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.

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 Marshall: Dennis, 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 Johnstone: Ah, 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.

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.