One of the constants of designing and building kit or custom 3D printers is the continuous exploration of ideas and changes to make things work more effectively or more robust and reliable. I started my 3D printing journey last september with a basic Kossel kit printer, and I've been reworking and refining parts of it ever since. I've compiled some of the better and current modifications below, along with some tricks that I've found that make working with the printers easier.
Micro Kossel Extruder
Mini Kossel Extruder
First up on my tour of modifications is the extruder module, probably one of the most critical parts of a 3D printer. There are literally hundreds of different designs available online, both DIY and commercial, but the one I'm using is the Prusa/Makerbot MK8, which is available online as an aluminum kit. I've modified mine with a stainless steel MK8 drive gear and a M6 pneumatic fitting that I've drilled out with a 5/32 inch bit to allow the 4mm bowden tube to reach the drive gear, it makes loading the filament much easier and allows for the use of flexible filaments as well. The other change I've made is to add a M5x10mm bolt(found at the local hardware store) to the spring to allow for higher compression, this helps grip the filament better and makes handling some of the cheaper brands easer.
Masking tape, BuildTak, UHU glue and a palette knife on my Mini Kossel build plate
Next is bed adhesion techniques. I've only worked with PLA, so most of this probably doesn't apply to the more unusual filaments. For printing without a heat-bed, I've used masking tape, plain and with glue stick on top, works fairly well but degrades quickly and doesn't work for parts with small footprints. Best unheated surface I've used to date is 'Buildtak', a branded PEI film sheet material, it comes in 3-packs in a variety different sizes, and according to the literature, most types of filament will adhere to it without any difficulty. For heated beds, I'm currently using lightly applied UHU glue stick on 3mm glass at 45 Celsius for PLA, provides good adhesion and lets go easily if you put the glass and print in the freezer for about 10 minutes to let things cool, just remember to wash the glass every 10 prints or so, otherwise the glue will eventually build up to the point that the print gets nearly permanently stuck on the build plate. If a print does get stuck, clamping the glass firmly to a solid anchor and applying a 5-inch putty knife to the bottom of the print with a hammer can usually fix the problem. Last up are a couple of Delta specific tips, a simple way to measure delta rod arm length and a simple add on that drastically reduces the noise generated by the printer.
Measuring delta rod arms for exact length step 1
Measuring Rod arms step 2
I recently had to rebuild the rod arms on my Mini Kossel, turns out that carbon fiber tubing will strip out over time if threaded ends are used. Regardless, I had to make a quick jig to get the lengths mostly the same, and I had a bunch of Lego bricks laying around, so I drilled a couple of holes for some M3 screws, and built the jig using one arm dry assembled to set the approximate length. After the jig was finished, I used some five-minute epoxy to lightly coat the threaded parts of the rod ends and used the jig to get them to approximately the correct length. After everything had dried, I rejigged each rod and used a spare Lego brick and my 6" calipers to measure the exact length of each arm. The spare Lego brick acts as a marking block, providing a point of reference for the calipers, since the arms are roughly 8.5" long.
And lastly, I found these useful little vibration damping feet while browsing Thingiverse. They're quick to print and easy to install, and the difference was immediately noticeable when starting my next print after installing them on the Micro Kossel, it's now very quiet and bumping the table doesn't disturb things at all.
After using my MPCNC bolted to the workbench last time, we had a bit of a heat wave here and the electrical tape I'd used in constructing the cables failed, turns out the adhesive is temperature sensitive. After unbolting it from the bench to check the connections on the x2 motor, I decided to make the machine more mobile, and a bit of research turned up slotted 3/4" MDF at the local hardware store, perfect for making the waste board top from.
Gluing and screwing the base board together
The final version of the base ended up being made of the 3/4" MDF glued to a 3/4" thick sheet of plywood, total thickness 1.5 inches, glued and screwed together. The result is a perfectly flat sheet that weighs about 20 pounds and takes two people to move, but it doesn't shake or move during operation. For solving the electrical problem, I found some 22-gauge wire crimp connectors when I picked up the MDF.
22-gauge insulated wire crimp connector, pack of 75
Electrical repair tools: needle nose pliers, wire crimp/stripers, X-acto knife
After letting the glue on the baseboard dry overnight, I screwed the feet of the MPCNC's frame into place and squared things up again, adding some extra screws through the ends of the outer rods to lock things down permanently.
Corner with rod locking screws installed
Once the frame was fully installed, I started printing some drag chains and mounts that I found on Thingiverse (Drag Chain, Z-Mount, XY-Mounts), took about 400 grams of filament all told. The XY mounts are designed around the older version of the MPCNC's roller carriages from before the 7/16 update, so the hole spacing was off by 1/4" but a few minutes work with a file fixed that issue. I also had to replace the 1.25" bolts on the back of the roller carriages with 2" ones, although it turns out that 1.5" ones would have worked just fine. I just used a couple of spare 6-32 screws and bolts left over from the initial assembly to secure the chain to the mount.
