ArticleIn this article, woodworking machinery expert, Les Winter, P.E. discusses jointer injuries. His discussion includes an overview of the machinery, an explanation of the most common injuries associated with jointers, and a description of the associated safety equipment and processes.
The woodworking jointer is a stationary, usually floor-mounted machine, whose purpose is to flatten a face or edge of a board. The flattening of the face or edge is accomplished by shaving off the high spots in a manner similar to a plow smoothing a dirt road.
The machine is comprised of an infeed table, to the operator’s right, an outfeed table to his/her left, and a cylindrical, rotating cutter head in between. The cutter head is driven by an electric motor. A vertical fence, behind the cutter head prevents the board from falling off the tables to the machine’s rear, and for edge jointing, provides a ninety-degree reference to ensure the resulting edge is square to one face of the board.
Each jointer sold in the United States comes equipped with a guard which covers the cutter head when a board is not present.
Two types of injuries occur when operating a jointer: kicked-back boards or pieces of a board and hand contact with the cutter head.
Standing in the operator’s initial position, in front of the infeed table, the rotation of the cutter head will appear to be clockwise, thus the knives will rise from the left and move over the top and descend on the right. A board or piece of one, resting on top of the cutter head will experience a force moving it to the operator’s right. If that force is unopposed by the operator adequately pressing the board down and to the left, the board may be thrown to the right. This motion is known as “kickback”. The operator or a passerby can be struck by the board as it kicks back to the right, causing injury.
Small pieces can be kicked-back as well, and can strike the operator or a passerby in the face. Personal protective gear (“PPS”) in the form of goggles or rated safety glasses are essential to reduce the likelihood of eye injury from flying pieces.
A cutter head that can shave wood can obviously cause injury if the operator’s hand comes into contact with it. Because of the shaving nature of the cutter head as opposed to the cutting action of a saw blade, cutter head contact with a hand does not result in an amputation. Instead, the cutter head will chop the hand or finger into tiny pieces that cannot be reassembled or reattached.
Two safeguards are used to reduce the likelihood of cutter head contact with the operator’s hand: push blocks and the cutter head guard.
Push blocks are hand held devices that are used to push the board through the machine. Because of their height they raise the operator’s hands to a safer distance above the board. If the operator should slip, the push blocks will reduce the likelihood of cutter head contact with the operator’s hands.
The guard on most jointers sold in the United States is a pivoting unit that covers the cutter head when a board is not present. It is held in the closed position by spring pressure. When a board moving forward encounters the guard, it pushes it open and exposes the cutter head. As the board exits the cutter head area, the guard snaps shut, shielding the operator from inadvertent cutter head contact.
Investigating Woodworking Machinery Mishaps
Our experts are regularly retained in casework involving lacerations, amputations, and deaths that are associated with the use or misuse of jointers and other woodworking machinery. The scope of our investigations can include equipment operation and maintenance as well as various safety features, such as guards and protective equipment. By employing scientific methods to the analysis, the responsibilities of the various involved parties can usually be determined.
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Woodworking Machinery Expert & Electrical Engineer
Les Winter is a professional engineer who specializes in woodworking machinery-related injuries. As a professional engineer and an accomplished woodworker, he is regularly retained in casework involving equipment operations and maintenance as well as various other safety aspects, such as equipment modifications and safety guards.