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How to get a good Kerf Setting for CNC Foam Cutters

What is the Kerf? Kerf is defined as the width of material that is removed by a cutting process. So in our case it’s the amount of foam melted by the hot wire.

To get accurate parts we need to know how much foam is melted away by the hot wire. So before we can ascertain that we need to run some tests on scrap foam and find settings that will give a good cut so we only melt the minimal amount of foam without the wire dragging in the foam. This will take a few tests with different settings. I leave the feed rate at 120 mm/minute and adjust the slider to get a nice cut without the wire dragging in the foam.

I use a 0.4mm nichrome wire that is connected to an MKS Gen L V1.0 board’s D8 connector on my machine. Recently I switched over to using 24 volts but did use 12 volts on the Arduino with a RAMPS 1.4 board. This is usually OK up to about 1000mm/39 inches.

Running the g-code

Run the g-code without any foam first just to double check it will run ok on your machine. I’ve tested it on mine several times and it works fine. Your machine may have some different settings so for peace of mind run it first without any foam/

Once we have settings for a good cut we can run some kerf tests. Use the g-code linked below called Kerf-Test G-code in the downloads section. This will make 5 cuts in a piece of foam.

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Kerf Test G-code (XYZA) 72.24 KB 315 downloads

Please follow the instructions in the ebook in the section entitled Kerf  …

I suggest you use a piece of foam 100 mm in length and 80 mm in height. The width can be any length. I just use the size of the foam I purchased which was 50 mm

Before you start, measure the foam as in the diagram above at “A”.

Place the foam on the foam cutter. Jog the axes to very near where the foam block bottom corner starts. Zero all the axes

Now load the g-code and switch on the hot wire, give it 20-30 seconds to reach its temperature. Run the g-code

When the g-code has finished cut the foam as in the diagram above so you have 6 pieces. Put them together and measure the size “B”. Subtract this from the original size and divide by 5 and that should give you a good value for the kerf setting.

Where to enter the Kerf Setting

If you are using free software that doesn’t have a kerf setting then you can add this value to the length of the root and tip. Although this won’t be as accurate as software that has options for setting the kerf it will get you close.

For wings where the root and tip have big differences in size, you will need to add a bigger kerf value for the tip. DevWing Foam 2 has a Smart Kerf option that can calculate this based on the wing dimensions.

How often should I check the Kerf setting.

If you use the same foam all the time and you haven’t change any settings on the hot wire then you shouldn’t need to do this very often. The type of foam makes a difference as well so if you change to a different type then run the tests again.

Hopefully you with this test you can get some accurate parts for you design. Check out my video where I show how accurate a CNC foam cutter can be using the design on this website.

Happy foam cutting

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