58 inch chinese ball screw whip

[LazyMan]

I know ball screw whip has been discussed before but...I'm planning to use a 58" from fixed support to free end support 1610 ball screw from linearmotionbearings on ebay and just wanting some feedback. I'm hoping to get 300in/min at least but not too optimistic judging from nooks critical speed calculator. I really don't want to use 2510 due to space constrictions. Any thoughts?

[Walky]

I got a 47" 1610 ballscrew from Chai (linearmotionbearings2008), it works ok but I had to straighten it because it was bent and whipping. A couple of wood v-blocks and some time later I had it straightened quite a bit. I think it still whips a little but not too much and mostly when the nut is at the ends of the travel. It has never stalled, so I guess it's ok. I get 350 IPM rapids easily with nice torque (I could actually get 450+ IPM with lower torque, but I wasn't confident running my machine with such a high pulse rate, considering I'm using 1/16 microstepping). I'm using 400 oz-in steppers with Probostep unipolar drivers at about 42V, 2.5A each. If you can get a Gecko G540 and a 48V power supply beefy enough to feed the steppers at Bipolar parallel (higher current, great torque and speed) it will be even better than mine. Pushing a 16mm screw that hard might be too much and progressively bend it or damage it, I guess (not an expert, just an assumption). I never cut faster than 250 IPM anyway as I don't need to (I usually cut on the 100-200 range).

I had space problems too (my machine was designed with other screws in mind and I decided to upgrade), so 16mm was my only option; if I had to get that length again for a new machine I'd go with 20mm or even 25mm. I don't see a "2010" screw, maybe that size is limited to a 5mm lead? (there is a 2510, though).

I needed to add some shims to my bearing blocks to preload them (there was some play in them), after that they worked fine.

I bought one nut per screw and I can't feel any backlash on them, so I won't use double nut anytime soon. Remember to use lithium grease on the nut and blocks, it smooths things a lot.

Chai's custom end-machining of the screws (by my specifications) was amazingly nice and accurate, good stuff.

These ballscrews are the best upgrade I've done to my machine along with the SuperPID and linear rails, the speed increase is great for long tasks like 3D engravings.

[LazyMan]

Yep, 20mm only comes in 5mm pitch and its like that with many different manufactures. Now I am concerned about it arriving bent so I may be forced to work out a solution with the 2510 screws or make my machine smaller. Have you actually measured backlash with an indicator or it just doesn't show up in the cuts? I planning to use two nuts and spring preload.

[Walky]

I can't feel any backlash. Actually, all the backlash I see is from the fixed block, and it's not much and only under pressure (I guess I need to add an extra shim, but it still works ok for me and can't see any pass marks). I would say backlash in the nut itself must be in the 0.05mm - 0.01mm range, which is actually within the precision limits that microstepping is allowing me to have (contrary to general belief microstepping is not 100% precise, so there is an error margin). OF course, different screws might be different so, it you want to play safe, double nut surely won't hurt.

I'll measure it when I can (I did once at the side of the machine before installing the table and got about 0.01mm, but there's some side play from my gantry so it might have been affecting it.

I bet a 25mm ballscrew is less likely to get bent in transit than the 16mm one, not sure but that's my assumption considering it would hold bad handling more nicely. I would get the 25mm screw (or even the 20mm, 5mm pitch is it worked for my design and drivers/motors) if I really needed the lenght and cost were not a problem, but that's a personal decision really.

Or... you can get the 16mm screw, straighten it if needed and try how it goes; if you don't like it you can sell it and get a bigger one. That way you can get your design unchanged and hopefully save money considering the 25mm screw will be more expensive, and shipping too since it will weight more than twice as much.