Can I get the rigidity with Openrail vee groove? V-Con?
Hello All,
I am in the process of designing a medium sized CNC machine to be used to cut thin aluminum sheet to build a homebuilt plane. Material is mostly 2024 and 6061 ranging from .020" to .125". The majority is in the .020 to .04 range. Also I will need to cut 3/4 MDF for the sheet metal forms. Travel of the machine needs to be 5' x 4' with very little Z so I intend to keep the Y Gantry boom fairly close to the material to cut down on flexing. I plan to use 4 axis with 2 motors being used on the long axis (Y). My question is if I use a large extrusion as the building block 40x120 can I get good rigidity with the Openrail system and metal Vee groove wheels? I once made an overhead gantry that had a travel of 10' x 20' and the vee groove wheels from bishop wisecarver worked great, however I was not worried about micro positioning. I am not worried about rapids as I am willing to travel slow while cutting since the material is thin metal anyhow. I plan to use teflon coated leadscrews with anti backlash nuts or cheap rolled ballscrews if I can afford them.
If the Vee groove system is not sufficient I have some THK HRW25 rails, but I dont think they have the travel I need. There in storage and i will have to see how long they are. I have been to the automation surplus site and they have some 30mm Hiwin rails that look promising, but i have never been a fan of Hiwin, but then again I am paying this time so I can possibly change my views to save money... I have some renishaw linear encoders I would love to use and run closed loop, but I may go open loop at first to keep things simple on the initial setup.
What say you? Has anyone built a decent machine from Vee groove wheels? The CNC mogul is close, but it looks a bit flimsy for my application.
I would check eBay for vee rails. If I'm not mistaken the open rails stuff is aluminum, and they won't last too long against the hardened steel vee bearings, weight of gantry, and forces needed to cut through aluminm sheet. You likely can feed at higher speed than you think as you should with aluminum. Pacific Bearing makes an integrated vee reail and extrusion if you want to go that route...
If you're not worried about micro-positioning and you're not using servos then the encoders might not be necessary. If you're using Mach3 I don't think there's encoder feedback to the software, the drives will just fault. I'd probably go for the HiWin rails over the BWC bearings...
I just added V-con as an option to the title. I just had a look at their design and it looks promising since its a cheaper alternative to BWC stuff and its hardened steel. I am sure the Recirculating rails are still a better option but curious for my application if the V-con would work? I would design my own CNC cut carriage plates to maximize rigidity rather then use the extrusion pieces as building blocks between the gantry portions.
I plan to design the gantry for steppers to run open loop. If I can find software that can use encoder imputs then that would be a plus. If not Mach3 will work in the meantime. Any idea if the Gecko 4 axis drive can take encoder inputs? I can always design them in for future expansion.
Can I get the rigidity with Openrail vee groove? V-Con?
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