This poorly stacked ductwork is an example of what not to do in the sheet metal shop. Picture courtesy of Dennis Sowards.

There is a third answer to the proverbial question, “Is the glass half full or half empty?” The “lean” answer is that the glass is oversized. Lean provides a different way to look at how we perform our work in construction. Here are some lean do’s and don’ts for improving work in duct fabrication and installation.

Don’t measure or focus on efficiency. Every duct shop measures efficiency - aka productivity - in terms of pounds - or tons - of metal per man-hour or man-day. While this measure may be useful in bidding jobs and for quick estimates, it has little real value in driving improvement. This measure means nothing to the customer who is paying for the duct. Managers who use this measure to judge shop performance are fooling themselves about its usefulness. Don’t focus on it.

Instead, use measures meaningful to customers - cycle time and on-time delivery.

Cycle time is how long it takes from the time a job is released for fabrication until it is ready to leave the shop. This is the total time spent at each fabrication step, plus moving from one step to another and the time waiting in between steps. Fabrication steps are, for the most part, value-added work in customers’ eyes. All waiting, sorting pieces, moving from process step to step are waste. By measuring the total cycle time, it helps answer questions about how much waste is in the process and where opportunities are for improving. Customers, internal or external, care about how long it takes to get product out of the shop because giving sufficient lead time is not always possible.

Most of the time

Customers also care about having duct when needed. All sheet metal shops say they deliver on time “most” of the time, so using this measure would have little value. The truth is that they usually delivery per the negotiated need date of the customer, not the real need date. Granted that field install crews usually ask for duct long before it is really needed, making the negotiated due date may be more realistic.

The lean way is to have the customer be honest in identifying the duct’s real need date and the shop delivering it on that date. If the shop cannot make the original need date, then a negotiated date is set between the two parties. Both the original, requested need date and the negotiated need date are recorded for performance. Field crews will become more truthful about their actual need dates when they see the shop is serious on meeting their needs.

Measuring cycle time and on-time performance are related. As the shop learns to reduce cycle time - cut out the waste - it is able to be more reliable in meeting its promised delivery dates.

Another don’t regarding efficiency is how duct is loaded for delivery to the job. Especially with the rising fuel prices, the tendency is to stack as much duct as possible, in any way possible, and into the truck or trailer. This may save some fuel, but it often increases the cost of unloading and installing, and may result in damaged duct.

Another example of ductwork haphazardly placed in the sheet metal shop. Picture courtesy of Dennis Sowards.

Take a load off

Instead, load the truck or trailer so that it can be unloaded quickly and, if possible, in the order it will be installed. Load all pieces together that are to be installed in the same area.

Coordinate with the field installation crews to deliver when and where the duct is needed and not too much before it is needed. Many general contractors have an inborn misunderstanding that if something sits on the jobsite in the same place for more than a few days, it should be moved, as if moving is real work. When duct is delivered too early at the job, the general contractor will ask to have it moved and then move it again. Each move is waste and runs the risk of damaging the product, causing more waste.

Ideally, we would deliver the duct to be installed the same or next day. Some contractors will cry “Impossible!” Yet you can find this done on jobs that are focusing on doing it lean. You can also find just-in-time delivery on jobs, usually in congested downtown areas, where lay-down space is severely limited and only the work that is scheduled to be installed within the next 24 hours can be moved in.

If you can deliver material just in time when it is urgent, you can do it any time. It is a matter of commitment and planning.

An additional benefit of not having too much duct on the jobsite is that it exposes problems. When the general contractor or another trade causes a change in weekly work plans you can see the impact more easily because excess material doesn’t hide it. If excess duct is available, the last-minute change is not noticed and the cause of the problem ignored. This enables the cause of the problem to happen again and again. If lack of duct inventory causes the crews to have to stop and determine the problem’s cause, effective countermeasures can be implemented instead of stopgap solutions. 

Ignoring problems

In construction, many people are too quick to do “work-arounds” and ignore the issue. Lean offers a different way of thinking: working to eliminate root causes. Less material inventory is better.

Another don’t in duct fabrication is to not burn or shear metal for as many jobs as possible and hope that “pushing” it through the rest of the process works. In a lean shop, you want the work to flow and avoid having material waiting on tables or carts. You also want to minimize the number of times you handle - but not add value - to the metal. Burning several jobs and placing all the pieces on the tables is batch work and causes waste. There are many times these pieces are sorted depending on which ones go to the edger, roller or press break. Sorting is wasted motion and is to be minimized or stopped.

Instead, burn or shear one piece of duct at a time and move it directly through the complete fabrication process with little waiting as possible. The programming for metal-burning machines will seek to optimize cuts and may cut more than one piece of duct on one sheet of metal.

As the cut pieces are taken off the burn table, put all sides for one duct piece on one table and the other sides on another table. This may seem like you are under-loading the tables, but you don’t want “efficiency” because it is short lived. You want value to flow one duct piece at a time.

Keeping all sides of duct piece on one table and moving them through forming, insulating and assembly as fast as possible (no wait) is the goal. As this is done, it will also allow for duct-forming equipment to be moved closer together, avoiding waste in moving pieces around, and smaller tables and carts can be used, freeing space.

The glass is not half full or empty but overcapacity. Your duct fabrication and installation can be operated from a different view: a lean approach to become more value added to your customer with less waste.

Dennis Sowards is an Arizona-based industry consultant and guest writer for Snips. His company is Quality Support Services Inc. He can be reached at or (480) 835-1185.