As I’m engineering a 1500x1500 CNC, I’m running into a lot of design decisions. One of those is linear motion, specifically selecting a ball screw.
Before I’d really done my research I ordered a 1605 x 1500mm. It is ever so slightly bent, with about 20-30 thousandths of runout at its very worst. It’s from Amazon, but was highly rated and the price was fantastic. Worth a try, and a learning experience.
As I got to doing my research I saw that for that 1500mm I was undersized and really needed something more along the lines of 25mm. I looked on Amazon and a few options exist, but wanting to avoid that experience again I looked elsewhere, too. I saw that it was going to be in the ballpark of $300-400 for a decent quality 25mm, at the least. That’s 3-4 times what this slightly bent 16mm cost.
As I weighed my options and played around with this one a bit more I noted the bend was only really an issue at high speeds. It was like a jump rope, swinging it’s mass out of balance. It was only 20-30 thousandths at worst though, and a problem only as speed increased. I thought, what if the nut was what spun, instead of the screw? The idea being that the bend isn’t an issue if it’s not spinning because the nut never catches anywhere, and if the nut is supported well it can push out such a small bend. I did some research and then found out that was a thing.
I deduced it wasn’t that the 16mm wasn’t sturdy on its own. It might sag due to its length, but the issue seemed to not be that so much. It’s just not sturdy when bent and spinning. So a potential solution is to do a rotating ball nut setup in lieu of rotating ball screw.
So, with all that prelude aside, are there any important considerations between a rotating ball screw and rotating ball nut setup? Is it reasonable that the diameter of the lead screw doesn’t matter to as great a degree with rotating nut vs rotating screw? Because if so, I’m finding that I can potentially keep costs lower, have less inertial mass to accelerate and decelerate, and potentially get muuuuuch higher speeds without actually reaching critical speed.
Any thoughts on this?
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