September 22, 2017

How to grind safely when using resin fiber discs

An angle grinder is a popular power tool used for grinding using abrasive products. Various types 
of abrasive products can be used for grinding, also known also as de-burring, fettling, polishing, sanding and buffing. Safety recommendations depend on the type of abrasive you will use on your hand-held machine: reinforced depressed centre wheels, flap discs, vulcanized fibre discs, resinoid cup wheels and diamond cup wheels.

80% of the accidents with abrasive products are due to their misuse or mishandling. 
The Federation of European Producers of Abrasives have produced a safety video to help
prevent end-users from getting hurt while using abrasive products professionally or for home projects.

Here are answers to a couple questions that were answered in this article on the "abrasives safety" webpage created by FEPA:

What is a safe product? What should I look for?
  • FEPA recommends that only vulcanised fibre discs conforming to EN 13743 and marked as such should be used.
  • Vulcanised fibre discs not bearing EN 13743 may not conform the highest safety standards.
  • The back-up pad should bear the mark “ISO 15636” to conform that it conforms to the requirements.
  • All discs and pack-up pads should be examined carefully for damage or defects before fitting on the machine.

How should I handle and store the wheels?
  • All vulcanised fibre discs are fragile. They should be handled with care.
  • Keep discs in their original packing on a flat, rigid surface until their immediate use. Avoid extreme temperature and damp.


For more tips and information on safety for grinding, please view this entire article on the "Abrasives Safety" webpage.

March 22, 2017

Does Changing Speeds On A R.O. Sander Make A Difference?


Q. How should the speed and grit of paper be used on variable speed random orbit sanders? My background is in aerospace manufacturing. In metal machining, fewer cutter teeth equals lower rpm and more teeth will allow higher rpm. By this convention, lower grits would run at the lower speeds and the speeds would increase for the higher grits. Bigger grit equates to less teeth and smaller grit to more teeth. I usually apply this convention, but I have tried reversing it or just using the same speed for all. Really can’t see much difference in the final surface. Maybe your resources can shine some light on this, or did manufacturers just give us variable speeds because we thought we should have it? I know some still offer single speed along with the variable speed sanders. – Dennis S. Cropper

A. Chris MarshallDennis, as you point out, I’ve seen no real difference either in cutting efficiency by varying the speed of my sander relative to the coarseness of grit I’m using. I think the bigger issue, regardless of speed setting, is to not push down on the machine while sanding in an attempt to speed the process along. The sander should be allowed to spin freely and under its own weight plus light hand pressure. It ensures that the orbital action will work properly so the grit abrades the surface as efficiently as it can. Beyond that, I’m not certain that variable speed control makes much difference at all to the final surface smoothness. I set my random-orbit sander to maximum speed for any grit I’m using and leave it there all the time.

Interestingly, a manual that came with a Bosch variable-speed R.O. sander I own makes some recommendations on speed settings to use for woods, metals or paintwork. While the dial can be set from 1 (low) to 6 (high) speed, the recommendation is from 4 to 6 on all surfaces and with all sanding grits besides light sanding on paintwork (2 to 3 is recommended, in grits ranging from 180 to 400). Setting 1 isn’t recommended for any sanding situation. So, at least according to this manufacturer, medium to full speed is suitable for pretty much every sanding task.

A. Rob JohnstoneAh, sanding, the root canal of woodworking. I confess that I do not adjust the speed of my R.O. sanders at all. I set it at full speed and that is it. When using abrasives to smooth a wooden surface the goal is to get a uniformly smooth result. So after you’ve started with an appropriately coarse grit to quickly and effectively remove the surface blemishes, scratches and glue blobs, the next goal is to remove the scratch marks that you just installed on the wood’s surface with the 60-grit (40-grit?) product you just used. (When you remove all the 60-grit scratches, you move up and remove all the 80-grit scratches, and so on.) There are two speeds to be thinking about when using a R.O. sander: the setting on the machine (which I’ve already said I ignore) and the pace at which you move the sander across the wood. Most of us move the sander far too quickly — like we are polishing our shoes or something. A correct pace is about 1-inch per second. When you first try it, that speed will seem SO SLOW! But it allows the machine to properly do its work, and you will soon learn that by slowing down in that regard, you actually spend less time sanding overall. My opinion is that once you get through sanding with 180-grit using a sander, it is time to move to hand sanding with 220-grit and higher.

This article can be viewed at the Woodworkers Journal.

And Abrasive Resource says...

A. A final consideration that isn't noted in this article from the Woodworker's Journal article: Heat. A fast-moving sanding disc is creating more friction than a slow-moving sanding disc. And friction generates heat. Could heat be a problem in your sanding application? If you are sanding plastic, foam, paint or other soft surfaces it can be. Warming up and possibly melting the surface will certainly clog your abrasive disc prematurely and could potentially damage your finish. If heat is a negative factor to consider during your sanding job... slow the sander down.

January 10, 2017

The most overlooked orbital sanding issue


The 5" random orbital sander is an essential part of most woodworking facilities. The tool allows rapid removal of material to create a flat surface that is ready to accept stain or coatings. Their shortcomings are well known. Orbital sanders can leave swirls and excessive polishing.
Orbital sanders use two types of movements simultaneously to product a random scratch pattern. The pad spins and orbits at the same time. The pad must spin and orbit to create the proper scratch pattern.
This is where the backup pad comes into play. The backup pad is the part of the sander that the sand paper attaches to via hook and loop (H&L) or pressure sensitive adhesive (PSA).
For flat surfaces, this pad must remain in good condition and it must remain flat. When the operator tips up the sander to dig out defects on a surface, not only does this dig a divot in the work piece, but it also damages the outside diameter of the backup pad. Over time, the pad starts to retain the curve induced when the sander is tipped up and it no longer maintains a full 5" circle of contact on flat surfaces. The reduced surface area makes flat surface sanding take much longer and it induces much more swirls into the surface. It is also much easier to miss spots, leaving streaks of inconsistent surface finish.
An out-of-balance or out-of-square backup pad can also produce defects. If you sand a flat surface and you feel the sander pulling back and forth across the surface of the wood, the backup pad needs to be replaced. If you feel the sander bouncing as the pad rotates, then you most likely need a new backup pad. The PSA disks are often harder to remove from old worn out pads, as shown by the amount of PSA adhesive that remains stuck to it. The H&L disks will fly off of the backup pad when worn out. An out-of-balance pad will put undue stress on the bearings as well as the body of the operator.
Backup pads usually need to be changed out once a month in high production shops and on machines running several hours a day. In lower production environments they will often need to be changed every three to six months. These pads are very low cost and responsible for doing the most important job in almost every woodworking shop around the country. A new backup pad is far, far less expensive than reworking entire jobs with swirls and inconsistency. 
This article can be viewed at Woodworking Network.

October 04, 2016

What causes grain to raise up on boards we've just sanded?



So-called raised grain is due to excessive pressure during machining, compressed softer cells, and then spring-back.

I do not know how many times I hear from woodworkers, both large commercial operations and small one-shop operations, who report that a surface was very smooth, but then a few days later, the surface was no longer perfectly flat. Oftentimes, this “un-flat-ness” shows up after a glossy finish is applied, as such a finish will reflect even the slightest imperfections. So what is going on?

There are two possible reasons why the surface changes.

First is that we have uneven moisture within the wood when it is first made, we prepare a perfectly flat surface, and then we have a moisture change. With the moisture change comes uneven shrinking and swelling. This situation arises on a gross scale. That is, a door will warp, a table top will distort, and so on over a long distance -- a foot or more. Obviously, the cure is to get the moisture uniform within the piece prior to manufacturing and then keep the moisture content from changing appreciably. This is not discussed further here.

Second is much more complex. To understand this second cause, we need to go back to the structure of wood. Basically, wood is made of very tiny cells, much like a mini-soda straw, with a length of 3 to 5 mm and a diameter 1/100 of the length. Within the growth ring for a given year, many species have the fibers that are formed in the springtime with very thin walls and somewhat low strength. However, as the growing season progresses, the cells have thicker walls with more strength. Perhaps a prime example is in pine where each annual growth ring has different color due to the variation of the cell walls.

End grain of southern pine shows the distinct light-colored, softer, weaker earlywood and harder, darker, stronger latewood.

Whenever a knife, sawtooth or even sandpaper passes over the surface of wood, the forces generated can actually compress the softer earlywood cells. This can happen when veneering (especially with the pressure bar that is used to prevent lathe checks), sawing (especially with a dull circular blade), planing (especially feed rolls and pressure bar), and sanding (especially with dull sandpaper).

In essence, the knife or blade and sandpaper particle asks itself “Is it easier to cut this fiber off or push it down and out of the way?” Obviously, the more pressure generated, the more likely that considerable compression will develop and the weaker cells will be compressed.

The compressed cells (remember that wood cells are like hollow soda straws), may recover or spring-back slightly toward their original size (much like a gently bent piece of wood will spring-back to flatness when the pressure is removed). However, with high pressure, many cells will stay permanently compressed. Actually, I should say “temporarily compressed” as with exposure to moisture (liquid such as from water in a finish, or vapor from a high humidity), most of the compressed cells will recover or spring-back close to their original size.

However, remember that the growth rings have both hard cells that were not compressed and softer cells that were compressed. So only the softer cells experience spring-back. The net effect is that a flat surface now develops small “hills and valleys” within the growth ring.

This similar effect can be illustrated with flatsawn lumber where the hard cells are pushed down into the softer cells right underneath during machining. With exposure to moisture, the softer cells underneath spring-back, giving a ripple or corrugated surface.

So-called raised grain is due to excessive pressure during machining, compressed softer cells, and then spring-back. In this case, the effect was so severe that the there is an actual separation between the growth rings.

Practical approach

It is impossible to control the veneer or lumber manufacturing process. Plus, with the presence of water in the living tree, it is likely that spring-back will occur during this initial manufacturing. However, excessive pressure at the end of drying or when planing or sanding can indeed cause the defect in such products. Even hand sanders with dull paper (which means lots of hand pressure) can compress the cells. So, to avoid this defect, first make sure that before final sanding all products are exposed to a very brief water misting or stemming to recover any collapse. Then finally sanding needs to be done with the sharpest paper and the lightest pressure possible.

April 28, 2016

Learning to Sand Wood by Experience


The objective of sanding wood is to remove mill marks, which are caused by woodworking machines, and to remove other flaws such as dents and gouges that may have been introduced in handling. The most efficient method of doing this is to begin sanding with a coarse enough grit of sandpaper to cut through and remove the problems quickly, then sand out the coarse-grit scratches with finer and finer grits until you reach the smoothness you want – usually up to #150, #180 or #220 grit.

You’ll have to learn by experience what works best for you.

How Fine to Sand
It’s rarely beneficial to sand finer than #180 grit.
Film-building finishes, such as varnish, shellac, lacquer and water-based finish, create their own surfaces after a couple of coats. The appearance and feel of the finish is all its own and has nothing any longer to do with how fine you sand the wood.
Oil and oil/varnish-blend finishes have no measurable build, so any roughness in the wood caused by coarse sanding telegraphs through. But these finishes can be made ultimately smooth simply by sanding between cured coats or sanding each additional coat while it is still wet on the surface using #400- or #600-grit sandpaper. It’s a lot easier doing this than sanding the wood through all the grits to #400 or #600. (See “What Is Oil?” in issue #154, April 2006, for a more thorough explanation of both processes.)
Only if you are staining or using a vibrator (“pad”) or random-orbit sander does sanding above #180 grit make a difference.
Fine sanding. Sanding finer than #180 or #220 is wasted effort in most cases, as explained in the text. In fact, the finer the grit the wood is sanded to, the less color a stain leaves when the excess is wiped off. In this case, the top half was sanded to #180 grit and the bottom half to #600 grit. Then a stain was applied and the excess wiped off.
The finer you sand, the less stain color will be retained on the wood when you wipe off the excess. If this is what you want, then sand to a finer grit. If it isn’t, there’s no point going past #180 grit. The sanding scratches won’t show as long as they are in the direction of the grain.
Sometimes with vibrator and random-orbit sanders, sanding up to #220 grit makes the squiggly marks left by these sanders small enough so they aren’t seen under a clear finish. Sanding by hand in the direction of the grain to remove these squigglies then becomes unnecessary.


Squigglies
. Random-orbit sanders are more efficient than vibrator sanders, but they still leave cross-grain marks in the wood. I refer to these as “squigglies.” The best policy is to sand them out by hand in the direction of the grain after sanding to the finest grit, usually #180 or #220, with the sander. Doing this is especially important if you are staining.
In all cases when sanding by hand, it’s best to sand in the direction of the wood grain when possible. Of course, doing this is seldom possible on turnings and decorative veneer patterns such as sunbursts and marquetry.
Cross-grain. Sanding cross-grain tears the wood fibers so the sanding scratches show up much more, especially under a stain. The best policy is to always sand in the direction of the grain when possible. The scratching that does occur is then more likely to be disguised by the grain of the wood.
Cross-grain sanding scratches aren’t very visible under a clear finish, but they show up very clearly under a stain. If you can’t avoid cross-grain sanding, you will have to find a compromise between creating scratches fine enough so they don’t show and coarse enough so the stain still darkens the wood adequately. You should practice first on scrap wood to determine where this point is for you.
Three Sanding Methods
Other than using a stationary sanding machine or a belt sander, which will take a good deal of practice to learn to control, there are three methods of sanding wood: with just your hand backing the sandpaper, with a flat block backing the sandpaper and with a vibrator or random-orbit sander.
Using your hand to back the sandpaper can lead to hollowing out the softer early-wood grain on most woods. So you shouldn’t use your hand to back the sandpaper on flat surfaces such as tops and drawer fronts because the hollowing will stand out in reflected light after a finish is applied.
 
