Evaluating the Monoprice MP Select Mini with the Kickstarter/Autodesk Test Print

These days, if you are in the market for a 3D printer, you have no shortage of choices. There are hundreds of different 3D printers from which to choose. With printers spanning a huge range of prices and taunting a laundry list of different features and specifications, it can be very difficult to fairly assess the relative performance and cost-to-performance of different printer options.

For other tools we have common methods for evaluating the performance of different products from different companies. For computers we have benchmarking tools, for 2D printers we have test pages, for cars we have fuel economy, crash test ratings, and standardized feature nomenclature. For 3D printers, there are some common testing procedures, like 3DBenchy, but nothing that can truly be called a universal rating system. A good universal rating system will generate a quantitative score from a testing procedure allowing a standardized comparison among different product options.

Kickstarter, a platform that has helped launch hundreds of 3D printers, and Autodesk, a software company that makes a variety of tools used by millions of 3D printer operators, have recently teamed up to solve this issue by creating a test print and associated grading procedure. 3D printer companies or 3D printer operators can use this procedure to generate a score for their printer and compare it with other printers.

Source: https://github.com/kickstarter/kickstarter-autodesk-3d

For the past couple months, I’ve been putting my new Monoprice MP Select Mini 3D printer to work on all kinds of prints.  It has been doing a good job in all of my projects so far, especially considering the very low price. However, I’ve never had a way of objectivly comparing the Monoprice MP Select Mini against other 3D printers I’ve used in the past or against prints I’ve received from services like 3D Hubs that were printed on other printers.

So, with the goal of uncovering the relative strengths and weaknesses of the Monoprice printer compared with others, I downloaded the Kickstarter/Autodesk test geometry from the GitHub repository and let the MP Select Mini take a crack at it. Below is the evaluation of the finished print based on the assessment protocol from the GitHub page.

For reference, the print was done with a layer resolution of 0.2mm. The Select Mini is capable of printing with a layer resolution of 0.1mm but I do most of my work in 0.2mm for the speed advantage. Wanting to test the printer’s performance using the setting I most commonly use, I chose a resolution of 0.2mm for the test print. I used a fresh roll of 1.75mm green PLA from Hatchbox. The test print was the first done with the brand new roll of filament ensuring minimal moisture in the plastic. Last, I did not perform any calibration on the printer prior to completing the test print. All the calibration on the printer was present out of the box.

1. Dimensional Accuracy

On one corner of the test geometry there is a stack of cylinders of decreasing diameter. To assess the dimensional accuracy of the test print, the actual diameters of these cylinders are measured and compared to the real diameter. Based on the average dimensional error, the printer is given a score from 1 to 5 (5 being the best score denoting the highest dimensional accuracy):

• Record a “1” if the magnitude of the overall average error is greater than 0.40mm.
• Record a “2” if the magnitude of the overall average error is between 0.31 and 0.40mm.
• Record a “3” if the magnitude of the overall average error is between 0.21 and 0.30mm.
• Record a “4” if the magnitude of the overall average error is 0.11 and 0.20mm.
• Record a “5” if the magnitude of the overall average error is between 0.0 and 0.10mm.

The table below shows the measured diameters of the cylinders on the X and Y axes.

This level of dimensional accuracy earned a score of 4.

2. Fine Flow Control

There are a set of nine spires on the top of the test print. These are used to evaluate a 3D printer’s ability to control the flow of plastic material out of the hotend and to control retraction.

• If the spires are less than 30mm long, assign a 0.
• If the spires are greater than 30mm, but there is stringing between them, assign a 2.5.
• If the spires are greater than 30mm long and there is no stringing between them, assign a 5.

The shortest spire on the test print produced by the Monoprice MP Select Mini was 35mm tall. However, there is some stringing among the spires. Therefore, the printer earned a score of 2.5 for this test.

3. Fine Negative Features

Along one side of the test geometry, there are a series of pins in holes. The pins have smaller diameters than they holes in which they are printed. Therefore, the pins should, in theory, be removable from the holes after printing. The fives total pins have progressively smaller gaps between the pin diameter and hole diameter. A 3D printer with poor fine negative detail reproduction will lock the pins in place as a result of errors in the size of the hole, the pin, or both.

