Extrusion Printing – A Quick Review of Strengths and Weaknesses

A stacked build with 47 parts for a 3D printed outfit.

When someone says 3D printing nowadays, they’re almost certainly referring to desktop extrusion printing of a single material, usually PLA or ABS. I recently did some technical edits for a book on 3D printing, and was surprised to see that this idea is so deeply ingrained in media and culture.  One of the points I emphasize in my 3D printing classes is that most of the weight put into this perspective is due to the marketing from companies trying to push printers or filament. As a consultant that puts me in an odd position when dealing with the consequences. Additive manufacturing has great potential, but it is important not to make statements that lead to false conclusions. Media and marketing often strive to present things with just the right level of evasion that will allow them to avoid taking responsibility for the confusion they create. The purpose of this post is to put, in a nutshell, the most important information that printer companies are not excited to tell you, but are essential to make a proper decision.

1.) Books about printing already assume you have decided to buy a printer, so look at other options first.  In reality you need to look at the size, material, and number of things you’d like to print. Home printing can be fair quality, but if you value your time your are probably not going to see a return on your investment unless you print several object per week for a year or so.

2.) Home printers are great for education, but not mission-critical business applications. DIY printers are designed to be inexpensive and repairable at home. Every business I know using a home model for continuous production has at least two, and a technician to operate and repair. If the printer is in regular operation, this is a busy job, since each printer has an “up-time” of about 60-90%. They are great in a support role for larger machines. When the industrial systems are occupied, inexpensive satellite machines are great for test prints and radically increase efficiency. Most small businesses I see using a single small machine have it sitting cold, for whatever reason, about 90% of the time.

3.) Single extrusion is limited. You can print anything…that doesn’t have an overhang more than about 45 degrees from vertical. Extrusion printers must always print on something, either a base plate or plastic on a previous layer. Many times it just isn’t possible to orient a design to print well. An unsupported section can lead to distortion, bad surface finish, or even a crashed build where your output looks like a pile of plastic spaghetti. Using auto-generated support mars the finish is labor intensive. Sharp tools are often used to remove support, making this method unsuitable for children.  Dual extruder machines often use a soluble support material that eliminates these problems. In fact, while it can waste some material, I have had great luck with stacked builds using these machines. One single build can output dozens of parts, saving tons of labor and set-up time. The 6″x8″x6″ build shown at the start of the article contains all the parts for an entire 3D printed outfit (she’s a petite 4’10, 93lbs).

To lay out and print the parts individually would have taken at least five overnight builds. The above stack was printed in about 40 hours. The pieces were roughly separated afterward to accelerate the chemical support removal process, so the whole job was done in 48 hours. Laser sintering works this way as well, with stacked builds being the norm, but easier cleaning (support is powder, removed with compressed air instead of chemicals).

4.) Outsourcing is usually easier. How many parts are you printing, how large are they? If your answers are “many”, and “small to medium”, do it with extrusion. If it’s a one-off project or cannot fit on a printer you might consider a composite of many prints, but accuracy will be low and labor high, so this is really only a solution if it must be done on a very limited budget. Desktop extrusion can be outsourced, too. Printer networks like 3D hubs enable you to connect with anyone in your neighborhood with a printer, and at $0.25 per cc, they make the creation of small but bulky parts very affordable. Note that by “bulk” I am speaking of overall density and the proportion of volume to surface area. Extrusion has a sweet spot in the middle. Beyond a certain size, outsourcing can overcharge for thick parts because they charge for the space inside, which is often sparsely filled. If you have deal with an individual, try to negotiate pricing based on material and print time.

I use extrusion printing all the time, and it is convenient to have a machine at home if you have the time and space to deal with it. Its great to wake up in the morning and having the part you modeled last night ready to go without missing a beat. If you want that feeling several times a week, or if you just want to tinker with the machine itself, DIY is the way to go. If you don’t have a clear idea of what you would make, and especially if you have not yet developed your modeling skills to make whatever you think of, I’d strongly suggest looking at other options – even other manufacturing methods – that might be better suited to your use and lifestyle.

[Edit – July 2015 – 3D Systems has now released a water-soluble filament for home printing. This type of material has been a challenge to create because home printers are not typically enclosed, making it hard to control the temperature, and therefore expansion, of the two different materials (build and soluble support). Another limitation was the caustic chemicals required. Makerbot has been selling a material that was soluble in limonene (that orange-smelling cleaning solvent), but hadn’t been marketing it loudly since it was tricky to work with. The new “Infinity” material apparently needs only regular water and washes away in about 15 minutes! A huge change from the 10-hour cleanings that have been standard.

This new material is available only in a cartridge for the Cube Pro. I do have access to one, and I am interested to give the new 3D Systems material a try in the coming months.]

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