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Build A Sheet Metal Brake

Sheet Metal Brake

Welcome to my sheet metal bending brake plans post. I’ve used this brake for many years for a wide range of jobs. Although it lacks the features of a commercial brake it also lacks the high price, making it one of my favorite home built tools! I’ve used mine for aircraft components, auto body repair panels, marine, electronics chassis, roof flashing and countless sheet metal projects.

About the “L” angle:
Selection of the 4″x 4″x 1/4″ 90 Deg. mild steel should be done with care. This material
comes in several grades from very rough to finely machined. The choice is dependent on
intended use and building budget.
The prototype was built from scrap yard material, but, this required quite a bit of rust
removal as one surface of each leaf must be smoothed to prevent marking the part being
The tube and plate:
Standard stuff. Mild steel.

Bill Of Materials
Now that you have lugged all that steel into your shop, would you agree that this project is
ruggedly built?

Step One
Mark and cut the mild steel tubing and “C” channel for parts #U1, U2, H1, H2. Drill a
1/2″ hole in H1 as shown.
Step Two
Make a template for part #EP. Lay out the pattern for the end plates (4 required) on your
1/8″ plate. Drill the hole for part #P1. Please take care, as this hole will form a bearing
surface. Check pins for fit and dress as required. Cut out the individual plates and file the
edges smooth.

Part “EP”

Step Three
Select the best part of the 12 ft. 4″x4″ “L” to be used for part #L2.
NOTE – You will notice that the 12-ft. L is slightly on the short side for cutting all three
leaves. Measure your material and allow for cutting losses, this will determine the best
way to cut.

The final dimension between the end plates of L3 should be 48 3/8” plus a
little hinge clearance, this little bit will be compensated for when welding on the end
plates by adding material and grinding flush.

Method 1
If your cutoff (L3) will be 48 1/4” or longer, Cut L2 and L1 as shown.


Method 2

If you find that L3 will be less than 48 ¼”, an alternative method would be to “short” L1
and L3 and equal amount. If you are cutting with hand tools this might be better, welding
will look after any uneven cuts.
Step Four
True the best edge of L2 and file a 1/8 radius along its length. Drill the “sight” holes in
locations that suit your needs and smooth the surface that mates with L1.

Step Five
Test fit parts and prepare for welding. The hold down bolts for L2 will be positioned after
welding. Final position of L2 will vary and can be used to compensate for welding or
material irregularities.

Step Six
Lightly tack weld the parts together and check for proper geometry. Adjust as required
and lightly skip weld, taking care not to heat the work too much. MIG or TIG is
recommended. Grind or file the weld fillet from the upper surfaces of parts #L1 and L3 to
avoid snags.

Step Seven
Position L2 on top of L1 and secure with large C-clamps. Lift the handle slowly and
observe the relationship between L3 and L2. If the gap between these parts is not equal,
adjust L2 and check again. Note this new position and try some sample bends using the
C-clamps as hold-downs.
Step Eight
Check several gauges as well as bend angles to establish what is best for the work you
will be doing. Several different radius setbacks require that several hold down bolts be

Step Nine
When you are satisfied, clamp and drill through L1 and L2 for the hold down fasteners
you have selected. Weld bolts under L1 or tap the table if you wish. The holes in L2 must
fit these fasteners tightly to maintain correct radius alignment.
Step Ten
Remove welding debris, sharp edges, grease, etc. Prime with red oxide primer and apply
two coats of enamel paint. Grease the hinge pins and lightly oil the hold down hardware.
Give the radius and final polishing with fine emery paper and oil lightly for rust
Step Eleven
Install pointers using machine screws or epoxy glue.



At times, when bending large sheets, the hold down bolts will have to be removed. Cclamp
the radius Leaf in position as during assembly.
For box bending you will need to build additional radius blocks or modify the unused
edge of L2 (fig 2A pg.9). Cut notches are required in L2. Locate L2 on L1 as before and
drill for hold down bolts.
(Fig2B) 4″ x 4″ “cut offs” are used in place of L2. A large C-clamp makes a good hold
(Fig.2C) 3/4″ Plywood or hardwood block. This type of pattern bending is well suited for
box making. Wood is an excellent material for short run custom radius work. The radius
can be cut perfectly with a router.

A little imagination and a rubber cord will open the brake at the end of each operation.
Just hook it wherever it works without interference.
Pages 10 & 11 show the basic concept of duplicate parts fabrication using wood patterns.
The block is used to locate bend lines without marking. The block is removed before each

Physical stops can be added for repeat bend angles. This is a simple matter and because it
will vary a great deal from application to application, the builder will find his or her own “best” location and contraption.

“Sight” holes provide for visual alignment of flange depth however, a dowel pin system
could be incorporated as a physical stop.


Sheet Metal Bend Allowance Formula:



Sample Bend 1/8″ radius

Sample Bend 1/8″ radius

Sample Bend


Aircraft Rib and Block

Aircraft Rib



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This entry was posted on Wednesday, March 6th, 2013 at 6:38 pm and is filed under Automotive, Aviation, Machine Shop, Marine, Metal Work, Recreational, Sheet Metal, Welding. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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