Carve Out Pockets with Your CNC

One of the most used toolpaths in CNC woodworking, the pocket toolpath works for many applications, such as carving recesses for inlays and trays, mortises and other joinery, and more. Take the plunge and dig yourself into a hole.
Randy Johnson May 31, 2022
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One of the most used toolpaths in CNC woodworking, the pocket toolpath works for many applications, such as carving recesses for inlays and trays, mortises and other joinery, and more. Once you understand the basic concepts, the door to creatively using pocket cuts swings wide open.

The basics

Simple and complex designs work with the pocket toolpath. Within that line, the router bit cuts a depth that you specify. You cannot use open shapes or unconnected lines.

The primary function of a pocket toolpath is carving out the inside area of a design, such as the square or hand shown in photo, above. The shape must be a continuous line, or a closed vector as it's referred to in VCarve. Selecting this line allows you to use the Pocket Toolpath panel (photo, below) to assign a bit to rout out this area, and control how that bit moves and cuts.

This article breaks the Pocket Toolpath panel, right, into five smaller sections. I'll walk you through the functions of each section.

When you first look at the Pocket Toolpath panel, the many settings may seem overwhelming. You may not use all of them, but focusing on the primary ones will increase your CNC capabilities. 

How deep will you go? 

The options on the left were used to first cut the square to a depth of .25". The options on the right then cut the pocket-within-a-pocket hand starting at .25" depth, removing another .25".

Starting at the top of the Pocket Toolpath panel, you find the Cutting Depths setting (photo, above.) These settings often confound new CNC users, because they are additive. The Start Depth represents where the bit starts cutting, and generally this setting is left at zero, so the bit starts cutting on the top surface of your board. The Cut Depth represents the amount of material to be removed. If you already have a pocket cut on your project (for example, the square in photo, above) and want to cut a deeper pocket (the hand) inside the first, set the Start Depth to begin cutting at the bottom of the first pocket and the Cut Depth to the amount of additional material to remove. This saves time because you don't "cut air" when beginning the second pocket cut. 

Pick a bit and set its options

Customize the tool database's options to match your router-bit collection and the settings for cut depth, speed, and more that you want to use with each bit. The window above the Select… button shows the bits that you choose for a job.

Moving down the panel, find Tools. In this section, select and configure the router bit(s) you want to use with the pocket toolpath. Clicking on the Select… button opens the Tool Database (photo, above.) From this list, select the bit(s). If you choose two or more bits, the toolpath uses the largest bit to clear out most of the material, and the smaller bit cleans up the details (photo, below.)

Using two bits allows you to use a large bit to clear large areas of the pocket quickly and cleanly, and a smaller bit for cutting finer details. The smaller bit skips areas cut by the larger bit.

Get your pass and directions

You can override the pass depth settings in the Tool Database by clicking on the Edit Passes… button. You can also adjust the depth of each pass with the settings at the top of the window.

The Passes section of the panel defines the number of passes it takes to reach the bottom of the pocket (photo, above.) Fewer, deeper passes reduce cutting time but increase the strain on the bit. In this section, you can also add a shallow final pass to improve the cut quality at the bottom. For starting out, I recommend using the defaults and running a few tests before changing the settings here. 

The Offset method cuts a pocket in a series of concentric passes starting in the center of the pocket. Although this method leaves a spiral pattern of tool marks at the bottom of the pocket, it cuts 10–20 percent faster than the Raster method, so it's a good choice when cutting hidden pockets, or in materials such as MDF and plywood. You can also select a Climb or Conventional cutting direction. Like climb-cutting with a typical router, the climb direction reduces chipping and tear-out when cutting solid woods.
The Raster method cuts the pocket with a series of back-and-forth passes. This leaves less-noticeable tool marks when run with the grain of the wood, so it's often the preferred method when cutting solid wood. The Climb/Conventional setting applies only to the Profile Pass (perimeter cut) since the actual raster cutting alternates between climb and conventional as it switches feed direction. The Degrees setting controls the direction of the raster. You can choose to cut the profile pass first, last, or not at all.

Below the Passes setting, you can specify an Offset or Raster method for cutting the pocket (photos, above.) Using the Ramp Plunge Moves setting reduces pressure on your bit and machine, improving the cut quality at the point of entry (photo, below.)

Adding Ramp Plunge Moves eases the bit into the material and reduces the dwell marks that often occur when plunging straight down into the material. This even applies to end mill bits but is essential for a non-end mill bit. On small benchtop machines, a ramp of 4–8 times the bit's diameter works well.

Save your allowance

The Pocket Allowance setting precisely increases or decreases the pocket's width and length. Adding a negative allowance increases the size of the pocket; a positive allowance decreases it.

The Pocket Allowance provides a way to overcut or undercut the sides of the pocket, a useful feature when you make parts that must fit together, such as a half-lap joint (photo, above.) Because a good CNC cuts parts precisely, adding some pocket allowance prevents parts from fitting too tightly. I also find it useful when the pocket must accommodate a part cut on a different machine, such as a tablesaw, because the part from the tablesaw may be slightly over- or undersized, or may have changed size due to shifts in humidity. This setting is also helpful for dowels that vary in size. 

Using the pocket allowance gives you a quick way to adjust the size of the hole, so the dowel fits perfectly. Below the Pocket Allowance option is a check box for Use Vector Selection Order. Use this option when you have multiple pockets and want to cut them in a specific order.

Specialty pocket options

The Project toolpath onto 3D model option bends the pocket to the contour of the 3D model. In this case, the hand pocket cut wraps to the top of the dome shape. Be aware that you may have to adjust tool settings to get the desired results. For example, when testing this design, I switched to a bullnose bit because a straight bit left a rough texture.

Find a couple of advanced settings at the bottom of the Pocket Toolpath panel. First, Project toolpath onto 3D model does just what it says (photo, above.) The next one, Vector Selection, allows you to select a particular vector type from your design. For example, if your design includes a variety of circles, use this option to select and associate all the circles of a specific size for this toolpath. It proves useful with complex designs or in production situations. 

A few more tricks

A bowl bit combines an end mill's flat end-cutting ability with the radiused corners of a ball-nose bit. This combination leaves a clean, flat bottom with a rounded transition to the wall.

Although it is common to use a straight bit with the pocket toolpath, you can also use other types. For example, combine a bowl bit with the pocket toolpath to create shallow bowls and trays (photo, above and opening photo.)

o address the rounded corners left by a router bit, VCarve can slightly overcut the corners. The first method, the dog-bone fillet, left, extends diagonally out from the corner. As a result, a portion of it remains visible after assembly. The T-bone fillet, right, extends only one side of the pocket and the adjoining part hides it. However, the T-bone fillet reduces gluing surface and may weaken parts with closely spaced fingers or mortises. Of course, you can skip the fillets and chisel out the corners by hand, which is what I usually do in hardwoods.

The pocket toolpath can also make finger and mortise-and-tenon joints. Because a router bit leaves rounded corners, VCarve provides two methods to allow the parts to fit together (photo, above.) Although using a profile toolpath, which cuts only the perimeter of the opening, is sometimes quicker, it leaves a small chunk of wood in its center that can jam the bit or damage the joint. I prefer using the pocket toolpath because it routs away all the material inside the mortise or finger opening.  

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