Original Prusa I3 MK3

A lot of plastic objects is slowly piling up since I got my Original Prusa I3 MK3 🙂

I ordered my Prusa as a kit in november 2017, and got it as promised the first week of February, in this odd-shaped package:

I took me one very long day to assemble it. The assembly manual is amazingly good, and probably one of the best that I have ever seen. If I have one complaint as a professional, it is the total lack of information about torque settings for screws, bolts and belts. I have built a lot of instruments and mechanical equipment over the years, so I am quite familiar with tightening nuts and bolts, and know where to be extra carefull. For a beginner without this “feeling” I think it could be quite difficult. On YouTube you can actually se people tightening M3 screws with high torque electric screwdrivers set to maximum….. and other horrible things.

In order to have a super stable building platform (reference) I assembled the printer on a stone plate with a very flat and polished surface. The first assembly was without any alteration, and my very first “frog test” was almost perfect (one front leg a little too thin). The printing took “forever” since I had unintentionally set the speed to 15% 🙂

Here is my first tiny frog:

After a couple of minor adjustments, and a couple of perfect prints, I started to make modifications and improvements(?). Some are probably not necessary or makes no difference, but again none of them are harmful. The main purpose of these modifications have been to learn more about the printer, to use the printer, and simply just to have some “nerd-fun”. Here is the setup as it looks now:

Descriptions and pictures of my modifications and add-on’s

I bolted the printer onto the stone plate: 4 bolts glued with epoxy into holes drilled with a  diamond tool-bit (under water). Soft-rubber vibration absorbers are put between the stone plate and table top. The printer is now completely silent, especially in stealth mode:

The whole thing sits on a special-built table, made of thick sturdy fiber-board bolted to the wall. The table legs are bolted to the floor, and the height is chosen for convenient operation sitting on my chair


I made struts from the top of the z-frame to the front of the stone plate, to make the frame less wobbly. This really reduced the wobbling, but I wonder if the prints get any better? I printed some of the fittings in ABS, and some are milled from aluminum bars. I use M8 steel rods (standard hardware-store items), and covered them with aluminum tubes to make them even more stiff and nicer to look at:



Small improvement of the y-belt-idler: Longer screws (two) to increase  adjustment span, and a longer axle-screw to make both bearings rest on the smooth part of the screw (and not one of them on the shreds). I tried a couple of “improved” solutions from Thingiverse, but all of them made the belt run hard to one side, and adjustment span was rather small. The modified standard solution is self-centering:


New (green PET) backplate on the x-carriage, to enable easy x-belt coarse adjustments and change. I believe this is now standard on new Prusa printers. I got it on Thingiverse, and donated a few bucks:


Extra x-belt-motor plate, also from Thingiverse, (green PET) to enable more belt tightening span. I believe this is also now standard from Prusa, but in a slightly different way with a dedicated adjustment screw:

To check and adjust x-and y-belt tension I have used an app on my cellphone. When you snap the belt (set to maximum length) the microphone records the tone-frequency from the belt, and calculates the tension.


The original spiraled cable-wrap (and the black filament inside) made a lot of creaking sounds, and all in all it also seemed too rigid and stiff. I changed the spiral wrap into woven wrap-tubes, and removed the filament. It certainly was not easy to get it all nice with all wires in parallel inside, and with the right flexibility without making it too floppy! I have made a double layer of tubing where the wires come out af the carriage. The result is now really good, nice and smooth, without any creaking. Time will tell if the wires will last longer:


I detached the LCD control panel from the front of the printer, and printed a little cover for the backside. With four adhesive rubber feet underneath and some cable ties it makes a fine little stand-alone unit that I can put anywhere and keep an eye on. The (green PET) control-knob is just to make it stand more out, and to make it match with the other homemade parts that I print in the same color. I think the green looks really nice with the orange and black:

The flat cable for the control panel was also put through a woven wrapping.


I installed a tiny 12 volt 40 mm fan on the EINSY RAMBo cabinet. Air is sucked in from the bottom of the cabinet and backwards out of the top. This will prevent the electronics from getting too hot, especially later when I will put up panels around the working area for ABS printing (this will block the ventilation holes on the side of the cabinet). The panel door can can still be opened, and the fan runs slow and silent on 8 volt taken from the 24 volt output (via 7808 regulator):


I also installed a 6-18 volt 80 mm fan on the PSU cabinet. Air is sucked in at the lower side of the cabinet and out at the top on the same side. I have heard that people have had PSU failure due to over heating, and this will certainly be even worse later, when I put up panels around the working area for ABS printing. The fan runs silent on 12 volt taken from the 24 volt output via a resistor. I cut off all the aluminum grille behind the fan, since these makes air-noise and also blocks the flow:


Remote control and camera with a Raspberry Pi Zero had to be tried. I made a small cabinet from a combination of parts from Thingiverse and own design. The camera is glued to the backside, an the whole thing sits on a removable and adjustable stand. I use the “standard” RasPi Zero camera, but I had to adjust it to a close-up-focus using a pair of pointed pliers:

I also put a nice green conver on the ugly light brown front-hotend-fan.


The flat-cable from RasPi Zero to the EINSY expansion plug is connected via a small PCB that I have placed on the side of the cabinet. The small PCB is covered by an unused part of a RasPi Zero cabinet. The PCB also has a couple of extra connectors that I made for other utilities plus an indicator LED, some power decoupling, level shifting and a jumper to disable the RaspPi:


Above the printer I have made an arrangement with two brackets protruding from the wall on each side of the printer:

  1. The main purpose is to carry two rollers, each fitted with two roller bearings. The rollers are where I put the filament spool, and this arrangement gives a nice and smooth turning of the spool when the filament winds off. The two pulleys to the left on the rollers are intended for “some servo arrangement” not finished yet.
  2. A transparent acrylic dust cover “roof” is placed between the brackets. In addition to this a soft transparent dust cover can be buttoned on, covering the frontside of the printer when it is not used.
  3. A fire alarm (with output signal) is placed under the dust cover. The plan is to make the alarm turn off the main power when fire is detected, and at the same time signal to my BMS.
  4. The brackets also carry an adjustable LED lamp.
  5. The last and rather peculiar thing I have installed on the brackets is a spring loaded filament tension detector. The plan was to make a servo mechanism with a motor that turns the filament spool to obtain a constant filament tension. The reason for this arrangement was a lot of problems with entangled filament on one of my PLA spools. The problem was solved in another way, and the servo will probably never be made.


Last but not least is a picture of my first professional delivery; a set of fittings for Purix A/S, printed in white PLA, and optimized for speed vs accuracy: