Wood Finishing & Sanding: Frequently Asked Questions
May 9, 2013 | 3:11 pm CDT

What are some of the common problems facing wood products manufacturers in their finishing and sanding operations? Here are some of the frequently asked questions and answers, as provided by the woodworking experts.

Finishing FAQs

Q: Why are transfer efficiency numbers different for the same type of gun?

A: Transfer efficiency is the amount of paint solids deposited on a part divided by the total paint sprayed. There are 2 primary test standards when measuring transfer efficiency. First, ASTM test standard which simulates a conveyor system. For conventional spraying, ASTM never has a transfer efficiency greater than 50%. The EN13699 test standard is the second type of test for transfer efficiency. This test is performed by spraying a pattern in the middle of a large target. The EN standard produces higher results for the same gun due to the way the test is performed. For example, an HVLP gun tested to the ASTM standard has a range of 25 – 32% transfer efficiency. The same HVLP gun tested to the EN standard has a range of 70 – 78% transfer efficiency. – submitted by Wendy Hartley, Worldwide Product Marketing Manager for Finishing Equipment, Graco

Q: How can I prevent tails and improve spray patterns in airless and air-assist applications?

A: Tails are normally caused by low fluid pressure can normally be solved by increasing fluid pressure. Often material is not flowing into the pump effectively and may need to be thinned to reduce viscosity. Sometimes the fluid delivery system, such as a hopper of siphon hose, is also not functioning properly and the pump is not being feed material consistently. – submitted by Skye Stapella, product manager, DeVilbiss, Ransburg, BGK, Binks

Q: How do you mix the base and catalyst with no mistakes.

A: There are mechanical and electronic mixing systems available. By going with these systems, the wastage on mixed products is drastically reduced. Freshly mixed and sprayed products maintain gloss levels. Accuracy of mixing is always there thus avoiding over or under catalyzation leading to cracks etc. on finished products. – submitted by S.T. Rajan, vice president, EXEL North America Inc.

Q: How can I best adjust fluid viscosity to achieve the best quality finish?

A: When related to an HVLP turbine spray system we always ask first the size of the system, which would be an indication of the maximum atomizing pressure. From there we offer a generalized guideline explaining that all coatings "behave" differently and then suggest looking at the end result. If the finish is what is desired, all is OK. If the finished surface is slightly wavy or orange peeled we suggest thinning or reducing the coating slightly and then evaluating the results. – submitted by Bill Boxer, Apollo Sprayers International Inc.

Q: What is LVMP/Trans-Tech/Compliant technology?

A: This equipment type was first seen in the mid 1990s and is a mixture of conventional and HVLP atomization methods. Trans-Tech makes more energy available for the atomization process but gives a higher Transfer Efficiency of coating material than the Conventional Air Atomizing method. This ‘complies’ with European government legislation by being able to transfer at least 65% of the sprayed material to the sprayed component (BSEN 13966 ‘Determination of Transfer Efficiency of atomizing and spraying equipment for liquid coating materials). Air Cap Pressure is typically in the region of 20 to 45 psi (1.3 to 3 bar) while using 9-20 cfm (250 to 560 l/min) to carry out its work. – submitted by Elizabeth Lisiecki, Market Development Manager, DeVilbiss, Ransburg, BGK, Binks

Q: How can you help me reduce costs?

A. Our approach is to not look solely at the finishing materials on a per-gallon or per-liter basis but with the complete view. In addition to the coatings chosen, there are other important factors such as recovery/re-use, catalyzed waste and transfer efficiencies. We believe that it is important to help customers understand applied cost – that which is beyond the “bucket price” – and how value added services from a total solutions approach can help lower those costs. – submitted by Bill Fiorillo, Global Market Director Kitchen Cabinets and Furniture, Product Finishes Division of Sherwin-Williams

Q: How do I set up my air assist gun to optimize transfer efficiency?

A: The proper air pressure and fluid pressure is critical for transfer efficiency. To optimize, take the following steps: 1. Bring the fluid pressure down into the heavy tails range, and use air to “Assist” away the tails; 2. Turn fan adjustment knob until the fan width is maximized; 3. Turn the air to the gun down to zero psi; 4. Slowly turn up the fluid pressure until you get acceptable atomization within the spray pattern. At this point you should still have tails at each end of the fan pattern; and 5. Start turning up the air pressure to the gun to “assist” away the tails. – submitted by Wendy Hartley, Worldwide Product Marketing Manager for Finishing Equipment, Graco

Q: What is the percentage of savings with new technology?

A: We can do this through beaker tests or through flowmeter tests to get the transfer efficiency of applicators leading to savings as compared to what they have. – submitted by S.T. Rajan, vice president, EXEL North America Inc.

Q: How do I reduce overspray in my spray gun application?

A: Adjust the fluid and air pressures for each application. Use only enough to get the job done, anything else is waste. Adjust the pattern size for the product and train the operator on proper spray technique. – submitted by Roy Young, account manager, DeVilbiss, Ransburg, BGK, Binks

Q: What equipment is available in the market to handle water-based materials?

A: All the pumps and guns are made of high grade stainless steel to handle water based coatings. We have special tips to atomize water based materials to give the correct level of atomization. We have larger ball and seats in pumps to handle water based coatings which are generally more viscous. – submitted by S.T. Rajan, vice president, EXEL North America Inc.

Q: What are some ideas on how to automate?

