Monday, 8 August 2016

Building a Mostly Printed CNC machine

     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.
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