Angle iron corner joints

Angle iron corner joints DEFAULT

Introduction: Welding Joints and Beyond

There are five kinds of welded joints that you will use over and over and over and OVER again. Butt, tee, corner, lap, and edge. This lesson goes over how to square, clamp and tack your joints, then weld them with minimal heat distortion and maximum strength.

Step 1: Cutting and Grinding Your Parts

In the Tools and Materials section of this course, we go over how to set up an angle grinder for use with a cutting wheel and flap wheel grinding disk. Cutting steel bar, rod, and tube is most affordably done using an angle grinder and cut off wheel. Making nearly straight cuts on flat bar with a cut-off wheel can be acheived by rotating the guard on the grinder, and positioning cut off wheel straight down perpendicular to the bar. This method can be imprecise and lead to more grinding work later.

For this reason, I prefer to use a horizontal band saw for metal cutting. They are far more precise and versatile, certainly worth the investment if you are becoming serious about metal fabrication. They allow you to work quickly and cleanly and save a ton of time. The one pictured here is very nice, but in other shops, I have used much smaller (and affordable) bench-top monted metal band saws that can do the same job with the right jigging.

If you are feeling particularly ambitious, check out this $80 solution to getting straight cuts with a sawzall by Instructables author joeynovak.

Step 2: Clamps and Tacking

Welding clamps are used to hold work together before you tack your parts together. Clamps come in more sizes and shapes than you can even dream of. My favorite and most commonly used workholding clamps for welding are:

Be sure to check your square as you tack pieces together with a steel square tool. If your tacks are not keeping your material square, you should be able to bend and twist (or even bang and hammer) them back to square before completing your weld beads.

We tack our material to minimize heat distortion on our material. Rapid expansion and contraction will cause your material to shrink toward your weld bead, so alternating sides as you tack can help reduce this deformity.

Step 3: Butt Joints

We prepare hot-rolled flat bar steel for welding by first grinding off the mill finish. This finish protects the steel from rusting while it is being transported from the mill to your workspace, but if it isn't removed, you will have a contaminated weld that could potentially break.

It is a good practice to use an angle grinder to bevel the edges of steel stock before it gets welded. By creating two bevels on the joining edges you create a tiny little valley for the weld pool to form in. Doing this for butt welds is a good idea to ensure good penetration.

Complete your first tack weld. To do so, positon your electrode sticking out of the gun between the crevase of bevel valley you created with the angle grinder. Your wire should barely be touching your base material. Squeeze the trigger for two seconds, and complete the tacking loop motion.

Repeat this action, alternating side to side so that the heat spreads evenly until you have tacks spaced 1" to 1.5" apart across the span that is being butt-welded together.

Run welded beads across your joint, start by connecting your tack on the outer edges than work your way towards the center. It's ideal to weld from the bottom of the stock up to the top, pushing the weld forward with the tip of the gun, however that isn't always comfortable or a good way to start learning. In the beginning, it's perfectly fine to weld in whatever direction/position that is comfortable and that works for you.

Once finished welding the the flat bar, you are left were left with a big bump where the filler material was added to the weld pool. You can leave that if you like, or you can grind it flat depending on what you are using the metal for.

If you find gaps ground in your weld, you may tack the gaps where the weld didn't penetrate properly, and grind the material down again. This typically means that you need to have more power and more wire to fill in the weld.

Step 4: Tee Joints

To learn the Tee joint, we first need to introduce the concept of fillet welding. Fillet welding refers to the process of joining two pieces of metal together whether they be perpendicular or at an angle. To perform a fillet weld, we change the way we position our welding torch against the material, so that we penetrate into the corner of our joint at an angle that will be well shielded and ensure strength.

The weld bead will not penetrate all the way through the other side of your base material like we see when we are welding on the sheet material from the Beginning to Weld Lesson.

The tee joint is when two pieces of metal are perpendicular to each other at a 90 degree intersection. Prepare your metal for welding by grinding off the mill scale finish. You only need to grind off the mill finish where you intend to weld, remember to keep considering how to minimize your grind time.

For a clean and close fitting weld, I recommend using magnets that will hold your material square to one another while you are making your first few tacks. Be sure to check your square between tacks using a slide rule or metal square.

Start by tacking each end, placing a tack weld on either side of the tee. Complete a tack in the center, before tacking the opposite side of the tacks you already placed in the center. Finish by tacking the back side of your previous center tack.

