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Building My First Prusa Mendel RepRap

My background: I'm a retired computer programmer who has never done any mechanical work, such as fixing my car. The last time I held a soldering gun was in the 1950s. I decided to build a RepRap because retirement is boring! This page is designed to note the things that I ran into as I began to build my 3D printer. It isn't finished yet. My goal is not to repeat what is on other pages, but to note:

  • How I made the choices I made
  • Where (and why) I bought parts
  • Questions answered by my mentor
  • What progress I am making and how I am solving problems.

I chose to build a Prusa because that is the model recommended for first-timers on the Main Page. I don't remember just what I did at first, but I think I said something on the Finnish RepRap User Group forum and on one other RepRap forum that I don't remember. I live in Finland (Finnish wife). Anthony Aragues was a stranger living outside of Atlanta, Georgia in the States. I was surprised to hear from him and to receive his offer to mentor my RepRep building project. I surmised that the slogan on the RepRap pages "Sharing is caring" actually means something to the RepRap community.

As a retiree, my funds are limited, so I thought that I could buy parts as I could afford them and put the machine together at my leisure. I don't have all of my parts yet, but I have been able to decide where to get those I don't have. I saw an ad on the RepRap main page for a Mendel kit for a total of $800. I'll spend about $725 for the parts of this machine and be sure to get just what I want. Basically, I want a machine that will not have to be tinkered with in order to keep it working. So, I've chosen to buy top of the line parts where I have a choice. I might add that PLA plastic filament will cost me an additional $45 for the first five pound roll, but that wouldn't change regardless of which RepRap I build.


At the time I first heard from Anthony, I didn't know that I needed a mentor or what a mentor could do, but I sure found out. Had it not been for him, I would not be building this machine, for he has been an encouragement when I've felt overwhelmed, too. If you are just thinking about building your first RepRap, I'd recommend that you find a mentor before starting out. It would be better to have a mentor that you don't need, than to need one and not be able to find someone. One of my motivations in writing this page is to tell you all what Anthony has told me (and will tell me), so that mentors will not have to repeat information so much. I'm going to refer to him as "my mentor" so that you won't have to refer back here to remember who Anthony is.

Here are some introductory hints my mentor gave me.

