The Maslow CNC sled is moderately unstable from a structural standpoint. This instability is most obvious in the lower corners, where the lateral tension is lowest, where chain sag most influences positional accuracy, and where the weight of the chain pulls the position out of the correct position.The sled is also torsionally unstable about the axis of the router, and parallel to the axis of the router. These problems are demonstrated by cuts that should be but are not straight, and the cutter pulling out of the router path. Several concepts have reduced some of the instability issues in critical locations, such as tensioning systems, slower cuts, shallower cuts, and improved calibration.
There is a way to get significantly improve accuracy and precision in a very simple and inexpensive way based on the concept of Single Minute Exchange of Dies (SMED). When preparing a 4’x8’ board for machining, two notches are first cut in the board at the top edge 4’ apart as shown in the first image at the top left labelled “1.”.
The size of the notches are exaggerated for visibility.
There are two and only two round pins upon which the material to be cut rests as illustrated in the second figure at the top right. The material to be cut is the light wood color, and the Maslow CNC is shown in the dark wood pattern. These pins can be placed in various positions along a straight line at the base of the Maslow CNC. In addition, there is a triangular pin that can be inserted at the base of the Maslow CNC on the centerline of the CNC. This pin was removed while machining the notches at the top. The material to be machined is removed from the Maslow CNC, the center triangular shaped pin is reinstalled and the board is rotated so that the notches are on the bottom with the notch on the left centered on the triangular pin. Note that the round pin positions are changed so that the center of gravity of the board being machined is always between the pins when the board is installed on the Maslow CNC!
This simple setup technique can assure that the board is accurately and precisely positioned relative to the Maslow CNC every time it is setup. Next we machine those portion of parts that are only within 25" of the centerline of the Maslow CNC such as left half of a star shown in red in Figure 2.
When all of the parts on the left half of the material are machined, the board alignment is shifted from the left notch to the right notch with the position of the lower round pins also shifted to the left as shown in the next figure. Shifting the board from the left notch to the right notch should not take more than 1 minute. The right half of the parts are machined, such as the right half of the star shown in blue. The misalignment of the red and blue cuts are within the accuracy and precision of the machine.
Because all of the machining is done in the center of the Maslow CNC, accuracy and precision of all cuts are very close the the best accuracy possible on the equipment, and the accuracy of the board setup from one setup change to the next can be within the accuracy of the notch cuts.
Naturally, when boards are narrower than 4’ wide, only one notch needs to be used in the board. Adding more notches makes it possible to cut parts from boards longer than 8’.