Hey Everyone!
The question of slab flattening comes up often in the intro to CNC class so we’ve put together a step by step guide below to help.
Instructions for Slab Flattening
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Lay your slab on the machine bed and use plastic shims to shim up any wobbles. We sometimes have shims laying around but you can buy them at home depot or amazon (Amazon.com).
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Restrain the slab in the X&Y directions using stops (1x or 2x material should suffice). Stops can be fiber nailed in (the plastic nails from the green gun). If the fiber nails don’t hold the blue Kreg screws in the blue box near the small CNC desk can be used. If using screws please be sure the screws are the proper size to screw through your material into the spoilboard but not the black phenolic below the spoil board. This should be considered a last resort after trying fiber nails. If the phenolic is punctured with a screw it will damage the vacuum suction. In most cases fiber nails are more than enough.
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When programming, use the manufacturer’s recommended speed settings and pass depth. Normally you’d start with a pass depth of 1/16" (.0625") or 1/8" (.125") but again the bit manufacturer can supply that information to you. The program you’ll create will be a rastered square/rectangle that you pocket out. In order to prevent having to “re-zero” each pass you can program the pocket to have a deep cut depth and simply stop the program once you’re satisfied with the surface flatness (Ex. program a pocket at 1" depth of cut with 1/16" or 1/8" passes).
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When you Z zero you may consider z zeroing using the “Paper Method” by lowering the bit to the surface of the material clicking “Menu+Z->0” and selecting “Clear Z.” You can also use the puck but it may be a bit difficult if the slab is really uneven. Keep in mind your first pass will pass over high points and low points in the material so the 1/8" or whatever you set the pass depth to be may be more or less aggressive on certain parts of the slab. It’s important to keep this in mind because of where you Z zero. If you zero the Z on a low point and have a pass depth of 1/8", when you get to a high point you will be cutting 1/8" + the difference between the high point and the point at which you Z zeroed. It’s recommended to run your first pass at 50% speed because of this. After knocking down the high points on the first pass you can increase the speed.
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Once the top side is flat you can flip it over and restrain the slab using the same stops. The vacuum table can help to add further hold down force in some cases. Zero off of this surface and you can run the same program you used to flatten the other side.
To visualize this please watch this short video Slab Slayer mesquite Slab, 1/8" pass at 400 ipm - YouTube of a mesquite slab being flattened on our Laguna Swift machine by @jamesfreeman.
Please keep this topic specific to questions, comments and information related to the process of slab flattening. If you have videos you’ve taken of slabs you’ve flattened on our Laguna CNC please share!