It is tempting to skip directly to designing a CNC router that meets my specifications, but there are tons of existing products and projects on the internet attempting to solve nearly the same problem. Even if I justify building a router for fun despite the presence of cheap commercial options that meet my requirements, there is plenty to learn from analyzing the existing designs on the internet.
Existing Kits and Products
There are three main categories of hobbyist CNC router that I found while researching this project:
- Routers made from profiled wood structures
- Routers made from aluminum extrusion and plate
- Routers made from steel tubes and plates
Although there are plenty of other ways to categorize the routers (spindle vs hand router, v-roller vs linear rails) the structure-based categorization seemed to group things pretty well.
Wooden Routers
The Blacktoe CNC is the product of many iterations from BuildYourCNC. It uses V rollers and roller chain for linear motion, and has a standard hand router as a spindle. The structure is made from cut and bolted furniture-grade plywood. At about $3,000 for a kit it seems to be pretty expensive for what it is.
The Evolution 4 CNC is a very affordable option from Bobs CNC at only $1,000 for the kit. It uses V rollers and acme screws for linear motion, and also has a standard hand router as a spindle. The structure appears to be made from laser-cut wood (much thinner than the Blacktoe’s plywood) but manages to maintain stiffness with tons of ribs on the X and Y axes. This model has a 2′ x 2′ work area, but it is easy to imagine how it would extend.
Aluminum Extrusion Designs
The Shapeoko Pro from Carbide3D is an upgrade from the older Shapeoko router design. The V-rollers on all axes were replaced with linear rails, but the belt drive on the X/Y axes and the screw drive on the Z axis were retained. The structure appears to be made out of a similar aluminum extrusion, but without the built-in V-roller guides. Several sheet metal components were replaced by thicker, beefier aluminum plates increasing the overall stiffness of the system. A hand router is included in the $3,000 price for the whole system.
The PRO4824 from Avid CNC is a solid, modular CNC router design. It uses linear rails for linear motion, with racks on the X/Y axes and a ballscrew on the Z axis. The 3HP spindle is sold as an add-on, along with other options like legs, larger motors, and even a 4th axis. The frame is made entirely of 40mm pitch t-slot extrusion, with different profile in different areas. The cross members are joined with tension hardware instead of simple plates. This model has a 2’x4′ work area, but by making a 4′ wide gantry they were able to make near-identical 4′ and 8′ long versions. The benchtop version with a spindle costs just over $5,000.
The Sphinx 1050 is one of many designs from the Open Builds Part Store that showcases how you can use many of the individual parts available in their store to build a fully functioning machine. It uses V-rollers and lead screws for linear motion (with the rollers actually riding directly on the t-slot extrusion). All of their machines appear to use a hand router as a spindle. The structure is build from 40×80 mm c-channels using 20mm T-slot pitch, which provides a stiff beam with convenient location to package the lead screw. The 20″ x 40″ version costs just under $2,000, including all of the electronics needed to get it running.
The Standard 2′ x 4′ CNC Router from Fine Line Automation has some interesting differences from the other routers on this page. While it uses V rollers for linear motion with rack gear on the X/Y axes and a screw drive for the Z axis (just like the Avid CNC), the raised Y axis rails provide a lot of extra stiffness for the gantry. It is unclear if the $2,000 price includes electronics or a spindle, but it may not matter because this version appears to be perpetually out of stock.
Metal Structure Designs
The Saturn 2′ x 4′ CNC Router seem like an upgrade from the T-slot extrusion version also offered by Fine Line Automation. The V rollers were replaced with linear rails, but the X/Y rack gear and Z axis screw drive were retained. The raised Y axis rail design was kept, and the structure appears to be even stiffer because it is made of welded steel tube instead of bolted aluminum extrusion. The $4,000 price does not seem to include motors, electronics, or a spindle.