• Record a “0” if no pins can be removed.
• Record a “1” if 1 pin can be removed.
• Record a “2” if 2 pins can be removed.
• Record a “3” if 3 pins can be removed.
• Record a “4” if 4 pins can be removed.
• Record a “5” if all pins can be removed.

Four pins were removable from the test print produced on the Monoprice, all but the pin with the smallest tolerance. For this test, the Monoprice MP Select Mini earned a score of 4.

4. Overhangs

Since this part was printed without support material, there is a section of the print, in the middle of the part, with overhangs that gradually approach horizontal.

• Record a “1” if the printer compiled the geometry but dropped loops and infill on the 15, 20, and 30 degree overhangs.
• Record a “3” if only the 15 and 20 degree surfaces differ from the 45 degree overhang.
• Record a “4” if only the 15 degree overhang differs from the 45 degree overhang.
• Record a “5” if there the surface finish between all four overhang surfaces is equivalent.

For a 3D printer lacking a dedicated part cooling fan, the Monoprice MP Select Mini performed well in this section. The 15 and 20 degree sections showed some separation of the layers resulting in a score of 3 for this section.

5. Bridging

On the side of the test print opposite the cylinders used to evaluate dimensional accuracy, there are a set of brides.

• Record a “1” if more than 3 are in contact with the surfaces beneath them.
• Record a “2” if 3 bridges contact the surfaces beneath them.
• Record a “3” if 2 bridges contact the surfaces beneath them.
• Record a “4” if 1 bridge contacts the surface beneath it.
• Record a “5” if no bridges contact the surfaces beneath them.

On the print produced by the MP Select Mini, the first three bridges do not show any contact between the lower bridge for each, and the lower surfaces of the bridges were smooth. The fourth bridge did not contact the third, and the lower surface is mostly flat. For this section, the printer earned a 4.

6. XY Resonance

Along one edge of the test print, there are a series of hash marks. These marks are used to evaluate the presence or lack of ringing. Ringing in a 3D print results from constructive feedback in the horizontal axes resulting in a wavy pattern on vertical faces of the print. The type of filament used for this test print is slightly translucent, rendering the internal structure of the print slightly visible on the outside. There is, however, no ringing on the part, meaning that, for this section, the Monoprice MP Select Mini earned a score of 2.5.

7. Z-axis Alignment

Under the platform on which the spires used to test fine flow control were printed, there is a vertical column used to evaluate the printer’s Z-axis alignment. A printer with a well-aligned Z-axis will produce layers of the same size stacked directly on top of each other. On the other hand, a printer with a badly aligned Z-axis will show periodic ripples similar to the XY alignment test. The Monoprice MP Select Mini demonstrates good Z-axis alignment so it earns a score of 2.5 for this section.

Scoring

The overall score for the test print, which can be used to compare the performance of the Monoprice MP Select Mini against other 3D printers, is computed by summing the scores for each individual section. The highest possible score is 30.

• Dimensional Accuracy 4
• Fine Flow Control 2.5
• Fine Negative Features 4
• Overhangs 3
• Bridging 4
• XY Resonance 2.5
• Z-axis Alignment 2.5

The Monoprice MP Select Mini 3D printer earned a very respectable score of 22.5.

For a printer costing under $200, the Monoprice Select Mini 3D printer performed remarkably well on these tests. According to the GitHub repository housing the Kickstarter/Autodesk test print, a score of 22.5 matches the Prusa i3 MK3, which is an extraordinarily well-reviewed and popular printer. Considering that the MP Select Mini is less than one third the cost of a Prusa i3 MK3, however, its performance per dollar is extremely impressive. There are several metrics for a 3D printer’s performance that are not tested by the Kickstarter/Autodesk test geometry, like overhang capabilities over a range of features, surface finish, printing speed, and support structure interaction. But, for the print quality factors evaluated by the print, the Monoprice MP Select Mini performed as well as printers costing many times more.