A fillet weld motion is not quite the same the chain of loops like we did for our butt weld, instead it is more like a rounded zig-zag shape, where we grab and melt the edges of the base material as we run the weld puddle across our joint. Run beads in sections along your joint, alternating side to side and back to front, working your way towards the middle. A nice fillet weld will form a neat even triangle shape between the pieces of perpendicular material.

Step 5: Corner Joint

A corner weld is a type of joint that is between two metal parts and is located at right angles to one another in the form of an L.

To complete this joint, begin by tacking the outside edges, then make the same curved zig-zag weaving motion we made for our filleted tee weld.

Corner joints can be hard because you can't often rest your hand on your material to steady your torch hand. You may want to practice a dry run along the joint to make sure you’re going to be able to weld comfortably, I've gone as far as clamping a vice grip to another piece of material to create a hand rest. Instructables author Phil B has a pretty cool hack to keep welds straight.

Step 6: Lap Joint

Lap joints will need to be completed when your project has one piece of material nested on top of another sheet or bar, with a large amount of surface area being mated. This joint is very similar to the tee joint, and we will need to perform a fillet weld to merge the material into one continuous piece of steel. Lap joints often necessitate slightly more voltage and a slightly decreased wire feed because there are no gaps in your material, and you are essentially welding onto a heat sync. The bottom layer of welding material is absorbing the heat energy of the top piece of material, dissipating the heat quickly.

Prepare the edges of your material to be welded. Begin by tacking the pieces together. Instead of making a small cursive E shape, place your consumable wire electrode on your top piece of material, squeeze the trigger, and gently drag the gun toward the bottom piece of material. You should be able to see the edge of the top material ever so slightly melt away through your welding hood as you complete this motion.

Complete your lap joint by first running beads along the outer edges, and work your way towards the middle. The angle of the gun should go into the corner at 45 degrees. The weld pool should visibly 'grab' the edge of the steel on your top piece of material. Remember that in a tee joint, your are not making small loop motions while you weld, but instead a slightly rounded zig-zag.

Step 7: Edge Joint

An edge joint is similar to the lap weld, in that we will be grabbing the corners of our sheet or bar material as we weld the edges together, melting them into our weld pool. Position the torch parallel to the edge and use the same zig-zagging motion as the torch moves along the path of the weld.

The heat affected zone of an edge weld is greater than any other joint we have gone over. Because the heat is spreading into two parallel pieces of material, with the same amount of heat being applied to both pieces, the material can burn out quickly. To avoid a gap in your weld or material, edge welds will often need a lowered voltage setting.

Begin by tacking the two ends, then place two tacks between the two edges, equidistant apart - four tack welds in total.

Run a bead on one end, then the other end, completing the middle bead last. By welding the ends first, we minimize heat distortion and potential burn-out.

If your material is very thin, consider using a small lap weld instead of an edge weld; as you perform this lap weld, you pick up the edges of both workpieces instead of just the top piece. You'll have an easier time manipulating your puddle and a slightly smaller heat affected zone.

Step 8: Class Project

For this class assignment, I recommend that you practice making joints by cutting down two 36" lengths of hot rolled flat bar, prepare it for welding, jig our joints, then weld them together.

Cut the bar into ten 6" sections. You only need to remove the hot rolled steel's mill finish from the areas you are welding on. Remember to always wear a proper respirator when grinding to prevent flu-like systems from inhaling metal particulate.

Share your results or anything you made with these skills in the Class Project uploader below.

Step 9: That's a Wrap!

That's it! You're officially dangerous enough to weld two pieces of metal together.

MIG welding is accessible at so many levels that many makerspaces and hackerspaces are beginning to offer welding equipment. To see if a hackerspace or makerspace near you offers welding, check out this list of global hackerspaces.

Now that you've familiarized yourself with the world of steel and electrified molten metal, are you ready to take on a more complex project?

Check out this perfect capstone project that will get you inspired to start making your own steel furniture as I guide you through how to work with square tube to make a simple stool.

Learning to weld is a powerful skill in a maker's toolbelt! Here are some inspiring builds, projects, and techniques that are great for taking your welding practice to the next level:

Check out this diamond plate fire pit from Instructables author cammers.

This easy pot-rack project by YoseiI is a quick welding job that is an awesome space saving solution for any kitchen.

Make you own welding clamps with this Instructable by TSSJ-ryan.

Make a shelf that won't quit, EVER! ozymandias87 guides you through designing and building shelves for your workshop.

