To ensure a high-quality surface finish from a spiral cutterhead, it is crucial to maintain the carbide inserts at a consistent height. To achieve this, cutterhead blocks are machined using CNC machines with a tolerance of approximately 0.005mm. This guarantees that the carbide inserts remain fixed in place once the screws are tightened.
Regrettably, a recent article made an inaccurate and misleading claim that a specific brand provides an adjustable radius height of 4", while another brand offers 8". It's crucial to clarify that the radius height adjustment is not related to the type of carbide inserts used by different brands. Sheartak utilize R150 round edges for their carbide inserts, while Byrd uses R100 edges, and these radii have no correlation with the radius height adjustment.
R150 edges (6" radius) have a flatter curve compared to R100 edges (4" radius), which results in shallower scallops on boards. However, the maximum radial difference between R150 and R100 edges is only 0.08mm. In order to generate shearcut, Sheartak and Byrd both angle the carbide inserts to the feeding. When this value is converted to the radial height of the spiral cutterhead, the variance is hardly noticeable.
The carbide inserts are precision ground to a certain degree of accuracy, typically +/- 0.0004" or +/- 0.01mm. This means that the inserts can vary in length by 0.02mm, which is a significant source of lines on boards that many woodworkers have noticed. To eliminate or reduce these lines, it's important to loosen the screws, clean any dirt off the inserts and seats of the cutterhead, press the inserts firmly into place, and prevent them from moving up and leaving a gap between the inserts and the seat face. In most cases, these issues with lines on boards can be easily fixed with all helical cutterheads unless they are poorly programmed or machined.
