Proper Sanding Belt Tension

How to Maintain Proper Sanding Belt Tension for Better Performance
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When consulting with customers, abrasives suppliers place a great deal of emphasis on choosing the best abrasive product for the job. To put that product to its best use, however, it’s just as important to select and set the correct machine parameters. One of the most overlooked aspects of wood sanding operations is maintaining proper tension on the coated abrasive belt once it is mounted on the sanding machine.

In basic terms, the amount of tension on the coated abrasive belt should be just enough to keep the belt from slipping on the drive wheel, and to keep the belt from tracking off the machine. Several methods can be used.

Some sanding machines have fixed belt tension. For example, portable sanders, such as the 3” x 24” machines, have fixed tension that is derived from a loaded spring. This tension is factory-set and is not readily adjustable.

However, most sanding machines have some type of adjustable tensioning device. These include use of weights, screw-type mechanisms, or pneumatic cylinders. On screw-adjusted tension devices, such as those found on edge sanders and some mould sanders, it’s often difficult to determine the proper amount of tensioning unless the operator is experienced with the machine. As a general rule, the belt should make five or more full rotations after the machine is turned off. If the belt comes to a stop very quickly, it’s likely that the tension is too high.

Pneumatic cylinder designs are the preferred type of adjustable device. They compensate for stretching of the abrasive belts, provide a range of delicate adjustment, and can be rapidly released and applied for quick belt changes. Using an air gauge installed on the sander can monitor pneumatic tension. Quite often, these gauges are not properly maintained, and will give incorrect readings. Air pressure gauges are relatively inexpensive, and should be replaced if broken.

Most wood sanding applications (such as mold sanding using narrow cloth belts) require a belt tension of approximately 40 psi. However, there are some special exceptions. For example, abrasive planing operations using coarse grits typically demand belt tension in the range of 70 to 90 psi.

Intermediate wide belt sanding (grits 60 to 220) normally uses a tension in the range of 60 to 75 psi for cloth belts. On these applications, tension for paper belts should be set at about 20 to 25 percent less than that for cloth belts. This is because cloth belts will stretch very slightly during use, while paper belts will not. In any case, the wide belt machine manufacturer should be consulted for specific recommendations regarding air tension settings. On drawer sanders, a specialized machine for sanding the inside lip of a drawer front where it joins the sides, it’s best to use the least amount of belt tension possible when installing a new belt. This means that you should be able to easily rotate the belt by hand with the machine turned off. After running the sander for 10 minutes, it may be necessary to slightly increase the tension as the belt stretches slightly.

Because the goal is to keep the belt from slipping, users sometimes err on the side of using too much belt tension. Several problems can result from excessive belt tension. They include:

• Premature bearing wear
• Excessive wear of the rubber contact drum
• Excessive wear of graphite covers on platens
• Excessive wear of mould blocks

Excessive belt tension changes the characteristics of a rubber contact drum; it makes a soft wheel act harder and decreases the effectiveness of the serrations. Excessive belt tension can also lead to belt failure. It can cause the belt joint to mark the work piece, and can cause tracking problems. But the leading problem caused by excessive belt tension is the generation of heat. One recent study showed that an increase in belt tension from 40 to 60 psi caused the sanding heat at the area of contact to jump by 100°F. Excessive heat often leads to premature loading of the belt and wear on flexible belts.

Consult with your abrasives supplier and machine manufacturer to ensure that you’re using the proper amount of belt tension. Maintained correctly, belt tensioning can maximize abrasive belt life, provide the best possible finish, and extend the life of the sanding machine components.

Please visit our website and check out our many sanding belts that are available to ship quickly.

**Original article can be found at the Woodworking Network.** 

Should you do an Abrasive Audit?

An abrasive audit is a detailed recording over a two week period of all the abrasives that are being used in your production, along with the details on how the abrasive is being used. Looking at the cost, usage and application of every abrasive product in your shop or plant can lead to productivity gains, improvement in processes, opportunities for supply consolidation and cost reduction.

We walked through this process a while back with a furniture manufacturer. After assessing their requirements over a few phone conversations and emails, we determined that our company could offer a significant savings to this furniture manufacturer in their abrasives purchases. We switched them to a new and improved abrasive belt material which reduced their pricing resulting in a savings of $59,142.00 for this customer in a one year period. In addition, our sanding belts lasted approximately 15% longer than the former supplier’s belts. Consequently, this customer was able to use approximately 294 fewer belts in the same time frame. Bottom line savings totaled 62% by switching to belts offered by Abrasive Resource.

