The Plane Truth about 12" Thickness Planer Snipe
In all my years in the business I have never been so amazed at how misinformation and propaganda can spread like wild fire. This is the case with head locks on some 12" planers introduced in 1997. We hear phrases in advertising like, "You can avoid snipe by using a lock or exclusive cutterhead snipe control lock." It is easy to understand how this type of information spreads when you have misleading multi-million dollar ad campaigns. Then we have some of the so-called teachers and experts saying this is the best thing since sliced bread. This causes people to jump on the band wagon and singing the praises of the 12" planer head locks. I guess I'm in the minority and this is my opinion, but I don't think head locks have any effect when it comes to what causes snipe on a board.
Snipe
First we have to define what snipe is. Snipe is the gouging or depression of the board at the ends. Snipe occurs either at the beginning of the board going into the planer or at the end of the board as it comes out of the planer.
How does a planer work?
On 12" portable planers there are two spring loaded rubber-coated feed rollers. The feed roller in front of the cutter head (toward the front of the machine) is the in-feed roller. The feed roller in back of the cutter head (toward the back of the machine) is the out-feed roller. Once these spring loaded in-feed and out-feed rollers grip the board they automatically push or pull the board through the cutter head and than out the back of the planer.
The length of the snipe on the board will usually be equal to the distance from center line of one of the feed rollers to the center line of the cutter head according to Cliff Rickmer, VP of Operations at JET Equipment & Tools.
The spring loaded feed rollers are designed to follow and grip (under pressure) the surface of the board. The cutter head is fixed in place and does not move up or down as the feed rollers do.
When a board is put into the planer, the spring loaded in-feed roller grips the leading edge of the board. It rides up onto the top surface of the board and pushes the board down and into the cutter head. The cutter head knives remove the set amount of wood. Once the board reaches the out-feed rollers they ride up onto the planed board surface and pull the board out the back of the machine.
The planing process
So, if we visualize this process we find that there is upward pressure on the in-feed rollers when it grips the board. Using a 12" planer that has no head lock or on one that is not engaged, the condition we would have is upward pressure from the in-feed roller gripping the board. This would force the cutter head up (not down) away from the board. It is that simple. If the cutter head is forced up it can't cause snipe (a gouge or depression) in the ends of the board.
So what does cause snipe?
I can't put it any better than R.J. DeCristoforo did in his article "A Planer Miracle" in the January 1998 issue Popular Woodworking Magazine. "Keeping the board flat throughout the pass is very important. "Snipe" - a thickness planer bugaboo that is actually a slight depression on either end of a planed board - is usually caused by failing to support the work on a true plane throughout the pass. Snipe can occur, for example, when the weight of a board entering or leaving the planer tilts the board up into the cutterhead so more wood is removed at the end of the pass. That's one reason that extending the length of your planer bed is a must" (DeCristoforo, page 23).
The bottom line
What this all means is head locks do not that controls snipe. Snipe is caused by the board not going into the planer level or not coming out level. It's just that simple. If you do not believe me, next time you see one of these planers being demonstrated wait for the sales person to say the head lock reduces snipe or eliminates snipe or controls snipe. Then ask if the head lock controls snipe, the in-feed and out-feed tables can be adjusted to an out-of-level position and still prevent snipe, RIGHT? Sorry WRONG!