  • I don't suggest going the local hardware store route. I tried that several times, ended up paying more money for fewer parts and only finding about 10% of what I needed. If you go through a place like McMaster Carr they have almost everything you need, don't charge much for shipping and you get packs of 25+ for the price of what you'd pay for 4 at Lowes, Ace Hardware or Home Depot. I can also send you a few odds and ends so you don't have to pay for 25 when you need 1.
  • Electronics... I run the RAMPS electronics... so do many others, popular one is from I know the guy who runs that, he's great. It's a reasonable route to go, biggest problem with it is that it requires stepper drivers that are constantly selling out worldwide. He's working on making his own though.
  • Motors: you'll need 5 NEMA17 Bipolar stepper motors... those can be difficult to track down as well, but easier than the stepper drivers I mentioned.
  • Power Supply: Keep your eyes out for a good deal on a big XBox power supply, or high power supply from a server or PC, should be able to salvage one for free.
  • Extruder components: One of the most difficult parts of the machine is the hot end of the extruder, there are 2 designs being sold that I think work well, I've tried the rest and they've failed MANY times for me... this part will cost around $50. When you're ready for that part I'll give you all the info for people who sell them, etc. It's usually the last part.
  • Belts: you should be able to pick up some steel reinforced timing belts, they don't need to be in a loop so you can buy a large one and cut it down.
  • Software needs:
    • Firmware development: That's the Arduino stuff. Some firmware works with some software chains, some features from one set need to be ported to others... less common components like paste extruders, heated bed, etc. are more difficult to configure.
    • Control Software development: There are currently 3 major software toolchains: ReplicatorG from Makerbot, Host software from RepRap, and Repsnapper. The unfortunate thing is that the hardware you get largely determines which software you use, and it shouldn't need to be the case. I personally prefer ReplicatorG and use it on my Old slow 3d printer, but my Prusa Mendel has hardware that only works with Repsnapper right now... in order to get replicatorG to work with it I'd have to get past the hurdle of getting it to recognize /dev/ttyACM0 port in Ubuntu. This doesn't even start to get into features that would be nice to have, best place to see lists of those is in the software repo for them.
    • gcode generation... GCode is the ancient language that the 3d printers use to communicate with the electronics. Objects are sliced into layers, given special instructions on extruder speed, etc. and converted mostly by an app called Skeinforge. It has a LOT of features, more are always needed and more than anything else it needs to be simplified somehow. This one benefits from pretty frequent development, biggest issue is that it's only integrated into ReplicatorG, outside of that app you have to run it separately.
  • Modeling and scanning and model manipulation. Creating models is one of the least developed things right now, OpenSCAD seems to be the most popular way to go that is open source. I like it but it can be daunting for a non-programmer type. I'm getting into 3d scanning as well... which is very immature in the open source arena, you have to tie together 3-4 apps to get a model from a pointcloud, then noise and model stitching is still a challenge.
  • Presentation / web stuff: RepRap is a great community and has a ton of ideas and hard working contributors. Makerbot has blown past them with marketing, presentation and making it simple. I talked to some of the RepRap leaders about doing the same thing for RepRap but they thought it would remove some of the openness and flexibility... something still needs to be done to make a simpler guide for people to get started. All of the getting started info is spread out and ambiguous as to which path is best to take because the RepRap community is so bent on not having anything be official or sanctioned.
  • The first hardware you'll need is the threaded rods, smooth rods, m8 washers and m8 nuts, 2x 608 bearings and you can put the whole frame together.
  • You can also clean up the parts a bit. You don't necessarily want bolts to slide through holes. It's ok if you have to turn them through.
  • The PLA bushings... slide them onto the rod, don't pop them on, they might snap.
  • The best tip I can give you when working with this stuff is heat.... even from a hair dryer make is very pliable, you can do wonders with a little heat.
  • When it comes to printing my own Prusa plastic parts my mentor mentioned a dropbox and said "I have all of the STL files there plus it's an easy way to collaborate on files. But they are also here: Prusa's Mendel site.
  • The endstop flag + x end idler can be gotten from AnthongRedbeard. (I think that this will have to be a modification because I'll have to have a working machine to make these parts.)
  • The general RepRap forums has a thread on the 1st page called Visual Prusa Instructions.
  • I agree on the extruder, don't be cheap, it makes a huge difference. I've been through about 4 cheap ones. The Arcol one is an easy assembly and very well documented. It WILL work with the filament drive block I sent you. The extras you could get from him are an extra PTFE tube, as it's the only part that is likely to have issues, and the hobbed bolt. I sent you an M8 bolt to cut teeth into, but the nicely machined ones are cheap as well.

In response to some questions I had regarding the Arcol hot end, my mentor said to :

  • Order from: Arcol. You may want to buy the "wades hobbed bolt" as well. Arcol's ordering FAQ is here. Laszlo has been great to everyone I know so far... (I can confirm that Laszlo is great to work with.)
    • Regarding different models of hot ends, sometimes they have multiple interchangeable parts for insulators, heat cores, etc. For the Arcol one the nozzle is the only piece that matters.
    • Regarding the nozzle sizes, 0.5mm generally is less problematic. Given the highly engineered design of this one, I think you are safe with .35mm.
    • Regarding the difficulty in assembling a hot end, Laszlo has very detailed instructions for assembly. I recommend you save the money on assembly.
    • A thermistor is essential but is available from other sources. It's only about $1.50 USD. It's a temp sensor.
    • You don't need any adapters like the Mendel block does.
    • In the parts list for the Prusa Mendel, it was stated that we should "Be sure to get ones with ~20mm of shaft length. Shorter shafts require modifications to the X pulley assembly and Z motor couplers. One of the five motors, for use with the extruder, should be capable of creating a holding torque of at least 40Ncm." I had asked my mentor how to make sure that motors met these specifications. He replied that it is safe to assume that the shaft length of the motors is sufficient.
    • I asked why I needed 5 motors. He replied that the Prusa design is unique in needing 2 Z motors by design. 1 for x, 1 for y and 1 for extruder.
  • Speaking of the extruder hot end, my mentor recommended getting a 3mm round file. His is a chainsaw sharpening file. It's very useful in making sure the path is not too tight for filament, a problem he's had a few times. (I don't have any filament yet, so I don't know if I'll need one.)
  • As for Thingiverse: If you sign up, you can just click the <3 button and it will save that item as one you like in your profile. I thought the <3 was a bit obscure and it took a while to find. (I still can't find it on some pages. I'm saving things I like as a Firefox bookmark in a structured set of folders.)

