MDF Spoilboards Spoilboard, sacrificial board, bleeder board; whatever you want to call it, you’ve got to prepare the board for use on a CNC bed, to remove the sealer and make it porous so the vacuum will pull through it and hold down the work piece.
The goal is to remove the sealer that comes on every piece of MDF. Recipes vary but here’s one that hasn’t failed me yet.
1. Start with 3/4-in. medium density fiberboard (MDF).
2. Using a 4-in. flycutter with three blades, it should be spinning at 12,000 rpm at 30 meters per minute; using a 3-in. flycutter at 12,000 rpm, run at 25 meters per minute. Overlap each cut by about 1 mm. (Shown: Amana’s $211 RC2252 Spoilboard bit.)
3. Take at least 0.5mm off both sides to remove the sealer that comes on all MDF boards.
4. You might notice small pieces near the edge of your spoilboard move more often than pieces in the middle. Try edgebanding the spoilboard, or use a sealer on all four sides to seal the edges to even the vacuum.
As a technician I often enter a shop only to find flycutter making a high pitch noise like a model airplane. The reason: dull blades, which cause the tool to polish material, sealing the board rather than opening it up with a fresh cut.Do not forget to rotate your blades.
One more thing: change your foam gasket material annually. It will lose density and shape over time due to usage and shop climate conditions.