This is the first in a series on the evolution of strategies for cutting lumber efficiently. In future editions, I’ll eventually get to my favorite saw subject – defining the proper role for your lineal saw.
Batch cutting was already well-established when I began creating cutting lists in 1982. The concept was simple: Component saws take 5 to 10 minutes to change from one setup to another, so let’s minimize the number of setups! Minimizing setups is accomplished by batching a large number of trusses (the more, the better!) and then sorting the pieces, by cuts, then by length. This then is our first strategy:
Strategy #1: Minimize Sawyer Labor
Best for: saws that take a long time to change from one setup to another
Number of trusses in the batch: as many as possible
Sorting logic: similar cuts, length
Advantages: minimizes setup changeovers
Disadvantages: lumber picking must include many different lengths, stacker must stage pieces from a large number of trusses
The Minimize Setups strategy was batch cutting for decades, but as saw manufacturers made improvements that reduced setup time, production managers longed to reduce the time it took to pick lumber. It seemed so inefficient to travel to several bunks and hand pick a certain number of pieces from each bunk and bring them to the saw. And if a piece needed to be culled, then another trip to the bunk was needed. The solution?
Strategy #2: Minimize Infeed Labor (or "Eliminate Picking")
Best for: semi-automated saws that have room for live deck infeeds
Number of trusses in the batch: as many as possible
Sorting logic: size/grade/species, stock length
Advantages: minimizes infeed changeovers
Disadvantages: more saw setups than Strategy #1, and stacker must stage pieces from a large number of trusses
During the heyday of the Minimize Infeed Labor era, a variety of creative live decks were designed, and many are still in use today. One bunk after another is moved into position in front of the saw and the sawyer cuts everything he can from that bunk before moving on to the next one. Saw manufacturers pressed on, and suddenly setup times were reduced to from the 1-2 minutes of the semi-automatic era to the current standard of 25-30 seconds. Saws were cutting so much that a second stacker was added to help organize all the pieces being cut. Enter the third strategy:
Strategy #3: Minimize Stacking Labor
Best for: automated saws
Number of trusses in the batch: a small number of trusses that will be built together (a table production group)
Sorting logic: varies, but one simple one is, "tops, bottoms and webs."
Advantages: keeps things simple on the back end of the saw
Disadvantages: lumber picking must include many different lengths, lots of saw setups
In very broad terms, the strategy you use is based on which part of the sawing operation you want to favor, picking, sawing, or stacking. Note that creating small bundles that can be taken directly to the assembly line can also help the people setting up and building the components. You may find in considering this discussion that your current strategy is based largely on "This is how we have always done it." If this is the case, you are not alone. A strategy that worked in the past will not be abandoned quickly, even after new, faster equipment has been purchased.
The final strategy is the extreme case of the "favor the back in of the saw."
Strategy #4 - Cut One Truss at a Time
Best for: lineal saws that are dedicated to one or two production lines
Number of trusses in the batch: one
Sorting logic: whatever optimizes the material on the lineal saw
Advantages: cut it, then build it; minimal material tied up
Disadvantages: If the saw goes down, you are stopped in your tracks
This strategy is the logical evolution of a 'just in time' production process. It raises challenges that will be discussed in a future article.
A Self-Test
If you want to analyze your own strategy, answer the following questions:
1. How many trusses are in a "job" sent to my saw department? (size of batch)
2. How many different lists do I create for each job? (parsing)
3. In what order are the pieces in each list sorted? (sorting)
4. How many people are needed for the overall sawing process? (fractions are OK)
Incidentally, if you are not using software to create a batch cutting list, you are not alone. But make no mistake, you are using one of the strategies nevertheless. Letting the sawyers themselves figure out how to cut a set of trusses usually means you are using Strategy #3 and probably using some variation of "cutting one truss at a time."
For each of the questions above, find out the answer and then write down exactly why you do it that way?" If you can't put it into words, they you are on your way to learning something important about your production. It is essential to understand the "why" for each part of your sawing operation. By putting it down on paper your will really be forced to think through each decision.” Once you have done this, evaluate your process and see if it makes sense based on your current equipment. "We have just always done it that way" is a sign that we really don't know why we are doing what we are doing - a sure sign that we may be able to be able to improve our efficiency.
