Breaking the Sanding Bottleneck
New and improved automated technologies are making it easier to sand profiled and recessed parts.
BY JO-ANN KAISER
Fine sanding raised panel doors and other profiled pieces is largely a labor-intensive process at most woodworking operations. The more complex the part or shorter the run, the more difficult it is to automate the process.
Fortunately, manufacturers of sanding equipment are rising to the challenge. In recent years, vast strides have been made to develop technology that will not only save time, but reduce profile sanding costs. What's more, several of the manufacturers and suppliers interviewed by Wood & Wood Products for this article note that the price of this technology is becoming more affordable.
Following are the thoughts and comments of nine industry experts.
Combining Belts & Wheels
"Sanding has represented a bottleneck in some manufacturing plants because the American market has put too little emphasis on sanding," he said. "The technology is not really new; what is new is the emphasis on the proper mix of techniques."
Kostelnik explained that one way to sand raised panels is to use a combination of sanding belts for flat surfaces and abrasive wheels for shaped surfaces. The machines can be as complex or simple as the profile. "If you need to sand two flat surfaces with a complex edge, for example, you would need two sanding belts and three abrasive wheels," Kostelnik said. "Today, abrasive wheels of the flapper type feature a combination of strip sandpaper and abrasive."
Kostelnik further explained that one of the biggest problems with sanding profiled edges is "cut through" because edges can be quite sharp. "The key is to use the proper amount of abrasive compounds because you are constantly fighting cut through on edges. The sharper the edge, the worse the problem," he said.
Automating to Reduce Labor Costs
"Today, there is a sophisticated approach in the industry to both shaping and sanding and this is giving a more precise and fine-tuned profiled piece. Rotary head sanding and its accuracies have played an important part to this approach. Now woodworkers talk in terms of one thousands as opposed to 32nds in terms of accuracy. That has helped the cause of automated sanding. In the last five to seven years we have seen a lot of people combine shaping with sanding. Accuracy is the big advantage plus the reduction in labor and the amount of steps necessary to produce a part.
"Also with a trend toward higher tolerances we are seeing a change in the philosophy that the sanding step is the place to correct all sorts of mistakes," Johnson added. "Now shaping problems are correctly being addressed on their own. Sanding is not supposed to be a shaping step, but a part of finishing. Manufacturers are learning to use sanding for what it was truly meant -- that is preparing the wood or other surface for a finish."
Automation Pays Off
"A real key to finishing a piece correctly is using the right profile sander," said Bosley. "If a piece is not sanded properly its quality suffers. Knife marks and chatter, compressed wood fibers and peaks and valleys in a piece will prevent a consistent finish and proper stain absorption. Separate automated sanding processes address the varied needs of profile sanding of linear profiled items, such as picture frames and caskets parts and profiled edges found in cabinet doors and drawer frames. The machines are similar in that they feature the same sanding heads, but have different machine bases," Bosley added.
Bosley said that properly sanding raised panel doors is a concern of the cabinet industry. "The automatic sanders feature heads on the left and right sides that allow for full 360-degree sanding." Bosley said he thinks picture frame manufacturers have been the quickest to embrace the new automated sanding technology offered for profiles while furniture manufacturers have been the slowest to turn to automated sanding.
"Part of the problem is in the way furniture is manufactured. We tend to assemble the furniture and then sand and stain it whereas in Europe the sanding and finishing processes might be done first and the piece assembled last." Bosley laughed and said that six to seven years ago, talking to manufacturers about profile sanding was a little like doing missionary work. "Today, manufacturers have accepted the technology and many are considering how it can work for them," he said.
Bosley concluded that profile sanding is becoming available for smaller manufacturers. "Compact versions of CNC machines are offered that give simple and economical sanding routines which include light sanding and buffing of wood or MDF profiles as well as denibbing stain coats and primers." Selected abrasives can also buff sealers and UV coatings, he said.
Flexibility a Key
"Sanding is an important step in terms of the overall quality of the finished piece," Derda said. If a piece is not sanded properly, there is no way to cover up the mistake. Automated profile sanders are in demand because of the high cost of labor to do these jobs by hand. I think the manufacturers are best served by profile sanders that offer flexibility in abrasives so that a user is not locked into one specific supplier, but has a sander that utilizes the abrasives of a variety of suppliers."
