How a butterfly shoves, or the complexity of a simple extruder

Good day to you, dear geeks and sympathizers! According to the results of the voting in my previous publication I want to start a series of publications about the construction of a simple and inexpensive, but fast and reliable 3D printer.

Why not just buy? The reason is simple: none of the affordable printers (up to 300 euros) do not have the required amount of parameters out of the box, and the idea of ​​buying a device with the need for significant rework did not inspire me too much.

Since the description of the construction of the entire printer will require too many letters and other characters, I will describe its functional blocks separately. With this approach, it is possible to describe the features of individual components of a structure much more deeply.

The most important part of the printer, namely the hot end, I described in my previous publication. It is time to move on to the most controversial knot: the extruder drive.

So, let's begin. Some lyrics: I dreamed of a fast printer. Observations on the ordeals of fellow enthusiasts convinced me that dragging the extruder drive mechanism along with the motor, although the end and fan with accelerations up to 10,000 mm / s² and speeds up to 200 cm / s is a bad idea, and therefore was appointed the savior of the giant of thought bowden extruder. The principle of operation is simple: a drive rigidly fixed on the frame pushes the filament through a long fluoroplastic tube at a hot end. The advantages of this type of hotand are related to the relief of the actual printing unit: less load on the supporting tires, motors, bearings, less vibration, etc. There are also disadvantages: additional resistance for the filament, worse response to changes in the feed rate of the filament, difficulties with adjusting the retraction , etc.

There are many models of extruders on the market, why bother with creating your own design? And then, so that the extruder satisfies the following requirements: compactness, simplicity, accuracy, reliability.

Compactness and simplicity: it is necessary to exclude the reducer from the design of the extruder drive by switching to a direct drive (gear directly on the shaft of the stepping motor). In addition, I excluded the clamping mechanism with springs. In this case, I was guided by the following considerations: for sufficient adhesion to the filament, the teeth of the drive wheel should be immersed in the filament material, when using a spring clamp, the immersion depth depends not only on the elasticity of the springs, but also on the temperature and type of the filament. If the clamp is set firmly, the teeth will always sink to the same depth, which will reduce the risk of the gear to slip and stop printing. To increase the moment of force applied to the filament, take the gear of the minimum diameter, at the moment it is MK8. What kind of effort can a regular NEMA17 develop with such a wheel? For example, take a motor with a torque of 0.5 Nm. What does this number mean? The easiest way to explain this is as follows: if a weightless wheel with a radius of one meter is attached to the motor axis, the motor can develop a thrust of 0.5 Newton on the rim of the wheel (approximately corresponding to the force of gravity acting on 49 grams of mass near the surface of our planet) . This is frustratingly small. The situation changes radically if we take the effort off with a significantly smaller radius. Premier for MK8: diameter on teeth 7 mm, respectively, radius 3.5 mm. 5 Newton, (approximately corresponds to the force of attraction acting on 49 grams of mass near the surface of our planet). This is frustratingly small. The situation changes radically if we take the effort off with a significantly smaller radius. Premier for MK8: diameter on teeth 7 mm, respectively, radius 3.5 mm. 5 Newton, (approximately corresponds to the force of attraction acting on 49 grams of mass near the surface of our planet). This is frustratingly small. The situation changes radically if we take the effort off with a significantly smaller radius. Premier for MK8: diameter on teeth 7 mm, respectively, radius 3.5 mm.

The force on the teeth will be as high as 3.5 mm less than the notorious meter. 1000 / 3.5 ≈ 285 times. Let's see what it will give us: 0.5 Nm * 285 = 142.5 Nm or conditional 13.965 kg of thrust. As they say, no comment. Of course, in microstepping mode, this figure will drop to 99.75 Nm and 9.775 kg, respectively. These calculations are valid only for high-quality engines, in the case of Chinese engines, these numbers can be safely halved or even divided into three.

Accuracy. What should be the accuracy of the drive? Let's calculate the necessary accuracy for an absolutely standard case: the nozzle size of hot-end is 0.3 mm, printing with a layer of 0.1 mm, printer resolution of 0.1 mm in all axes.

The ratio of 1.75 mm filament to a diameter of 0.3 mm nozzles of the hot end: 34.03. That is, in order to obtain 0.1 mm extrusion from a 0.3 mm diameter nozzle, it is necessary to push 0.1 / 34.03 = 0.00294 mm of a filament with a diameter of 1.75 mm into the hot end.

Gear MK8: notch 7 mm in diameter, circumference 22 mm.
The number of steps for gear MK8 to provide extrusion with a length of 0.1 mm from a nozzle 0.3 mm: 22 / 0,0171 = 7483
The standard number of steps of a stepper motor: 200

Required microstepping: 7483/200 = 37.415. We round to the nearest standard value, i.e., to 32. Of course, some inaccuracy will be present, and it is better to apply 1/64 microstepping. If the driver is not capable of this feat, you can use the motor with 400 steps per revolution.

UPDATED: The above calculations have been checked and adjusted on the basis of a benevolent and constructive criticism and comrades mdsa Andy_Big, for what they are great thanks :)

So, all of these estimations and calculations led to the creation of the next prototype:



It should be noted that in the prototype used gear MK7 for, judging by the delivery time, the MK8 Chinese carried me on foot, overcoming the hardships, deprivation, smooth and cold.

It is a pity that the photo of the all-metal proto-prototype, with the help of which the plastic part of the prototype was printed, was not preserved.

With the help of this prototype, a working version was made:



My imagination sometimes beats a fountain, and in the outlines of a plastic part I saw a butterfly.

The extruder has acquired the proud name of the Schmetterling Extruder. It sounds like a title for some Rammstein song.

I have already quoted the video of this version in a publication about hot end:


Scheme of the design (I really love PeZhE DesignSpark Mechanical):



I think this picture needs no explanation. Bolt for fixing the bearing: M7 or M8, the main thing - a fairly flat hex or square head. Depending on the inner diameter of the bearing, a thick sleeve may be necessary to prevent play between the bolt and the bearing. Without a sleeve, everything will hang out, no puff will help. Why is the bearing so big (outside diameter 30 mm)? This is due to the design of the NEMA17 stepper motors, they have a protruding ring on the front flange, which does not allow the bolt head to move closer to the axis.

After that, quite a lot of water flowed, the butterfly's entrance channel wiped endless filament meters, and an improved version was created:



Since it is not interesting to have an extruder and not to print, I type. For example, the case for the Chinese audio DAC from PETG printed. Why do I need it? The laptop in the workshop completely refuses to produce sound through the standard connector, the motherboard has partially died out. I buy greedily for new, and it was interesting to try a separate DAC.



The red arrow shows the power harmonizer. Of course, many will say that this power harmonizer is very similar to a simple inexpensive (2-3 euro in Germany) surge protector with inductances and condensers, but we all know the truth: only magic with a price of two kiloboxes is able to provide power to the device for creating a sound worthy of the delicate ears of all sorts of audiomaniacs.

The magnificent laurels of the myth-destroyers do not give me rest, and I decided to conduct tests. And not just tests, but tests of fractal diffusers. The extruder never stuttered, and the diffusers came out just great: The



yellow color hints at the little gold and thus emphasizes the premium and the elitism of the product. Frankly, I did not expect such a powerful effect: when installing the diffuser on the DAC lid, the sound changes so dramatically that it seems that the other person is singing. This is magic, gentlemen. The video confirms the effect:



To enhance the effect of the use of diffusers, I installed self-printed spikes on the bottom of the case. The effect is obvious: at last, the flies that are firmly sitting on the table have ceased to create the “booze” effect in the columns. To finally make sure of the highest quality of spikes, put the car on the device:



It is seen that the thorns withstood the test. Of course, the car is a toy, so the thorns are from PETG (it was impossible to get anoptanium).

A small bonus for those who have read this far, a convenient case for the popular GM328 tester:





A battery charge control module and a boost converter (the tester operates at a voltage of 9V) are glued to specially designed places.

→ Here is a folder with 3D models.

Published under the WTFPL license.

Well, and traditional: Have fun!