Popular Woodworking 2008-08 № 170, страница 41

previous articles on safety? On the planer that means that your hands should be at least 3" from the front or back opening of the machine along with any guards, shields, pulleys or anything that can grab or pull you in.

Planer Kickback

Kickback on a planer can occur for many reasons. If wood does kick back it will more than likely be thrown toward the infeed side. However, if a piece of wood shatters in the process of cutting creating a kickback, these bits of shrapnel could ricochet on the inside of the machine and fly out the either the front or back of the machine. This is why rule number one is to never stand behind your work. Always stand to one side of the machine on both the infeed and outfeed side. Never stoop down to watch a board being surfaced. Never stack boards on top of one another and run them both through the machine. Kickbacks most likely will occur because of one of the following reasons:

• Knots. Knots are not always solid. Loose knots can be pulled or knocked loose from the board. Once they are free inside the machine, they can easily come in contact with the rotating knives and be thrown out.

• Short Stock. There are definite rules about running short stock through the planer. Never run stock that is shorter in length than the distance from the infeed roller to outfeed roller. This is why the 12" rule exists. If your stock is less than 12" long, you should take a moment of pause and determine if that piece is too short for your machine. In the case of the planer the rule is the shortest board that the machine can handle should be 2" longer than the distance between the infeed and outfeed rollers. That way stock will always be supported by one of the feed rollers. If the stock is shorter than that distance, it can get trapped between the two rollers with no support at the point of action, creating

a kickback. When surfacing several pieces of short stock, (short meaning stock that it is still longer than the distance of the infeed and outfeed roller plus 2") they should be fed by butting the ends. These butted pieces will help

push each other out of the machine and they will be less likely to stick under the chipbreaker or pressure bar.

• Wood that shatters. Thin stock can easily shatter under the force of the rotating knives. The grain direction and character of the grain, such as curly, swirly or burl wood, or wood with serious defects, can shatter while being planed. If the chipbreaker is set too high, the stock can tip up into the cutterhead causing the stock to split or tear unevenly. Forcing the feed or taking too much of a cut can cause the wood to shatter as well.

• Nails or debris. Always check the wood before planing to make sure that it is not embedded with foreign material. Even dirt or small bits of sand can nick the knives, which in turn could grab the wood awkwardly and possibly throw it out of the machine. Be especially careful with old lumber that may have hidden nails or debris. Foreign objects such as old nails, bolts or staples can cause the knives to break or be pulled out and be thrown from the machine. Glue lines or wood that has an existing finish on it could cause undue wear on the knives, and dull knives can cause potential kicking forces.

Distorted Stock

Wood that is warped, cupped, twisted or bowed could cause inconsistent contact with the blades, which in

turn could cause kickback. It is best to joint these boards on one face before planing. Serious stock flaws cannot be removed by the planer alone. Never feed two or more boards through the planer at the same time that are not consistent in thickness. Most consumer planers do not have sectional infeed rollers and sectional chipbreakers to accommodate wood of varying thicknesses. When surfacing a number of pieces to a given thickness, it is a good idea to run the thickest pieces first. Once these thicker boards become equal in thickness to the remaining boards, you can then run them all together at the same setting.

Limitations

Planers do have obvious limitations. They are limited by the length of the knives and the opening depth of the machine. You will be limited by how long a board you can send through the machine by the walls in your shop. In my first shop, I situated my planer in front of the garage door so that all I had to do was open the door to send long stock through the machine. If your planer is portable then length will not be an issue. We have already discussed that the shortest length of board you can send through your planer is based on the distance between the infeed and outfeed roller plus 2".

How thin stock you can plane will

The planer train. When planing short stock, you should always butt the ends of the boards against one another as you feed them into the machine. This will reduce kickback and snipe.