We Gonna Rock Down To Electric Ave…

As I described in an earlier post, really all a 3D printer is is a computer-controlled hot glue gun. Another big decision is what computer to use to control the printer. As always in the hobbyist 3D printing world there are lots of options.

First, let’s define what I mean by “computer”. In this case it’s not a tower or laptop that you might be familiar with (although those can and are often used in this manner!). It is a tiny board not more than a few inches long on a side with a special chip called a microcontroller at its heart. All a microcontroller does is keep doing a set of predefined tasks – in this case, it keeps checking for commands sent to it (or changes in input conditions), then does things based on the input.

For a 3D printer, for instance, let us say it receives the command ‘G1 X50 Y25.3 E22.4’. This tells the microcontroller it needs to turn the X-Axis and Y-Axis motors until the print head is 50mm away from the X home position, 25.3mm away from the Y home position and turn the extruder motor until 22.4mm of filament is extruded. The microcontroller then allows power to flow to the motors until the desired positions are reached.

Anything electrical is controlled by this device – the extruder heating element, the bed heater, fans, etc, so this is absolutely a critical piece. Since the hardware it controls is generally quite similar even for different models/manufacturers, most boards differ mostly in the number of inputs/outputs, how much memory they have, what flavor of computer control language they use, etc. This article from the Reprap.org wiki (a GREAT resource for 3D printing info, but since it is a wiki the usual cautions about crowd-sourced information applies) goes into great detail about the different electronics available.

For FrankenCore, rather than go for some specialized (and expensive) alternative, I’m going with what is really the workhorse of the 3D printing world – RAMPS. I’m using this for several reasons: 1) I’m already using it with FrankenPrusa and have never had an issue:

RAMPs

2) Whereas FrankenPrusa runs on 12V, FrankenCore will run on 24V and the modifications to the RAMPS to use 24v are trivial; and 3) I already have a spare RAMPS board in my possession from my failed attempt to get a Kossel (Delta) style printer running.

Build Log

The X and Y axis assemblies have been printed and attached to the frame. Currently I still need to add the majority of the belt guides and run the belts before this segment is complete, but we have linear motion!

I hope the above video gives the idea of how this printer moves vs. FrankenPrusa. Notice how the printbed only moves up and down. This means that the bed ONLY moves when dropping a layer, at which time the x-y axes are still for that microsecond. This should reduce printing errors that result from mis-positioning of the print head due to the cross motion of the bed and head in the other design.

One of the disadvantages of a build like this where there are no “step-by-step” instructions and detailed pictures is that occasionally things are missed – like my math error that resulted in the frame re-cuts. In this case, rather than having a set of 3D files ready for printing like other designs, these parts had to be exported from a source file. Unfortunately, I didn’t realize that the spacers in these assemblies were not combined with the parts, so I have to print these spacers out. However, I think I will actually try to cut these spacers out of aluminum tube to add strength to these pieces.

Next time: The all important first layer and the belts go on, maybe some wiring completed too!

Life in Plastic…It’s Fantastic!

For the majority of Fused Deposition Modeling-type printers, their lifeblood is filament. It’s the raw material from which the electronic dreams of their creators are made into reality. Today I will touch on the major types, and maybe some of the more exotic materials.

By far, the two major types of filament used in 3D printing are Polylactic Acid (PLA) and Acrylonitrile butadiene styrene (ABS). PLA is a biodegradable filament made from cornstarch, sugarcane or tapioca chips. It is a harder plastic than ABS, but has a lower melting point, so applications where strength is needed but the temperature does not get to high are ideal. Because of the materials it is made out of, many users note that it smells like waffles, maple syrup or even French toast when printing with it.

ABS is the same material LEGO bricks are made of. While it seems like it is the toughest plastic in the world when you step on it at 2:30 in the morning, it is actually a soft plastic. However, it has a higher melting temperature than PLA, so is suitable where higher temperatures may exist, but with the understanding that it can’t take as much stress as PLA.

Both PLA and ABS are available in a wide range of colors, even glow-in-the-dark!