Things important to know during an abrasive audit:

1. What are the abrasives currently being used for each part and what is its cost?
2. What is the number of pieces or parts you are able to finish per abrasive product?
3. What is the amount of each abrasive you buy in a year?
4. Are there bottleneck areas where the sanding operation is slowing things down?
5. Does one operator or operation consistently consume more abrasives than another?
6. Have there been changes in technology that might help improve productivity or cost?

If you would like to prepare for your own abrasive audit, gather past order information on the abrasives you purchase. You will want to make a list of all the products that you buy along with specifications and quantities. Your abrasive supplier will be happy to walk alongside you during this audit—giving suggestions, sending samples and providing quotations so that you can assess your particular situation and improve the grinding and finishing processes in your plant. If you have any questions, don’t hesitate to call us at Abrasive Resource. Abrasive products are all we do. And if you’re not makin’ dust, you’re eatin’ it!

Cleaning Your Sanding Belts

Is it worth it to clean your sanding belts?

It depends. How much has the material loaded the sanding belt while it is still sharp?

Cleaning sanding belts can be worth your time if they have prematurely loaded while sanding something soft—like pine wood or a non-ferrous metal like aluminum or brass. Once you have cleaned the belt out, there is usually enough sharp abrasive material left that it will still perform well.

Attempting to clean an abrasive belt that was used to finish hardwoods or sand harder ferrous metals like steel doesn’t make much sense. At the point they load the sanding belt, the life of the abrasive grain has been diminished and it will not be sharp enough to continue effective sanding anyway.

If you decide that cleaning your sanding belts is worth trying out, there are two options you should consider:

1. Next time you purchase the smaller sanding belts for a soft wood application, ask about ordering a belt cleaning stick. These handheld erasers can easily clean away wood particles and resin on cloth backed abrasives. No solutions needed, simply hold the stick firmly against the moving belt or disc.
   
2. If you are interested in cleaning wide belts or belts used for metal finishing, you will need to look into the option of pressure washing them and possibly using some sort washing solution or chemical cleaner. We have heard of cabinet shops using a non-toxic, environmentally safe product called Simple Green. Just make sure that you are ordering a sanding belt with a 100% poly backing so that it is 100% waterproof—you don’t want a poly cotton blend backing or your belt could stretch and lose its shape. Always clean while the belt is standing up (not lying flat) and let dry for a minimum of two days before reusing them.
   
   Questions? Just give us a call at 800-814-7358. You can have sanding belts made in any material, any size and any grit from Abrasive Resource!

Sanding with Consecutive Grades of Sandpaper

As you sand, you must use several consecutive grades of sandpaper, working your way from coarse to fine to achieve the degree of smoothness you want. Remember that the grains create a scratch pattern in the surface. The larger the grains (or the coarser the grade), the larger these scratches will be. When you move to the next-finer grade, you trade the first set of scratches for slightly smaller ones. If you jump grades, the fine abrasive grain may be too small to level the scratches without a lot of extra work - it will be like leveling a mountain with a garden spade. 

As a result, the surface will be left with an uneven scratch pattern, with deep scratches in among the fine ones. Because these deep scratches fill with fine sanding dust, they may be nearly invisible to you until you apply a finish. Then the finish will darken the torn end-grain fibers in the deeper scratches, making them stand out from the surrounding surface. This will ruin the smooth consistent appearance of the surface.

Article provided from "The Workshop Companion, Sanding and Planing, Techniques for Better Woodworking" by Nick Engler. Permission of use granted by Rodale.

Why and How Do You Scuff Sand?

The Woodworking Network started a new blog series on Finishing. Here's the portion of the article that's most useful for our readers of The Sandpaper Blog:

Why do you scuff sand?
• Modern coatings get hard and some get chemically resistant within hours. Subsequent coats will not rewet and blend with the layer below. The only type of bond that is possible between coats may be a mechanical bond created by sanding scratches.
• It’s true, in my experience, that most first coats make you look like a monkey’s uncle. They look horrible! But if properly scuffed, a good seal coat will make you look like a rock star after your second coat.
• The lacquer makes wood fibers stand up.
• Surface tension in the lacquer attracts it to those fibers and it builds up around them creating “pimples” in the lacquer that must be sanded away.
• Surface tension causes lacquer to pile up around the pores.
• Surface tension creates fat edges that need to be attended to.
• There’s always dust that appears as if by magic or “spooge” out of the gun that lands in the first coat
• There’s always a bug willing to commit suicide in your wet lacquer.
• Heaven forbid! You just created a run or sag.
All of these and more are the enemies of a glass smooth finish. And lest I forget, it is über-important to get rid of the sanding dust that you create. Again, it may not be rewetted by the next coat. Dust and debris are your enemy!
At the same time, the guy who sands his work and perspires onto the surface is the first one to call and say that he has fisheye issues. Wear at least a short sleeve shirt. The oils of your skin and certainly the deodorant that you wear will contribute to fisheyes. That’s doubly important with water-borne coatings. Remember, oil and water don’t mix.

If you would like to read the blog article in it's entirety, visit the Woodworking Network.   For more information on sanding sponges, visit the Abrasive Resource website.

Replace Hand Sanding with Power Sanding

Bodyshop Business (www.bodyshopbusiness.com) has a new, updated website that includes links to articles that were published years ago in their print magazine. Here's a portion of one of their sanding related articles from March 2010 titled "Why You Should Replace Hand Sanding with Power Sanding":

Removing Material

This is the portion of the work that’s seldom done by hand by anyone. All you vo-tech grads probably still have the long board (a.k.a. the idiot stick) that you started school with and maybe even drag across a troublesome panel once or twice a year, but in large part everyone recognizes that removing old finishes or shaping body filler is a job for power tools. This rough work can be accomplished quickly by using a:

• Grinder. While the 24 or 36 grit 7-inch grinding disc will rip material off the surface fast, it also generates lots of heat. Any tool spinning at 3,000 to 5,000 rpm gets the sandpaper and the surface really hot. When you get the old paint or new body filler hot, it melts and clogs the expensive grinding disc. Let’s not forget also that it takes a manly man to shape filler with any kind of finesse when the tool is heavy and whirling at 5,000 rpm.

The other part of the equation is that once the material is ripped off with the grinder, the tech now has to fill and smooth those 24 grit scratches, adding more labor time to the repair. A better choice to strip paint and shave filler with 36, 40, 50, 60 or 80 grit paper might be a hog sander.

• 8-inch hog sander. This tool operates at a much lower rpm (900 to 1,000) and therefore runs much cooler. Because it spins slower, you can sand off the material with a paper disc rather than cloth. Materials are much cheaper. Whether this style of tool runs in a rotary (straight circle) or a rosette (offset circle) pattern, it removes the old finish or the body filler quickly and with lots of control.

To get the maximum benefit, make sure to hold the sander flat against the surface rather than up on the edge like a grinding disc. There are still some techs who think that to keep a long panel straight, they need a tool with a longer pad than the 8-inch round ones found on this style of sander. They prefer to use a file board.

• File board. With a 2-3/4-inch by 16-1/2-inch pad, this powered “idiot stick” is the staple of the industry. If you’re old enough, you remember when this tool was equipped with a 14-inch metal file rather than a sanding pad, and metal men used them to power-file down high spots in the steel and shave body solder (lead). Hence the name “file board.” Today, virtually all file boards are equipped with sanding pads. These tools can run in a straight line (back and forth) and be powered by a single piston with two ringed ends or by two pistons, one to push the pad forward and the other to push it back. Or they can run with an orbital wiggle (jitterbug) pattern.

Both styles have their advocates and strengths. In either case, it’s a great way to keep a long panel straight and chop off unwanted material quickly. Keeping piston-driven air files well lubricated will minimize the stalling of the pad. When the air pressure is equal on both ends of the stroke, the tool won’t start up when the trigger is depressed the next time. Many techs slam the end of the sanding pad to get the tool started back up, but keeping the cylinders well oiled is the key. And just a light push on one end or the other will start the tool back up smoothly.

Shaping the Surface

Shaping sanders are tools designed to prepare surfaces for paint. Power sanders do this rapidly, increasing the adhesion of the new coatings and featheredging the chips in the old finish. A smaller version of a file board sander with a straight line action could also work well to block the surface flat.

Prior to 1957, this type of sanding was often done by an orbital sander with a 3-inch by 8-inch or 3-2/3-inch by 9-inch pad called a jitterbug due to its wobbling action. Orbital sanders with various size pads are still useful today. Several sander manufacturers offer square or rectangular pads on a drive motor with a 3/16-inch orbit. In fact, most tools in this category (based on my arbitrary definitions) have a 3/16-inch or larger (3/8-inch) stroke – fast and aggressive enough to quickly shape and prepare the surface.

Just a reminder about how important thorough sanding is to ensure adhesion of the new coatings. It’s possible to double the contact of the surface area by sanding it well. How can that be? Imagine a distance on a flat surface from point A to point B. Now sand that same area and the distance from A to B (the contact area for the new coating), including the surface on both sides of the scratch (trench). Down one side of the scratch, up the other, down the next, up the other side – you get the idea. It will provide twice the surface to stick the new finish to.

A rotary or orbital tool runs the pad in a circle. A random orbit sander runs the pad in two circles, one inside the other. In 1957, the National Detroit Company patented the first random orbit sander widely used in refinish. In an effort to describe the circle-within-a-circle pattern, they called it “Dual Action.” It has become so pervasive in the market that its brand name has become a generic term. So when you say “D/A,” you likely mean a random orbit sander, now made by dozens of quality companies – kind of like when you say Kleenex and mean facial tissue, originally made by the Kimberly-Clark Company, or when you say Bondo® (a trademark of 3M Company) and mean polyester body filler, originally made and successfully marketed by the Bondo Corporation (now 3M Company). Or, if you’re in the South and say Coke, you really mean a carbonated soda made by any one of dozens of brands!

In this middle category of power sanders, most random orbit tools use either a 3/8-inch (very aggressive) or 3/16-inch (less aggressive but still fast) offset. The size of the offset determines how far the pad travels in each rotation. Bigger offsets cover more area but cause the tool to vibrate more.
In addition, some of these tools have a built-in wobble in the pad that interrupts contact with the work surface, and with the pad always changing planes, the sandpaper doesn’t load up as quickly and the pad runs cooler. What sort of wobble? Take a dinner plate, set it on its edge and spin it like a top. As the plate slows down, it will wobble through the last few rotations just before it stops and lays flat again. The pad works the same way, lifting its edges at the outside, allowing the sanding residue to be cast out from under the pad.

Sandpaper grits that would be used in this shaping tool segment run from 80 to about 400. By the way, there’s a two-grit jump from hand sanding to machine sanding. For example, if the tech hand sands with 400 grit, he or she can get the same scratch by using 320 grit on a random orbit power sander. The power tool moves much faster. As another example, if the tech runs 180 grit on the D/A, he or she will need to move up two grits to 240 grit to get the same scratch by hand. In many shops, it’s common to see the painter run a random orbit sander with 320 grit and then hand sand the same area with 400. Hello, it’s the same scratch! So stop hand sanding, or at least move to 500 or 600 grit to see a finer result.

Race to the Finish

This is the point at which many techs pick up the rubber block or foam sanding pad, believing that the sanding must be done by hand to get quality results. In addition to a change in attitude, they need a very smooth-running sander! Final block sanding can be accomplished with super smooth versions of almost every tool we’ve described so far.

A straight line sander with a small stroke and velvety action is how craftsmen achieve the high-gloss finish on fine wooden furniture. Orbital or random orbital tools at this level will have a smaller offset, typically 3/32 inches, half or less than the sanders previously listed. These tools will remain in contact with the work surface (no pad wobble) and run in a nice, silky stroke. The three main offsets for random orbit sanders get smaller by half each time. The largest, most aggressive offset is 3/8 inches (6/16), with the next being half that or 3/16 inches (6/32). At the final finish level, the typical offset is a short and smooth 3/32 inches.

In my experience, small-stroke, smooth-running sanders are the type missing from many techs’ toolboxes. The reason, I believe, is techs’ fear that these sanders won’t run smoothly enough and be controllable enough to ensure the work will turn out perfect. Also, these tools are expensive, and power-sanding final detail work requires a change in procedure that many techs are uncomfortable with. In the end, far too many folks pick up a rubber block and scrub away at the surface at 67 cents per minute ($40/hour) labor time. If you buy the idea that more work could be done at the same or better quality, then you’re in the market for a super smooth power sander.

Pads: 5-Inch or 6-Inch?

Two common choices of pads are 5- and 6-inch diameter models. There are still some painters who use 5-inch pads, arguing that they can get closer to the edges and moldings with smaller ones. If you’re one of those folks, please do this little test: Take a 5-inch sanding disc and a 6-inch disc, and lay the 5-inch disc as close to the corner of a piece of notebook paper as you can while still keeping the whole sanding disc on the paper. You can’t get any closer to any car molding than this. Draw along the edge of the disc. You’ll have a curved line about a half-inch back from the corner. “See how close I can get?” say the 5-inch disc advocates.

