anybody in the group hacking direct drive with screwballs ?  i've been playing with

anybody in the group hacking direct drive with screwballs ?
i’ve been playing with 3 42" screws driven by 2amps steppers , experimented with dual screws per axis driven by a single pololu (this failled as the 2 screws where not synch 100%) and i’m back to single screw with 4 linear bearing on 2 7/16" shafts , but still getting some wobble on my X axis , trying to space out my bearings to 4" see if this will solve it , but has anyone gone that road ?

best reg. alls
keep on hacking

Is it possible that the wobble is due to inaccuracy in the screw? If so, look for a used preloaded screw on eBay. Last time I looked, there were quite a few extremely precise screws in Asia, removed from obsolete semiconductor equipment. I haven’t actually used one of these screws, but given the precision of semiconductor equipment, I think any screw you could find will still be overkill for the needs of a mere mortal.

hey mark , no it is a high precision screw with 10 rotations per inch , i think it has more to do with the bearings and the size of the thing (42" screw with 36" real travel) the wobble is barely noticeable but over 3 feet it does make a diff

When you say wobble, do you mean the screw is bent? I believe that Keith Fenner ( has at least one video on precisely straightening shafts. It may be possible to straighten it enough to work for you.

If it isn’t bent (i.e. the relationship between rotations and table position is not a straight line), then I would not call it precision. Look up the part number and see what grade it is. Here’s some info on grade:

no basically the base of my Y frame was wobbling at the extremities , it’s fixed now with a new bearing holder at those extremities i still need to properly align my smooth shafts but it’s already much much better , i’m doing all this with recycled materials and a whole lot of epoxy resin :wink: