Fly Cutting a CNC Spoilboard

When you're using your CNC, it's got a spoil board on it, and some operations are going to call for cutting all the way through your material. And that means we're going to cut into the spoil board. And if you look at this spoil board, not only does it have cuts in it, but it's also got dimples. It's got little pucker marks where I ran a screw into the MDF, took the screw out. And then when that screw comes out, it leaves a high spot. Now this one isn't horrible, but I'm going to take advantage of its condition to show you how to fly cut your spoil board. One of the things to look at here is, let's compare cuts on here and talk about good versus bad. The through cut here, that's just right. That barely penetrates the spoil board. That's how all your through cuts should be if you've got everything set correctly the through cut that was done here, that was way deeper than it needed to be. If you do a lot of this, you're going to be fly cutting your spoil board a lot more frequently. And of course we don't want to do that. So stick with shallow cuts. Let's talk about bits for this. One thing we want is diameter. The bigger the bit, the faster this whole thing is going to go. We have a lot of ground to cover on here. And of course there's a step over every time we cut, which is just part of the diameter of the bit. We don't get a full pass each time. So the larger the diameter, the better you're going to be. Let's compare this cutter to this cutter. This is just a kind of a standard off-the-shelf router bit. Notice that it does not have flutes across the bottom. This one does have flutes across the bottom. I like this a little bit better. It's going to give me a little better surface on my spoil board, but don't consider it a deal breaker. Don't consider it a must have, but it is nice to have the flutes across the bottom. Now there's another alternative which is going to add some money to the deal. This is a nice big diameter and these are carbide inserts. So, when one side gets dull, I can simply loosen the bolt, rotate it, use another side, another side, another side, replace the inserts when I'm done. With that big diameter, we'd fly cut very quickly. So bits like this are a great choice too. I'm going to use this one, really because of the expense of the large cutter. I want to show you the cut quality we can get out of this bit. I'm going to do a little bit of setup here and then we'll be ready to get started on fly cutting our board. On the programming side to get ready for fly cutting, in your software, create a rectangle that's slightly bigger than the size of your spoil board. And then what I do is what's called a pocket cut. And we're going to have the bit cut inside that pocket, so that we take the whole spoil board down. One of the things you might need to find out with your particular machine is how much outside of the machine will your spindle travel. We don't want to get to the end of the proximity switches. We just want to make sure though that the rectangle we're cutting is large enough to come all the way out to the edge. Depth of cut. Really good way to handle it is with digital calipers. Find the worst spot on your spoil board, take a measurement and then whatever we read there, go just a little bit beyond that in order to make sure that we're taking enough wood out. If you've handled your spoil board correctly and not over cut it like I did, somewhere around a 16th of an inch should be plenty. And the other good reason for doing this, which I neglected to mention earlier is even if your machine is brand new or when your machine is brand new, it's a good idea to cut the spoil board. Because we want to make sure the plane of the spoil board is perfectly parallel to the travel of the spindle. So it's quite possible, this is a man-made material, if it's not exactly the same thickness on one end as it is on the other, when you put a piece on there that's real sensitive to that thickness, V carving would be a great example of what kind of work where it could affect it, a little high on one end or a little bit low on one end. That's going to screw up your cuts. So you should be fly cutting a brand new spoil board before you use it for the first time. We are ready to go. Dust collection is important 'cause we are cutting MDF. And we'll let her happen here. Well, I've stopped the machine. It's going to run for a little while yet. This does take a while to make the whole spoil board fly cut, but looking at this, you can get a good idea of what an improvement that is. So again, we gain a couple of things. We make sure the spoil board is perfectly parallel to the travel of the spindle. And when you got over cuts in there, like I did and screw puckers, we're going to cut those right out. I'm going to let my machine get back to work, finish my fly cut. Make sure you do the same thing to your CNC machine.