The cut-and-rip line: still a viable choice
by: Dr. Fred M. Lamb
In this era of gang-rip-first rough mills, it is unfortunate that we are forgetting the usefulness of the traditional cut-and-rip line. For many operations, the cut-and-rip line is a viable choice offering reasonable production technology in relation to operating costs for the manufacture of parts or rough dimension.
The cut-and-rip line is essentially a manual crosscut-first operation. For decades, we produced billions of board feet of parts for furniture, cabinets and other secondary products with this cut-up system. Furthermore, there is a considerable amount of information and experience on how best to structure, organize and operate this type of rough mill configuration. Although there are many modifications, the conventional cut-and-rip line is essentially organized around cut off saws producing pieces of wood that are fed to straight-line ripsaws to be cut as either fixed width or random width stock. A planer and a salvage saw area completes the configuration.
Various Configurations
There are numerous opinions as to what is the optimum configuration for a cut-and-rip line. Many operations used the conventional layout consisting of cut off saws, followed by a planer, and then the straight-line ripsaws. Other operations chose to plane prior to the cut off saw. By providing planed lumber to the cut off saw, the saw operator is better able to recognize defects that may have been harder to see at production speeds in the rough lumber.
There are some other minor variations to this arrangement, such as the use of edging saws to produce gluable surfaces on the outside edges of the stock to be ripped. Regardless of the details of the configuration, the essence of this system was cross cutting the board prior to ripping.
Eventually, yield questions began to plague the cut-and-rip line, as many felt that rip-first, especially gang-rip-first operations, produced a higher yield. Such comparisons are difficult. Today’s gang-rip-first operations are built around more complex cutting bills, with numerous parts grades, scanning systems and numerous sorts (all of which are the real advantages of these systems). On a simple cutting bill of three to five part lengths, all clear two-face cuttings, and smaller quantities, the differences in yield are more like two to four, maybe five percent, depending on many other factors. This is significant but not enormous.
Advantages of Cut-and-Rip
The batch processing of the cut-and-rip line offers a significant amount of flexibility. This is probably one of its greatest strengths, the flexibility and adaptability for both small-lot runs with fast turn-around times or longer runs of a more traditional quantity and duration. The cut-and-rip line is one of the more versatile configurations especially for the smaller-sized operation.
The cut-and-rip line is less sophisticated technologically, thus it is easier to operate, supervise and maintain. This makes the configuration more affordable. When properly operated, the cut-and-rip line is capable of producing reasonable yields, making it a cost effective and efficient system especially on simple cutting bills.
Another advantage of the cut-and-rip line is its ability to efficiently cut-up that portion of the lumber resource whose characteristics cause problems (yield reductions) in gang-rip-first operations. Such lumber characteristics would include excessive crook, defects clustered in groups across the width of the board, and boards where the defect pattern on one end is drastically different than the pattern on the other end.
It is for this reason that some larger operations are considering using twin lines, that is, both a sophisticated gang-rip-first line and a smaller traditional cut-and-rip line. This twin configuration system allows the flexibility to optimize the cut-up of today’s increasing variable and lower quality material.
Length versus Yield and the Operator’s Role
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| Figure 3. An old styled paper-type back gauge. Prior to this, colored golf-tees were used. Today’s electronic systems are far superior. |
Because it is a crosscut-first operation, there is an overall tendency of the cut-and-rip line to produce shorter material on average than the rip-first operations. This varies to some extent depending on the operational philosophy of cutting that is being used, that is, whether or not saw operators are instructed to cut for yield or to cut for length. These two practices are slightly different. Because of the tendency of the cut-and-rip line to produce on average somewhat shorter cuttings, many operations instructed their personnel to cut for length first, and then to cut for yield.
Operator skill plays an important role in the efficient operation of a cut-and-rip line. The decisions made by the operators have a significant impact on both the production rate and the yield. Although all operator decisions are important in this type of rough mill, those made by the cut off saw operator are the most difficult and have the most significant impact on yield.
In this time of general labor shortages, the lack of knowledgeable, skilled personnel has a real impact on the operational efficiency and effectiveness of a cut-and-rip line. Good people making good decisions is the essence of a cut-and-rip line, not sophisticated technology.
Operator Assisting Guides
The cut-and-rip line is most effective and efficient in cut-up practices if certain operator-assists or guides are used. For the cut off saw, the most important of these is a back gauge. (The use of front stops is obvious.) With a back gauge, an operator can effectively deal with three to five lengths and optimize the yield of those lengths from a board, regardless of whether the instructions are to cut for length first or to cut for yield.
A back gauge is indispensable to effective operations of the cut off saw. The sophistication of the back gauge does not matter — whether it is an electronic version with whistles, bells and flashing lights, or something a little more mundane. (Note: The new electronic versions do provide much more useful information than the old passive, manual systems.) A properly installed back gauge, and an operator trained in its use, makes a significant difference in yield optimization at the cut off saw.
Pop-Up Gauges and Laser Shadow Lights
For the ripsaw, the two most important guides (other than the obvious rip fence) are a pop-up gauge on the table and an overhead laser shadow light. The pop-up gauge allows the operator to immediately have the capacity simply to edge the board with minimum waste in the edging strip. The pop-up gauge can be easily over-ridden if the stock is to be ripped to a fixed width or for ripping out defects.
The other guide is the laser shadow light. The laser light allows operators to rip the stock more precisely in relationship to the defects they are either trying to remove or trying to incorporate into a segment so that the salvage saws can become more effective. (In the past, the shadow light was truly a shadow line cast by using a wire and a light.) The laser beam is aligned with the sawblade and is of approximately the same width as the saw kerf so that operators can see where the saw kerf will fall on the piece as they push the stock through the saw.
Recovering Salvage
An important component of a cut-and-rip line is the efficient and effective use of salvage saws. At a minimum, the salvage area should be a crosscut or a chop saw. This allows waste material coming from the straight-line ripsaws to be sorted by the off bearer, and that material containing useable wood sent to salvage for the recovery.
A good salvage operation can improve yield by one to three percent. Depending on the cutting bill and other considerations, I believe that the salvage chop saw should be replaced by a salvage station that includes both a salvage chop saw and a salvage ripsaw. This gives the salvage station the potential to do both crosscutting and ripping, which generally provides an increase in yield. It also allows the straight-line ripsaw operators to make a broader range of decisions as to how they are going to cut the material when they know there is a processing station beyond them that is capable of both cross cutting and ripping.
Fred M. Lamb is Professor and Extension Specialist, Department of Wood Science and Forest Products, Brooks Forest Products Center, Virginia Tech, Blacksburg, Virginia. Dr. Lamb can be contacted at 540-231-7256; Fax: 540-231-8868
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