The 2 x 4 Benchtop CNC Router Kit from Style CNC is an affordable, hobbyist level router from a manufacturer that makes/imports CNC machines across the entire spectrum of feature and price ranges. It uses ball screws and linear rails for all three axes, and even has an option for a 4th (rotary) axis. The base structure is made from stiff cast iron with an aluminum T-slot bed, although the single Y axis rails and thin gantry columns don’t take advantage of that stiffness. There are a few spindle options in the 2kW range, but in general the total cost for a full system is about $3,000 plus shipping (and taxes?) from China (potentially $2k+). There are plenty of similar machines on AliExpress and other websites for about the same price but with my same skepticism on quality and support.
The Laguna iQ by Laguna Tools is definitely over my budget at $7,000 for a 2′ x 3′ model, but it is a great example of a professional, well documented, desktop CNC. It uses linear rails and ball screws on all axes. The build is extremely similar to the Chinese routers with similar gantry supports and centered single Y axis ball screw. However, the Laguna comes with a 3HP continuous duty cycle spindle which makes it better for production work. There are plenty of other similar machines available, like the Probotix GX2550 and Next Wave SHARK HD520.
Key Takeaways
Your frame needs to be stiff. The wooden frame designs tried to compensate by using massively thick plates or tons of repeating ribs. The stiff aluminum extrusion designs preferred compressing cross members with tensioning hardware instead of using angle brackets. The support columns for the gantry need to fight a lot of bending, and there are tons of ways that people seem to be doing this (limiting Z axis travel, using big thick columns, or simply raising the gantry rails above the bed). Making the frame from steel (casting, welding) definitely seems like the cheapest way to make it stiff, but isn’t as accessible to hobbyists.
Your linear motion needs to be stiff. V-rollers appeared to be a popular option for the linear constraint, but using stiffer linear bearings didn’t seem to impact price too significantly. While some designs used belts and chain to drive large axes, the more rigid machines used screws and racks. With the exception of the Chinese models, screws longer than 36″ did not seem to be in use, due to screw whip and buckling concerns. Using rack and pinion drives did seem to correlate with much higher system costs because of all of the extra components required to make those systems work.
Your router/spindle power should match the capability of your machine. Less stiff machines tended to pair with corded hand-routers as a spindle. Bolted aluminum frames did best with spindles in the 1kW range, and steel frames with larger axis motors had 3kW+ options available. In order to avoid overbuilding or overpaying on one system in the design, the stiffness, motion capability, and spindle power all need to match together.
Path Forward
Because I want to be able to cut aluminum reasonably frequently, wooden frames don’t seem to be an option. However, because I am willing to sacrifice traverse speed and depth of cut (increasing my part run time) and don’t need to run the machine 24/7 spindles in the 1kW range are probably more appropriate.
If I were to buy a machine the Style CNC router, or a similar one from a different vendor, seems like the right fit for my needs. However, my fear with a direct-from-china vendor is that the resolution for a major failure (like a cracked casting, broken bracket, or mystery electrical problem) would be for me to pay to ship it back to China, or worse fail to receive any support and be stuck with a $3,000 shop table. Reddit also seems to have some pretty negative opinions on the quality of these machines and the cost of the import process.
If I were to build my own machine it would probably end up very similar to the Avid CNC design. I like that it uses real linear guides, but I may substitute out the racks for ball screws to reduce complexity, part count, and cost, even if it impacts high speed performance. It has a very sturdy frame that I could fabricate without welding. While I would certainly enjoy the experience of designing and building a router myself, building my own shop tools pushes back the timeline for all of the other exciting projects on my list. However, with a machine completely designed and built myself I can have confidence that I can find a fix, or upgrade, for any problem!
With all of that said, a custom built T-slot frame machine, like the Avid CNC, is the right approach for me. There are plenty of paths to save dramatically on cost (ball screws instead of racks, cutting and prepping my own extrusion, more efficient gantry stiffness) as well as great opportunities for improvement (space for a laser engraver, better integrated electronics, reduced part count). Using just a miter saw and some drill jigs I should be able to construct most of the components for the assembly. Now that I have committed to designing and building my own router, the next step is to dig into the mechanics and dynamics of the system to roughly size the machine.