Other than PLA and ABS, there are other filament materials out there. Many “exotic” materials are generally powdered and use PLA as their carrier material. Laywood, which use wood particles mixed with PLA is an example. One of the most popular materials after PLA and ABS is Nylon. However, it prints at a higher temperature than even ABS, so an all-metal hotend is almost required to print this material. There are also flexible filaments, metal composite filaments, even carbon-fiber filaments. This page on matterhackers.com is a GREAT resource for learning the different capabilities, uses and printing techniques for the many types of filament out there.

As I alluded to in the previous post, when this printer is built, it will be using PLA and ABS almost exclusively, while FrankenPrusa with it’s all-metal hotend will become my testbed for trying out the exotic materials.

Build Log

The printer is starting to take shape. The aluminum bed came in today and I have mounted the threaded rod and smooth rods the Z-axis will move up and down on and mounted the build plate to the Z-axis carriage.

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This bed was reclaimed from a Lulzbot TAZ printer and while I did have to drill a couple of extra holes for mounting, I was also able to use some of the existing holes.

One of the benefits of doing a project like this is learning new skills or techniques. In order to mount the cantilevered arms to the carriage, I had to learn how to tap a hole. Tapping a hole means cutting threads into it so an appropriately-sized bolt will screw into it. I had never done it before and was kind of trepedatious – I didn’t want to have to cut more extrusion if I messed this up! However, it turned out to be really easy and those arms are not going anywhere.

Next time I’ll start talking about the electronics and the different options available, and I might be able to start the “core xy” part of this build, where I put together the X and Y axis assemblies!

Turn, Turn, Turn

Probably the single most important choice one can make when putting together a 3D printer is the choice of extruder and hotend. The extruder drives the filament into the hotend, which melts the filament, and forces the filament out the other end through the nozzle into a smaller thread, which is then laid down on the build plate. If this component has issues, you will never get a decent print.

For the extruder the most common types are Direct Drive and Bowden. In Direct Drive, the extruder motor sits directly above the hotend (and often the hotend is inserted into the extruder body) so the filament only has to travel a short distance into the hotend.

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FrankenPrusa Mk1 used a Direct Drive style extruder as seen above. The biggest drawback is weight. With the weight of the motor on the carriage, the max speed it can travel is reduced. To get around this the Bowden extruder was developed. In this, the motor and gear is moved off the carriage to a fixed spot usually on the frame of the printer. The filament is usually guided by a tube into the hotend that must remain mounted on the carriage. This reduces the weight on the carriage and allows the print head to move at faster speeds. I recently converted FrankenPrusa Mk2 to Bowden style, as seen below:

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The extruder motor is at the top of the wooden frame. The filament feeds into it from the rear – the black reel sitting in the Home Depot bucket – and feeds down into the hotend. One of the biggest issues with Bowden style is that with the long length of filament from the gear to the hotend there are issues with retraction of the filament. Retraction is necessary to help keep the molten plastic from oozing out of the nozzle. If the retraction is set incorrectly, it can result in the filament being stripped as the gear teeth chew up the filament.

For FrankenCore, I have chosen to use a dual-extruder setup with direct drive motors:

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I can print more complex items in one extruder and print water- or chemical-soluble support structures in the other, print two colors, or even use the same color in both extruders.

As far as the hotend, there are also several type. Most fall in 3 categories, J-head, all-metal and hybrid. The J-Head style usually have a plastic filament guide path. This can cause problems if the heat from the hotend creeps up to the extruder body, which often is printed from ABS, which has a melting point in the 240 – 250deg Celsius range. There is also a limit to the temperature of the hotend, since too hot and the PTFE lining these have will melt inside the hotend. As an alternate, there is the all-metal hotend. Because the entire hotend body is made of metal, there is usually a fan constantly blowing on the “fins” of the body to keep it cool. This prevents heat creep and allows the hotend to run at much higher temperatures some exotic filaments require. Then there is a hybrid. While the body is all-metal, it still has a PTFE liner on the inside. It tends to be lighter than the J-head, but can be cooled easily by a fan.

