Introduction: Bend Your Own Metal Components (Like Furniture Legs) Without Special Tools
Working with metals as a hobbyist can be an intimidating prospect but with a few simple tools, a little planning, and some muscle I hope to make it, or at least one aspect of it, feel much more attainable.
While you'll see this process used on a set of legs for a large desk in this guide, the steps that follow can be applied to all sorts of projects, and despite the title, even for things that aren't furniture legs.
It is also important for me to note upfront that I am strongly in support of the things you make, looking like things you've made so there may be more complicated, or expensive, methods that would give more accurate or professional/commercial looking results. If that's what matters to you, or your project calls for, then you may need to find another guide. On the other hand if you're down to embrace the minor and cosmetic flaws, reject the pursuit of perfection, and celebrate the process of creating while learning, then you're in the right place.
- Hot Rolled Steel Bar - .188 X 1.5 X (4.0, 66.0, 70.0) : I'll discuss material sizing more in the next step but suffice it to say there are lots of options depending on your project and the sizes listed here are just what I used for mine.
- Hot Rolled Steel Round Bar - 2.0 x 2.0 : This is for the die you'll bend your bar over. The radius of the die is the radius of bend you'll get but be aware the listed sizes are typically diameters (r x 2). It should also be slightly longer than the bar you're bending is wide.
- Bench Vise: The larger the better and it should be mounted to a secure bench or table.
- 2 - 5 lb Hammer: It should have a large, smooth face and be of decent weight but you should still be able to swing it with one hand. Mine was 3 lbs.
- Gas Torches: We used one MAPP canister and one propane canister at the same time. The MAPP provides high temperatures in a narrow jet while the propane's wide flame helps keep the area soaked. If you're bending softer materials like aluminum it may not be necessary to add heat to the bend.
- Angle Grinder & Cutoff Wheel (Likely Optional): In case you need to cut your raw stock to length. I went as narrow as I could find (1mm) for better precision and faster cutting but only used it on the shelf brackets I welded on later.
- Water Bucket: For cooling the metal. A wide metal container is ideal but you can get away with plastic, if you're careful about not letting the pieces directly contact it while hot.
- A Friend(Optional) - Not required but a second set of hands will make controlling the bends a bit easier and faster. It's also a bonus if your project requires welding and they know how to weld (shouts out to my father).
- Eye protection - An absolute requirement when grinding and hammering metals.
- Hearing protection
- Heat resistant gloves - You shouldn't have to directly handle anything hot but there will be a lot of hot metal around, the die in particular holds a lot of heat that you inevitably will accidentally bump, so better safe than sorry.
- Respirator - Should be used while grinding or cutting.
- Fire Extinguisher
Step 1: Material Selection
You can't finalize your design before you choose your material but you will need at least a basic idea of what your final pieces will look like and the requirements for strength and durability they need to meet. The number of bends, need for welding, weight they will hold, and the environment they will be used in should all be considered.
For my application I needed four bends per piece, had to do some welding to join secondary components, needed them to support a very heavy, 8ft long, solid oak desk top, and it will be kept inside the house. This drove the use of the more expensive and harder to manipulate steel over aluminum because of the higher strength, better weldability, and not being overly concerned about corrosion. Specifically I chose A36 hot rolled steel which is a mild (low-carbon) steel that is abundant (i.e. cheaper) and considered easy to work with. The raw flat bars lack precise dimensional control but for my use that wasn't a big concern.
To minimize weight and cost, and increase work-ability, I chose 3/16"(.188) x 1-1/2" (1.5) flat bar. This was definitely on the thinner side given the weight of the table top but with essentially eight legs taking the force I felt confident enough to risk it over something like a full 1/4" that would be much harder to bend.
Be aware that for consistent bends, the width of the bar should not exceed the distance on your vice from the outer edge of the jaw to the closest edge of the central bar. (i.e. the full width of the work piece should be gripped by the vice when held vertically and extending past the bottom of the vice.) We will work out the needed length for the raw material in the next step. Additionally, the thicker your material, the larger the minimum allowable bend radius, or you risk developing cracks. Typically for steel the minimum radius is equal to the thickness of the part.
