Hello all, First post, long time reader. I am planning on building a 1500mm X 1500MM CNC machine. I wanted to build one on the cheap but that does not seem feasible since I am realizing that for what I want to do I will need more expensive parts. I would like to be able to cut hard woods and aluminum. I have a few questions about parts as I am sourcing them. First off I am looking at Nema23 High torque steppers. The open builds are 345oz/in torque with 8mm shaft, but I found some others that are 425oz/in with 10mm shaft. Does the higher torque make that much of a difference, is it better to have? The next problem I have run into is 10mm bore pully gears, I was thinking about using GT3 belts but its almost impossible to find 10mm bore gears for GT3. I was leaning towards 8mm Lead screws but read that there are issues with that length and I'm guessing there is the same issues with ball screws? Now I am leaning towards gear and pinion but I am not sure if I will need different size gears and if so what size, or just a direct drive from a gear on the stepper, I will have to sit down and do the math. Next on the list are the motion rails, I am trying to figure out if I should use V-slot polycarbonate wheels, V-guide metal wheels, or linear slide rails. In everything I have read everyone likes the linear slide rails as they have the least amount of movement/flex. I currently have aluminum C-frame for the build and just discovered the high Z and how that makes the Z access stiffer so I may have to change up my build plans. I am planning on buying the blackbox motion control for the brains. Any and all input is appreciated, and thank you all for your great posts and information! I have learned so much from this forum.
Correction, our NEMA23s both have 6.35mm shafts only See docs.openbuilds.com/blackbox (; We stand by our products, Xtreme wheels on V-Slot rules!
Look at the torque curves. Which has better performance at the microstepping rate and RPM range you're planning on using? Steppers are rated at max torque, which is at extremely low speeds with full stepping. 8mm lead screws definitely see fairly significant performance improvement at 1500mm from being tensioned, and would work for most hobby machines, but you're not gonna be able to crank up some crazy rapids with them. Ball screws aren't gonna suffer the issues quite as badly because their root diameters are much larger- probably about 10mm for 1204 and about 13mm for 1605/1610. It's the actual solid material in there that determines the "dangerous rotation speed". A 1605 in a fixed-fixed (similar to a tensioned lead screw setup) operation can do up to about 1500rpm. That's 7500mm/min. Double that for a 1610 screw. There's a lot more flexibility in ball screws, because they're made for so many more applications. They're great, but a lot of people have trouble with them because they don't know that they have quite precise mounting tolerances as a product of their precision nature- you really need to sweep them in in both directions with a test indicator. If you're willing to put in the work, they beat out everything for rigidity except box/dovetail ways, and those they beat on speed. Everything is basically modeling clay when you start looking closely enough- metal is soft when you heat it red hot, and it's soft at room temperature, just different levels of soft. Simulation helps, but it's a lot of work: That's one from my current build.
As always great info Rob. I didn’t think about the torque curve just the torque number. Moot point now as they were 4.2A and black box only supports 4A peak so it’s Open builds Nema 23’s
With motors bigger is not always better. Excessive amounts of power only gives the system the ability to destroy itself, either by stripping teeth off a belt or by bending the frame should a bit get lodged or a carriage unexpectedly reach the end of the extrusion. The 270 oz-in range is pretty much the sweet spot for most hobby grade systems. 425s are far too big unless the rest of the system is beefed up accordingly. GT3 belts are not even an option with 425 oz-in steppers.
I'm looking at a 2hp 28000rpm router one speed. would a variable speed CNC spindle with lower RPM's be a better choice? I would think higher RPM would be better unless I'm cutting acrylic?
Actually lower speed is more useful than high speed. In over 50 years of using routers I have never found a use for the top speed of any router. I use a (Chinese clone) Makita palm router, bottom speed 10K rpm - which is what I use 90% of the time. I have cut mdf, hardwood, pine, plastics (mostly thin polystyrene sheet) and aluminium with it. You said you had some aluminium C section for the frame, but didn't specify the gauge or dimensions - its a matter of designing a system that is in balance - will the frame be rigid enough to minimise the flex from the weight and the forces from cutting using that powerful spindle to its full capacity? Alex.
Cutting aluminum with small carbide tooling usually taxes top speeds because there's not really such a thing as an effective top surface speed for Al. Not too much else though.
Well now I want a variable speed router, does the blackbox motion control, control the rpm? looking on amazon the cnc spindals are 220volts and not 110 plus a router seems much more affordable. recommendations please.
You would need an adaptor for the controller to set the RPM. Personally, for what I cut (aluminum, plastics, and wood), I know what speed each cutter needs and I set it manually to that speed before starting the program. With aluminum, sometimes when cutting at a speed that has worked many times before, something may start to sound not 'right' and I manually adjust the speed of the router until it is optimized. Since the machine does not have an automatic tool changer, and when using Estlcam during a tool change pause, I can read what my tool is supposed to be cutting at as I am changing the tool because it pauses at that code line. After manually changing the tool, I adjust the speed on the router and continue the job. Like others, I prefer a Makita because it has a larger RPM range, but then you have to source a 65mm mount for it, or add a shim. If I were to start over fresh, I would probably get a DeWalt for the easy mounting. I find a lot of the stuff I cut is at the lower end of the DeWalt range of 17,000rpms and because it is so popular among hobby CNCers, there are a lot of video resources and other online resources related to feeds and speeds for various machines.
I 3d printed two PETG mounts for my Fake-ita and it's so solid you can't move it if you pressed all day long on the router. I would have used it if not for the fact that the shaft was drilled crooked.
