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GRINDING DOWN WELDS – SHOULD YOU & HOW TO

angle grinder with flap disc

This is one of the most dividing topics among all the welders out there, whether to grind your welds or not? The truth is that there are some pros and cons of both sides of the argument and at the end of the day you have to decide what you want and need. The process of grinding might sound straightforward as a technique but there are some tips and tricks which can help you out. There are a lot of details which you should pay attention to before starting the grinding.

In short, you can grind your welds, but you should weigh in the pros and cons of grinding your weld before you go ahead and do it. You might need to invest in some tools, and it can be dangerous too. There is a chance that your workpiece might lose some strength if the grinding is not properly, so make sure to practice.  

Let’s dive in

DOES GRINDING DOWN WELDS WEAKEN THEM?

While I was researching for this article I was surprised to see the difference in opinions on the internet. Some people claim that grinding will definitely reduce the overall strength of the weld and the material while others state that no such difference is made.

While grinding your welds, you end up removing some of the thickness from the weld and the base metal which I believe will inevitably lead to a reduction in the strength of the weld. If you don’t have to make your welds look flat and pretty then I wouldn’t recommend grinding them. You need to make sure that you have achieved sufficient penetration before grinding away to ensure that the strength is maintained.

A properly done weld like a fillet or a butt weld can have the same strength as the base metal when it comes to tension and compression forces. If you are careful when grinding the weld to not remove too much from the base metal itself, then I guess the strength can be maintained. This shouldn’t be a problem if you are working on a home project but can cause a lot of issues if industrial-grade strength is needed.

SHOULD YOU GRIND YOUR WELDS?

Of course, there is no compulsory requirement for you to grind your welds. And the decision whether you want to grind or now depends on what your final requirements are. If you messed up your weld, and don’t really care about the look of the weld, you don’t need to go for the extra effort of grinding.

In some cases, oxides and remnant slag can also be removed through grinding which can increase the life of the weld. If you are working on a home project or as a hobbyist then you don’t need to take the extra effort of grinding.

You might need to go through the grinding process if you are working on something which has to adhere to a strict code or be pleasing to the eye. Grinding can solve some of the fatigue performance issues which can come up and you might need to take care of this.

WHAT TO USE TO GRIND WELDS DOWN

There is no one answer to this question, just as there are different methods of welding, each with its own list of pros and cons, there are different methods of grinding. Each method is great in itself and each of the methods has specific things they are most suitable for. Let’s have a look at some of them.

  • One of the controversial members of this list is the cutting disc. The reason for it is that it is not technically meant to use for grinding. As the name suggests it is used for cutting metals. But it is considered an important member of the grinding family. A cutting disc is the most efficient way of cutting down metals both in terms of quality and cost. I have to admit, I have used the cutting disc to do small grinds here and there, but it is better to forget it as an option. There are countless videos out there making the same mistake, and by all means, you should not do it because of the dangers that come with it.
  • The second item on this list is the grinding disc. It is one of the best ways for bevelling edges or for grinding beads down. It is not my favorite option, but it can get the job done nevertheless.
  • Another way is using the flap disc, it can be compared to using sandpaper. It is also my favorite way to grind welds and make bevels to the base metal. Usually, flap disc, as the name suggests are flaps of sandpaper that are placed around on a disc. The main use of this device is for smoothing out the surface of the metal. One way to go about is to start from a rougher grade of flaps discs and then work towards a finer grade. The end result can be quite smooth if done properly.

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  • Another similar piece of machinery is the sanding disc. The use of this is very similar to that of the flap disc. As a matter of fact the only difference is the presence of a grinding disc in one piece instead of flaps. The use of this method highly depends on what the user prefers to use as the end result can largely be the same.
  • The last entry to this list would be the wire wheel. This is not for grinding welds down, but it can make your life really easy for post-weld cleanup. One advantage of this over something like a flap disc is that it doesn’t hurt your base metal significantly. Even flap discs can leave some scratches but a wire wheel will make an old piece of metal look like new. This method is very popular for removing rust, paint, and other contaminants from the surface.
flap disc

HOW TO MAKE SURE YOU GET GOOD RESULTS AFTER GRINDING

The process of grinding can be divided into three phases when it comes to welding, although only one of them involves actual bead grinding. The pre-weld processes, the actual weld, and the grinding. All three steps are equally important to make a good product and if you are not careful in any one of them, the entire look and the integrity of the piece can fail.

The first step would be the cleaning process which you need to undertake. Most of the workpieces you will be working on will contain a good amount of contaminants and the quality of the bead will be affected by the oxidation, paint, or corrosion present on the surface. This will further lead to a bad weld and consequently a bad grind.

You can even try to grind down a thin layer of the base metal if it has a protective coat like zinc, which will affect the quality of your weld.

