Friday, June 8, 2012


I'd like to introduce a new printer mainly of my own design but heavily influenced/inspired by dkennel's Pocket Printer.  I call it the K1-Rap.

This is a work in progress.  I'll be updating this as things progress.

I really liked the idea of using aluminum extrusions for the main structural components of a reprap.    My Prusa i2, constructed mostly of threaded rods, worked flawlessly but I wanted something a little more sturdy. 
I saw Dkennel's Pocket Printer on Thingiverse and actually started out attempting to replicated his.  I didn't have any PLA available and ABS did not make for a good slide material.  ABS was too soft and did not "slide" reliably.  Since I had smooth rods and lm8uu linear bearings on my Prusa, I decided to cannibalize it and start a "new" design.  It should be noted that this is really Dkennel's basic design adapted for 8mm smooth rods.  They really deserve the credit for the initial idea.
I attempted to design the printer around a few constraints (much like dkennel's original idea).

1. I wanted to keep the moving mass low (arguably didn't do a very good job)

2. I wanted to keep the amount of hardware (screws, bolts, nuts, etc.) to a minimum.  I loved the simplicity of the Prusa i2 design. 

3. Like the Pocket Printer, the extruder had to move only in the Z direction. Eventually, I want to add a second Plastruder to the printer and the added weight would make a "mobile" extruder hard to accomplish. 

4. I wanted roughly the same build envelope as I had on my Prusa. 

Keeping these ideas in mind, I started off by mimicking Dkennel's basic design.  I then added the smooth bars to the exterior of the 2060 extrusions.  All axes slide on 8mm smooth rods with lm8uu linear bearings.  In doing so, I had to then redesign the basic structural components on the printer. 

You'll notice the smooth rods sticking out on all the axes.  This was done purposely so I didn't have to cut the rods to length.  Mainly I was afraid this design wouldn't work properly and I didn't want to cut my prusa smooth rods and then not have a single working printer.  In the final designs, I will enclose all rod brackets and cut the smooth rods to length. 

The smooth bar "brackets" fit within the interior of the Al extrusion.  This is a pretty snug fit and friction is the only thing holding the majority of the printed parts in place.  The X axis connects to the Y axis with lm8uu bearing fittings reminiscent of the Zip-Tie bearing holders used on the Y axis of a Prusa.  Connected to the X to Y bearing holders are the 2020 Al extrusions that make up the X axis.  .
I'm using a NEMA 14 on the X axis.  This is the only real deviation in electronics from the Prusa.  I had this laying around and its lighter than a '17.  I would highly highly recommend using a '14 instead of a '17 simply because of the added mass a '17 would give to the X axis assembly.  (As a matter of fact, my '14 is a little bigger than I really need, Dkennel lists a better motor for use with the Pocket Printer).
Once again smooth rod brackets fit into the extrusions.  The build plate then sits on top of the X axis smooth bars using Prusa's i2 lm8uu Y bearing holders. 
I'm using a thin sheet of plywood with Prusa's Mk1 PCB heated build plate on top.  I will likely swap this out for a sheet of aluminum. 
The Z axis consists of a vertical 2060 extrusion with 8mm smooth rods on either side.  The cantilever extends out over the build plate and rides up and down on the smooth bars. 

I used 2 Z motors only because I wanted to maintain speed when I eventually add a second extruder.  I'm sure you could get away with a single Z if you wanted. 

I'm using my Plastruder Clone and it sits on a printed extension off of the Z cantilever.  The Pocket Printer used a nice aluminum plate for this, I would recommend that instead of the printed part.  Unfortunately I didn't have access to equipment to make that plate, so I designed a printed part instead. 
My RAMPS 1.4 sits on the back using Dkennel's RAMPS box.  My X ends are essentially printed versions of his.  The Y motor bracket is once again Dkennel's design.  I'm using the T5 belts/pulleys I had on my Prusa. 

Current Build Envelope: X-200, Y-120, Z-180. 
Actual Build Envelope: X- 200, Y-200, Z-180. (Once my replacement Y Al Extrusion comes in)

To Do List:

Brace the vertical Z axis.  Currently I'm using 90 degree brackets and they still allow the Z to wobble very very slightly.  Bracing the more will allow for faster printing speeds. 
Replace the ZipTie brackets on both the X and Y.  These seem to work fine, but I just want something a bit more sturdy. 
Make a single X carriage.  I will eventually design an X carriage that is all inclusive.  Currently I have a belt clamp bracket mounted onto the plywood between the X bearing holders.  I want to integrate all of these into one bracket like the Pocket Printer design has. 
Extend my Y! A miscalculation resulted in a Y extrusion that was 80mm too short.  This is an easy fix just a longer belt is needed. 
Enclose all smooth rod brackets.
Integrate cross bar (The bars on the bottom the feet are attached to) brackets into the Y axis end brackets. -I've already actually done this, I just haven't printed out replacements. 


Allows the extruder to remain mostly stationary.  Except Z travel.
Entire assembly is very rigid even at travel speeds speeds of 200mm/s.
Other than the a few 5mm bolts and the associated aluminum extrusion nuts, there isn't much in the way of hardware, as everything push fits into the aluminum extrusions. 
Will likely allow for some light milling, if so inclined.  ( I probably never will attempt this)
Can easily be built out of a retired Prusa.  -Motors, smooth bars, bearings, HBP, etc
I designed and built it myself! (Ok, this one really just applies to me, but none the less, it's a good feeling to see something you imagined come to life.)


Entire alignment of each axis relies on perfectly aligned printed parts and straight aluminum extrusions. If the parts aren't printed correctly and fitted correctly, then the axes won't be squared and level to each other.  
There isn't an easy way to fix misaligned parts. 
Requires both aluminum extrusions and smooth bars.  This adds to the cost slightly. 
There is still a significant amount of mass being moved by the Y motor.  I don't know the exact weight but its higher than I hoped for.  This means a fair amount of vibration at higher print speeds.  This is where the bracing between the Y and Z extrusions comes into play.  Without proper bracing, the extruder end of the cantilever can bounce up and down causing ugly prints.  I'm printing reliably around 70 to 80mm/s depending on the part being printed. 

I’d like to thank DKennel for the Pocket Printer design and Prusa for his design, allowing me to steal parts of both for this design.  All of the parts are on Thingiverse if anyone is interested.  I will post a BOM including lengths of extrusions and smooth rods shortly.  Feel free to leave feedback in the comments!

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