New Methods for Sanding Cathedral Doors
Stiles also pointed to tests done by his company on disc versus belt sanding to study the life factor of the two. "We found that belt sanding units with 120 inches of abrasive belts have a life factor of four to one compared with discs, with only about 25 inches of abrasives. While the belt sanding equipment costs quite a bit more, the life of the belt makes up the difference in cost in 12 to 18 months. Our study showed that the `old fashioned way' of sanding with a belt is really much cheaper when factored over two to three years. In addition the belt shoe gives more contact with the abrasive to the surface being sanded, which adds to the quality of the sanding job."
Stiles said there is still a place for disc sanding, especially when sanding sophisticated profiles. "I would say the best sanders for woodworking applications that include profiled edges would give the user the option of using discs and belts," he said.
In addition to quality and production advantages, Stiles added a third reason for automating sanding operations: worker safety. "Workers face a real problem when doing repetitive work on a daily basis. Those that hand sand all day face the risk of developing carpal tunnel problems. Also, sanding with a machine removes workers from the immediate area of the dust. Prolonged exposure to dust is believed to pose health problems for workers who breathe it," said Stiles.
CNC Facilitates Consistency
"New technology has made it possible to design a machine with a solid shaft drive rather than belts and a series of wheels. The one-shaft, one-motor method pulls all the sanding heads at the same, delivering constant feed speed which gives a uniform sanding job. One shaft also translates to less maintenance," Stringer said.
Stringer also pointed to technology that allows CNC programming of profile sanders. "Before, an operator who changed the set up had to adjust the X, Y and Z axis for each sanding head. If the machine had 20 sanding heads, you were talking about a very long changeover time -- up to 30 minutes in some cases to reprogram a machine. With computerized controls of profile systems the changeover times are drastically reduced. CNC allows the operator to program infeed speed data, shaft speed information, setups for all three axis and any special needs. One program may tell the machine to use only 10 of 20 available sanding heads."
Stringer added that these types of CNC machines are designed for "the big boys, but a trend will be to see their use in all facets of manufacturing. Sanding has been the red-headed stepchild of the manufacturing world, and profile sanding in particular has been the last area to be addressed with new technology and automation, but that is changing. I envision companies at the medium to small level becoming interested in computerized profile sanding within the next two to three years as the technology becomes available in all price points much the way CNC boring has become available for a variety of manufacturers. The computer controls take away the problems of human error because operators no longer are responsible for the manual set up of the machinery."
Quick Set-up Features
Allison explained that automating sanding gives a much more consistent finished piece. "Automated profile sanders are hot items. The new machines offer a high degree of control for the piece being sanded even with irregular shapes." Allison added that profile sanding had traditionally been a labor-intensive process, and thus a bottleneck. "In some plants it is not uncommon to see one-third of the workforce performing hand sanding. Anything we can do to reduce the cost of labor while offering accuracy and consistency and an improved sanding job is going to be attractive to manufacturers."
Identify 'Sanding Problems' Before Sanding
Cardwell said he sees the newest developments in sanding in the area of abrasives, allowing the new machines to sand a piece fully -- including every crack, crevice, edge and corner. "Sanding discs with flatter blades are used with raw wood, especially with hardwoods and whitewoods. Now a brush with discs is being used successfully to sand primer and sealer coats. The combination of the brush and disc does a good job with profiles and for sealer coatings, but sanding UV coatings and some waterbornes requires a different type of abrasive.
"I tell people to visualize a paint brush with a piece of sandpaper moving in a paddle wheel fashion," Cardwell continued. "This offers the aggressive type of abrasive sanding good for UV finishes and also used for moulding to remove chatter marks. A coarser grit disc sander is best used with waterborne finishes."
Brush Head Improves Sanding
To illustrate his point, Weber said that manufacturers who use a CNC router to make one-piece MDF raised panel doors have to take extreme care with their sanding. "Proper sanding here is crucial. Any fuzz or small lines left in the piece will affect the gluing and telegraph through. Foil is very sensitive and with these panels if the piece isn't sanded correctly, you can't rework it. It is a loss," he said.
Weber pointed to brush head technology as an area where profile sanding has improved. "A nylon bristle with silicon carbide impregnated into the bristle is one new development. This product conforms to the shape of the piece and gives a very uniform sanding. Another important development is the variable speeds of the conveyors and of the brush RPM," he said.
Weber also described another brush as a bristle and abrasive strip combination that works for deep sanding needs such as crown moulding. Abrasive strips are 1/8 inch to 1/4 inch wide and offer a deeper penetration with more stock removal.