How to Joint & Plane Large Boards on a CNC

If you have access to a CNC machine, then using it to joint and plane large boards can be really useful. I had a large piece of cherry that was really twisted and warped. The piece was too large for my jointer and my planer, and while you could clean it up using handtools, that would be a lot of work. So, instead I opted to use my CNC machine which offers a couple of benefits that you won't get with traditional tools.

I made a video going over each of these steps as well, if you prefer to watch instead of reading.

Step 1: Secure the Wood

The first step is to secure the wood to your spoil board. When you surface you'll be interacting with the entire top, so you can't place any clamps on the top of the piece. If the board is not flat, but warped and rocking, the first step is to get it flat using wedges.

To secure the piece, I prefer to use hot glue. A little bit goes a long way! I like to put some just around the edges, one dab on each edge, and don't forget to add a little to the wedges as well, so that's not a weak point. If you put too much hot glue down, you'll be spending a lot of time removing it lately, and it'll rip some of your spoil board up as well.

Step 2: The Routing Bit

While some people prefer to use a large surfacing bit, like the 2nd picture, I've found that kind of bit produces a lot of fine dust, and I prefer to create chips instead. So I use a 1/2 inch spiral upcut bit (there's a 1/4 inch upcut bit next to it for comparison). If your machine can handle that size bit, then it's a great choice, you can run the machine faster and it produces less dust and a great surface.

Step 3: Finding the High Point

The next step is finding the high point. Since the board is so uneven, you'll have to manually find the high point, and it can be useful to see how great the difference is between the high and the low point and get an idea just of how much you'll be needing to remove in order to get a flat surface so you can flip it around and surface the other side.

If your board is very uneven, I like to measure out how large the high point area is, and then start by cutting that section off. If you run the machine over the whole piece, you'll be spending a lot of time cutting in the air.

Step 4: Cut in Sections

Set up your software, and start by cutting smaller sections at a time. I did 1/4 inch cuts at each point, and slowly expanded the area to include most of the whole piece of wood. Once the majority of the board was flat, I decided to turn it around.

Step 5: Flip It Over & Secure

To remove the hot glue, simply score with a knife and it should come off pretty easily. Make sure to clean up the area of any debris, before putting the wood down on the flat side. Secure again with hot glue and get it ready to cut again.

Step 6: Cut the 2nd Side

Use the same technique as last time - find the high point, and cut the piece in sections, slowly expanding as you flatten out the piece. If your board is a lot thicker on one side, and thinner on the other, you can surface it into two or three different thicknesses - if you don't need the entire board for one project. I decided to surface it into two different thicknesses as I needed a thicker cut for some parts, and I wasn't looking to surface the whole board into one piece.