I built a 4x8 CNC Router with a only one center X axis ballscrew
They said it's a bad idea, they said it wouldn't work, but I did it anyways
When I was designing this I never liked the idea and added complexity and expense of using either two ballscrews for the x, one on both sides, or whatever other method. Using two open loop steppers on either side also sounds like a nightmare to me, one skips a step and now your gantry is out of square. Not to mention within the 2 weeks I've had this deal operational I ran it into "hard stops" quite a few times, heck, the "hard stop" is my idea of homing it currently. :rainfro: If I were to use a dual ballscrew/rack and pinion design in the future and was open loop I would do it with one stepper with a belt drive system driving both...but that's me.
My machine uses 2x6" 3/16 wall steel tubing to clear span the 8ft. That's the minimum I had calculated to not flex, and it doesn't it's extremely solid. The other advantage to this design is only having four points touching the ground, which I added "leveling feet" which is really just nuts welded to the bottom with some carriage bolts inserted, sitting on steel plate and concrete block. I intentionally made the table to be extremely sturdy from wobbling in any direction but not so rigid to where it won't twist because then I can just use the "leveling feet" to level out the four corners with an accurate digital level to ensure it's as flat and true as I could get it. If you lift up (jack up) one corner it will surely lift up the opposing side but has enough twist in it for adjustment. If I had attempted to just make the table rock solid it would've never been true, things warp when welding and a lot of guessing involved.
My gantry is also steel tube and weighs in at 200lbs. The whole machine may not look that heavy but it certainly weighs at least 800lbs. It's all welded, I did attempt to bolt a portion of it together so I could dissassemble it to move it in the future but I just ended up welding it all. Don't ask me how I could ever move it out of this shed because I have no idea I would like to rebuild the gantry in the future, I warped the crap out of it when welding the steel tube and that's why I had to attach my linear guides to aluminum angle which is then tapped and threaded to the steel gantry, because the steel gantry itself is no longer true. I spent a lot of time with a digital level still making sure everything is flat and straight up and down, some shimming and finessing involved. The linear guides attached to the aluminum angle and machine screwed in place actually turned out to be a blessing anyways as it allows for adjustment that wouldn't have been there without it.
My Y axis will cut 49.5" and it's really something like 53" between the rails.
Alright time for the question everyone wants to know....Does the gantry flex with the single center ballscrew?????
No!....well yes, but mostly no.
If you punch it on one side, it will vibrate a little but in no way is it flimsy or hinders the accuracy. I would attribute this to a few things. The very wide stance I have the gantry on the linear guides is one thing helping. The other being the gantry being extremely rigid. It was worse until I added a brace to the bottom bar of the gantry which stiffened things up more now it's almost nill. I however have hit a couple higher feed rates where it will start chattering ever so slightly. It's almost like a resonance thing so if you go below or above that feed rate it stops. For me, this is no big deal because this deal won't even run those faster feed rates with the router I've got in it right now in most materials.
In conclusion I'm very satisfied with this for my first router. If I build another one, the only reason I'd build another one would be to run very high feed rates so yes to accomplish that I would run a ballscrew on either side of the x axis ...but for running 100ipm and under this is great.
PS. For the record I have something like $1300-1500 in parts and materials for this deal
Re: I built a 4x8 CNC Router with a only one center X axis ballscrew
Thanks man!
I already bought ballscrew, slides and complete actuator for gantry... just before reading this post i was worrying may be one screw would not work for long axis...
I am building 43"×72" machine with one ball screw at center for long axis
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I built a 4x8 CNC Router with a only one center X axis ballscrew
I would like to rebuild the gantry in the future, I warped the crap out of it when welding the steel tube and that's why I had to attach my linear guides to aluminum angle which is then tapped and threaded to the steel gantry, because the steel gantry itself is no longer true. I spent a lot of time with a digital level still making sure everything is flat and straight up and down, some shimming and finessing involved. The linear guides attached to the aluminum angle and machine screwed in place actually turned out to be a blessing anyways as it allows for adjustment that wouldn't have been there without it.
