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!