Combine Roughing Cutters and Spiral Finishing Cutters.

Looking for an excellent finish when CNC routing solid timber?  the best way to achieve it is with a combination of a Roughing Cutter and Spiral Finishing Cutter

10mm 3 wing upcut roughing spiral

1st Pass – Roughing Cutter

Roughing Cutters are an ideal cutter for removing material fast. You can run the first profile cut stepping down multiple times with a 1mm offset (1mm outside the desired finished profile). With a roughing cutter you can use a faster feed speed and greater cutting depth than an ordinary up or down spiral cutter or a straight cutter.

Typically, you would leave an “onion skin” on the bottom of the work. That is, instead of cutting right through you would finish the cut about 2mm from the underside. This maintains both the vacuum seal and also keeps the whole job in one piece.

It depends on the CNC Machine you are using, however a good place to start when it comes to cut depth for each pass is slightly more than the cutter diameter. For example, with a 6mm diameter cutter you would start with a cut depth of about 6-7mm. This is only a guide so please take into account the machine you are using and the material you are cutting.


2nd Pass – Spiral Finishing Cutter

Once you have completed the passes with the roughing cutter, leaving the 2mm “onion skin” on the bottom, you can then make the final cut at full depth with the down spiral in one pass. The cutter is only removing 1mm of material plus the “onion skin” so the cutter is not doing a lot of work.

If the material is thick, you can also do the cutting in two passes.

You are then left with the finished product with a very fine surface finish, even on end grain.

Although this process take a bit longer to run on the CNC, the time saved in sanding is well worth it.


8mm downcut 3 flute spiral router bit

Discount on Your First Order

Enjoy 5% Off Your First Online Order

Simply enter the code ROUGHING at checkout and a 5% discount will be automatically applied to your order.