Sanding raised panels and profiles does not have to be a bottleneck in the manufacturing process, according to industry representatives. With proper set up, modern equipment and accurate machining of material, much of the slowdown in the profile sanding process can be eliminated. Here is what four experts had to say on the subject:
Efficient raised panel door sanding depends upon accurate machining.
“Sanding can be easy or difficult depending on how the door arrives at the sander,” says Keith Paxton, product specialist for HolzHer USA. “Accurate machining, both in sizing parts and in the cope and stick joinery, produces a much flatter door than doors that are built straight from the lumber stack, assembled and fed to the sander for calibration. Pre-machined parts allow a hard contact drum to calibrate with a finer grit belt.”
“One common problem in sanding can be inconsistent profiles on the parts,” says Riccardo Azzoni, president of Atlantic Machinery. “In this case, a shape-and-sand machine is an excellent solution, as the parts are being both machined and sanded on the same machine in one pass, thus virtually eliminating this problem. Some manufacturers even offer tilting spindle features, which eliminate the need for (and cost of) special tooling.”
Proper set-up eliminates bottlenecks.
“Set-ups can create or eliminate bottlenecks,” says Paxton. “PLC controls can be used to set sanders with various degrees of control ranging from total set-up to basic control functions. PLC controls work well when consistent groups of parts are sanded, when multiple operators are present, and in upper and lower sanders. However, if a good set-up mechanism is built into the sander, it can be extremely fast, very reliable and offer more versatility than the PLC.
“Efficiency is increased by selecting the right grit belts for stock removal, removing reasonable amounts of material and giving the abrasive enough time to work. Starting with a 100 grit belt produces a much finer surface than starting with an 80 grit belt.
“Also, adjusting the variable speed conveyor to the product is often overlooked, yet it produces dramatic results. Throughput is often very different from conveyor speed. If a belt is going to be heavily taxed, give it time to work, without allowing it to load and burn. The 60/30/10 percent formula for stock removal, starting with the coarsest grit through finish, is a good guideline for three belt sequences.”
Constant passline height solves several problems, when well engineered, according to Paxton. “When conveyor height is fixed, fixed height entry and exit tables or conveyors can be used. This allows solid part support end to end, regardless of part thickness or length.”
Pay attention to the wood grain.
“Because of the grain in wood, linear sanding and cross grain sanding may require different amounts of attention,” says David Joslyn, regional sales manager for Mereen Johnson Machine Company. “Even when sanding cross grain, different areas may require more or less attention. This makes it difficult to always get the desired results when sanding on a machine versus hand sanding. Matching and keeping the profiles the same between machining and sanding is also key in good sanding results.”
There remain processes that require hand sanding, according to Joslyn. “Sanding of the arch of a cathedral panel is still a problem. This requires using a sanding wheel but typically of a diameter too small to provide enough sanding surface. Proper sanding of the arch is still best done by hand.”
“Attention to lumber species is critical,” says Paxton. “Poplar sands differently than cherry due to the grain and density differences. Amount of stock removal and sanding pressure often require some adjustment. Use of proper and varying grits also may be required when sanding poplar. Tuning the conveyor speed to the application can change adequate sanding to excellent sanding. Minor adjustments can eliminate potential re-work.
“Eliminating cross grain scratch is a constant challenge. In species such as oak and ash, finishing with soft drums creates easily camouflaged cross grain scratches due to the short scratches. Platens produce longer, shallower scratches that are easier to remove with conveyor fed orbital sanders, or in hand sanding, than the deeper scratches left by drums. Because of the long scratches that platens produce, they are more apparent.
“Conveyor fed orbital sanders remove cross grain scratch only if the wide belt does its job. Orbital sanders demand very accurate door calibration and a fine grit finish with shallow scratch pattern to work properly. With their wide platens, they are not stock removal tools. They are often blamed for problems caused by poor wide belt sanding.”
The most important part of the finishing process? Raw sanding.
“Raw sanding of profiles is the most important part of the finishing process,” says Steve Bosley, sales manager, Delle Vedove USA Inc. “A good sanding of the profile (whether on the edge of a panel or on a moulding) is the first and most important step to the finishing. Sanding allows the stain to be evenly absorbed and applied to the surface, takes out small defects, creates a uniform look on the entire surface, and takes down raised grain and dust on the substrate. Typically, a good raw sanding speed is between 60-80 fpm (much slower than both the moulding and finishing operation). The only way to speed the process is to configure the sander with enough sanding heads to properly sand the profile and run at the speeds required for production.”
Today’s sanding technology increases quality and production.
“Most American manufacturers still do edge and profile sanding by hand!” exclaims Azzoni. “There are a number of imported and domestic sanders available that would certainly alleviate this problem by increasing quality and production. These machines range from simple edge sanders, preferably with belt oscillation, to throughfeed sanders with either single or multiple stations.
“In most cases, oscillating belts are better than wheels, unless there are tight and/or 90 degree corners that need to be sanded, in which case an abrasive wheel with automatic compensation of the wear is a better choice.
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