individual radius cutters are only part of the setup.

The distance between them must correspond with the workpiece.

Product Selection Guide

First Question: Top or Bottom?

Do not begin with radius. Begin with the cutter's position in the assembly.

A replacement top cutter requires the RH version.

A replacement bottom cutter requires the LH version.

Once position is established, select the matching 3mm, 5mm or 8mm radius.

This simple sequence reduces the risk of ordering the correct radius with the wrong rotation.

Then Choose 3mm, 5mm or 8mm Radius

The individual cutter diameters change with radius:

3mm radius — 28mm cutter diameter
5mm radius — 32mm cutter diameter
8mm radius — 38mm cutter diameter

For an existing assembly, match the documented cutter specification.

For a new profile, consider how the chosen radius relates to timber thickness & the finished edge.

Match Top & Bottom Geometry

A double-edge radius works as a system.

If the design requires matching top & bottom curves, the corresponding RH & LH cutters need to provide the intended radius relationship.

Do not assume that any top cutter can simply be paired with any bottom cutter because both fit the same arbor system.

Understand the Complete Assembly

Carbitool's R670 assembly is more than two cutters.

The manufacturer documents:

• Bearing

• Spacer

• Washers

• TA20 replacement arbor

• TB12 replacement bearing

These components allow cutter spacing to be configured around different material thicknesses.

Where broader Carbitool machine & cutter accessories need to be organised alongside the tooling, Power Tool Accessories provides an additional Industrial Shed category pathway.

Account for Timber Thickness

Carbitool provides assembly guidance for several workpiece thicknesses up to 30mm.

The published combinations include changes to the bearing, washers & spacer rather than one universal gap between cutters.

That makes material thickness a setup dimension—not merely an application detail.

Rad Cutter or Conventional Edge Bit?

A standard bearing-guided edge-forming bit often carries its profile on one cutter body.

The Carbitool Double Edge Radius system works differently.

Separate top & bottom cutters are arranged around the timber.

If the project only needs one corner rounded, a different edge-forming solution may be more appropriate.

Expert Tips

Read the Entire Part Number

A single suffix changes the cutter's role.

T 194-5 M RH identifies the 5mm top/right-hand cutter.

T 194-5 M LH identifies the 5mm bottom/left-hand cutter.

When ordering replacements, record the complete code rather than relying on “5mm Rad Cutter” written on a workshop list.

Keep Matched Components Identifiable

Once a working assembly has been established, store the related cutter pair & setup components so their relationship remains obvious.

Mixing similar 3mm, 5mm & 8mm cutters across jobs creates unnecessary setup risk.

A labelled storage system can be more valuable here than a drawer containing several visually similar cutters.

Measure the Workpiece Before Setting Cutter Spacing

The spacing system exists because material thickness changes.

Measure the actual prepared stock rather than relying only on nominal timber dimensions.

For workshop measurement equipment, Carbitool Measuring Tools provides a useful supporting category.

Treat the Spacer & Washers as Setup Components

They are not leftover hardware.

Carbitool documents specific combinations of bearing, washers & spacer for adjusting the distance between cutters.

Keep those components with the radius assembly so the manufacturer's spacing system remains available when material thickness changes.

Preserve a Sample From Repeat Jobs

A routed sample captures several decisions simultaneously: radius, cutter spacing & finished relationship between the upper & lower edges.

Label the sample with the cutter size & relevant setup information.

Months later, that piece can communicate more than a brief note in a job folder.

Inspect Before Assuming the Radius Is Wrong

A deteriorating edge does not necessarily mean a different radius cutter is required.

Check cutter condition, assembly components, material preparation & setup first.

The Black Print: Blade Sharpening 101 Sharpen Or Replace provides broader guidance around assessing cutting-tool condition before deciding what needs attention.

Keep the Assembly Clean Without Losing Its Setup Logic

Cleaning several components separately can create another problem if spacers, washers or matched cutters are mixed afterwards.

Industrial Shed's How To Clean Your Gear Without Ruining It provides broader equipment-care guidance, while labelled organisation helps preserve the cutter system itself.