work selfie

Building a 3D Printer for Reliability and Safety

Why I'm qualified to speak about reliability and safety

realiably built 3d printer

I have ten years' experience as an Industrial Maintenance Technician. Over the course of my career, I've seen what can happen when well-meaning but unqualified people fail to follow installation guidelines and best practices. I've also been active in the Maker and 3D Printing communities for a long time and come across many "My 3D Printer nearly burned my house down" posts. These are usually caused by low-quality parts and improper wiring procedures.

I've had my own 3d printing business since 2019 and currently own ten 3d printers including an E3D Toolchanger and the Wildbot, which is a corexy that I designed and built myself.

Solid State Relays

For controlling a mains-voltage heated bed, Solid State Relays are preferred because relays with moving internal parts often can't handle the current required. However, when an SSR fails, it will tend to fail shorted. That is, in the "on" position. Your controller will be unable to cut the power from the device and your device will continue to heat up until it catches on fire.

As such, it's important to use high-quality SSRs (Opto-22, Omron, Crydom), in line fuses, and thermal cut offs mechanically clamped to your device. Solid State Relays suitable for controlling a heater for a 3d printer heated bed tend to run $30-$50 USD. However, many online retailers of general merchandise list several SSRs in the $8-10 range. These often carry counterfeit UL logos so be vigilant. This is not the kind of component on which you want to go cheap. Underwriter's Laboratories put out a press release on the subject with instructions on how to spot a fake.

solid state relay

Here is the SSR that controls the 120VAC heated bed on the Wildbot.

  • UL Recognized for safety
  • CSA and CE certified for quality assurance
  • RoHS compliant for hazardous substances
  • Made in USA
burned 3d printer

Thermal Cutoffs and fuses

An in-line fuse will blow and remove power if the 'hot' wire becomes shorted to ground. Otherwise, a shorted hot wire would pull more and more amps until a breaker tripped which may or may not a happen before your wiring starts a fire. Since I used a 120V 200W silicone heater on the Wildbot, I used a 3 amp inline fuse before the SSR. [Fuse rating = (watts/volts)x1.25, using next highest fuse rating after the calculation] So if a ground fault occurs, no AC power will travel past 120VAC panel. See also the section on proper grounding.

A thermal cut off is similar to a fuse but instead of limiting amperage, it 'blows' if heated to a certain temperature. For the Wildbot, I used a 115C thermal cutoff wrapped in a layer of Kapton tape (which provides electrical but not thermal insulation) and clamped mechanically to the build plate. So if the build plate temperature gets above 115C, the TCO will blow and power will no longer be supplied to the silicone heater. This protects against a failed/stuck/shorted Solid State Relay.

Proper Grounding

When dealing with AC (mains) voltage, proper grounding is very important. You want to make sure every part of your machine that can conduct electricity has a very good path to ground so that if a "hot" wire somehow becomes to shorted to that part of your machine and you touch that part of your machine, you don't become the shortest path to ground. My advice is just put ground wires everywhere. There's no such thing as "over-grounding". The Wildbot has green wires all over the place. Also, remember, green is always ground, ground is always green.

Back EMF

On belt-driven systems, your belts will generate some static electricity which will arc over the windings of the stepper motor. This can lead to driver chips failing prematurely. Because of this, it is recommended to ground the casings of your stepper motors.

grounded stepper motor

Proper Connections

Crimp connectors as opposed to solder

Crimped connections are preferred over soldered ones in most instances as soldered connections are rigid and tend to fail when used on components that move. It is important to know how to properly make a crimped connection, however. A big part of it is using the proper tools and choosing the proper terminal.


When using crimp terminals, don't just smash 'em together with your channellocks like a flunkie maintenance man. Use proper crimpers. I use Klein crimpers and I cannot say enough good things about them. These will be the last ones you ever need to buy. But you can buy cheaper ones and they will probably work fine. I'm just a bit of a Klein fanboy.

Bootlace ferrules

You always want to use ferrules to terminate stranded wire. This avoids loose strands that can short out with nearby connections. It also helps get a tight clamp with screw terminals since the strands can't just fan and flatten out. Always use the smallest ferrule that will fit over your wire. At work, I use a set of manual ferrule crimpers made by Knipex because they take up less room in my tool pouch. I prefer the ratchetting kind when doing home projects, though.

Spade/fork/butt connectors

Ground wires that attach via a bolt should always be ring terminals as opposed to fork terminals or, worse, bare wire wrapped around a screw (bad maintenance man). Always use proper crimpers as stated above. These are sized by color so always use the correct size. It's also important to note that crimp terminals should only be used on stranded wire, never on solid wire. On something like a 3d printer, you'll probably only be using stranded wire since you'll have moving components but I felt it worth mentioning anyway.


See NASA Workmanship Standards on crimped connections for more information.

Crimpers for fork/ring terminals.
Crimpers for bootlace ferrules.

Where to get Materials and Parts

In short: eBay but I'll go into more detail. I like high quality parts and tools. However, I'm very frugal. I work hard for my money and I want to keep as much of it as I can. As a result, I've spent a ridiculous amount of time searching various suppliers websites and comparing prices and quality. I'll share the fruit of my labors with you here.

Linear Rails

I used THK brand linear rails for the Wildbot. THK rails are made in Japan and are some of the highest quality rails you can buy. HIWINN is another good brand. These are premium, industrial brands that come with a premium, industrial price tag. The way I found around this is the miracle of “new old stock”. This term refers to parts that are unused and still in the manufacturers packaging but have been sitting on a shelf in some company's supply room and never got used. These will sometimes be models that have been replaced.

For the Wildbot, I used THK RSR12 rails and carriages. The RSR line has been replaced with the SRS (not confusing at all, right?) and because of that, I was able to get my rails for ~$100 per pair as opposed to ~$600 per pair. Also, for industrial rails, used is definitely an option. As long as you buy an industrial name brand, even used industrial rails, when used on a home 3d printer, will probably outlast you. A few of the rails/carriages I bought were lightly used and perform as well or better than the “new-old-stock” rails.

linear rails
**NOTE: Never remove the carriages from the rails.

Cast Aluminum Tooling Plate (MIC-6)

Mic-6 aluminum tooling plate is the best material for your build plate, period. It's extremely flat and conducts heat really well. Also, it's pretty. Let's get into some crunch before you guys revoke my man card for calling something pretty.


Each side is machined to a maximum 20 microinch or 0.50-micron smoothness. The tolerance for any thickness is ±0.005” /±0.127mm. Maximum deviation from flat: Specified plate thickness maximum variation: 3/4” and over: .005” / 19mm and over: .127mm 1/4” to 5/8”: .015” / 6mm and over: .381mm I love me some crunchy data. You don't have to understand the data. Suffice it to say MIC-6 is very, very flat. It doesn't get any better than this for a build plate on a 3d printer.


The best way I've found to cut aluminum tooling plate is with a tablesaw but I've also used a jig/sabersaw. You can clamp a bar or straight-edge to it to make a fence to keep your cut straight. One note: Don't lift the saw off your material until the blade stops or it will break your blade. Don't ask me how I know that. I buy Bosch jigsaw and bandsaw blades.

If you need to mill your aluminum, use two-flute endmills. Aluminum is kind of “gummy” and tends to stick to a four-flute end mill so you end up cutting through your chips. Two-flute end mills are much better for chip clearance. For keeping your cutter cool, a lot of machinists use kerosene when cutting aluminum. Mineral spirits works fairly well, in my experience but I'm no machinist so I'm sure someone will come along and tell me how wrong I am. For endmills, Niagara Cutter makes some of the best cutting tools on the market.

Where to Buy

Hopefully, you didn't go and google where to buy MIC-6 before you finished this article. If you did that you probably saw the high price tag and closed my website. We just need relatively small pieces of it for our 3d printers. There's a lot of sellers on eBay selling remnants for ~$20 or so. I've bought several pieces from eBay seller USA Metal Online. I highly recommend them. If you're like me, go ahead and order two plates so you don't have to wait on a new to be delivered when you wreck the first one. Also, I covered my MIC-6 plates with painter's tape to protect the surface while I was cutting them out. Aluminium is soft so be careful with clamps.

mic 6

Useful Resources