By John Forbes, NWFA
Although situations vary, the big machine’s first job normally is to flatten the floor. This “flattening” is a key first step to delivering a quality product. NWFA Sand and Finish Guidelines suggest the first cut should be at a minimum 7 to 15 degree angle to the length of the boards. When the first cut doesn’t produce the desired results, the traditional approach is to increase the angle of the cut (up to 45 degrees) in proportion to the unevenness of the floor. The aggressive scratch pattern left by a cut exceeding 15 degrees requires the subsequent straight cut to be made with the same grit.
Rather than increasing the angle of the cut (which will leave an aggressive scratch), an alternate approach is to make two cuts at a 7 to 15 degree angle in opposite directions to each other. This more-conservative sanding approach can yield excellent results without adding an extra step to the process. From that point the subsequent straight cuts may allow you to move to higher grit paper.
For additional resources, check out the NWFA’s Sand and Finish Guidelines at NWFA.org.