Introduction: Under $50 Monoprice Select Mini to "Mega"

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About: Mechatronics Major

Warning this guide is intended towards the more advanced modder and very mechanically inclined. I completely advise against attempting this mod if you have never taken your printer apart before.

That being said this mod is for those who are looking to upgrade the printing surface area on a budget. In this instructable I'll be showing you how I increased the print area to about 210mm x 210mm from the standard 120mm x 120mm. In this guide you will find mention of various mods I have installed to get to the point I am at. I will not go into large detail on these mods, rather I will direct you to the source of information for your own use. I would also like to inform you that this is more of a "loose" guideline, since many people have different tweaks already and they may not want to completely copy my setup. One good thing about this mod is that as long as you do not damage any components during disassembly, you can simply revert back to the original setup. I do encourage you to complete read the entire instructable and get absolute clarity on the endeavor you are about to undertake before starting the mod yourself. This has been a very painstaking process to document as well as my first instructable. With that being said if you have any questions or need elaboration on anything please let me know.

Here is a list things you should know or have before proceeding.

  1. Pre-Printables that are required before start
  2. Knowledge
    • the ability to fix electrical connections(solder, tape, sleeves, heat shrink)
    • how to disassemble the printer
  3. Tools
    • Aviator or sheet metal snips
    • Multi-meter( in case something doesn't work after being put back together)
    • Soldering Iron w/ accessories
    • Various hex bits for a driver
    • Wire cutter/stripper
    • Drill bits
    • Metal forming tools

Step 1: Materials and Sourcing

The following is a list the of "core" materials you will need to complete this mod. There are various tools, paint, and fasteners that i have not included in material list. These choices are up to user preference. All pricing and sourcing are current as of the publish date. I can not guarantee future availability or pricing accuracy.

This brings the total to $38.93 ( does not include shipping)

Step 2: Disassembly of the Printer

This section is going to be brief as it has been well documented before. Here is a link for further instructions.

Step 3: Fabricating the Base Plate

After disassembling the printer you are going to need to fabricate a new base plate to support the new print area.

Here is quick summary of how I made the base plate.

  1. Using 1pc of angle I cut "v" notches and then bent the angle 90° at every cut. The dimensions I used for the shape was 240mm(X-axis) X 303mm(Y-axis). As you can see in the first two pictures.
  2. I then traced the perimeter of my formed angle onto the 26ga galvanized steel. (as seen in picture 3) I added 3/4 in. all the way around to account for covering the angle framing completely.
  3. Using tin snips I cut the excess metal off. and the proceeded to use the original trace lines as break lines. So flange all sections in the same direction.
  4. After you finish, you will be left with a pan. Take this pan and fit it over the angle you made earlier as seen in picture 5.
  5. Now you can join/fasten the cover to the angle. I use rivets as seen in picture 6, but you are more than welcome to use whatever method you think is best. [WARNING: make sure that whatever method you decide to use will not interfere with the mechanics of the printer]
  6. I finished my base off with a few coats of this.(as seen in picture 6) This is completely optional.
  7. I also include pic 7 for size comparison.

Step 4: Fabricating the X and Y Axis Expansion Rods and Installing

  1. Your going to want both rods for the y-axis to be 300mm in length. You can order these to exact length from the link i provided in the materials section.
  2. for the x axis your going to cut the shorter one at 290mm(bottom) and the longer one at 340mm(top)
  3. After the rods are cut to length simply swap them out with the old ones make sure to install the y axis brackets before proceeding to install the base plate.(shown in picture 4)

Step 5: Installing the Base Plate

Before installing the base plate you need to transfer the holes from the old plate as shown in the first two pictures that way it does not interfere or catch on to any of the undercarriage mechanisms. At this point you will want to install your bed leveling screws as well. I templated these holes from the mk2b heater board.The next two photos show that I installed mine in a 3 point triangle formation which makes leveling a whole lot easier in my mind compared to the 4 point system that comes standard with the printer. The last few images show how the glass I cut is secured to board by fitting snugly underneath the leveling screws. Make sure the heated bed is installed within the range of your hot end on both the x and y axis!! This is very crucial to ensure you have maximum print area.

Step 6: Installing the Timing Belts

Using the adjustable belt tensioners you printed out before hand cut some new belt and install utilizing the clips. This should be pretty straight forward utilizing the provided pictures.

Step 7: Testing

After all of the hardware components are installed, reconnect the electronics and test to make sure everything is in working order. The following are the steps I would take:

  1. Connect every component back to the controller board. The printer does not have to be fully assembled.
  2. Power the printer on.
  3. Verify LCD is reading normally
  4. Go to manual movement
  5. Check the y axis full range including endstop detection
  6. Do the same with x axis
  7. Do the same with z axis
  8. Check extruder including retraction
  9. Do a preheat cycle on both hot end and bed
  10. Verify thermisistors are working properly
  11. Verify cooling fan is working
  12. Do a home test

Step 8: Final Touches

If your electronics test went well proceed to reassembling your printer and congratulations on becoming a new monoprice "mega" owner. Here are a few things you need to keep in mind.

  1. You will have to update the print area inside your chosen slicer since your bed size has changed.
  2. Make sure you oil/lube the linear rods.
  3. Make sure the belt tension is adequate.
  4. The adjustable z axis endstop I recommended printing at the beginninging of this guide is used for solving any z axis height issues you may have due to bed height changes.

If you any questions or concerns, any at all feel free to message me here or message me thru mod mail on this Subreddit. We are a very active and welcoming community focused on all things related to the monoprice select mini V1 and V2 3d printers.

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Before and After Contest 2017