Round Top & Bottom Timber Edges Together

Why machine one edge, turn the workpiece over & repeat the setup if the component can be profiled from both sides in the same operation? Carbitool Double Edge Radius Bits are 4-flute, carbide-tipped router cutters designed to round the top & bottom edges of timber at the same time, making them particularly useful for repeated furniture, shelving, benchtop & joinery components.

The complete assemblies combine opposing cutters with a bearing, spacer & washers, allowing the setup to accommodate timber up to 30mm thick. For the closest supporting tooling, start with  Carbitool Router Accessories &  Specialty Woodworking Tools.

What Are Carbitool Double Edge Radius Bits?

Think of the cutter assembly as two coordinated edge-forming tools sharing one setup.

Instead of routing the upper radius first, flipping the timber & attempting to reproduce the profile on the lower edge, the Carbitool assembly positions a top cutter & bottom cutter around the workpiece.

The documented complete-tool range includes:

Carbitool also supplies corresponding RH top cutters & LH bottom cutters separately.

All three complete assemblies use 1/2" shanks, 4-flute cutting geometry & a ball-bearing-guided arrangement. Carbitool specifies TB12 as the replacement bearing & TA20 as the replacement arbor.

Those replaceable assembly components make  Ball Bearings & Accessories directly relevant when maintaining this type of tooling.

Why Choose Carbitool Double Edge Radius Bits?

Two Finished Edges From One Coordinated Setup

The productivity benefit is straightforward.

A conventional single-edge rounding operation may require one pass for the first edge followed by repositioning or flipping the component for the second.

Double Edge Radius tooling brings both profiles into the same operation.

That can be especially valuable when producing a batch of shelves, rails, furniture components or other repeated timber parts where both long edges require matching radii.

Opposing Cutters Help Keep the Profiles Related

Flipping timber introduces another setup variable.

A difference in reference position, stock thickness or cutter adjustment can make the second radius subtly different from the first.

Here, the opposing cutters are already arranged around the workpiece.

That doesn't remove the need for accurate setup, but it changes the process from two separate edge-forming operations into one coordinated machining operation.

Four Flutes Put More Cutting Edges Into the Job

Carbitool uses four-flute cutters in this range & identifies the arrangement as providing longer cutting life.

For workshops machining repeated components, cutter condition still deserves inspection throughout the run. More cutting edges don't eliminate the effects of contamination, timber variation or an incorrect setup.

Common Applications

Shelving With Fully Rounded Edges

Shelf fronts are a natural application for double-edge radius tooling.

Where both upper & lower corners need softening, machining them together can produce a balanced edge without turning every shelf over for a second matching pass.

The visual effect changes considerably between a 3mm & 8mm radius, so profile scale should be considered alongside shelf thickness.

Furniture Components

Table components, cabinet parts, rails & exposed furniture edges can require matching rounding on both faces.

A repeated component is where the workflow advantage becomes obvious.

One piece may not justify much concern over an additional setup. Fifty pieces can.

For production stock that needs dimensional preparation before edge forming,  Jointers & Planers provides a useful upstream category.

Benchtop & Table Edges

A square slab edge can feel visually heavy.

Applying corresponding radii to its upper & lower corners softens the profile while retaining a flatter central section between them.

The selected radius controls how strongly that transformation reads.

A 3mm treatment remains comparatively restrained. An 8mm radius removes considerably more visual sharpness from each corner.

Cabinetry & Interior Joinery

Exposed panels, shelves & purpose-made timber components often benefit from an edge that's comfortable to handle & visually consistent.

Batch work makes repeatability especially valuable.

Before routing begins, separate components by finished thickness & confirm the assembly is configured for the actual stock rather than a nominal sheet or timber dimension.

Repeated Workshop Production

The real efficiency gain appears when the same profile runs across multiple parts.

If the stock is prepared consistently, one established assembly can remove a repeated flip-and-route stage from the workflow.

For a broader look at preparing equipment before busy production periods, Spring Jobsite Prep Getting Your Gear Ready provides useful workshop context.