Optionally if you really want/need a bend radius below the minimum you can cut a shallow notch on the inside of the piece at the bend centerline. This will effectively reduce the thickness just at the bend and can help prevent cracks from forming. Depending on your application it may be advisable to then weld the inside of the bend to re-strengthen the area thinned by the notch.
Step 2: Design
By making use of Fusion 360's sheet metal workflow, and some well placed parameters, we can remove most of the tedious math involved in choosing a material stock size that properly accounts for the stretching and thinning that occurs when bending metal.
This may not be the cleanest method to setup, Fusion is not my "native" CAD package, but it does work and it's very easy to tweak your design by simply adjusting a couple of parameters:
- Set up your User Parameters: The total number you'll need depends on how many bends your project has but you'll need: one each for material thickness and width, one controlling each bend location (measured from fixed points on the piece i.e. the ends or middle), at least one for a distance to a bend that is adjustable, and one for the total length (whose expression is the sum of all the other length parameters and that make up the full length. Don't just input a value).
- Sketch the raw stock bar: Use your width and total length parameters to set the dimensions.
- Create your solid: Extrude your first sketch with the thickness parameter.
- Sketch the bend centers: Use the top surface of the solid as the sketch plane and the bend location parameters to set their positions.
- Create a Sheet Metal Rule: This is where you set your bend radius, also, use your thickness parameter here. I used the default K-factor because getting an accurate number is not simple and even a better guess for .188 steel, like .47, provides accuracy that will just be lost in the fabrication method.
- Bend the solid: You'll need to convert the regular solid to a sheet metal solid first. You may need multiple bend operations depending on your part geometry.
- Sketch the final bent part: This sketch is fully referential (driven dimensions) and you'll only want sketch dimensions for the actual final dimensions you care about. For me that was the height and internal width.
- Fine-tune the parameters: Now you simply tweak your adjustable parameters until you hit the target lengths for the dimensions in your previous sketch (which are easier to track if you favorite them in the parameter editor window.)
- Use the value of the Total Length parameter to order material
While I found the Sheet Metal Rules system a little clunky (it was my first time using it and I may be doing it wrong) I was able to model three potential radii relatively simply by re-using the same sketches on different solids, which really helped when choosing the look that I wanted.
It's also helpful to make and print a quick drawing in Fusion for reference while in the workshop. By creating a Flat Pattern of the folded solid you can get a drawing view with the compensated bend start/end lines already in place.
Step 3: Die Construction
In order to get consistent, and relatively accurate, bend radii we will use a type of tooling called a die. In our case this is a piece of steel with a radius that matches the bend radius we want in the piece. Obviously if you have multiple bend sizes you will need multiple dies.
The die I used was constructed by welding a scrap piece of flat bar tangent to a 2" x 2" piece of round stock. The round will sit on the top of the vice so it is supported while the bend is being hammered and the work piece will be clamped against the die's bar. Be sure to grind your weld flush before use.
If you don't have the ability to weld you could attempt to simply clamp the work piece and the round directly in the vice but be very careful (and probably wear safety shoes and long pants) because you're at risk of sending the heavy and very hot die flying if it works loose while hammering. Using more heat and notching (described later) might help reduce the bending force required and make this setup more viable.
You'll also want to find and mark a centerline, perpendicular to the support piece, on at least one end of the die. This will be used to align our work pieces with the die.
Step 4: Considerations for Bend Sequencing
If you have multiple bends to make in a piece the first thing you need to do is decide on the order to make those bends. There are a number of factors that go into this and how important each one is will vary from project-to-project and with your workspace. The three biggest factors to consider are:
- Stacking tolerances/errors: Every bend will have a little bit of error (twist, angle, radius, location, etc.) and if you make the bends in sequence down the part those errors stack up, leading to a final bend that, in relation to the first bend, has an error that's the sum of all the errors along the part. An obvious statement probably but a phenomena that can easily result in unusably out-of-tolerance parts if not taken into consideration. Mitigate this by working from the middle out, pushing the error stack-up towards non critical areas, and locating bends from a common datum and not each other.