Acquiring Parts

I live in a small town in Finland, so I thought I'd try to get parts locally, or, at least, within the country. I found an Arduino MEGA 2560 at Paeae. At this time, I had no idea how specialized some of the parts are. I went to the local Rautia store (sort of a Finnish "Home Depot") with the hardware list. (It's fun being an English speaker in a store where Swedish and Finnish are the main languages. How are you supposed to know the names of parts in those languages?) The bottom line was that, while Rautia had some of the parts, they lacked many of them. It would be quite expensive for me to go into Helsinki to look for parts, so I decided to go the mail order route.

The term "Vitamins" as used on the RepRap site are the non-plastic parts. I don't want to give you the impression that I think that the choices I made and am making are the best ones for everyone. These are just my choices.

Plastic Parts (RP)

My mentor offered to provide me with a set of plastic parts. In return, when this machine is completed, I've agreed to send him a set of RP parts for a Prusa Mendel. Of course, I'll be happy to do that for others, too. I reimbursed him for the shipping costs from near Atlanta, Georgia to Finland. That was $31.00.

Hardware Kit

I am, even now, unqualified to select the best hardware, for I don't know how everything goes together. I decided to get a hardware kit from Thingfarm in the UK. (If you're in America or Canada and want to do business with these folks, they are at Thingfarm (North America).) My money starts out in a bank account in the States, so it's easiest for me to buy things in USD. Something I appreciated in the UK Thingfarm is that they have buttons that give their prices and allow you to order in $, € or £. It was cheaper to buy a whole Prusa hardware kit than to buy parts that would go into a kit. My mentor had suggested getting hardware from McMaster Carr in Cleveland, Ohio. I don't remember why I didn't go with them, but it had something to do with shipping limitations or shipping cost.

Hot End

I ordered my hot end unassembled from Arcol. Assembling it myself saved 30€. The only problem is that the connecting wires for the thermistor are finer than a human hair. If you have "banana fingers", it may be well to buy it assembled. I had some confusion regarding the instructions for assembling the hot end because the instructions are for version 3.0 and Laszlo sent me version 3.0.1. Until Laszlo gave me this picture, I had difficulty matching the instructions with the items I had on my table.

Laszlo had five motors that he didn't need. I think that he is not in the motor sales business, but had bought a lot of them to get a reduced price and wanted to sell some of what he had. His motors are of a higher quality than a RepRap really needs, and are priced somewhat higher than those you might get elsewhere, but I wanted to buy from as few sources as possible.

Arcol will allow payment in USD and in euros. He prices in euros, but gives the exchange rate that he is working with. The hot-end parts, a heated bed and the five motors set me back $292.95.



My mentor thinks quite highly of the folks at Ultimachine. I think I'll buy my electronics from them as long as I don't know any better.


I really didn't want to have to solder any parts, because I don't own a soldering gun at the moment, but I'm going to have to get one to finish off the Arcol hot-end. (If I'd bought it assembled, I wouldn't have had to.) It appears that I'm going to have to solder some for the opto endstops, too. So, I suppose that I'll save a little more money and buy the RAMPS DIY (do it yourself) kit, which will require soldering.


RAMPS is the acrostic for RepRap Arduino Mega Pololu Shield. I asked my mentor how the Arduino is wired to the RAMPS board. He said that the Arduino and the RAMPS just plug together -- no wiring. I'm not sure what the trade-offs are with the Gen3 and other Gen variations of electronics. I think that they are used on other models of RepRaps and other folks may be more familiar with them.

Stepper Drivers

I'll need four stepper drivers. They are mounted on the RAMPS board and are used to control the stepper motors. I'm pretty sure that I'll only need three stepper drivers, but they can be blown while testing, so I'll have an extra.

Opto Endstops

It took me a bit to figure out what these are. As I understand it at this point (I haven't seen a RepRap working, except in videos), the hot-end moves back and forth (the X-axis) and up and down (the Z-axis). The bed upon which your project is built moves forward and back (the Y-axis). Apparently, there's a need to limit the travel of the bed and the hot-end. Whether that is for emergencies only or whether these are for normal use, I don't know. But three endstops are needed. I can get them from Ultimachine, too.

There are two types of endstops, mechanical and optical. I have the idea that, should I decide later on to build a RepRap with a major variation from a Prusa Mendel, it will be easier to reuse the endstops if they are optical.

PLA Plastic Filament

I've not decided where to buy my first 5 pounds of PLA plastic filament. Shipping charges and currency exchange rates are an issue for me.


I'm following the Prusa Mendel Assembly page. It is very well written and easy to follow.


My hardware kit included a bunch of threaded rods. The problem was in telling what rod goes where. I didn't see any documentation that told me. So, here's what I have figured out. Each rod below is described as quantity x length (in mm).

  • 6 x 370 -- Each side is an equilateral triangle. Therefore, it requires 3 rods of the same length. Because there are two sides, I'd need 6 rods of the same length. This is the only rod length in a quantity of six.
  • 4 x 294 -- The front and back of the frame each have 2 rods, for a total of four. This rod length is the only one remaining with a quantity of four, so these must be for the front and back.
  • 3 x 440 -- This length of rod is the only one remaining that is long enough to connect the frame sides at the top of the frame, so I used them. There is a problem in that pictures show these rods as just long enough to bridge the width of the frame plus enough extra to go through the Z motor supports. In fact, I have about 3.5cm of rod extra, but I have no other rods that I can use, so these must be the ones. That takes care of two of the rods. The third one goes across the bottom of the frame. I had built the frame with this rod on top of the bottom side rods, but later information indicates that it's better to put this rod on the bottom of the bottom side rods.
  • 2 x 210 --
  • 1 x 50 --

Assembling the hot-end

When I first decided to buy the hot-end, it was back ordered. So also was the RAMPS board. This is a hobby, so I didn't mind waiting. The hot-end became available first, so I bought those parts. Laszlo of Arcol said that he could let me have a PCB heatbed MK1 for a decent price, so I included that in my order. I assembled the hot-end while waiting for the stuff to assemble the Y-axis. I won't know if this assembly was successful until I am able to put power to it and test it. I think I may need a multimeter for testing it.

Assembling the Y Axis

To do this, I need the print top plate, the print bottom plate, a stepper motor and other stuff. I don't have the tools to make the print plates, so a friend of mine is doing it for me. He is a woodworker, so we decided to make them from plywood, even though the instructions don't say what to make them of. If you plan to use a heatbed, as I do, plywood is the logical choice, or says this Thingiverse page.

My mentor suggested that I slide the PLA bushings on to the 406mm smooth rod from the end. Snapping them onto the rod could break a bushing. There was no point in taking a chance, so that's what I did. When I installed the first smooth rod, I found that it didn't want to go into the bar clamps. I tapped it into place and used a vise grip to twist the smooth rod to "help" it in. I also used my power tool to ream out the bar clamps a little. It was a real chore.

The bushings were too tight on the rod. The instructions call for loosening the bushings by immersing the end of the rod in boiling water. I didn't want to do that, for I'd have to take the smooth rod out of the bar clamps. It was too hard to get the rod in. I didn't have a tool that my mentor recommended, but is not in the instructions: a hair dryer. I bought one in a nearby thrift store. For the second rod, I used the hair dryer on the bar clamps for about 30 seconds. The rod slipped into the bar clamps like a charm. (I should have bought the hair dryer first.) I also used the hair dryer to heat the bushings, then slid them back and forth on the rods. That, too, worked beautifully.