The most efficient use of sandpaper when backing it with just your hand is to tear the sheet into thirds crossways and then fold one of the thirds into thirds lengthways. Flip the thirds to use 100 percent of the paper.
The most efficient use of sandpaper for hand-backed sanding is to tear the 9″ x 11″ sheet of sandpaper into thirds crossways, then fold each of these pieces into thirds lengthways. Sand with the folded sandpaper until it dulls, flip the folded sandpaper over to use the second third, then refold to use the third third. This method reduces waste to zero and also reduces the tendency of the folds to slip as you’re sanding.
Hand sanding.
If you are sanding critical flat surfaces by hand, you should always use a flat block to back the sandpaper. If the block is hard (wood, for example), it’s best to have some sort of softer material such as cork glued to the bottom to improve the performance of the sandpaper. (I find the rubber sanding blocks, available at home centers, too hard, wasteful of sandpaper and inefficient because of the time involved in changing sandpapers.)
Block sanding. The most efficient use of sandpaper when backing it with a flat sanding block is to tear the sheet into thirds crossways and then fold one of the thirds in half. Hold onto the block with your thumb and fingers as shown here. Flip the folded sandpaper for a fresh surface, then open up the sandpaper and wrap it all around the sanding block for a third fresh surface.I made my own sanding block. Its measurements are 2 3/4″ x 3 7/8″ x 1 1/4″ thick, with the top edges chamfered for a more comfortable grip. Any wood will work. I used sugar pine because it is very light in weight.
To get the most efficient use of the sandpaper, fold one of the thirds-of-a-sheet (described above) in half along the long side and hold it in place on the block with your fingers and thumb. When you have used up one side, turn the folded sandpaper and use the other. Then open the sandpaper and wrap it around the block to use the middle.
Most woodworkers use random-orbit sanders because they are very efficient, easy to use, and they leave a less-visible scratch pattern than vibrator sanders due to the randomness of their movement. For both of these sanders, however, there are two critical rules to follow.
Random-orbit sanders are easy to use and efficient for smoothing wood. To reduce the likelihood of the squigglies these sanders produce, use a light touch. Don’t press down on the sander. Let its weight do the work.
First, don’t press down on the sander when sanding. Let the sander’s weight do the work. Pressing leaves deeper and more obvious squigglies that then have to be sanded out. Simply move the sander slowly over the surface of the wood in some pattern that covers all areas approximately equally.
Second, it’s always the best policy to sand out the squigglies by hand after you have progressed to your final sanding grit (for example, #180 or #220), especially if you are applying a stain. Use a flat block to back the sandpaper if you are sanding a flat surface. It’s most efficient to use the same grit sandpaper you used for your last machine sanding, but you can use one grit finer if you sand a little longer.
Removing Sanding Dust
No matter which of the three sanding methods you use, always remove the sanding dust before advancing to the next-finer grit sandpaper. The best tool to use is a vacuum because it is the cleanest. A brush kicks the dust up in the air to dirty your shop and possibly land back on your work during finishing.
Tack rags load up too quickly with the large amount of dust created at the wood level. These sticky rags should be reserved for removing the small amounts of dust after sanding between coats of finish.
Compressed air works well if you have a good exhaust system, such as a spray booth, to remove the dust.
It’s not necessary to get all the dust out of the pores. You won’t see any difference under a finish, or under a stain and finish. Just get the wood clean enough so you can’t feel or pick up any dust when wiping your hand over the surface.
How Much to Sand
The biggest sanding challenge is to know when you have removed all the flaws in the wood and then when you have removed all the scratches from each previous grit so you can move on to the next. Being sure that these flaws and scratches are removed is the reason most of us sand more than we need to.
A lot of knowing when you have sanded enough is learned by experience. But there are two methods you can use as an aid. First, after removing the dust, look at the wood in a low-angle reflected light – for example, from a window or a light fixture on a stand. Second, wet the wood then look at it from different angles into a reflected light.
For wetting the wood, use mineral spirits (paint thinner) or denatured alcohol. Avoid mineral spirits if you are going to apply a water-based finish because any oily residue from the thinner might cause the finish to bead up. Denatured alcohol will raise the grain a little, so you’ll have to sand it smooth again. 

October 30, 2015

Making your own Abrasive Belts


Every so often at Abrasive Resource, we get an email or call from someone that is interested in either repairing a broken belt or making their own belts at home and they are wondering if we sell any DIY belt splicing materials. Unfortunately, we do not…and here is why:
  • The splicing tape is a specialized product designed for bulk abrasive belt manufacturing. It is very thin (from .0025” to .0085”), yet has a tensile strength up to 380 lbs/inch.
  • The tape is manufactured with an exact thickness of dry, thermosetting adhesive that is applied to the yarn surface of the splicing tape.
  • The rolls of tape are cut and wound into 76 meter lengths—that is the shortest length you can buy.
  • They are sealed into a plastic bag and shipped frozen—on dry ice—in insulated cartons via air freight. Once they arrive at our facility, they are stored in a deep freezer at -20 degrees or lower to maintain their 90 day shelf life.
  • After the abrasive material has been cut to the desired angle and length, the backing material is abraded and a special two part adhesive is applied to both belt ends.
  • The tape is then applied and permanently affixed in a belt press, applying between 2000 and 3000 PSI at 165-185 degree temperature.
This is all done, of course, to insure that the joint will not break and fly apart—which could potentially cause damage to your belt sander or injury to the operator.

Tips to facilitate a longer life for your Sanding Belts:

Sanding belts DO have a shelf life! We always advise our customers to only order the quantity of belts they estimate they can use within a year.

  • Don’t purchase abrasive belts in bulk to get “a better deal” and risk having the joint age out and potentially break in a year or two or three.
  • In addition, do not buy sanding belts if you do not know when they were manufactured! Purchasing belts on closeout from a retail store that may not get enough traffic to “turn” their inventory or online from an importer is always risky since you do not know how long ago the belt was manufactured or the condition it has been stored in. Abrasive Resource makes all of their belts “to order” so you get the freshest belts possible!
  • Store the belts in a dry, stable environment. Perfect conditions would be in a protected area that is humidity controlled like an air conditioned office, storeroom or shop.
  • If a “new” belt breaks at the seam—one that you have had less than 90 days—then there is most likely some sort of manufacturing defect and they should be replaced by the manufacturer. Keep your broken belt (s) to show the manufacturer how they broke and they will be able to identify the reason and make sure that you receive a n/c replacement. It doesn’t happen often…but when it does, you want to make sure that you are able to directly contact the manufacturer of your belts to get the problem resolved quickly.
If you have any questions, or need to order new sanding belts—please give us a call at 800-814-7358 or visit our website for standard size sanding belts!

September 23, 2015

Choosing the right Fiber Disc for your grinding application


An angle grinder is a useful tool for any shop! You can use bonded grinding wheels, cut-off wheels, overlap discs or standard fiber discs all on this same tool for many different applications in metalworking, woodworking and stone or tile.

Abrasive Resource just lowered their prices on resin fiber grinding discs, so we thought it would be a good time to review all of the different applications where a fiber disc would be effective:

Aluminum Oxide: A general purpose abrasive used for metal or wood. Removes small welds and imperfections along with light stock removal, blending and finishing. Wood applications include log furniture and homes. These AO discs are also used in light-duty metal applications on low alloy steel or when loading is a problem, such as painted surfaces or aluminum. 

Zirconia: The workhorse of the fiber disc world. Zirconia refractures for longer life when used in high pressure applications like stock removal on Chrome and chrome-nickel steel or high-alloy steel. Used for applications that include blending, deburring and weld removal. Generally lasts twice as long as an aluminum oxide disc when used in the proper application. 

Ceramic: A premium abrasive for high heat generating applications such as stainless as it resists glazing and provides long life. The choice of metalworking professionals due to self-sharpening characteristics that provide high stock removal rates. Features cool cutting technology for reducing heat and increasing performance. Ideal for grinding and blending welds. 

Silicon Carbide: Excellent on titanium, fiberglass, plastics, and stone, tile and masonry products. Sharp silicon carbide abrasive grain quickly “bites” to remove any coatings such as adhesives, paint, acrylics, mastics, etc. Aggressive cutting action provides a clean, smooth finish on concrete, marble, granite, and other stonework. 

To purchase any of these discs at the new lower price, please visit the Abrasive Resource fiber disc home page on our website to find the discs best for you!

Basic Sanders

The basic styles of portable sanders haven’t changed very much over the years. We have some old advertising posters from the Rockwell Manuf...