The 10 biggest fabrication mistakes in HVAC shops - and how to avoid them.



Every sheet metal shop can improve its productivity and efficiency. Not all shops suffer from the same problems, but most are burdened with enough to substantially affect their profits.

Since as little as a 10 percent change in shop efficiency can affect profits by up to 50 percent, shop managers would be wise to look at important areas of their operation.

Here are the 10 biggest mistakes in duct fabrication. (Don't be surprised at what turns out to be the No. 1 drawback to dramatically improving your shop productivity.)

Be sure to use a quality snap-lock seam. Illustration by Jim Segroves.

10. Impractical use of seams and connectors

The most practical longitudinal seam for the assembly of low (and some medium) pressure ductwork is "snap lock." However, many shops do not use it.

Snap lock is a good, productive seam when formed and assembled properly, but if the snap-lock roll-forming machine is worn, out of adjustment or clogged with galvanized metal flakes, which prevent the male buttons from being formed properly, the seam will fail.

As long as the machine is kept in good working order, forming and assembling duct using snap-lock seams is 36 percent faster than those that use Pittsburgh-style seams.

Another important longitudinal seam-creating device not found in many shops is the 18- and 16-gauge Pittsburgh machine. In shops without this equipment, duct is usually welded, which is extremely labor intensive.

Relative to connectors, the most practical combination is flat slips, flat drives, standing slips, roll-formed and frame. Some shop owners may wonder where to stop using standing slips and to begin using roll-formed or frame connectors. Most shops have elected to set this break point at between 18 and 36 inches.

Some studies indicate that at 36 inches, sealed or "brush-on" slips and drives take up to 10 percent less labor to install than some frame or roll-formed types.

Spray — don’t roll-on the duct-liner adhesive. Illustration by Jim Segroves.

9. Inefficient duct-lining operations

Perhaps the most common productivity problem in shops of all sizes is the "duct-liner bottleneck" syndrome. Even with coil lines, plasma tables, high-speed roll formers and efficient shop layout, work can still pile up at the duct-liner table. Here are a few tips to help prevent this common problem:

- Spray on glue; don't roll or brush. Use a diaphragm pump in 5- or 55-gallon containers.

- Spray a thin coat - the thinner the better.

- Use a liner-cutting table with a "pizza style" roll-cutting wheel, an imbedded tape measure, a raised straight edge on the operator's side and a large "T" square for second cuts. Another option is to use a computer-controlled cutter.

- Always work as a team, with one person designated a sprayer and another the "pin person" on larger batches of work.

Precut full joints for straight duct from a duct-liner-cutting list.



Make sure your shop is properly laid out. Illustration by Jim Segroves.

8. Inefficient materials handling and storage

Inefficient material handling and storage can be a very costly situation in any shop. A significant factor in deciding whether to buy steel in coils or sheets is the advantage of coil when it comes to handling and storage.

This is not to say that all shops can justify coil lines, because most shops use sheets and will keep using them. The point is that most shops can greatly improve their sheet-handling efficiency by doing the following:

- Use open-arm, forklift-loadable sheet racks with adjustable arms spaced 12 to 15 inches vertically. This will accommodate five levels of 5,000-pound skids of sheets.

- Position the open-arm rack between the plasma cutter and your power shear's squaring arm.

- Place your most used gauge, typically 26 gauge, the same height as the plasma machine and power shear, with 24 gauge above and 22 gauge at the top.

- Use open-arm racks rated for 5,000 pounds at each level that holds 5-foot-wide sheets. Five-foot-wide sheets nest better and can reduce the number of full straight joint connections by 20 percent on long, straight runs.



7. Inefficient shop layout and work-flow paths

Use each work station to move the product closer to the assembly or shipping area. Minimize backflow and cross movements. Remember, if employees average $35 an hour, each footstep represents about 1 cent, and a worker can make a million steps a year. Here are a few suggestions to improve efficiency:

- Create the fitting patterns deep in the back of the shop, then move work to the beading machine (if not beaded prior to plasma cutting), edging machines, roll-formed-connector machine, rolling and bending machines, the liner-cutting table, glue spraying and pinning, assembly and shipping.

- Have vanes and connectors positioned immediately adjacent to the assembly operation.

- Position all assembly hardware within the "three-step limit" of the assembly table. The "three-step limit" sets a maximum of three footsteps for a worker to reach everything needed to perform that specific work-station task.



Use open-arm sheet racks that can be loaded from a forklift. Illustration by Jim Segroves.

6. Not equipped with the right machinery

The only thing worse than a shop being poorly equipped on machinery is for a shop to be well equipped with the wrong machines. This is a very common problem. How does this happen? You may be buying machines to do a task that your shop should not be doing at all. For example, you might purchase a machine to produce turning vanes and rails, but at your wage scale and volume, you could purchase them cheaper already finished.

In order to have a properly equipped shop, equipment must be appropriate for the type and volume of work you perform.

- At minimum, a low-volume mostly manual shop needs:

- Open-arm sheet-storage racks.