The next step was to glue the print bottom plate onto the bushings. I can't get the glue that Adrian recommended, so I asked my wife what she had. It was an all purpose cement. Included among the things it was good for were wood and plastic, which is what I have. I glued them and adjusted as much as I could. The glue set in about 5 minutes, but the instructions for it recommended a full drying time of 24 hours. After that, I found the print bottom plate is whuppyjawed about a millimeter. I think that should still work OK. It is a joy to push the print bottom plate back and forth along the smooth rods and have it travel easily.

I went to the hardware store to get some miscellaneous things this project requires: a multimeter, calipers, drill bits, wire stripper combo tool, zip ties and other little stuff. It set me back 80 euros. I had already calculated that this 3D printer was going to cost me $725 in parts, but I hadn't thought of the tools and little parts that I'd have to buy. Of course, many folks already have those things. Take that into account when you budget for your RepRap.

Somehow, I had the idea that the RP (plastic) parts were ready to use. Wrong. The pulley that goes onto the motor shaft didn't come close to fitting. I don't know about other people's motors, but the shaft of my motor already has a flat spot that the grub screw should butt up against after it passes through the side of the pulley. The shaft of my motor is 4mm in diameter. My Dremel-like power tool, with its tiny working ends, was essential for the fine work of cleaning up the pulley. After screwing the motor onto the Y bracket, I used zip ties to make the motor tight to the frame. It took two, connected together, because one wasn't long enough.

The instructions called for snapping the bushings off of the smooth rods in order to remove the print bottom plate for the purpose of fastening the belt clamps onto it. I didn't want to do that for fear of breaking the bushings in the process of removing or replacing the print bottom plate. I used my power tool to drill the 3mm holes for the first one. After getting the belt clamped down and running it around the bearing at the back end of the printer, I observed that the first belt clamp was misplaced. I positioned the back belt clamp, marking the location for the holes with an awl. After drilling the holes, I finished threading the belt and clamped the belt down. Up to this point, I had not tightened the nuts that hold the rear bearing. I adjusted the position of the bearing with the belt in place and tightened the nuts. I removed and changed the position of the front belt clamp. After drilling new holes, I screwed the belt clamp down again.

The belt is still a little loose on the bottom. I won't mess with it until later when I test it when I run the motor electrically.

I didn't think to take pictures earlier, but here are a couple of shots of the frame and the Y-axis:

Prusa Frame and Y-axis 1.jpg       Prusa Frame and Y-axis 2.jpg

Assembling the X Axis

The instructions and embedded videos are real close to perfect.

I'm using PLA bushings until I can make bearing holders with my working RepRap. The bushings are stiffer than the bearings shown in the video. Once again, it was the hair dryer to the rescue to make the bushings travel easy.

In the bottom view of my X-Axis assembly you see four M3 x 10 bolts on each end. As noted in the instructions, they feed into M3 nuts that are on the inside of the smooth rod channels. The video didn't show the effort in locating the nuts, then feeding the bolts into them. For me, that was almost a show stopper. I got some in, but others... Thankfully, I have a helpful wife with small, strong fingers.

One of the rod channels had shreds of plastic in it. My mentor told me that I might find that because he made some of my parts with the Arcol hot-end and other parts with another hot-end. This sure demonstrated the superiority of the Arcol hot-end. I cleaned it out with the drum sander attachment of my power tool.

Top view of idler end
Side view of assembly
Bottom view of assembly

Heated bed

This entry is out of sequence for the time being, but I found some things to say about it and here is as good a place as any to say it.

I ordered a heated bed at the same time that I ordered the hot-end. I'm not sure how to wire the thing. Imprinted on one edge of the heated bed is a reference "Assembly Info and Downloads:". The page has nothing on it. I did a search on MK1 and found a link to a Thingiverse page. Some instructions are there, but others are linked on this page to a reprapsource page, where the heated bed may be purchased. These instructions call for cables, LEDS, Resistor and cables and Polimide Tape (whatever that is). This Thingiverse page told me what material to use for the base: plywood.

On the bottom side of the heated bed, I see two points that are obviously solder points for the power wires. Between these two points are two sets of solder points: the left set has four points arranged in a square and the right set has two points side-by-side. What to solder there is something I have yet to find out.

(Perhaps PCB Heatbed#Optional LEDs?)

--to be continued

--Alan Lake 17:49, 21 June 2011 (UTC)

Further reading