Both Circular Gang Saws and Bandsaws Offer Advantages for Resawing Process
Both Technologies Have Benefits
By Alan Froome
Date Posted: 7/1/2004
To resaw with a gang saw or band resaw -- that is the question.
With apologies to William Shakespeare, there is more than one method of secondary breakdown.
The nature of the pallet and sawmill industry and its people tends to result in independent thinking. Just as in business and in life, there are always ‘different horses for different courses.’
This article takes a general look at what machinery and methods are available today for the secondary breakdown phase of processing logs -- resawing squares or cants.
After the first cuts are made in a log, the pieces produced -- namely cants, slabs and flitches -- are passed on to some kind of secondary breakdown machine center. The method used varies from mill to mill. Whether a mill is cutting softwood or hardwood may be a factor, too; cutting speeds are naturally less with the harder species as well.
In the softwood dimension sawmill industry, where feed speeds and production rates are higher, gang saw technology is used in the majority of mills for secondary breakdown. In recent years machinery manufacturers have developed ways to feed curved material through gang saws with sophisticated computer controls. These curved or shape sawing systems are expensive, and payback to the sawmill owner is related directly to production. Optimum recovery is the name of the game at almost any cost. Most mills using this technology are high-volume facilities, running three shifts and producing 1 million board feet daily. Many of these softwood mills also use horizontal band resaws in order to recover boards from round back slabs; gravity helps feed the slabs flat side down on a belt bed or roll conveyor.
The pallet industry is by nature much smaller in terms of daily board footage production, and, of course, it has much different needs and priorities. The circular gang saw has been used for years by pallet companies to resaw sized cant material. In the last 10 or 15 years, however, narrow blade horizontal bandsaws have gained in popularity for resawing material in both softwood and hardwood mills.
There are some differences between circular gang and the horizontal bandsaws which may not seem so obvious. Both types of saws have been around the sawmill industry for years, and a lot of the older machines still give good service. In the newest models, saw kerf has come down and feed speeds have gone up. This has proved a real challenge to the saw filer in many mills.
Looking around the entire wood products industry, the principal types of secondary breakdown machines used today are:
n horizontal bandsaw
n single and double arbor circular gang saw
n vertical arbor circular gang saw
n vertical band linebar saw
By far the most popular types used in the pallet industry are the first two, the narrow band horizontal bandsaw and the horizontal single or double arbor gang, and the following comparison will focus mainly on them.
Several machinery makers were interviewed and asked to recommend what machine is best for a particular application and budget. When cutting the same size cant, for example, which type of machine has the thinnest kerf, hence highest lumber recovery factor (LRF)? How do the feed speeds and maintenance requirements compare from one type to the other? Which offers the best payback? There were similarities in their comments on the pros and cons of each type of machine.
Saw kerf is less on bandsaws, so machinery manufacturers agree that bandsaws offer greater yield (recovery) compared to circular gang saws.
Sam Baker, CEO of Samuel Kent Baker Inc., said, “At this point in the game, our 1-inch blades are down to approximately 1/16-inch kerf, so we can get four stringers plus a leftover board from a 4x6 cant. This translates into some additional revenue for the owner, and it could mean $200 extra a day to a small mill.”
Paul Gilles of Brewer Inc.-Golden Eagle remarked, “It means an extra board when cutting ½-inch boards from 4x6 cants.”
Kevin Corder, vice president of Wood-Mizer’s industrial division, said, “Material supplies are getting tight, so in my opinion yield is the main issue.”
The initial cost of a typical horizontal bandsaw also is less than a gang saw. This is very important to small businesses in the industry or somebody just starting out. However, several bandsaws or multiple ‘heads’ may be needed to do the job. As always, payback relates directly to production and sales.
The horizontal bandsaw is more flexible and can make more products. Mike McNail, CEO of Baker Products, said “By tilting the feed table, you could make bevel siding, for example.”
Many small mills cut various lumber products on their horizontal bandsaws. Originally they used them for recovering boards from round back slabs, but soon they started customizing them for different jobs.
Horizontal bandsaws also require less horsepower. The typical horizontal bandsaw needs a 20 hp or sometimes a 30 hp motor to drive it. On the other hand, a gang saw may need 100 hp because it is driving numerous blades on the same arbor.
Circular Gang Saws
One of the main advantages of a gang saw is that it is capable of higher production than a horizontal bandsaw. Bandsaws may be set up with multiple heads – some lines may have as many as nine or 12 – to provide almost continuous resawing as the cant material passes from one head to the next. However, a circular gang saw produces multiple boards in a single pass -- and in a relatively small space. Sam said, “Gang ripping is a more rigid way to cut cants.”