- Getting proper work holding: It is possible to have bends placed or sequenced in such a way that it becomes impossible to properly hold the piece in the vice for the bend. To prevent this, carefully think through your bend sequencing and measure workbench clearances before starting any bends. You can see in the third picture that if the legs were slightly narrower we wouldn't have been able to bend them like that without running the part into the workbench.
- Having hammer access: Similar to above but when improperly sequenced bends leads to a position where you don't have the necessary clearance to hammer the next bend, even if it can be held properly. The solution is also as above, thoughtful sequencing of the bends.
Step 5: Bend Preparation
To prepare each bend you need to get the piece clamped in the vice, against the die, with the start of the bend aligned with the centerline of the die. For the purposes of this guide the start, versus the end, of the bend is on the side of the bend that when aligned with the die centerline leaves the center and end of the bend above the die (see the last photo above).
Following your bend sequence and drawing dimensions, measure and mark the start of the bend. It's helpful to mark the edges of the bar so that you can easily align it with the die centerline. Place the piece and the die in the vice, making sure to check both the vertical alignment with the start point and centerline but also that the piece is square to the face of the die. Be careful, if this isn't your first bend the die will be retaining a lot of heat and can still burn you after the previous heating for longer than you think.
Step 6: Safety!
The steps that follow involve extreme heat and the application of targeted violent force, it is imperative that you are using the proper PPE (personal protective equipment) and are focused solely on the tasks at hand.
At a bare minimum side-shielding, or wrap-around, safety glasses should be worn whenever metal is being struck. While the tool steal of the hammer is much harder than the mild steel being bent there is always some risk when using metal tools on metal work pieces.
While the work pieces will cool relatively quickly, especially if you are using water, the bending die has a lot of mass and doesn't get cooled between bends so it will retain a lot of heat. Wearing some type of heat resistant glove is strongly recommended when working around the die because inevitably you will accidentally touch it.
Step 7: Heat the Joint
Using your torch(es) apply heat to the bend area. You're looking for the metal to take on a reddish-orange glow. We found that the quickest way to get a decently even heat was with a MAPP torch on one side and a propane one on the other.
Step 8: Forming
While applying pressure on the free end of the piece, either from someone helping you or with your own off-hand, begin hammering the piece around the die. You want to work your blows low to high, starting at the tangent point and only moving further along the bend once the piece has come in contact with the die. It's important that most of the actual deformation comes from hammering and not pulling on the end or else you won't get a clean radius in the location you want.
Once it looks like you're close to the angle you want start checking with a square, or protractor/angle finder, every few hits. If you over-bend just carefully lift the piece from the free end while using light hammer blows just below the spot the piece meets the die.
Step 9: Cooling
Once you are happy with your bend you'll want to cool it before moving to the next bend location. The easiest way to do this is dunking it in water for a minute or two but if that isn't an option then the part should air cool to a handle-able temperature in 10-20 minutes depending on the thickness and how much heat you put in initially.
Once the piece is cool you can repeat the steps above for the next bend.
Step 10: Finishing
At this point you've finished the forming part of your work piece(s) but before putting them to use you should seriously consider putting a little work into finishing the surfaces both for protection and aesthetics. There are way too many surface finish and coating options to cover in the scope of this guide but for the pieces pictured in this project I simply cleaned the raw steel and applied a beeswax coating. You can read the step-by-step instructions for that process HERE.
For a first time doing any serious metalwork I'm really pleased with the results. Somehow everything came out pretty straight and equal but you can absolutely tell they were handmade, in that the hammer marks and scale give them a ton of personality that's tough to capture in an image.
That isn't to say there weren't mistakes along the way. Once I measured to the wrong side of the bend and another time I took my measurement from the wrong end of the piece and both times we didn't discover the mistake until after the bend was finished. The best method we found for straightening the bends was heating the bend back up and and placing it horizontally in the vice, which we then closed to flatten out the radius. There's definitely a little wave in the piece at that location, there's no putting the dislocated metal back where it was before, but nothing extreme enough to cause an issue for my particular use.
As always thanks for reading and please feel free to leave any questions or tips in the comments and I strongly encourage anyone who follows this guide to add pictures of their completed project as well!
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