Product Selection Guide

3mm, 5mm or 8mm Radius?

Don't begin with the biggest cutter.

Begin with the finished edge.

3mm radius: provides the most restrained rounding in the documented range & can suit components where the objective is primarily removing sharp corners without dramatically changing the profile.

5mm radius: creates a more visible curve while retaining a substantial central edge section on appropriately sized stock.

8mm radius: produces the strongest rounding of the three & deserves careful consideration around stock thickness & the amount of flat edge you want to retain.

A sample cut answers this question faster than staring at cutter dimensions.

Stock Thickness Changes the Assembly

Here's where this collection becomes more interesting than a conventional rounding-over bit.

Carbitool provides a specific spacing guide for the opposing cutters:

The bearing, spacer & washers therefore aren't incidental hardware. They are part of configuring the assembly around different timber thicknesses.

Measure the actual workpiece before building the cutter stack. Calipers (Digital / Manual) can support closer dimensional checking where nominal stock size isn't enough.

Double Edge Radius or Rounding Over Bit?

Both create rounded timber edges.

Their workflows are different.

A conventional rounding-over bit normally addresses one edge at a time.

A Double Edge Radius Bit positions cutters to round the upper & lower edges together.

If only one corner needs machining, a double-edge assembly may add complexity without benefit. Where both sides of repeated components require matching radii, its purpose becomes much clearer.

Complete Assembly or Replacement Cutter?

Carbitool lists complete TDA assemblies as well as separate top & bottom cutters.

The replacement cutter range includes:

► T 194-3 M RH & T 194-3 M LH – 3mm radius
► T 194-5 M RH & T 194-5 M LH – 5mm radius
► T 194-8 M RH & T 194-8 M LH – 8mm radius

Identify whether you're purchasing a complete setup or maintaining an existing assembly before ordering.

Confirm the Machine Can Handle the Assembly

All documented complete tools use a 12.7mm / 1/2" shank.

That does not mean every router accepting a 1/2" collet is automatically suitable for every operation.

The assembled cutter diameter, operating method & machine manufacturer's cutter-capacity requirements still need to be considered.

Expert Tips

Measure the Finished Stock—Not the Size Written on the Invoice

Nominal thickness can mislead a cutter setup.

Machined timber, sheet material & prepared components may not measure exactly what their product description suggests.

Take readings from representative pieces after preparation.

The cutter stack should meet the timber actually arriving at the router.

Build the Stack on the Bench Before the Production Run

Bearing.

Washers.

Spacer.

Top cutter.

Bottom cutter.

Each component has a job.

Confirm the assembly arrangement against the intended timber thickness before starting the batch rather than making hurried changes once material is moving through the machine.

Keep Opposing Cutters as a Matched Profile

Replacing one damaged cutter deserves more thought than simply matching its outside diameter.

The top & bottom cutters need to create corresponding radii.

Identify the correct RH or LH replacement & radius before rebuilding the assembly.

Give Repetitive Stock a Consistent Reference

If component thickness varies, the relationship between the upper & lower radii changes.

That's why stock preparation matters more on this cutter than buyers may initially expect.

For preparation, jigs & controlled bench work around repeated components,  Clamps & Vises can support the surrounding workflow.

Look at the Edge Straight On

After the test pass, don't inspect only the top surface.

Hold the sample at eye level & examine the complete edge cross-section.

Are the radii visually balanced?

Is the central flat the width you expected?

Does the chosen radius suit the component?

That view makes incorrect spacing immediately easier to understand.

Clean Before You Start Re-Spacing

A deteriorating finish doesn't automatically mean the washer arrangement is wrong.

Inspect the cutting edges, bearing & assembly for contamination before changing a setup that previously worked.

For broader maintenance practices, How To Clean Your Gear Without Ruining It provides useful guidance for workshop equipment.

Preserve the Radius Through Final Preparation

Both routed corners can lose definition if the finishing stage becomes too aggressive.

Follow the formed curves rather than flattening them.

For suitable timber projects moving from machining into coating or surface treatment,  Wood Finishing Products provides a relevant next-stage category.