Hello everybody, after a long time since the publication of my last instructable, I will explain step by step how I converted a Chinese low-quality 3D printer to a high precision dual 3D printer.
If you have seen one of my last instructables in which teach how I built the small HEXDRAKE hexapod, you may know the problem of creating moving parts by hand. Each piece is different and that leads in a big problem at the time of programming. Each leg had different values for each position of the hexapod. So I decided to get a 3D printer for future projects and achieve better results.
After looking at many forums, pages, etc; I search for a kit of a Prusa i3 to buy. I ended up buying a complete kit in Alliexpress. After mounting, set up and calibrate, I’ve been using the prinet for a long time, getting poor quality prints. And it was all due to poor quality parts, poor design of certain parts of the printer as components of bad quality.
The process involves design and print new and customized parts for the kit like: support for auto leveling, twin direct drive for the bowden system, twin spool holder, etc. Also a set of homemade PCB for new applications and new features for the printer. About firmware and software although the instructable is concerned about a dual printer much information is also useful for configuring printers with single extruder. You just have to skip the steps related to dual-extruder configuration in steps referred to firmware and software.
So let’s start with the process below to transform the printer completely.
Video of the final result, made with time lapse function of octoprint:
Task 1: First mount the original kit
The kit I purchased in Aliexpress was a Prusa I3 with a single extruder whose name was Jietai. The ad was similar to this, which is also from the same seller:
I will not go on the kit assembly instructions, because this falls outside this instructable. But I think that even so with the pictures and both pdf is more than enough to mount this kit for those who need it.
But I will go into the problems I had with my kit. I’m not saying that all kits have the same problems. These problems are based on what I said in the introduction: defectives and badly designed parts, and some components of very poor quality.
On the one hand the pieces to which I refer are those that are part of support for the coils. The printed pieces that hold the PVC tubes to the aluminum frame. These pieces were badly printed, the hole where it is supposed to intruduce pvc pipe was oval. In addition it was practically internally hollow. Something bad if has to support the weight of a new coil filament. Another piece was the piece that hold the EndStop for the Y axis. This piece in place where it stood it not allowed to use the whole Y-axis travel.
On the other hand the poor quality component to which I refer is the extruder that came with the kit. I had to replace the heater because the other broke in the 3rd printing. But besides the extruder had a big problem: inside the extruder the filament passed through many areas formed by various materials. The problem was that the joints between these parts was not good and the filament go through this joints. The extruder worked worse and needed more temperature to extrude due to the amount of extra plastic.
This is one of the main reasons why I decided to change the extruder. As would have to design and print a new support for the extruder, I thought about going a step further and put two extruder and change to the Bowden system.
Prusa I3 Build Manual.pdf
Assemble instruction of the extruder.pdf
Task 2: Designing everything for upgrading
I designed all parts using SolidWorks. In the assemblies of both the direct drive, X axis carriage and the complete assembly of the printer, I designed only the necessary things to design properly and seamlessly each of the pieces. I have not placed screws or nuts, only what is necessary and sufficient, such as certain rods.
One of the parts is used to keep the motor shaft and better subject. Also the Y axis endstop have repositioned using another piece to use all of the axis travel and the entire print area. Another added are a diagonal threaded rods to give more stability to the printer.
On the X axis carriage is designed for two E3D V6 with a 27mm separation between nozzles. Behind is the servo for auto leveling. And finally it’s have two ends where to place the duct for cooling the printing.
The duct has positioned fans so that the air reaches all areas of the duct. Air passes straight through the small holes to the nozzles. Also the air flows down to the piece being printed.
The axis carriage allows for the X axis travel of this printer, use fully the printing area leaving no dead zone for both extruders.
The drive Bowden consist of 4 pcs, 3 of which are part of the body and the other is the fitting where is housed the small bearing. Is designed for a 696Z bearing and a Mk7 for 1.75mm filament.
To finish the coil holders are designed for coils with a diameter from 30mm to 90mm.
In principle I did not upload the files of the parts but if anyone is really interested send a private message.
Task 3: Printing!!!
The title says it all. All the pieces were printed with the old extruder and the old printer status. All except the duct for layer cooling because with the problems of the previous extruder I commented It could not be printed properly.
Cones coils were printed with a height of 0.4mm layer. The remaining pieces with a height of 0.2mm layer. The 4 cones and the piece that hold the servo for auto leveling need support to be printed properly.
Returning to the problem of previous extruder, after printing all the parts printed using this extruder, some parts I had to fix a few glitches, but that I will discuss in the next step.
Task 4: Repairing and preparing the pieces
First thing is to remove the supports of the cones and the part that holds the servo. It is removed without much trouble, then clean the surface with sandpaper.
Then to fix small surface imperfections of some pieces, I take a little acetone with ABS and covered the gaps with the mix as you can see