Homebrew Auto Parts Manufacturing

Sometimes, you just can’t get the right parts from someone else, and have to take matters into your own hands. Whether you need the part now or nobody makes the part you need, you’ll be looking at fabrication. This is the beginning of a series of posts about diy-level parts manufacturing for daily drivers.

For many parts, you can get by rather well with nothing more than store-bought sheet metal, a drill, cut-off wheel (or sawzall), and a rivet gun. If you’re looking to make something more complex (like an intake manifold), you’ll have to go through serious machining and welding, or you could go with composites.


Metalworking is the process of modifying metal to take on a more useful shape. I’ll break it down into three basic types of metalworking, additive and subtractive, and forming. Additive methods (welding) bond new material onto your existing part. Subtractive methods involve cutting material off of your part (machining). Manipulation doesn’t add or remove material, but changes the shape of existing metal.

Machining (basic)

v. To cut, shape, or finish by machine.



Photo courtesy of  NAVFAC under Creative Commons

Consider that a hand drill and hacksaw are both considered machines, and you don’t need a fancy Bridgeport or CNC to start machining. With nothing more than a hacksaw, drill, and a vise, high quality sheet metal parts can be fabricated. This is a common approach to underbody covers, mounting brackets, and blockoff plates. A simple set of hand tools will open up new worlds of capabilities in your garage at minimal cost. For a first-time fabricator, this is absolutely the place to start, and next week I’ll discuss machining sheet metal in detail, with a full walkthrough of a blockoff plate I recently made.



Women Welders, 1943

Photo courtesy of oocha under Creative Commons

Machining involves removing or bending metal, but adding material to metal is another skillset (and toolset) entirely. Your only options to add material to metal are welding and brazing (similar techniques with some important distinctions). It’s an extremely useful skill to have, but you could spend your whole life learning it. In a future article, I’ll go into more detail on the art of electric arc welding with a master welder/fabricator, and get some advice directly from her. For now, just consider it an advanced skill that can yield great rewards.


Side Bender

Side Bender

Photo courtesy of Roberto Cipriano

Forming involves any kind of bending, hammering, and otherwise changing the shape of metal without adding or subtracting material. Nearly any part needs to be formed before it’s ready for use, whether you’re using a sheet metal brake, vise, body hammers, or a hydraulic ram.


Composites have become popular recently, due to their high strength relative to their weight. Manufacturing with composites is a completely different process than metalworking, as you won’t add or remove material. The process essentially involves shaping the fabric, then locking it into shape with an epoxy.


Carbon Fiber

Carbon Fiber

Photo courtesy of the359 under Creative Commons

Carbon fiber, kevlar, and fiberglass are examples of the most common composites out there. Fiberglass is the least expensive, the easiest to work with, and the most economical. It’s perfect for almost all parts. Kevlar (from DuPont) is the most abrasion-resistant of the three, and the most shock-proof. It doesn’t have the strength density of carbon fiber, and isn’t quite as rigid, but its inherent flexibility gives it the ability to absorb harsh vibrations rather than cracking. Carbon fiber is the most sought-after material, because race cars use it. It’s lighter and more rigid than almost all metals, and has excellent thermal insulation properties (perfect for intake ductwork, it’ll keep your cold air cold). It’s also very expensive.

The difficulty with composites is creating a good mold to work from, and we’ll go over both common methods later (creating a reverse mold from an existing part, and creating a mold from scratch).

3d Printing

3d printing is similar to welding, but using droplets of melted materials. It’s an industry that hasn’t fully matured yet, but has exciting implications (especially for the home do-it-yourselfer). With several diy-priced 3d printers available and multiple online manufacturers ready to print your 3d designs, the only thing holding you back from 3d printing parts is your lack of 3d files.

3d Printing

3d Printing

Photo courtesy of David Mellis under Creative Commons

For parts that don’t need to be as physically rugged or precise (like spark plug wire holders, for example), you could use Blender to create a 3d model of the part itself and have that 3d printed. It saves quite a bit of expense and time, and sometimes this is the method I’ll use for test-fitting a part prototype. It’s also invaluable for creating first-run molds to use with composites.

Is it worth it?

On a purely economic scale, fabricating your own parts is not worth the time, money, or skills required. In many cases, designing a part and having a fabricator manufacture it for you is a better option than making it yourself.

On the flip side, fabricating parts can be one of the most satisfying aspects of owning a car. In some cases there is no alternative, where the necessary part simply can’t be sourced. It’s incredibly empowering, and prevents “gumption traps” from stopping a project in its tracks.

More about the Auto Parts

Must-Haves for Every Car

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