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Cutterheads 101
This article was reprinted with permission from Wood Tech Tooling, www.woodtechtooling.com. Cutterhead Selection
Many factors determine proper cutterhead selection. One of the most important factors is feed rate. Most small shops use a feed rate of 50 Feet Per Minute( FPM) or less and have, as a result, a single-knife finish. For this application, a Straight Bore cutterhead is most commonly used. Accuracy is limited due to the "slop" necessary to physically fit the cutterhead onto the spindle shaft. The bore on the head is normally .001" to .002" oversized to accomplish an easier fit. The end result is that one knife in the head will be higher in the cutting circle, thus producing a single-knife finish. 
Straight Bore Tolerance 0,05mm (0.00196") Many older "push-feed" machines, with feed rates from 35 to 250 FPM), use Self-Centering Sleeve (SCS) heads. This head incorporates a removable sleeve that locks the head onto the spindle. Accuracy is again affected due to both the "slop" tolerance from the head to the sleeve, and also the "slop" from the sleeve to the shaft. This can result in tolerances of several thousandths of an inch. The condition of the head, and the machine's spindle, is critical to produce quality material out of the moulder. These heads can be jointed, but extreme care must be taken not to over joint the knives. Hydro Lock head use is normally reserved to companies with high speed machines with the tightest of machine tolerances. In house grinding capabilities are a must to get the full benefit from the tooling. Hydro Lock heads use a pressurized sleeve to create a much tighter fit on both the grinder and the moulder. 
Hydro Lock Tolerance 0,005mm (0.000196") The further use of the jointing process produces a cutter capable of increased feed rates because all knives are in the same cutting circle. This process uses an abrasive stone that strikes the knives while the head is rotating. Jointing actually "dulls" the knives, so care must be taken not to over joint the knives. Spindle Type and Condition
The use of a Safety Locking Collar is highly recommended to reduce possible head, or spindle, damage resulting from a Hydro Head spinning on the shaft. 
Jointed Knife Machine Condition
Only 5% of "tooling problems" are truly related to tooling. Proper operator knowledge and training is a very important factor more commonly overlooked than you might think. An operator that understands the nature of the tooling and machinery being used is better equipped to produce quality products. This article was reprinted with permission from Wood Tech Tooling, www.woodtechtooling.com. Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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