Drag chains waiting for installation
Drag chain mount fully installed
X axis drag chain fully installed
After installing the drag chains, it was time to install the electronics housing. I'd printed a Ramps case from Thingiverse, and after a bit of modifying with a hand saw, I screwed it to a spare piece of plywood that is fixed on one corner of the base. Wiring up a Ramps 1.4 set is fairly straightforward (see Reprap.org). Only thing left was to assemble the hold-down clamps.
Hold-down clamp parts
I decided to use a combination of a printable Shapeoko Clamp (red in the picture) and this knob (silver in the picture). Add a 5/16" washer, 1/4" nut, and 2"x1/4" carriage bolt, and it makes a simple, solid hold-down for anything up to 1 inch thick.
Hold-down assembled
Full set of hold-downs
After all that, only thing left was to start things up and make something! I found a RIGID palm router on craigslist and installed it for use as a spindle, cuts through wood without any difficulty.
Over the past month or so, I've been building a new tool, a 3D printed CNC router table. It's called a Mostly Printed CNC, designed by Ryan Zellars, and is capable of working as both a router table, 3D printer, laser engraver or just about any other device with similar motion mechanics.
Mostly Printed CNC waiting for RAMPs installation
Building wise this is a fairly straightforward project, the main tools needed are a 3D printer with a minimum 170*170*170mm or 6*6*6 inch cube build volume, a hacksaw or reciprocating saw, a pair of 3 inch or bigger clamps, a miter box, a 5/16" or 8mm wrench and ratchet socket, phillips screwdriver, needle nosed pliers, a 2.5mm allen key and a decent set of digital calipers. Materials include 2 kg of PLA filament in whatever colours you like, 24 feet of 3/4" steel electrical conduit that I'd suggest getting first since it affects which of the 3 variations you print, about 20 feet of 4-strand electrical wire, 55 608zz bearings, a RAMPs 1.4 kit, a sturdy and flat-topped table or bench, and about 100 different bolts and screws (See the parts page on Ryan's blog for exact part counts).
For the 3D printing part of the project you'll first need to measure the outside diameter of the electrical conduit and download the appropriate variation of the parts from Thingiverse (23.5 mm North American version, 25mm international version, 25.4mm (1 inch conduit) version for extra strength/heavy use). Once you've downloaded the correct parts set, it takes about 90-100 hours of printing create all of the parts. I'd recommend keeping a close eye on how much filament is on the spool before starting some of the parts, particularly the 2 large 'Center XY' ones in the center assembly, they take 8.5 hours each and about 200 grams of filament, not something you want to hit the end of a spool on.
Center XY bracket undergoing bearing installation
Assembly of the parts is quite well documented on Ryan's blog, only section that I'd recommend doing differently is the center assembly since the 5 inch bolt is a bit of a pain to line up correctly if you're adding parts from top to bottom. I found it's much easier to combine the outer 4 parts and then add the 5 inch bolt and brackets for the z-axis threaded rod.
Center assembly parts with dremel spindle in background
Recommended method for assembling center block
The other main tricks and gotchas to be aware of are that the roller design was updated around the middle of july, main difference is that the top clamp and motor mount have been combined into one part, otherwise assembly is more or less the same. I'd also recommend glueing the leg caps to the bottom of the corner assemblies, otherwise it's a potential shearing point and could fail unexpectedly if unglued.
Updated roller carriages with bearings and belt guides installed
Applying 5-minute epoxy to corner bracket base for strength
Corner base and leg cap glued and clamped
Once the corner brackets are glued and all of the bearings installed, you'll need a large level surface to assemble and square the frame on. I found it's useful to have a building square to check the corners with, that and measuring the diagonals with a tape measure (if both diagonals are the same lengths, then the frame is square, if not the same use the square to check the corners and correct the issue).
Me assembling the main frame, note the installation of the roller carriages
Securing frame to 3/4 inch plywood for squaring
Installing motors and securing motion axis with wiring harness in foreground
As for the electrical install, I'd recommend referring to Ryan's Ramps and Stepper wiring guides if you're using the Ramps 1.4 board set, otherwise I'd suggest referring to the official documentation for whatever control board you decide to use. After testing that everything is wired correctly, I'd recommend installing one of the pen adaptors and testing the motion mechanics for any errors.
Ramps installed and pen tool mounted for initial testing
For a carving spindle a DeWalt 660 laminate trimmer/drywall saw is the recommended option, but just about any rotary tool, palm router, or laminate trimmer will work with some variable limits on speed and maximum material hardness. I'm currently using an old Dremel 250 rotary tool that's been gathering dust in the shop for a few years, and it's proven perfect for delicate detailed surface engravings with softwood (old pine mainly) and probably most other kinds of wood with the right tooltip. I'm eventually planning to upgrade to a Makita compact router (model number RT0701C) since it's the cheapest option I've found with a full speed control and stabilizer option. Here's a short video of the machine in action.
First engraving test result
Engraving with 1/32 inch ball tip engraver
Overall, this machine was a lot of fun to build and I'm looking forward to learning more about CNC work with it. One thing that I did change was to modify the stock firmware (Marlin from Ryan's blog) and disable all of the thermistor inputs since I'm only planning to use this machine as a CNC for the foreseeable future.
