Back to the Grind

You’ve got your work piece bent, and welded at the seams.. Now what? Do you just leave the exposed weld and paint over it?

Sometimes you’ll want to leave that exposed weld for aesthetic purposes or because shaping and polishing the weld not necessary for the application of that particular part (for example, internal components of machinery sometimes don’t require exceptional finishes since they are not seen).

But! If you want the final product to look like it has continuous bends and no seam (like it was milled out of a solid billet, regardless of how big it is); you’ll want to grab a grinder and shape that weld!

To some it’s a daunting task, while others think it’s an elementary task and requires no skill. [Boy oh boy! are they ever wrong].

Using a hand-held angle grinder can be challenging at times; but, it’s more of an art form once the operator is experienced.

There are a few choices when it comes to the tools available:

Electric Grinder

I believe that any “handy man/woman” or “mr/ms fix it” should have an angle grinder in their toolbox. Easily the most available (and affordable) is the electric powered angle grinder.

They can be had for as little as $50 for a pretty well made model. Or even cheaper if you’re a harbor freight regular and don’t plan on doing any heavy tasks with it.

There are a few options when it comes to disk size as well, though the most common is 4-1/2″. I recommend 80-grit disks for most metal work, because it is versatile enough to be used for metal varying in hardness (aluminum vs stainless). Some people swear by “flap wheels” which are disks containing multiple overlapped layers of sandpaper in a circular pattern; I personally have no experience with these.

Plug into any 120V outlet, and let the little monster rip!… And tear through those globular welds. With most motors spinning at 10,000-12,000 RPM on the 4-1/2″ models, and 6,500 RPM for 9″ models.

If you’re constantly on the go, most big name brands of power tools (DeWalt, Milwaukee, etc) carry an 18V or 20V model CORDLESS angle grinder. [I know… It’s a dream come true]. Plus, they actually work pretty well in my experience.

Pneumatic Grinder

Same outcome, only a different power source. The design is a bit different and less ergonomic also, with a much smaller body in most cases (since it doesn’t have to house all of the electrical components, like a brushed motor and coils of copper).

These simple tools are anything but simple when it comes to price. They’re typically at least 4X expensive compared to their electric counterparts.

The benefits come out when you look at capability. In a manufacturing setting, the pneumatic grinder will shine. Since there are no electrical components sucking up metal dust and creating shorts over time (burning up your electric grinder), longevity comes into play.

Sure we have to dish out another $150 over the price of the electric unit, but we’ll likely get years and years of service in less than ideal conditions (assuming the tool is oiled with air tool oil regularly).

This is not to say that all of the electric units will short out eventually, it really depends on the environment. In my experience, aluminum will devour these poor unknowing tools in a matter of a few months with heavy use; especially if they are not regularly cleaned out (even taken apart to clean).

Pneumatic grinders can be had from 2″ up to about 7″ at the largest that I have seen.

Okay, now pick your grinder of choice; then keep reading

Likely, there are people who think grinding is very easy and maybe even mindless (your boss might be one of those people).

But, it takes focus and precision to take down material without going too far, and simultaneously shaping it. Plus… If you’re at work, you’re always looking at the clock, because the project you’re working on has to keep moving to meet the customers’ delivery date.

It’s very important to have the right gear!

  • Safety Glasses are a MUST
  • Hearing protection (this can be ear buds with music, or simply ear plugs to block out the high pitched sounds)
  • Gloves (please take this advice and just get some decent gloves that are NOT RUBBER). Rubber melts if the grinder gets loose and drags across your hand, you’ll have a cut with melted rubber embedded… Not fun.
  • Leather smock (or a cloth one you won’t mind catching on fire… a lot)
  • Respirator or dust mask (if grinding aluminum, go with a respirator for sure)

So how do you focus? Easy. Get comfortable with the grinder by practicing on some flat pieces first, then move on to seam welds (usually on the outside of a corner is perfect to start).

It helps to have a good welds to start with. If a grinding department gets works from other welders to finish, you’ll want to have good communication between the two departments to constantly improve the process.

The best critic for a welder is the guy or gal who is grinding their work! If they don’t want to listen, and they’re not interested in improving their welding skills, have your boss make them grind their own work for a week and see the improvement.

The main idea is to get to a point where the only area being ground is where a weld is present. We don’t want to have to grind out 2-3 inches from the weld just to “blend”. Blending can be done with an orbital sander; the object is just to take down the weld and make it more uniform with the material.

Making smooth “dragging” motions or “strokes” with the grinder is key. Keeping a firm grip on the machine is important, as the danger of catching an edge and the grinder reacting violently is very real; which is why focus is very important, and carelessness is not welcomed.

The key to a super easy-to-sand grind is to slow down, and apply very little pressure on your final pass. This puts the grinder “licks” or circular scratches very close together, forming almost a milled surface (or a fly-cut machined surface).

Once the weld looks smooth and even, break out the sander and make it uniform. Then onto the next process!


You’re going for a grain finish (#3 or #4 smooth grain).

The grinds should be tight, and minimal on these projects. Don’t end up in the middle of your work piece away from the weld. Keeping the grinder super tight to the area you’re taking material down on is the difference between an invisible blend and an obvious hack job.

Orient your grinder in the direction of the grain. So the circular “licks” are running parallel to the grain direction. This will make re-applying the grain much easier.

Tools to re-apply grain will vary depending on the individual. But I like to use a Dynabrade 13204 Straight Finishing Tool with a sanding belt first, followed by a scotchbrite wheel.

I follow that up with a jitterbug sander (one that only has a forward and backward motion, not an orbital or elliptical motion). With either scotchbrite or medium grit sand paper (180 grit) followed up with a scotchbrite to finish.

At the end of the day, the way we all grind can be different (and that’s okay). Humans make mistakes, and learn from them. Perfecting the art of grinding can take different amounts of time for different individuals, but with proper safety to prevent accidents, and some experience using the tools, anyone has the potential to create great quality grinds.

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