It seems so easy, a couple little welds and you’re good to go. How could anyone possibly screw up tacking? The truth is, you could be tacking wrong and never know it. This is because most of the problems with tacking incorrectly often don’t become apparent until much later in the process. As a result, tacking often goes overlooked when troubleshooting issues. But with a few simple tricks, you can rest easy knowing you’re tacking the right way.
Using More Than You’d Think
Often welders worry about tacking too much, or making their tacks too large (potentially causing warpage). In fact, many welders have been taught that tacking shouldn’t penetrate your workpiece at all, but instead hold the pieces together by resting on top like a piece of scotch tape. This leads to weak tacks that allow the pieces to shift around or break apart.
If you’re using clamps and tacking in the correct spots (tip #2 and #3), you won’t have to worry about too much tacking. When tacking, you need to get enough heat to penetrate both pieces. Otherwise, fusion won’t occur and your tack won’t stay.
Many welders think of a tack as a quick weld in one spot. But often this doesn’t get enough penetration into both pieces. When you’re tacking, penetration is key (just as normal welding). This can be done by doing a circular motion (vs. welding in one single spot) or a u-shaped motion. Regardless of which approach you choose, the goal is to make sure both pieces of metal are being fused together.
Dealing with Warpage
When metal is heated, its molecules expand. Then when it cools, they contract in a different place then where they started. This is why welding pieces at perfect 90 degree angles can be a nightmare. Every time you weld, the metal changes its composition.
In an attempt to avoid warpage, many welders will do quick tacks that don’t get a lot of penetration. This leads to a host of other problems (tip #1). There’s a better solution. First is to pay attention to where you’re tacking. While every situation is a little different, a decent guideline is to try and tack all sides of the piece equally. In a perfect world, this would mean your piece was affected equally on all sides and should therefore be fairly close to its original position before you started tacking. Of course, we don’t live in a perfect world, which leads us to tip #3:
Clamping and Re-Measuring
We all do it. We try to use tacks instead of clamps. While a tack might hold your pieces together like a clamp, they can’t replace a clamp’s ability to regulate warpage. Good welding clamps are designed to hold your pieces in the correct spot even while warpage is occurring. Some experts will tell new welders to even think of metal as elastic. If you don’t have it strapped down while it’s being heated, it’ll going to move on you. With workpieces that require a lot of precision, it’s not uncommon to have more clamps than metal.
No matter how many clamps, tacks or any other trick (pre-heating, etc.) you use, your pieces will often shift during tacking. If your project requires precise angles and distances, it’s vital to make sure you check your measurements after tacking each side. If you notice an issue early on, you can often use a clamp, brute force or tack the opposing side to correct the issue. If you’re not re-checking your measurements, you could end up tacking a piece well enough the only way to fix it is with your old friend, the grinder.
Unfortunately, there’s not enough bandwidth on the internet to explain every situation you might face when it comes to where and how much you should tack. But by even paying a little more attention while tacking, you’ll find your pieces are easier to weld and don’t end up crooked or shift positions.
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