There has been a big push to reduce labor. In response, more than one equipment vendor has suggested that component manufacturers (CM) should purchase linear saws directly tied to roof gantry tables. The idea is simple: fewer crew members and more automation to increase efficiencies and reduce labor costs. As shown in Figure 1, there are two workstations with four assemblers and one sawyer because of the automation of lumber picking and material movement to the two workstations. However, given my actual case study results from current clients, this simple idea is flawed. This article will prove, beyond any shadow of a doubt, that this configuration could cost companies millions in lost profits with very little or no labor savings.

Our starting point is determining if assembling roof trusses on a gantry table, regardless of automation of jigging on the gantry table, has any real difference between two-person versus three-person crews. Auto-puck jigging is for reducing the setup time, not a reduction of assembly of the trusses.

Figures 2 & 3 – The quantity is eleven trusses each of a 32’ Common truss and a 44’ Piggyback truss, and first we disregard the setup time and focus only on the assembly time of two- versus three-person crews. The setup time and assembly of the first truss are not being used for this case study, so the net quantity is ten trusses and the figures show a run of five for each crew.

Each row in Figure 3 represents the number of crew assembling a quantity of five of each truss type. For the 32' Common, the two-person crew has a total shop time of 15.1 minutes, versus the three-person crew completing five trusses in 10.63 minutes. Notice that the total man-minutes (MM) is slightly more for a three-person crew on the 32' Common of only 1.69 MM, but for the 44' Piggyback trusses the three-person crew has a savings of 8 MM. In other words, there is an increase in total labor for the two-person crew for the 44' Piggybacks instead of a reduction. When there is a lot more material (pcs) and longer spans, there is far more walking and climbing up and down off the gantry table for two-person crews than three-person crews.

Each of you should be paying attention to the Takt Time (shop minutes per truss) and the Quantity Rate per Hour; specifically, how many trusses can be produced per hour will determine the actual profitability of the crews. Figure 3 shows there is a significant increase in the number of trusses per hour with the three-person crew versus the two-person, and it’s not particularly close. How many CMs are limited by the capacity and, therefore, their profits for the past year?

So, what about all the assumed labor savings promised by this setup? One must keep in mind that the linear saw with an automated lumber retrieval system can be configured without being directly connected to the gantry table. But when you connect a single linear saw to the gantry table, as shown in Figure 1, the vast majority of linear saws can only produce at a rate to keep pace with three to four assemblers. Hence the two workstations of two-person crews. Adding a third person to either or both assembly teams will not produce more trusses per hour because the linear saw cannot provide the material any faster. The gantry production is limited to the piece cut rate of the linear saw. This case study is a perfect example of the Theory of Constraints principle.

As you can see using $0.40/MM in Figure 4, the labor savings are not guaranteed by having a two-person assembly crew versus the three-person. Any labor savings is quite frankly a token’s worth of labor savings when it comes down to where the real money is being gained or lost.

How to lose millions of profits with linear saws and two-person crews should be very self-evident by the data shown in Figure 5. In essence, the maximum sales and margin dollars produced are cut down by a third using only two-person crews. How much would your company lose with a third cut to the total manufacturing capacity?

Did you notice how little the margin dollars differed between the two- versus three-person crews? It looks like the argument of the two-person crews having expected significant labor savings gains adding to the margin is not a valid point.

There are numerous other reasons why pairing a linear saw with a gantry, as shown in Figure 1, is fraught with problems.

Figure 6 clearly shows the vast discrepancy of using BF/Hr for labor efficiencies. Why do so many continue to bang their head trying to use BF/Hr for their truss manufacturing? I have written numerous articles on this very flawed labor measurement method. Hopefully, no CMs were persuaded to invest in this equipment configuration by the BF/Hr blatantly obvious false productivity efficiency numbers.

I should also mention that using the piece count method weighted with an average setup time is almost as unreliable as BF/Hr for estimated labor. PCS/Hr discrepancies become apparent when the quantity count is low which creates too little estimated labor, or when the quantity is very high which creates too much estimated labor hours. Figure 6 PCS/Hr is showing actual results of PCS/Hr, not an estimated labor time.

The Drummond Method understands there is only one reliable method for properly scheduling, measuring manufacturing efficiencies, developing productivity incentive programs, and estimating true labor cost. Only properly developed motion and time standards that estimate man-minutes (MM, RE, or SU time units) will be effective for roof truss manufacturing.

For many, the obvious solution to the single linear saw paired to the gantry table is to add another linear saw. In other words, as shown in Figure 7, this idea is to have a dedicated linear saw per workstation. Yes, this may work for some situations, but it will not work in all conditions. Too many fall into the trap of one size or configuration fits all. The Drummond Method takes into consideration all the many different variables that each CM experiences.

One of the many variables is how the material savings that linear saws are supposed to produce is all but lost when pairing to the gantry table. Once you lock the linear saw to the gantry table in this configuration, combining many different truss labels to optimize lumber use is all but abandoned. Another variable is that many will ask whether to use cheaper shorter-length stock lumber versus the more expensive longer-length stock lumber for their operation. The answer to that is sometimes yes and sometimes no. The Drummond Method understands the costlier longer-length lumber is sometimes actually saving a company money, and other times it is not. It depends on some key factors that must be considered.

The one size simple solution can be very costly. A fair warning to those considering this type of setup (Figure 1 or 7) is that this configuration is not optimal for many scenarios. Companies who insist on using this linear saw and gantry configuration:

  • Use more expensive equipment.
  • Need more square footage of manufacturing floor space.
  • Have questionable labor savings only to move material to the tables.
  • Are potentially losing millions in lost sales and margin dollars because of limited capacity.

Automation in itself does not guarantee increased efficiencies and greater productivity. As with every industry, more significant complexities of the overall processes must be understood by those who make such investments. Just keep in mind that as the example of the linear saws paired to the gantry tables, it was by the request of CMs that the vendors responded to try and offer a possible solution to the labor issues.