- A power shear, preferably 10 foot by 10 gauge mechanical, with a 5- or 10-foot squaring arm on front and a front-operated back gauge.

- A 16-gauge by 10-foot notcher. The 16-gauge capacity will allow manual shops to notch two sheets of 26 gauge or 24 gauge at once, which doubles the productivity on full straight-duct joints.

- A power brake with disappearing pins, preferably 10 foot by 10 gauge.

- A snap-lock roll former for 26-, 24-, 22-gauge and Pittsburgh-style roll formers for 26-, 24-, 22-, 20- and 18 gauges.

- A duct-liner cutting table with bidirectional pizza-style roll cutters and a spray gun for gluing

- A power-tap notcher

- A minimum 15 kilovolt-ampere spot welder

- A dedicated assembly table that includes a Pittsburgh air hammer

- A properly designed and located work center for vanes and connectors, near the assembly area.

- If not a computer-controlled plasma table, at least a computer-driven fitting, blanking and shop-ticketing system.



Buy the right sheet metal for the job.

5. Ineffective purchasing of sheet metal material

While there is no way to control this upward price movement, these guidelines will help ensure that you are getting full and effective use of every piece of metal purchased, and at the best unit cost available in your area.

When you make your next purchase:

- Never request sheet metal quotes on a cost-per-pound basis. This can open the door for some vendors to sell you thicker metal than you are planning to use. Although the quoted price per pound may be slightly less than a competitive quote from another vendor, your real cost per square foot can be considerably higher.

- Request all sheet metal quotes be priced per square foot, by gauge. This keeps all quotes similar. This puts burden of having thicker-than-minimum gauges in inventory squarely on vendors.

- Periodically request quotes from several vendors.

- Convert your actual cost per square foot to an equivalent cost per theoretical pound to ensure compatibility with your estimating, job cost and plasma machine software.

To convert your actual paying price per square foot to an equivalent theoretical median price per pound, use the following formula:

Actual cost paid per square foot divided by the theoretical weight per square foot at median thickness

So if the price per square foot was 40 cents and the weight were 1.156 pounds, the formula would be:

40 cents divided by 1.156 pounds = 34.6 cents

So, your cost per theoretical pound for 24-gauge steel would be 34.6 cents per pound. This formula assumes that estimating, job cost and plasma-machine software use a theoretical median thickness of .0276 inches and a corresponding weight of 1.156 pounds per square foot.



Reducing the number of transitions and eliminating “nested” fittings can reduce costs. Illustration by Jim Segroves.

4. Using more sheet metal than required

Simply reducing the number of transitions in trunk lines, and eliminating "nested" fittings by using rectangle and round taps, can greatly improve performance and reduce duct fabrication and erection costs.



Use the proper labor codes to keep track of your time and costs. Illustration by Jim Segroves.

3. Not tracking time and recording costs

Without having a reasonably accurate record of your shop's productivity rate, you could end up bidding on a job you shouldn't go after or miss a job you should get. The bigger the job, the less contractors keep track of costs and the more likely they are to estimate labor needs incorrectly.

How many shops have operated for decades only to have to close after one big, incorrect, job estimate?

The most common problem is estimators using published productivity numbers that do not match up with their specific or unique shop and field operations. Even if you have cutting-edge shop equipment and building facilities, that can be more than offset by poor communication between mid-managers, field supervisors and workers.

It's relatively simple to track productivity, but it does take time and monitoring to ensure accuracy. At some point, management must ask if the relatively small time and cost required to confirm estimating numbers is worth the long-term ongoing risk of submitting a potentially fatal bid.



An example of how shop tickets should be designed.

2. Poor information flow to the shop

Computer-controlled plasma machines are near-universally accepted in HVAC shops worldwide. Ask most owners why the plasma machine is so valuable in their shops and many will point out that it eliminates the need to lay out fittings.

Despite this great time-saver, few realize the impact the machines' computer-generated shop tickets have on productivity. These "shopping lists" contain information needed by other workers even before the first pattern is created on the plasma machine. Now the vane assemblies and connector frames can be waiting on the ells.

So, if these computer-generated accessory lists are the ultimate shop information system, what's the problem? Many shop managers do not provide the lists to their workers. The mistake costs them half of their potential productivity gains possible by computer-generated or even manually produced lists. The information is every bit as valuable in increasing overall shop productivity as the plasma table is to increasing pattern layout and cutting productivity.



1. Fear of change

The No. 1 barrier to increasing productivity in most sheet metal shops is a basic belief by management that productivity cannot be significantly improved without substantial investment. The risk element is often bolstered by the ever-present fear of change.

Management must believe that commitment can improve productivity. For a number of years, efficiency experts have embraced a concept called the "theory of constraints." It operates on the principal that there exists certain barriers or restraints in shops that hold productivity at its existing level.

Based on that approach, to increase productivity one must only remove those barriers that restrain the productivity. And the good news is that most of those restraints are management associated and management changes, not investment dollars, are the key.

All 10 of these common problems require little or no financial risk, but all require management commitment.