Kiteman takes commonly available steal stock and transforms it into a minimal, functional, and portable BBQ.

Instructables community author rrybarczyk goes over great technique for squaring and cutting in their steel box tutorial.

Now it's time to tell your DIY story! Share your welded creation with everyone by showing off your process in an Instructable! Perhaps you'll even be eligible to enter one of Instructables' fabulous contests, and win an awesome prize! Can't wait to see what you make :D

Step 10: Thanks and Feedback

Thanks to the folks at Molten Metal Works in LA for letting me bang around in their shop and take lots of pictures while I developed this class.

Extra huge thanks to the Pier 9 shop staff for letting us take up so much space in the shop for a few days while we shot this class.

Ultra hugest of thanks to Trent Still and Paige Russell for staying late and being the best shop buddies a gal could ask for.

Thanks for following along! Hope you were able to build your knowledge of MIG welding and develop a skillset that will make you a little bit more confident in the workshop.

I'd love to hear any feedback you have about this class or see any resultant welding projects (or really anything) that came from skills you learned from these lessons. Reach out and say 'HEY!' .


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Angle iron corner joints

Let's take a step back.

Strength is simply not an issue for the junction between the border pieces for the top of a bench. The important joint -- from that perspective -- is going to be the one that joins the legs to the top frame, along with what other type of support the legs might get (lower crossmembers, diagonals, etc.).

That said, the interlocking joint has one advantage over a miter joint. It's less likely to tear open like a zipper if you were prying the two pieces apart. A weld is theoretically as strong (or stronger) than the metal it joins. In practice, that's often not the case (we'd all like to be theory-level perfect welders, but we aren't). Interlocked seams might not fail in the same kind of zipper-like fashion (meaning: one straight-line seam that can be opened a millimeter at a time instead of having to fail all at once).

Then again, I'm not an engineer. So I could be way off base.

But as I said, the corner really gets no stress at all. I mean, you're attaching a top to this thing, right?


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Otto Nobedder wrote:

AdVirMachina wrote: How do you cope a square tube? I'm not seeing how that would work.

Sent from my HTCONE using Tapatalk

Coping square tube is rare; The nature of square tubing reduces the benefit of coping over a miter unless the loading is through torque. The time involved in properly coping square (or rectangular) tube is significant, as well.

I attempted to draw a square tube cope profile, but I've had too much food and way too much beer to pull it off. I'll attempt it again tomorrow right after work, if no one beats me to it.

I can make a cope on box tube or angle in 30 seconds with my porta-band. I've seen guys try to use a chop saw to miter and when that blade gets flexing it might be a 45..or not. My cold saw works great for mitering but at $100 a blade, I save it for more important cuts. I bet I can cope a piece as fast as anyone can miter one. The porta-band RULES!


This is the corner of my patio table that I made. I weld the outside corner, the inside corners and the butt and left the top unwelded and it looks clean except for that tiny blade overrun :oops:. I guess I could have full welded it and then ground the welds off flush but it doesn't make sense to weld something and then grind it off some times. Grinding time and wheels are money.

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Chapter 14: Fabrication & Repair Tips

Chapter 14

Everyone is a genius at least once a year. A real genius has his original ideas closer together.
—G.C. Lichtenberg

Section I – Frames & Brackets

Fabrication Steps

Many a good weld design is ruined by mistakes made in fabrication. This chapter will help you avoid the most common mistakes, and also a few uncommon mistakes. Though not all of the following steps are used on all projects, the typical weld fabrication steps are:

  • Get or make a fabrication sketch or drawing.
  • Develop a well thought out step-by-step procedure.
  • Gather tools and materials.
  • Make patterns, jigs, templates and fixtures, if needed.
  • Put together a cut list.
  • Lay out and cut the materials.
  • Make edge preparations and clean the metal areas to be welded.
  • Position and clamp materials prior to welding.
  • Tack weld assemblies, check dimensions, setup and squareness.
  • Place the final welds and assemble the final fabrication.
  • Grind welds smooth only if necessary.
  • Paint the fabrication, if needed.

Angle Iron Frame Corner Designs

There are three common methods for making corners on angle iron frames: mitering, notching, and notching and bending a single length of angle iron. Figure 14-1 shows mitering and notching.

Figure 14-1. Two corner joint designs using angle iron.