A. Look at vertical hanging conveyor systems or flat lines with reciprocating arms or flat line with carousels or robots. Depending on the jobs we could even look at floor conveyors for handling. – submitted by S.T. Rajan, vice president, EXEL North America Inc.

Sanding FAQs

Q: How do I eliminate the bottleneck that hand sanding causes in my shop?

A: Hand sanding is a tedious and time consuming process. Adding a brush sander to your shop is an affordable way to automate the sanding process. Using a brush sander cuts down on the amount of time it takes to sand stock, as well as the number of employees required to do it. Plus, there are more consistent results when machine sanding. Where it might have taken five employees to sand stock by hand could potentially take only two employees feeding the brush sander, allowing the other three to work on additional projects. – submitted by Warren Weber, manager, SuperMax Tools

Q: How can I avoid abrasive belt tracking problems on my widebelt sander?

A: Simple maintenance, like cleaning the sander and keeping an eye on the volume in your dust collector’s bags and filters will help assure that you are keeping the tracking system on the sander functioning well. By getting enough cfm of air moving out through the sander’s dust chute you will keep the tracking system working optimally.Keep up on regular maintenance like cleaning and grease key points in the machine including bearings and bushings will help ensure a long life of these main components of your wide belt sander.  - submitted by Shawn Larkin, sales manager, Safety Speed Manufacturing

Q: How can I minimize the sanding marks often created by belt oscillation and/or belt defects?

A: The solution often requires the use of sanding heads which can pivot to various angles, from the standard 90 degrees to the conveyor belt. Using a pivoted sanding head, the defects on the belt are shifted slightly side-wards with each rotation and do not grow and build to form lines that show on the workpiece. – submitted by Rick Hannigan, vice president-sales, Holz-Her US Inc.

Q: How much stock can I remove in one pass?

A: Stock removal on a widebelt sander is determined more by the abrasive belt than by the machine. Each abrasive belt is designed to remove a certain amount of stock, and if that amount is surpassed, the life of the belt is affected. As a rule, you will need to use the lower grit belts for heavy stock removal (36-80 grit belts can remove approximately 1/8 inch to 1/32 inch respectively) and medium grit belts for lighter stock removal (100- 120 grit belts can remove approximately 1/32 inch to 1/64 inch respectively). Belts in grits from 150 on up should only be used for finishing and are not considered cutting belts. Other factors affecting stock removal are: abrasive belt speed, type of sanding head, feed speed and available horsepower. – submitted by Gary Besonen, national woodworking equipment manager, Timesavers Inc.

Q: What special equipment is required to sand sensitive materials (gloss, finishes)?

A: Options which are often required, include: vacuum conveyor beds (for accurate part holding), variable speed sanding heads (to adjust belt rotation speed), electronic segmented sanding pads (to eliminate sand-through), and programmable controls to store the proper settings for all specialized and standard applications. – submitted by Rick Hannigan, vice president-sales, Holz-Her US Inc.

Q: What causes chatter?

A: Chatter marks on the product are most often caused by the sanding belt splice. A good way to check is to use a black crayon to mark the splice. Then, run a new, clean workpiece through the machine. If the belt splice is the problem, the black crayon will mark the workpiece with chatter marks. Most of the time, using more pressure or making a heavier cut into the product will cure chatter. An exception to this guideline is a product application on a machine with a hard contact drum, that is not designed for finishing. Causes include: belt splice, worn contact drum bearing, vibration in the machine, worn drive motor bearings, worn idler roll bearings, loose or worn drive belts, flat spots on the drum, out of balance drum or idler, and conveyor bed not feeding at a constant rate. – submitted by Gary Besonen, national woodworking equipment manager, Timesavers Inc.

Q: How do you solve chatter?

A: Actions to cure chatter marks include: use an abrasive belt with a butt splice; replace the contact drum bearings; identify and stop the machine vibration; replace the drive motor bearings; replace the idler roll bearings; tighten the drive belts; replace or dress the contact drum; balance the contact drum; check the conveyor bed drive coupler/drive belt; or relieve tension from the abrasive belt when it is not in use to avoid flat spots on drums. – submitted by Gary Besonen, national woodworking equipment manager, Timesavers Inc.

Q: How can I create a distressed look without hand sanding each piece?

A: A brush sander equipped with a wire head is an excellent way to achieve a distressed finish on wood. – submitted by Warren Weber, manager, SuperMax Tools

Comment: Most questions we hear are basic maintenance issues from “dressing” the feed mat and drums to what is the best way to calibrate the head alignment. Another frequent question which actually falls into place with head alignment/adjustment is in reference to proper stock removal based on the belts the customer uses. This is a very important question as if machines are set up properly and the operator is removing the proper amount of stock based on the sand paper they use then you can get better results in finishing and longer belt life. – submitted by Mike Fogel, product manager for Sandya products, Scm Group

Comment: I have customers that are squeezing every drop of production out of their machines because they have held off in updating their machinery until they see a continued increase in the economy and steady growth. They are asking, how do I get more out of my existing machine; different abrasives, different settings and scheduled machine tune-ups. – submitted by John Becker, president, SlipCon USA Inc.

Comment: While traditional questions on normal maintenance remain, our customers are asking more and more questions pertaining to non-traditional sanding procedures. Some of these include applications like structuring, handsawn appearance and high gloss applications. Also, for many years high volume companies have requested solutions for sealer sanding, but now we are seeing an increase in small to medium companies wanting to bring their finishing back in house to provide more value added to their product. - Mike Johnson, North American Brand Manager –Viet, Biesse America

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