A current trend in our industry is that the component manufacturers are being advised that one should have a fully automated lumber retrieval system linked to an automated linear saw that pushes the cut lumber directly to the assembly table with an auto puck system. This type of setup is often touted as being the best for truss assembly to lower the cost of labor and get the most from your investment. Well, is it really in all cases?
Any of the different manufacturers’ equipment could be set up in this configuration. This setup involves a four-person team, with three on the table and one cutting. This system is frequently being hyped as the perfected just-in-time cut and assembly system. By the way, the just-in-time lean principle is one of the most often misunderstood and misapplied tools in lean terminology. Now, is this the best system for every condition? Is the just-in-time tool being used effectively?
Labor savings is normally the biggest point of this four-man team configuration. So, how many people are you saving? Let us agree that any linear saw that is or is not linked to the truss table could be paired with an automated lumber retrieval system. Having one person on the linear saw is not the issue in this setup. It comes down to how many linear saws you have and the material movement toward each of the assembly workstations. Matching one linear saw for each assembly workstation is an expensive investment and needs further consideration of other factors. Nor is the factor of an auto puck system on the table a condition of this type of configuration. One could have auto pucks with or without this pairing of the linear saw with each workstation.
- Point #1 - Pairing the linear saw with each assembly table and using a chain or roller system to move the cut material to each assembly table will reduce the labor count by 1/3 of a person or 1/4 of a person. For example, if one would have a person moving the cut material using carts, one should expect this person to keep up with at least 3 or 4 build teams on a full-time basis. This means, so far, the true reduction is at best 1/3 of a single crew person.
- Point #2 - Where does the conveyor system position the cut lumber every time? Is it all along the span of the truss, so that each of the pieces requires only a few steps for placement and carts can be positioned with ease? An example is if the top and bottom chords (T1 & B1) are positioned on the left end of the span, and the last chords are positioned on the other end of the truss span, which would mean less walking and therefore fewer man-minutes per unit. Or is all the material being positioned in the center of the span, no matter the span of the truss, which would mean more walking and therefore more man-minutes per truss the longer the truss span? There is too much walking the longer the spans with this system.
- Point #3 - Having a three-person build crew versus adding additional personnel can be a true hindrance when pairing the linear saw with each build workstation. Most linear saws cannot consistently cut more than what a three-person crew can assemble (called line balance in industrial engineering). TDC has yet to conduct a time study involving a single automated linear saw feeding the stock pieces and cutting each piece while averaging 400 pieces per hour with precision cutting. The one linear saw coming close to that output has an accuracy of +/-1/4”, which is not recommended by TDC (see linear saw performance report offered by TDC). Knowing that what if you have a run quantity of 40 trusses with a span of 55 feet? To maximize the gross dollars per hour or day, one needs to add personnel to the assembly team so that more trusses per hour can be produced. More personnel equal more people to move material onto the table to assemble each truss more quickly. With a 55-foot truss, one could easily have five or even six people assembling that run of trusses. If one did add personnel to the assembly workstation beyond the three or four-person team, the linear saw’s output would be exceeded. Limiting the output of the assembly workstation is not a proper use of the just-in-time lean principle. The goal of the company should be maximizing the gross margin dollars per day and not getting blinded by reducing the number of personnel at each workstation in the hope of reducing labor cost. One can increase the number of crew and yet still maintain or reduce labor cost per unit with added efficiencies.
- Point #4 - If more than two personnel are removing the lumber from the linear saw’s live deck system, they can be in each other’s way. How can three or more personnel remove long lumber from a single point without being in each other’s way? The answer is they cannot. However, if multiple carts are positioning the lumber along the span of the truss, it could be much easier for multiple people to move material onto the table from any point along the span.
- Point #5 - Regarding a linear saw versus an automated five-blade component saw, they each have unique roles. Cutting the material needed for a run of one-one-one is the realm of the linear saw. But cutting a much greater quantity run is easily done more quickly by the auto five-blade saw so that the greater the quantity needed, the more noticeable the difference between the two types of saws. If the quantity run on the table exceeds the breakeven process time of a linear saw versus a five-blade component saw, why would you think the linear saw works in all conditions for every build table? The answer is it does not, and this is especially true for large-span trusses with large run quantities.
- Point #6 - A linear saw can reduce the lumber cut waste by batching and combining different cuts of various pieces (lumber optimization). However, this cannot be easily done when the linear saw is only cutting the trusses as the trusses are being built. To maximize the assembly time, theoretically one would only cut a quantity of one every time, no matter the run quantity, thereby losing the lumber optimization benefits of the linear saw. Otherwise, the truss assemblers must sort all the lumber at the table after waiting for the entire quantity run to be cut, which would be a huge time-wasting mistake.
- Point #7 – Pairing a linear saw with each workstation creates such a rigid system that, if one part of the system fails, the entire system comes to a standstill. A single burnt motor, lost drive shaft key or computer failure and the entire workstation comes to a complete stop until every position is working again. Whether it is a brand new linear saw or an older one, they all break down. No experienced industrial engineer worth his/her salt would ever design a process without allowing for flexibility to keep the work flowing during unforeseen events.
When does the pairing of a linear saw with each workstation make sense? It is simply when the quantity run is the lowest, such as one-one-one, and the span is not so great that it would make sense to add more assemblers to the workstation. The greater the quantity run and the greater the span, the less it makes sense to pair a linear saw with every build workstation. One configuration of equipment is simply not the best for all conditions.
Most operations need a blend of different equipment and vendors to have the very best of everything. When you are ready to have the very best system to meet all your needs, combined with the very best of true lean manufacturing principles and industrial engineering practices, give TDC a call. TDC provides unbiased advice for the very latest and best practices known in our industry that works consistently.
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