Both methods work, but with notching it is easier to get good results and this technique is more dimensionally tolerant because the joint gaps between the angle irons’ length can be adjusted to bring the frame square and the side lengths equal. After welding and grinding, both methods will look equally good and be equally strong. In general, use mitered corners when you have a bandsaw or a notching tool to cut perfectly matching corners.

The third approach for making square and rectangular frames from angle iron lends itself to production work because it requires notching and bending, which is best done on a machine like an Ironworker. These versatile machines can perform the functions of a press brake and a bending fixture, such as bending and notching angle iron. As shown in Figure 14-2, getting the correct bend-allowance gap is critical because this gap provides the extra material needed to go around the outside corner when the bend is made. To make these mitered and bent corners, begin by setting the bend-allowance gap to slightly less than the thickness of the angle iron and go from there. This method only works if corners are bent by machine. Heating the corners and manually freehand bending them will produce rounded corners—and scrap.

Figure 14-2. Notching and bending to make a single-piece frame: (A) corner detail before bending, (B) corner detail after bending, welding, and grinding, (C) notched angle iron frame ready for bending, and (D) the completed frame.

Checking for Squareness

There are several ways to check frames for squareness:

  • When welding a very large L-shape, where a square is too small and there are no diagonals to measure, use a 3-4-5 triangle. Here’s how it’s done:
  • Measure off four units on one leg, or member, of the frame.
  • Measure off three units on the other leg.
  • Adjust the hypotenuse by moving either leg of the L-shape until the hypotenuse measures exactly 5 units. Following this procedure makes a perfect right triangle. See Figure 14-3.

Figure 14-3. Using a 3-4-5 triangle to set members at a right angle. Remember to reduce the overall length of the frame sides to allow for additional joint root spacing, otherwise your frame will be oversized.

  • Check for equal diagonals between opposite frame corners using a steel measuring tape. This method is used in Figure 14-7.
  • On large frames, check the squareness using a carpenter’s square, and on smaller frames, check squareness using a machinist’s square.
  • If the sides of the frame are to be plumb and level, a large level can be used.

Improving the Odds of a Welded Frame Being Square In decreasing order of effectiveness:

  • Secure all members in a rigid fixture, tack them, weld them, and let them cool down in the fixture. This is the best method.
  • Clamp members to a steel table and then tack and weld them.
  • Use a fixture to hold members for tacking, then weld the tacked members outside of the fixture. This fixture can be as simple as a sheet of plywood with wood blocks fixed to it to hold the work in place while the tack welds are made. For an example of this type of fixture, see Figure 14-4.
  • When tacking is complete and you have checked the frame for squareness, weld one corner, and then weld the opposite corner. Weld the same relative corner in the exact same sequence on all four corner joints. Next, weld all outside faces, then all top corners, and finally all bottom faces. Make each weld in the same relative direction and give each weld time to cool before starting the next weld.
  • Begin by tack welding each of the corners together using a Bessy-type clamp each time, then check for squareness. If needed, bend the part back into squareness. If the tack welds are not too large, with moderate force you will be able to straighten the frame by hand without using hydraulic jacks. After tacking, begin your final welds at opposite corners.

The Around-The-World Rule: Do not start welding at one end and travel sequentially using a corner clamp—the last two corner pieces of the frame probably will not meet.

  • Use magnetic corner tools. These are effective only for light sheet metal and light angle iron because they lack the strength to resist weld-induced distortion—but they will allow you to place initial tack welds.

Corner joints iron angle

Thread: Angle iron - 45 degree or notch?

Hey guys,
I'm a very new to this, and although I stayed at a Holiday Inn last night I don't call myself a welder. I'm just a guy tinkering around trying to practice and pick up a few tips along the way.
I have about a 100 feet of 1-inch x 3/16" angle iron laying around my dad's house that was left over from a construction job. Anyway, I have started tinkering around with my Hobart Handler and want to know what you pro's think.
When joining angle iron at 45 degree corners, should I...
- notch and cope the two pieces, or
- cut at 45 degree angles?

Personally I like the look of 45 degree corners rather that the notch and cope method because I grew up as a carpenter and a 45 degree miter cut comes naturally to me. But is there a "correct" way to do this? What do they teach in welding school? Is one way stronger that the other?

Thanks for the help

Joining angle iron at 90 degrees using 3 easy joint methods - cope \u0026 mitre. Welding preparation

Coping Steel Corners

The cope joint is a good alternative to mitering metal pieces if you do not have a dead-on accurate miter saw. Coping the joint can be quicker and just as strong.
Clik image to enlarge

Flat 90-degree corners without the miters!

