What Is Bar Bending & How To Make A Bar Bender
Rebars are used as a reinforcing element in reinforced concrete members. They are often bent to make stirrups or longitudinal bars. In this article, we will discuss how to bend rebars and how you can make yourself a bending machine at home.
What Is Bar Bending
Need of rebars
In many cases, reinforcing bars must be bent into different shapes. This is done for several reasons. Let us return to the reason for reinforcing concrete with steel-it is to increase the tensile and compressive strength.
As an example, you might compare the hidden action within abeam from live and dead loads to breaking a stick over your knees.
When you apply force, the splinters next to your knee push toward the middle of the stick, while the splinters from the middle to the opposite side pull away from it. A similar phenomenon occurs inside the beam.
Consider a simple beam (one that rests freely on two supports near its ends). Whenever a beam bends or sags, it is due to the dead load (weight). As the forces increase from the center to the bottom, the bottom portion of the beam tends to stretch or lengthen.
The steel reinforcing bars are required for this part because it is in tension. The tensile strength in the beam is enhanced by the combination of concrete and steel. This prevents the beam from breaking because of the force of the load.
There is no stress in the exact center of the beam, between the compressive and tensile stresses.
When we bend rebars
For continuous beams, it is a little different. It is possible for the top of the beam to be compressed along a section of its length and taut along another section. That’s because a continuous beam is supported by more than two points.
As a result, the beam DOES NOT bend in one direction, but in reverse as it travels over intermediate supports.
Engineers design the bends of reinforcing steel in such a way that the steel sets into the concrete just where the tensile stresses occur to help the concrete resist these stresses. It is for this reason that some reinforcing rods are bent almost in a zigzag pattern.
Several of the important ways to increase and maintain bond strength include joining each bar with the next, anchoring the bar ends with concrete, and overlapping two bar ends.
Some precautions when bending rebars
Reinforcing bars should not be bent too sharply when bent. Bars may crack or weaken if they are bent too sharply. Therefore, certain minimum bend diameters have been established for the different bar sizes and for the various types of hooks.
How To Make A Bar Bender
What you need
To make your bar bender at home you need the following tools and materials.
- Angle grinder
- Cutting disk
- Grinding disk
- Drill or Drill Press
- Welding machine
- Tape measure & Vernier
- Center punch & Pen Scriber
- Clamps or Vice grips
- Drill bits: ø4 to 16 mm
- Taps set: M6x1 & M12x1.75
- Tap handle
- 1 pcs Tube. (This is for the main unit)
- 1pcs Round stock steel (bushing)
- 1pcs Round stock steel roller die)
- 1pcs Rod (rotating pivot)
- 1pcs Flat bar (bending unit)
- 1pcs Flat bar 30x3x100mm (addition)
- 1pcs square tube 20x20x1.5mm or heavier (handle)
- Some bolts and matching nuts
- You might need some washers
Preparing the pivot set
- Use a saw machine to cut a piece of steel of 32mm in length.
- Use a file to smooth the profiles.
- To make the hole in the tube, punch a centers punch at the point where the hole will be. Do the hole in the tube, starting with a *4mm drill bit and finishing with a ø16mm drill bit.
- By using a countersink, enlarge the hole of the bushing from *14mm to *16mm.
- Use the drill press and Scotch Brite to polish the 16mm rod/axle.
For the pivot of the bushing, cut a piece of this rod 70mm long
- Bushings should be welded
- To drill a 10mm hole at the base, drill a hole with a center that is 38mm larger than the bushing center.
- To cut the threads, use an M12 set tap.
- Place the roller die (*34/12x20mm) in the hole at the base of the bending unit.
- Between the head of the bolt and the nut must be the sum of [the roller+2 washers+(1*1,5mm)].
- This allows the roller to rotate freely.
The base for pivot
- To attach the bending unit to the main unit, make a small pivot base.
- You will need a M16 nut approach with a ø16mm drill bit and a M6 headless socket bolt.
- Use a M6 set tap to cut the threads after drilling a *5mm hole in the middle of the nut side.
- Fasten the screw after inserting the pivot into the nut and adjusting.
- Insert the pivot from the bottom into the holes in the main unit.
- Connect the nut to the main unit with a weld.
To sum up, bar bending is required on almost every construction project. It is used for making stirrups and longitudinal reinforcement. You can make your own bar bender at home using some basic tools and old metal parts.
I found it interesting when you said reinforcing bars need to be bent to help increase tensile and compressive strength. I imagine this might be the case as well when it comes to steel tubes that need to be bent for manufactured products that need them as components. I’ll take note of this in case I ever need tube-bending services in the future.