I decided to build a larger format CNC. I have completed the torsion box for the bottom which is approx 52x120 in. I am awaiting some parts to install the Y-axis rails and blocks. My next step is to machine the Y-gantry supports using my existing Openbuilds 1510 and then use 8020 to build the remaining parts. As part of the building process, and once I have fitted all the parts, I would like to use the motors and blackbox from my existing machine to operate the larger format CNC just to ensure that it will work and to work out any bugs. At some point I will upgrade to larger NEMA 34 motors and appropriate drivers. I intend to try using a chain drive for the y-axis initially as a low cost solution before upgrading the drive system. This project is as much a build and learn at a minimal cost with the ability to upgrade over time. Does anyone see any glaring problems with this approach?
I am curious why you are switching to Nema 34? A 52 inch gantry is smaller and lighter than a 60" (1500mm) which can easily be driven by the regular, or high torque Nema 23 motors. I can see if the gantry got significantly heavier, or if you were using really long and heavy ball screws or acme threaded rods, that you may need larger motors. Have you considered rack and pinion for the y axis? I was just looking today at McMaster-Carr at options available in rack and pinion. The price does not seem to prohibitive.
I have looked at rack and pinion but not seriously. However, I have not ruled it out and will have a look tomorrow. It does fit in with some of the ideas/price points that I have been looking at. Other ideas?
I agree with Griac about the stepper size. My Gantry (the X axis) is overall 58" with a 1.5kw air cooled spindle. The Y axis has two NEMA 23 276oz/in steppers and they drive the gantry without breaking into sweat.
A motor’s viability is a function of the type of drive system. A TR8x8 lead screw has roughly 7.5x the mechanical advantage of a 20 tooth pulley on a GT2(3mm) belt. When torque losses due to motor speed are factored in the torque difference could easily be a factor of 15. So to argue a specific size motor will do for every system is not necessarily the case. As for using a chain drive, probably not a good idea. Chains stretch as they wear. The minimum sprocket size will also be huge, decimating resolution. I would suggest a 12 to 15mm wide belt with a 3 or 5mm module. As far as pulleys, probably 20t for a 3mm belt or 15-16t for a 5mm module belt. Be sure and use idlers both sides of the pulley to where you can maintain at least 200 degrees of grip.
Can you elaborate on this statement: I would suggest a 12 to 15mm wide belt with a 3 or 5mm module. Can you point me to a source where I can visualize what you are recommending?
You might take a look at sdp-si.com, bbman.com, or at powge. For the 3mm module I would probably stick with the GT2 or GT3 line. Can’t specifically say which is best for the 5mm module. I’ve seen it used several times here on the forum but didn’t pay attention to which style they were using. module = tooth spacing
OK, I had a look at the GT3 line. If I am on the correct page, metaphorically speaking, the 3mm x 15mm wide belt would be the better choice along with a 20 tooth pulley. I presume these have to be matched? Therefore, for my project I would need, just for the Y-axis, about 22 ft of belt (11 each side), 2-20 tooth drive pulleys, and 4-idler pulleys. Will that do the trick? Would a 3mmx25 mm wide be a better option?
Seems fine as long as the pulley is from the same line as the belt. And yes, would probably stay with the 15mm belt.
I have had a look at the three websites that were suggested and the number of belts and pulleys/idlers is overwhelming. Therefore, is there someone that can recommend the exact belt, pulleys, idlers that I would need for my project. Thus far, my requirement would be 3mm pitch, 15mm wide, 20 tooth stepper pulleys, and perhaps belt end clamps.
I looked at SDP/SI and your real limiting factor is your length requirement of 3000mm. There was only one 15mm timing belt available in that length but it was 5mm pitch. Catalog | Designatronics Store | Stock Drive Products/Sterling Instrument
The Powge store was easy. They sell a matching set. 24 Teeth 3M Timing Pulley Bore 5/6/6.35/8mm + 3M Open Belt Width 15mm PU Black | eBay And if you want less teeth, PU Black arc HTD 3M Open Synchronous Timing Belt Width 6/9/10/15mm Polyurethane | eBay plus HTD 3M 20 Teeth Timing Pulley Bore 5mm-10mm for Belt width 10/15mm HTD3M 20Teeth | eBay. There are other pully sizes, but currently not in stock in 15mm wide.