Text, photos and video by Tom Hintz

Posted – 2-9-2011

Making square and flat 90-degree corners with steel angle stock can be frustrating which almost guarantees sloppy results. Mitering the corner is one option if you have an abrasive wheel (or similar) saw and when done right results in perfectly square and flat corners. The problem is getting all four of miters just right without spending an afternoon grinding small corrections into the pieces to get the joint right. Of course if you spend much time fitting the joints your chances of grinding away too much material increase dramatically and your target dimensions will be compromised.

The good news is that coping is another corner-making process that you can do with common tools, including a simple jigsaw (also a band saw or hacksaw) and an angle grinder. I prefer a good jigsaw equipped with a metal-cutting blade because it is faster and with a little care can produce better results much faster than I can get with a hand-operated hacksaw.

As easy as the coping process is taking the time to make a few “learning” joints with scrap material before jumping into production of a real project. This is also a good time to become familiar with how to measure and cut you0r project pieces to the right length to end up with the finished dimensions desired.

The Basics

I use the piece that will fit into the cope as a guide (left) and scribe a cut line. Remember that this line defines the outside edge of the piece so our cut has to leave the line. A good jigsaw fitted with a metal cutting blade (right) is a good choice for this cut as you have lots of control and will limit the amount of fitting needed.
Click images to enlarge

Coping a joint simply means removing overlapped material to create a flat secure joint that has both pieces on a single plane. In the case of angle material coping can be an easier procedure than cutting perfect miters. In many projects having at flat bottom is necessary to support something that is going to use that flange as a base. The only tricks to coping are to remove only the overlapping material and to remember to allow for the thickness of the steel itself. Forgetting this in one corner is bad enough but make the same mistake in all four corners and a frame that was supposed to be square won’t be.
Once the pieces are cut and fit you can weld them in place on the inner or outer faces, whichever is most compatible with your project. I use my Bessey Angle Clamps to hold the pieces for fitting and welding a 90-degree corner but depending on the situation using some other device or technique could be a better choice.

Mark and Cut

One thing to keep in mind when cutting the raw pieces to be coped is that we usually have to allow for at least one thickness of the metal at each corner. When we cut the notch in the bottom surface that brings the surfaces 90-degrees to it into contact with each other. The hard way to deal with this is to grind or cut a sliver off of the upright side we are cutting the notch in. The easier way is to cut one set of opposing sides short by twice the thickness of the metal. Then we can cope the ends of the longer pieces to accept the shorter sides and still come out with the dimensions we want. This is way easier to show in the video later on this page than in words here.

After getting the fit just rigfht (left) you can weld the pieces up. I welded the outside seams to keep this interior flange (right) smooth so it can be used as a base for a machine or other object. Coping the joint makes this easy.
Click images to enlarge

To cut the notches we just lay the corner pieces together as they will be in the project. Trace a cut line on the piece to be notched, keeping that line as close as possible to the piece that will fit into it. Then remember that because you scribed the line around the piece that will fit into it that line should remain after you cut the notch. To get a proper fit we want to remove the material inside of that line, not on or to the other side of the line. This is where precision and patience pays off. Take your time and get the fit these notches right and welding the corners up later is easy. Once you cope a few corners it gets to be much easier.


After fitting all of the pieces and laying them out to check their fit as an assembly we can move on to welding. Taking the time to do a test fit and tuning up any corners that need it will save lots of time later as well as making it easier to get a finished piece that fits the dimensions that you need.

For most square-cornered projects like the frame built in the accompanying photos and video I use my Bessey Angle Clamps to hold the pieces while I tack them all in place. I also have used my Bessey Magnetic Squares to hold the pieces for tacking. Then I can take the assembly out of the clamps for finish welding or I might do most or all of the welding with the clamps still in place. That decision is based on what is easiest for that project and generates the best results.


Coping a 90-degree joint is very easy once you do it a time or two. While it is used most often on 90-degree corners as in this story you can cope joints of virtually any angle or shape. This is a great way to join material with different shapes to one another and do it seamlessly. The procedure remains the same regardless of the angle or shape.

I think that in many cases coped corners are easier to weld than traditional miters. I know that there will be exceptions to that but for the most part I think beginner metalworkers (and many veterans if my email is at all representative) will find coping one of the easier, more durable corner-making techniques.

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