Now take the 6-inch disc and slide it as close to the edge of the notebook paper as possible and draw a line on its curved edge. Guess what? The line from the 6-inch disc is within 1/8 inches of the 5-inch line. My point is that the 6-inch disc will get just as close to edges and moldings as the 5-inch one, but it has 44 percent more surface area. The tech would sand 44 percent longer between disc changes and the cost is only about 35 percent more per disc – a bargain and a great production aid, too! The final finish power sanding I’m describing will require sandpaper grits from about 400 up to 2,000. Remember that two grit jump: 1,200 on a D/A is about the same scratch as 2,000 by hand.

All Wet

Much of the work at this level is the sanding required on the clearcoat prior to a buff and polish. As much as 90 percent of this work is done with dry sandpaper, but I contend there is still a place for power wet sanding. Extra fine grits of dry sandpaper work so well because the abrasive manufacturers have done wonders with the lubricants they build into the latest versions of today’s papers.

The very first lubricant added to dry sandpaper was zinc stearate. These sandpapers were white instead of brown and were advertised as no-load or free cutting. The residue from sanding is correctly called “swarf.” It’s composed of both the sandpaper disintegrating and the dust from whatever you’re removing. Lubricants in sandpaper help to slide the swarf out of the way. Current dry-sand fine-finish papers use an even more sophisticated lubricant to prevent the paper from loading.

Wet sanding has always been useful for making sandpaper last longer as the water washes the swarf completely out of the way. The water also acts as a lubricant, cools the surface, extends paper life by three to five times and, when final sanding clears, allows for a bigger margin of error. The error we’re talking about is the clear resin that re-forms into a ball from the sander’s heat and gets caught under the pad.

I contend that painters who still hand-sand do so because they tried power sanding and dragged a ball of clear across the finish and left a 220 grit-sized scratch they couldn’t polish out. Fine finish wet sanders either pull water up to the surface by suction (caused by the rotation of the pad) or force-feed the water by connecting the sander to a faucet. Because the water will flush the surface completely, the chance of dragging a lump of melted clear across the finish is minimized.

The downside of wet sanding is that it’s messy, it can rust the tool’s components and it’s potentially dangerous when the floor gets slippery. One solution is to wet-sand using a spray bottle of water to flush the swarf away. If you prefer to dry sand, make sure to use plenty of interface pads, which act like a cushion and soften any contact between pad and work surface. Vacuum attachments will also serve to collect any hunks of swarf before they can damage the clearcoats – and keep the shop much cleaner too.

Some great information, huh? If you'd like to read the complete article, here's the link: "Why You Should Replace Hand Sanding with Power Sanding"

Using sanding discs for refinishing your wood deck...

10 Steps for Refinishing Your Wood Deck:

1. Inspect the deck for any repairs that may be needed. Check for loose boards and nails or screws that may have worked their way out of the wood. Make any necessary repairs to insure that the boards are even and the nails or screws are set just below the surface of the decking.
2. Sweep the deck surface to clean any twigs, leaves or pebbles from the surface.
3. If you need to get rid of any mildew buildup, scrub the area with a combination of water and household bleach or use a commercial deck cleaning product.
4. If your deck is discolored or older and neglected you may need to use a power washer. After washing, let the deck dry completely.
5. Prepare to sand the deck surface. Since the process of sanding involves the removal of material it creates airborne dust. Please wear safety glasses, work gloves and an approved dust mask/respirator.
6. The easiest way to sand off the existing finish is to rent a random-orbit floor sander that uses sanding discs. These are gentler than a drum or belt sander on the wood.
7. You can purchase sanding discs through your rental store or an online supplier of sanding discs for floor sanders. Start with an 80 grit to get down to the fresh wood and roughen the surface. Proceed carefully, taking off only as much wood as needed.
8. Go back over the decking with a 120 grit sanding discs as your final sand prior to the application of stain or sealer. Sanding the wood opens it up for better absorption of the finish.
9. When done sanding, sweep or vacuum all of the dust away. The more thorough your cleaning job is, the better the finish will absorb.
10. Coat the deck right away with your finish of choice, following all manufacturers’ instructions for application and safety. Research by the US Forest Products Laboratory shows that even a few days of exposure to sunlight can affect the wood's ability to accept stain properly.