A gang saw machine requires less maintenance compared to a multi-head bandsaw line. David Greenwood of G-Tek Industries said, “We build both types of machines, and it can be a challenge to keep six or more bands running well in a line.” Sam said, “Ironically, the bands are the machines you love to hate. There is a big gain from the thinner kerf, but you have to stay on top of their alignment and maintenance.” Kevin said, “From the filer’s point of view, the circular blade is more forgiving than a band.” He added, “Some mills resist running bandsaws, but throw-away bandsaw blades are one way to deal with it.”
Circular saw blades produce chips during the cutting process while bandsaw blades make sawdust. This can be an advantage, depending on the pallet customer. Paul said, “People in the computer or pharmaceutical industries specify that there can be no dust on their pallets.”
David commented, “Pallet stock produced by a gang is pretty near 100 percent dust-free. Air blast de-dusting band-sawn lumber never gets it all.” (Note: de-dusting machines may utilize brushes to scrub boards clean.)
Both Brewer Inc.-Golden Eagle and G-Tek have no particular bias with respect to circular gang saws or bandsaws since they manufacture both types. Both companies reported that sales of the two types of machine are running about even. Samuel Kent Baker Inc., Wood-Mizer, and Baker Products manufacture bandsaw machines for resawing.
As noted above, circular gang saw machines are more compact and have a smaller footprint than multi-head bandsaw lines.
Machinery manufacturers were asked which type of saw they would recommend for which lumber product if cost was not a factor.
David said, “The horizontal bandsaw is ideal for making deck boards, and the gang is very efficient for stringers.” He added, “If the raw material cost of pine was the same as hardwood, most people would pick bands to do both. But some people just hate bands and pick gangs anyway.”
Paul remarked, “Generally the higher production mill will buy a gang. I feel production over 20,000 board feet a day indicates the need for a gang, and under that figure most likely indicates a horizontal bandsaw.” Others mentioned the same volume of daily board feet production – 20,000 -- as a general rule of thumb to decide between the two saw types.
Mike believes the figure is higher -- 30,000 board feet a day. He said, “The main thing generally considered is the better yield with the bands, and most folks somewhat overlook the higher maintenance required.”
Kevin said, “The more production you make with bands, the more savings there are in yield.” As an example, he mentioned two mills that produce over 100,000 board feet a day from cedar using only narrow blade bandsaws. “Most people running bands use kerf which is twice the thickness of the blade. In other words, 0.070-inch kerf with a 0.035-inch blade and half-set is the industry norm – one tooth left and one tooth right.” Final saw selection depends on the application and intended use, he added.
As for sawing accuracy of the two machine types, there seems to be little difference. Like others, Mike remarked, “Accuracy depends largely on the maintenance skills of the individual operator.”
To summarize, the horizontal bandsaw has the edge in terms of recovery and yield due to its thin kerf. Mike said, “As a rule of thumb, you can gain a board for every 10 you cut.”
However, Paul noted that a gang’s circular saw kerf could be competitive up to a 4-inch deep cut, although at 6 inches or more the bandsaw was better.
Bandsaws require more maintenance, although saw sharpening costs are about the same on both types of machine. Bandsaw blades are cheaper but are thrown away after one use or only good for two or three sharpenings, according to Sam. For optimum sawing performance, he said, companies start with a new blade in the morning and change them at mid-day. Circular saw blades cost more to buy, but with inserted teeth blades they can be re-sharpened almost indefinitely.
Over the last 15 years or so, horizontal bandsaws have made a big impact in the pallet industry and are being used in more and more ways. Smaller mills use them to cut all types of material, including blocks, stringers and deck boards. Sam noted that narrow blade horizontal bandsaws also are used now for grade lumber recovery from cants as big as 16x16.
When selecting a bandsaw, Kevin suggested that larger diameter band wheels are important because blades get work-hardened quicker going around small diameter wheels on some machines.
Not all multi-head bandsaws require a lot of floor space, noted Mike. Baker Products manufactures a ‘Bang Saw’ that runs two blades with four wheels in a kind of figure eight configuration; it makes four cuts in a much smaller space than an ordinary four-head bandsaw line.
Gang saw kerfs have been reduced, making them more competitive with bandsaws in the yield arena, and there have been other improvements, such as better access for saw blade changes.
For quality control, lumber exiting gang or bandsaws may be monitored with the aid of systems that include a camera and desktop computer. These systems are able to monitor the lumber and notify the machine operator with an alarm if the saw begins to cut lumber that exceeds size tolerances. The same systems also can provide production reports.
In conclusion, when trying to decide which machine is right for you, the first question to ask is: what is the planned production? If you plan to cut less than 20,000 board feet a day, the horizontal bandsaw will do a good job at a lower cost. If your production target is 30,000 to 50,000 board feet or more, the more expensive circular gang saw would seem to be the best choice. As the bandsaw advocates note, however, ‘the more you cut, the more you save.’
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