Orbital wide belt sander, proper grit eliminate cross grain scratch problem
Whenever grains run in different directions, as in the production of frame doors, for example, there’s a risk that the sanding process will scratch across one of the grains. Even the slightest scratches show up as imperfections in the finishing process. One common solution to this problem is hand sanding with orbital sanders. This can be time consuming, however, as well as labor-intensive.
Wayne Pickurel, plant manager for Hooker Furniture, Martinsville, VA, recently faced this problem and found a different solution.
“We made the decision a few years ago to make a lot of our own doors in-house,” Pickurel said. “For the first year that we were making our own doors, we were running them down a production line, which was primarily a bed and mirror cabinet line, where we would sand the doors by hand with hand-held orbital sanders. Of course, when you are sanding doors you aren’t making any beds and mirrors, so that line was constantly behind schedule. Something had to be done.”
Doug Williams, Hooker Furniture executive vice president of manufacturing, agreed. “When you build a frame door and put the joints together, whether they are mitered joints or cope joints, you are left with grains that cross. Even after all of the time spent hand sanding, the finished product often is inconsistent. The employees might have sanded thoroughly for half the day and then slacked off after that,” he said.
The solution was to invest in a Timesavers Model 200 orbital wide belt sander. “About the time we were having our problem, Timesavers had developed this orbital sander,” Pickurel said. “We were among the first to purchase one and it has worked great for us.”
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| The Timesavers Model 200 orbital wide belt sander has allowed Hooker Furniture to effectively remove cross grain scratches from its door frames. |
The sander has a wide belt in the front of the machine and four oscillating heads behind the belt. “When I say it has four heads, it actually has four bars with abrasive material on them,” Pickurel said. “The bars vibrate, which creates the oscillating effect. You step down the grits just as you would if you were using a standard wide belt.”
The first belt that the frame comes into contact with is the wide belt. Hooker uses 180 grit on this belt which is responsible for removing any scratches on the frame. As the frame moves forward in the machine, the oscillating heads sand it. Wrapped around these heads is a very fine 60-micron paper, which is responsible for the finish sand.
“With the oscillating motion and the use of very fine grits (up to 220 grit depending upon the material being sanded), we can eliminate any cross-grain scratches,” Williams said.
The sander worked so well it created a separate problem for the company. “The sanded doors were so slick that the stains would not penetrate the surface,” Pickurel said. “We quickly learned that we needed to back off of the grits being used.”
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Critical on-the-spot inspections lower furniture rejects
The time to catch imperfections or defects in a wood product is before that product reaches the finishing process. “Because the use of stain on wood makes even the slightest of scratches or chips visible, it becomes critical that a manufacturer have a series of nets to catch defects before they get stained,” said Don Barrett, resource manager at Councill Craftsmen.
Councill Craftsmen, located in Denton, NC, is a producer of high-end residential and office casegoods. The company employs a unique manufacturing philosophy that allows it to make all products to order. “We call it synchronous manufacturing,” Barrett said. “In order to have a reasonable lead time, we place our parts in bins. When the order is taken and the proper time to release the parts onto the production floor has been determined, we pull the parts out of the bin and send them to the assembly area.”
This is where the thorough inspection process begins. Before the parts are placed into the bin, they are visually inspected and measured for cut accuracy and for any wood defects or imperfections. When the part comes out of the bin, it is assembled. “Once the parts are assembled we inspect them again,” Barrett said. “Immediately after we have the pieces loaded onto the finishing line we inspect them once again.
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| Councill Craftsmen arms its inspectors with hand-held lights that allow for easier detection of imperfections. |
At Councill, it is not enough for an inspector to walk around the part and search for defects. The company arms each of its inspectors with a hand-held light that allows for easier detection of imperfections. “Our inspectors use these inspection lights at every inspection point,” Barrett said. “In one hand they hold the light and with the other hand they are marking with chalk or tape.”
Still, not satisfied, the company now uses a special fluorescent light manufactured by 3M to aid in defect detection as well. Although its use is on a trial basis, Barrett hopes to utilize the lighting system throughout the entire plant and not just in the inspection areas. “We were given an opportunity to test out the new lighting technology developed by 3M in May of last year and it has been very effective,” Barrett said. “The automotive industry uses these lights, which fit in a standard sized fluorescent lighting fixture, and has great results. Now 3M is trying them in the woodworking industry.
“3M is talking about bringing us more. We were hoping that the new lighting technology would allow us to discontinue the use of so many on-the-spot inspectors. Although the system has worked great, I don’t think we will ever be able to stop the amount of visual inspection we perform. Product quality is just too large an issue in this industry.”
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