Custom CNC Brackets

Should a custom bracket be machined or laser cut and bent?

Custom machined brackets are CNC milled from plate or bar, and the print usually shows why: a bore that sits a set distance from the mounting face, a hole pattern located from a face at right angles to it, a pocket that saves weight next to a boss that takes a bolt, or a seat for a pressed bearing. Those features have to be cut. A tab with two holes, an L with one bend or a cover plate has nothing a bend cannot hold, so it is usually cut and bent. The quote recommends a route rather than pricing only the one you asked for.

The difference is how a bend is toleranced. Sheet varies in thickness: typical 10-gauge A36 runs ±0.006 in, anywhere from 0.129 to 0.141 in, and in an air bend that alone can swing the angle by as much as 4 degrees (source 1). The same article calls a 0.005 in tolerance on a formed part just about impossible for many press brake operators, especially across several bends, and asks what a part would lose if its formed tolerances were opened to ±0.010 in, or even 0.020 in, and its angles to 1 or 2 degrees. The more bends a part has, it says, the more variation it should allow (source 1). A machined face or hole is cut to its dimension rather than formed, so it carries the machining tolerance instead. When a hole has to sit a known distance from a bent flange, that distance inherits the bend’s variation. Either the bracket is machined, or it is cut and bent and that hole is machined after forming, located from the bent part, on the same order; secondary machining on laser-cut parts covers that route.

The sheet route in full is on custom laser-cut brackets and mounts, and bend radius, reliefs and how close a hole can sit to a bend are on laser-cut and bent brackets.

Which custom mounting brackets get made to print?

Most fall into five shapes. A flat mounting bracket or mounting plate locates a motor, sensor or sub-assembly against a known face. An angle or L-bracket joins two planes and takes its load at the inside corner, where a fillet in place of a sharp corner spreads the stress over a wider area (source 2). A gusset bracket adds a triangular rib across that corner. A motor or actuator mount carries a pilot bore and a bolt pattern. A billet bracket is cut from one block in place of a part that used to be welded from several pieces.

Cutting a bracket from solid removes the weld, and in 6061 the weld is the weak spot: after welding, the metal near the weld has the properties of 6061-T4, a loss of strength of around 40% (source 3). Brackets that stay welded into a steel frame are the other common case, and machined details for weldments are covered on machined parts for fabrication and welding shops.

A replacement for a bracket that broke, or a single bracket nobody stocks, has its own page: replacement and one-off brackets. A plate drilled on a grid of tapped and dowel holes to hold parts during machining or assembly is a fixture plate rather than a bracket, and it is on aluminum fixture plates.

Custom metal brackets: aluminum, steel or stainless?

Start custom aluminum brackets in 6061-T6, and move to 7075 when a 6061 bracket has bent, since 7075-T6 yields at nearly twice the stress (sources 3 and 4). Do not move to 7075 because a bracket flexed. How far a bracket flexes under load depends on the modulus of its material and the second moment of area of its section (source 5), and for a rectangular section that moment grows with the cube of its depth (source 6). The table below shows 6061 and 7075 are almost equally stiff, so a bracket that deflects too much in one deflects nearly as much in the other. Stiffness comes from a deeper section, a rib or a gusset, or from steel, which is nearly three times as stiff as any of the aluminum grades (sources 3, 4 and 7). 7075 is also vulnerable to stress corrosion cracking (source 4). The 6061 vs 7075 comparison covers the rest of that choice.

5052-H32 is the sheet grade for the bent route, with strong resistance to seawater and salt spray (source 8). Hydro’s bending guide calls 5052 a popular choice for sheet metal work where bendability and corrosion performance both matter, and says the bending ability of 6061 drops significantly in the T6 temper (source 9).

Steel suits a bracket that gets welded into a frame, since A36 is readily welded by all welding processes (source 7); 1018 and 4140 bar cover machined steel brackets, and the grades are on the steel page. 304 stainless resists a wide range of atmospheres and is used in food-handling equipment, which covers washdown and outdoor mounts, but it can pit in warm chlorides (source 10). That is where 316 takes over: its added molybdenum resists chloride attack, and it is used in marine applications (source 11). Delrin (acetal) is stiff for a plastic and low in friction (source 12), which suits a bracket that a shaft or slide runs against. Other alloys and plastics quoted on request. Name the grade on the print.

What finish and hardware should a bracket have?

On an aluminum bracket, Type II (sulfuric acid) anodize adds corrosion and wear resistance, and the coating can take a dye, which is where black and colors such as blue come from (source 13). Each surface grows by about half the coating thickness, so mark a bore that has to fit after finishing (source 13).

Powder coat suits steel and any bracket that needs a durable color: a dry powder applied electrostatically and cured under heat, leaving a thick, tough film more durable than conventional paint, and a smooth film may need a build of more than 50 micrometers, about 0.002 in (source 14). Passivating a stainless bracket removes iron left on the surface and restores the oxide layer that keeps it from rusting (source 15). An aluminum or stainless bracket that lives indoors can also be left bare. A finish called out on the print is quoted with the part. The brackets come back finished.

A sheet bracket can take threads from self-clinching fasteners installed into a round punched or drilled hole. PennEngineering puts the usual minimum sheet at 0.030 in (0.76 mm) or 0.040 in (1 mm) and needs the panel to be a ductile material softer than the fastener (source 16), so put the hardware part number on the print rather than a note that says "PEM nut". Where the section is thick enough, a machined bracket takes a tapped hole directly. Callouts and part numbers are on hardware insertion.

What should a bracket print show?

Start with the datums, the faces the bracket mounts from, and dimension the holes from them. A position tolerance on the hole pattern says what the bracket has to do, and GD&T can allow over 50% more tolerance zone than plus-and-minus coordinate dimensions in some cases (source 17). Position, perpendicularity and runout callouts are quoted from the print. Then mark every hole tapped or clearance with its thread, show any adjustment slots, and write the grade with its temper (6061-T6, not just aluminum) and the finish.

Draw inside corners on a machined bracket with the largest radius the design can take, not a sharp corner. On a bent bracket, give the inside bend radius, the angle and the direction of each bend. The inside radius is quoted as drawn, with a note if it won’t form.

Add one line on the load. A note such as "holds a 25 lb gearbox, 6 in out from the mounting face" tells the team which section matters and catches a thin web before material is bought.

A fully dimensioned 2D PDF is quoted without a CAD line. No model or drawing yet? A dimensioned sketch, a photo or a new sample bracket can start a quote. The sample ships back with the parts. CAD from a sketch or sample is quoted as its own line, and reverse engineering covers remaking a part from the part itself.

How are quantities and repeat runs quoted?

How a single part of any kind is priced is covered on one-off CNC machining. Past one piece, the per-piece price drops as quantity rises, because setup is spread across more parts. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each.

A bracket that reorders on a schedule can go on a blanket order: one quoted quantity, delivered in releases. Price, release schedule and lead time per release are set in the quote. Reorders at the same revision: send the last quote or PO number and it’s requoted.

Sources

All accessed 27 September 2026. Where a figure here differs from your print, the print governs.

1. Tim Heston, "Reasonable tolerancing for press brake bending", The Fabricator, 11 September 2018: thefabricator.com (10-gauge A36 at ±0.006 in, 0.129-0.141 in; up to 4 degrees of angular variation; 0.005 in on formed parts; ±0.010 or 0.020 in and 1 or 2 degrees; tolerance loosens as bends are added).

2. Wikipedia, "Fillet (mechanics)": en.wikipedia.org/wiki/Fillet_(mechanics) (fillets distribute stress over a broader area).

3. Wikipedia, "6061 aluminium alloy": en.wikipedia.org/wiki/6061_aluminium_alloy (T6 at least 290 MPa ultimate and 240 MPa yield; modulus 69 GPa; near-weld properties those of T4, about 40% loss).

4. Wikipedia, "7075 aluminium alloy": en.wikipedia.org/wiki/7075_aluminium_alloy (T6 510-540 MPa ultimate, 430-480 MPa yield; modulus 71.7 GPa; vulnerable to stress corrosion cracking).

5. Wikipedia, "Deflection (engineering)": en.wikipedia.org/wiki/Deflection_(engineering) (cantilever end-load deflection FL³/3EI, with E the modulus of elasticity and I the area moment of inertia of the section).

6. Wikipedia, "Second moment of area": en.wikipedia.org/wiki/Second_moment_of_area (rectangle I = bh³/12; resistance to bending as a function of shape).

7. Wikipedia, "A36 steel": en.wikipedia.org/wiki/A36_steel (at least 36 ksi yield, 58-80 ksi ultimate; readily welded by all welding processes; modulus 200 GPa).

8. Wikipedia, "5052 aluminium alloy": en.wikipedia.org/wiki/5052_aluminium_alloy (H32 228 MPa ultimate, 193 MPa yield; modulus 69.3 GPa; resistance to seawater and salt spray).

9. Freddy Leijon, "Here are the best aluminum alloys for bending: a complete guide", Hydro, 13 January 2021: shapesbyhydro.com/en/knowledge/here-are-the-best-aluminium-alloys-for-bending/ (5052 for sheet metal work where bendability and corrosion performance matter; 6061 bending ability drops in T4 and especially T6).

10. Wikipedia, "SAE 304 stainless steel": en.wikipedia.org/wiki/SAE_304_stainless_steel (resistance to a wide range of atmospheric environments; food handling equipment; pitting and crevice corrosion in warm chloride environments).

11. Wikipedia, "SAE 316L stainless steel": en.wikipedia.org/wiki/SAE_316L_stainless_steel (molybdenum for resistance to chloride attack; marine applications).

12. Wikipedia, "Polyoxymethylene": en.wikipedia.org/wiki/Polyoxymethylene (used in precision parts requiring high stiffness, low friction and dimensional stability).

13. Wikipedia, "Anodizing": en.wikipedia.org/wiki/Anodizing (Type II is sulfuric acid anodizing; corrosion and wear resistance; porous coatings absorb dyes; each surface grows by half the oxide thickness).

14. Wikipedia, "Powder coating": en.wikipedia.org/wiki/Powder_coating (dry powder, applied electrostatically, cured under heat; a thick, tough finish more durable than conventional paint; film build-ups over 50 μm may be required for a smooth film).

15. Wikipedia, "Passivation (chemistry)": en.wikipedia.org/wiki/Passivation_(chemistry) (removes exogenous iron and restores the passive oxide layer on stainless steel).

16. PennEngineering, "FAQ": pemnet.com/resources/faq/ (0.030 in / 0.76 mm or 0.040 in / 1 mm minimum sheet; panel ductile and softer than the fastener; round punched or drilled hole).

17. Wikipedia, "Geometric dimensioning and tolerancing": en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing (over 50% more tolerance zone than coordinate dimensioning in some cases).

18. Wikipedia, "Stepper motor": en.wikipedia.org/wiki/Stepper_motor (NEMA 17 is a 1.7 by 1.7 in faceplate; NEMA ICS 16 covers stepper motor dimensions).