I was wondering if I can get some of your thoughts. I have the Workbee 1500mm x 1500mm. I like it alot. I like the design and everything. However, I am getting bigger projects to do for my clients. I want to build another cnc machine but bigger using the workbee design. The only item that needs changing are the side extrusions and the supports in the middle. I want to build a CNC machine with the x axis to 8 feet and leave the gantry length the way it is at 1500 mm (5 feet almost). So essentially I want to build a 8 foot x 5 foot CNC with the design of the workbee. As far as I can see, I would need to change the 2 outside and the support rails to 8 feet and maybe get 4 larger stepper motors say NEMA 34. What does everyone think? Could this work or do you foresee problems. Let me know your thoughts. Vince
I forsee belt stretch as being a potential issue. I would look into rack and pinion. If your gantry remains the same size and weight, I do not know why you need bigger motors.
It's not quite as simple as just doubling the length. With the Y-axis rails clear spanning the entire length with no intermediate support, doubling the length gives you 8 times the deflection. So an imperceptible 1/128" deflection in your current system becomes 1/16" in the new system which won't be so imperceptible. For this to work at 8', you're going to need to revise the design to having cross members supporting the side rails which lets out using the WorkBee or Lead style gantry plates which ride both sides of the beam. Not saying it's unachievable you're just going to have to rethink it. And as Craig notes above, you're going to have to think about belt stretch. Easily resolved but you're going to need a much wider belt, probably something in the 12 to 15mm range. Rack and pinion may be a better option. As to the need for larger steppers, no. While the length has changed it doesn't take any more strength to move 8' along a rail than 4'. In the grander scheme of things though there's a reason Openbuilds doesn't sell or in any way promote 4'x8' systems. The aluminum extrusions were just not designed to go that far. And pushing them that far often leads to unsatisfactory results. If you truly need 4'x8' and have the customer base that'll help you pay for it I suggest PRO4896 4' x 8' CNC Router Kit | Avid CNC. There is another option to spending a lot of money to build a bigger system and that's using pin registration / tiling. Do a search on youtube. You'll find it's fairly easy to cut 4'x8' sheets on a 4'x4' system.
