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CNC Guide

A guide to using the Shopbot CNC machine in MAKE ll at Library 21c

Clearance Tools

For pocket cuts and similar toolpath types, you can use multiple tools to clear out the interior area of a closed vector. In most cases, the larger the bit, the faster it can carve out the area - the bit has a larger surface area, can move faster, and has a greater cutting depth. However, larger bits cannot fit into narrow spaces, limiting what can be carved. Note that if the chosen bit cannot reach an area, the machine will simply ignore it. Using multiple bits of different sizes can help find a balance between the need for shorter run times and the need to carve small areas. When using multiple bits, the software determines what sections can be removed by each tool, leaving behind any areas that the bit cannot reach, starting at the top of the list and working downward.


While you can choose any bits (and any number of bits), it is often best to use two and often the best two are the largest bit that can still reach everything and one that is twice the diameter (e.g. use a 1/8" and a 1/4" bit). While a much larger bit can be used, it is often less efficient. It will carve the wider areas faster, but there will be significantly more areas that have to be left to the smaller bit.


When exporting a toolpath that uses mutliple tools, VCarve will create separate .sbp files for each tool used. The last tool will be named as written in the toolpath creation window, and the rest will have [Clear 1], [Clear 2], etc. appended to them starting at the top. For example, if a pocket cut named Pocket 1 uses 3/8", 1/4", and 1/8" bits, it will create the following toolpaths and files:

  • Pocket 1 [Clear 1] - the 3/8" bit
  • Pocket 1 [Clear 2] - the 1/4" bit
  • Pocket 1 - the 1/8" bit

Running the Cuts

Cuts should be run in the same order that they are listed in VCarve (so Clear 1, Clear 2, etc). This not only ensure that the cuts are run in the most efficient order possible, but the least amount of wear is done on the bits. The final cut will not only clear out any remaining areas, but will make a pass around the outline of the pocket, smoothing out the edges.