Mini Sheet Metal Brake

For the past few years, I've been working on an EV charging solution for people who park on the street and need access to charging there. This work has involved a ton of prototyping and custom tooling to prototype specific parts I need. One of those parts is a 1mm thick brass electrical contact (sheet metal) that gets two 90° bends. After looking around at sheet metal brakes and not finding anything that would fit my size requirements, budget and could bend 1mm brass, I decided it was best to make one myself.

Several years back, I put together a larger sheet metal brake that didn't involve welding. I decided to loosely copy this design and scale everything down.

I used the following materials:

A section of 3/4" steel angle iron

A section of 1/2" steel angle iron

Two 2" wide hinges

10-32 Screws (x15)

Spray paint

Tools that I used:

Basic Clamps

Hacksaw

Angle grinder with a cutoff disk (Could be done without if you are ambitious with the hacksaw)

Dremel tool with a cutoff disk (Not needed)

Metal File

Drill

5/32 or #21 metal drill bit

3/16" metal drill bit

10-32 Tap

Driver for the 10-32 screws (Mine had a Torx T25 head on them)

Step 1 is to cut hinge reliefs in the corner of the 3/4" angle iron. These reliefs allow the hinge barrels to rest inside the angle, putting the pivot point as close to the corner edge as possible. The closer the pivot point to the edge of the angle, the more accurate and tight the eventual sheet metal bends will be. Unfortunately, the hinge barrel offset of my hinges prevented the pivot from being perfectly along the edge of the angle.

To cut the hinge reliefs, I first laid the hinges over the angle to mark their end positions. Note that the distance between the inside edges of the hinges will determine the maximum bending width. I only need a bending width of up to 1 inch, but I kept the hinges around 4 inches apart.

After marking the hinge positions, I used a hacksaw to cut the ends of each relief. The length of the relief can be cut using either a cutoff wheel (angle grinder) or a hacksaw. I used both methods, starting with the angle grinder and finishing with the hacksaw. The cutoff wheel was used to clean up the relief after the cut.

The angle iron with the hinge reliefs will be the brake's bending surface. This bending surface angle iron is cut slightly beyond the hinge reliefs. My bending surface angle ended up being 8.75" long.

The length of the bending surface angle defines the length of the similarly long fixed base surface, which is cut from another length of 3/4" steel angle.

To best align the hinge pivots to the edges of the bending and base surfaces (angle irons), the hinges must be mounted to the bottom of the base surface angle iron. I accomplished this by cutting a slot through one face of the angle so that one of the hinge flanges could pass through it.

First, the slot's position was marked on the base angle. Next, I used the angle grinder and cutoff disk to open the initial slot in the angle. Because of the disk's large diameter, cutting the slot to its full depth across its width was impossible. I used a Dremel tool with a smaller diameter disk to finish the slot.

Note that this step was somewhat redundant and should be skipped and replaced with Step 6.

After the bending and base surfaces were finished, the hinges were placed in position, and the two angle irons were clamped together to hold everything in place. Take care when aligning the bending surfaces. The brake will produce inaccurate, crooked beds if the hinges and angle irons are misaligned during this step.

After clamping the hinges and angles, the 5/32" or #21 drill bit is used to drill the holes for mounting the hinges to the base angle. The holes in the hinges are used as a positioning guide for these holes. Next, each hole is tapped using a 10-32 tap. Finally, six 10-32 machine screws are used to secure the hinges to the base surface angle iron.

The process of attaching the hinges to the bending surface is nearly identical. First, the two angle irons and hinges are clamped together, ensuring precise alignment along the bend line.

The six hinge holes are used as a drilling guide for the 5/32" or #21 drill bit, with these holes tapped to a 10-32 thread. Six 10-32 machine screws secure the hinges to the bending surface angle iron. With both angle irons connected by the hinges, the bending alignment can examined by bending the angles relative to one another.

In Step 3, slots were cut into the base angle to allow for mounting of the hinges. However, once the hinges were mounted, I realized that during operation, the machine screw heads on the bending surface side of the hinge would strike the section of base angle above these slots. Solving this problem was as simple as cutting away the portion of the base angle above the hinge (and hinge slot). In other words, the hinge slots were unnecessary, and a simple cutaway of the base angle (for the hinge) is what I should have done in Step 3.

In this step, I also used the angle grinder and cutoff wheel to trim the lengths of the machine screw protruding through the angle irons.

The hold-down clamp is needed to secure the sheet metal being bent. I made the hold-down from a section of 1/2" steel angle, with the length defined by the distance between the inner edges of the hinges (4" in my case). After cutting the angle to length with the hacksaw, a 5/32" or #21 drill bit was used to make holes in each end of one face of the angle.

Next, the hold-down was accurately positioned and clamped to the base surface angle iron. Once again, alignment is super critical here. The hold-down should be positioned such that a slight gap remains between its front edge and the bending surface when this surface is rotated into the bending position. This gap is needed to account for the thickness of the metal being bent. If there was no gap, the metal would bind during a bending. This is more critical as the thickness of the metal increases. Since I would be bending 1mm thick brass (moderately thick), I left the gap slightly below 1mm.

After clamping the hold-down to the surface angle, I drilled the holes through the surface angle, taped them with a 10-32 tap, and secured the hold-down to the surface. Note after drilling through the surface angle, the holes in the hold-down were enlarged to 3/16" in diameter. This operation was done after drilling through the surface to ensure perfect alignment between the holes in the hold-down and the surface angle.

Finally, the hold-down is secured to the bending brake using two 10-32 machine screws.

A handle was needed to provide leverage to the bending surface. I made this handle from a length of 1/2" steel angle iron, which was cut to length using the hacksaw. A second 45° cut was made at the end of the handle to allow it to sit tightly against the inside corner of the bending angle. This is necessary due to the radius on the inside corner of steel angle iron.

The handle was clamped into position relative to the rest of the brake, and the 5/32" or #21 drill bit was used to drill through the handle and bending surface angle. The 10-32 tap prepared the hole for the 10-32 securing machine screw. I mounted the handle slightly on the inside of the one hinge, but it could be positioned differently depending on your needs. A single securing bolt isn't ideal, as the handle can pivot about it relatively easily. However, I found that by sufficiently tightening this screw, it held pretty well.

This was the last step in fabricating the structure of the brake. All that was left to do was paint it and get to bending.

After painting, I secured the brake to my bench using two small wood screws and got to bending.

Each of the 1mm brass contacts requires two 90° bends. As seen in the images, the brake did a good job bending these parts - perfect for my current needs. I wish the hinges had a pivot point closer to the interface line between the base and bending surfaces. The pivot is slightly offset, resulting in more curvature during the initial bend. However, I found that this issue could be corrected by overbending slightly (beyond 90*) and bending the part back to 90°.

I may invest in a better brake in the future, but for now, this thing meets my needs very well.