Another tip that is not related to grinding is the protection precautions. Both grinding and welding and sometimes even cleaning can lead to harmful particles and gases in the air which can have very bad effects on your health. Make sure to have a good respirator and work in a well-ventilated room.

Moving on to the welding part, a full penetration will of course ensure a stronger work piece after welding.

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Welding trade facts
SOME TIPS ON HOW TO GRIND

The best grinding jobs can be recognized if you can’t tell the pieces have been welded at all. The piece might look as if it was manufactured that way. The prime examples of this can be seen in industry level welds where the welded area is visible to the public, they try to make it look like it is made up of one piece. You can also see this on food-grade equipment. The good news is that if you take care of a few things you can also achieve this.

The first step would be to remove a layer from the weld bead to make it semi-flush with the base metal. The details of the processes might differ depending on the metal, type of weld, and location but broadly the process is the same. You can use a grinding wheel to get it done. Keep one thing in mind, only remove layers from the bead and not from the surrounding base metal.

The next step will be to use finer equipment to further make the weld look smooth. With the first step, you have made the weld look semi-flush so now you can move on to using a sanding disc or a low grit flap disc. Again, be careful about not removing metal from the workpiece, only the weld bead. You should also be careful about the amount of pressure you are applying on the grinder but this is something that will come with practice.

One doubt that many people have over this is what will happen to the strength of the weld when you grind away so much. The truth here is that if your weld had enough penetration then you don’t need to worry about the top layer, a weld does not or at least should not act as a tape if done properly.

GRINDING WELDS ON BODY PANELS

Welding body panel in itself can be tricky if you are new to welding, I would not recommend grinding your welds when dealing with thin sheet metals or body panels unless that part of the weld is going to be visible.

One thing you should always take care of if you do decide to grind the weld is to avoid touching the panel as much as you can as making it too thin can affect its structural integrity and make the panel too weak. It is always better to be on the safe side and leave a bit extra.

I would recommend using a 3M reinforced grinding wheel to do the job, you can also try using a wire wheel along the seam of the weld to take care of any spatter around the area.

WHAT IS GROUND FLUSH WELD

The name here pretty much is self-explanatory, a ground flush weld basically means a weld that is even with the entire workpiece. Usually, the top of the weld bead is ground or polished to make it flush with the surface. You don’t really need to do it unless the grooves or the top part of the weld bead will interfere with further assembly.

GRINDING WELDS IN TIGHT CORNERS

Grinding welds in tight corners can very tricky for people who have never done it before. One way to go about it would be to look for a professional who has the necessary tools to get it done. But I am guessing you are looking for ways to get it done yourself, brace yourselves as you might need some practice to get it right.

If you are serious about it then I would recommend investing in a few tools, some of these tools are designed to be used in tight spaces and can make your life way easier. One of the most common devices that I have seen people use is the die grinder.

A die grinder does exactly what the name suggests, it is most commonly used to grind dies and molds. These devices can easily help grind hard to reach surfaces.

HOW TO SMOOTHEN METAL AFTER GRINDING

As I stated earlier you use finer equipment to further bring shine and smoothness to the weld and the entire piece. Some of the most common equipment used is the sanding disc or low grit flap disc. They do a phenomenal job and I can not think of a better alternative.

If you are dealing with sheet metal or car body panel repair, a lot of times a special body fillers are used to cover and hide the welded area to make everything smooth and prepare it for painting.

FREQUENTLY ASKED QUESTIONS

Grinding is not only a controversial topic it can also be tricky. If you are going to tackle this, it is important to have all the doubts cleared. I will try to address some of the most common queries related to this topic. Hope it helps.

CAN THE GRINDING MACHINE’S WHEEL GUARD BE REMOVED TO REACH TIGHT PLACES?

I would never recommend you to do this as the safety concerns outweigh the job. There are a lot of tools out there that you can opt for instead of doing this. I would suggest going to a professional shop if you don’t have the necessary equipment.

HOW CAN I CHECK IF I AM USING THE GRINDER CORRECTLY?

One trick that is most common is listening to the grinder’s pitch. If the pitch is too low then you might need to let go of the pressure a little bit. On the other hand, if the pitch is too high then you should apply more pressure. The perfect technique will result in a constant pitch.

WHAT SHOULD BE THE CORRECT WORKING ANGLE FOR THE GRINDER?

Most of the grinders out there are designed to be used at a 5-10 degree angle. That can be a good rough estimate to keep, but it can vary depending on the type of discs you are using.

CONCLUSION

To sum it all up, grinding can be tricky when you are trying it out for the first time. Make sure you have the right tools for the job and that you are taking all the safety precautions. You don’t need to grind the weld anyway unless that part of the weld will be visible to the public on a job that doesn’t call for it. Welding body panels and tight corners can be especially tricky so make sure to practice a lot.