FrankenCore will use the hybrid – 2 E3D Lite6s for the reduced cost – it’s almost half as much as the all-metal. While I will use the ability to print at higher temperatures, I generally wouldn’t be doing that with this printer. This printer is going to be used to make larger parts, so I’ll be sticking to PLA and ABS. FrankenPrusa has an all-metal hotend, so I will be using that for the exotic filaments and any testing. The FrankenCore will run nozzle sizes nearly twice the diameter of standard hotends. This will allow me to print the large parts faster. I may lose some detail, but that usually won’t matter on these large size prints.

Build Log

Well, Misumi came through and got my new extrusion faster than I expected. After cutting it to the CORRECT length, I assembled the basic frame – see the Featured Image at the top of the post. I have placed a sheet of PEI that will be placed on the build surface that is 12″x12″ to give a size comparison. I have also temporarily assembled the extruder motors and mounts (see previous picture in the article). Looking good.

Next time: Filament – what do all these acronyms mean? And work on the printer continues, with the Z-Axis assembly starting.

When a Problem Comes Along…

When dealing with filament-based printers, while all essentially do the same thing – melt plastic and push it through a computer-controlled nozzle, there are many different ways of accomplishing this and I’ll highlight a few.

Most filament printers can be classified into two groups – Cartesian and Delta. In a Cartesian printer there are three axes, X (left/right), Y (forward/back) and Z (up/down):Axis

Two of the most popular of the Cartesian printers are Prusa i2 and i3 styles, or as I like to call them the A and the L styles because their frames look like those letters when viewed from the side. The picture above is of my original FrankenPrusa i2. It’s a little difficult to make out, but this is essentially an A-Frame which is obvious when viewed from the size. Its biggest disadvantage is the inability to make very tall prints, as the X-axis carriage can only go so high before the angled bars restrict movement. The i3 (or L-shape) removes this limitation by mounting the Z axes to a stiff vertical mount and re-orienting the X-axis rods accordingly. As seen below, this allows for virtually unlimited height, just cut a taller frame and use taller rods.

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The biggest disadvantage to this design is that the head and the build plate are both moving (see the video in my Printing a Printer… post), often in opposing directions at the same time. This simultaneous motion can affect the accuracy of the print, especially if there are a lot of directional changes.

The Delta-style machines were designed to remove part of this extra motion. A Delta consists of three towers arranged 120 degrees apart around a circle in a triangle formation, or like the Greek letter Delta, where it got it’s name. The build plate stays stationary while the three towers move a set of connected arms up and down in coordination to move the print head. One downside to the Delta is the need to convert the Cartesian coordinates in the g-code file to Polar. This requires extra processing power that some of the low-cost printer controller boards just don’t have.

Back in the Cartesian world, the CoreXY design takes out the counter motion by moving the build plate up and down rather than the extruder/hot end and limiting all X and Y motion to one plane. This allows for more precise placement of the print head and is one reason why I selected that style. The other reason is because in my attempt to build a Delta-style machine, I purchased a lot of extruded aluminum and this let me reuse the extrusion, motors, belts, screws and fittings and electronics. The additional materials I needed to purchase were minimal compared to building from scratch.

BUILD LOG

Starting with this entry, I’ll be adding my build log to the end of my main article. Today I put the frame together and quickly discovered something. My design was going to be larger than the reference design in all directions. The G&C uses a standard 8″ (or roughly 200mm) square build plate, while I am using a 12″ (or 300mm) square plate. This means that each dimension will be about 100mm longer to accommodate. While discussing this with the designer, he mentioned that the frame pieces should be 10cm longer. In my head, I translated that to 10mm longer and cut the pieces accordingly. I measured twice and cut once, but didn’t check my conversions twice or do a sanity check. The result means I have to get new extrusion and cut them to the correct size. The featured picture is the initial frame assembly before I noted my mistake. So I am at somewhat of a standstill until I get the new metal in, but I’ll find something I can do.

Next blog I’ll get to the actual extruder and my choices for that most important piece – and maybe more construction!