Acme LeadScrews

I found some Acme leadscrews for relatively cheap here: [openbuildspartstore.com] would these work well for a 3d printer? I have a Reprap i3x and the threaded screws I have now are crazy bent so these I am hoping will eliminate all "banding". I would get these and anti backlash nuts for them along with flexible couplings. Is this a good set up?

They should work very well for your Z-axis. Where are you planning to get the anti-backlash nuts? I haven't seen any at a reasonable price. For what it's worth, there are other causes of banding. The biggest problem that I have seen is selecting the wrong layer height which results in fractional numbers of steps for z moves. The motors will settle at the closest full step and that can result in a "fat layer, skinny layer, fat layer, etc." pattern throughout the print. Refer to the prusa calculator to see if you're using an optimal layer height first. If not, try running a few prints with a recommended layer height. I think you may be surprised by the results even if you see obvious wobbles in your z-axis lifting rods.

Quote
stonedcoldskier
They should work very well for your Z-axis. Where are you planning to get the anti-backlash nuts? I haven't seen any at a reasonable price. For what it's worth, there are other causes of banding. The biggest problem that I have seen is selecting the wrong layer height which results in fractional numbers of steps for z moves. The motors will settle at the closest full step and that can result in a "fat layer, skinny layer, fat layer, etc." pattern throughout the print. Refer to the prusa calculator to see if you're using an optimal layer height first. If not, try running a few prints with a recommended layer height. I think you may be surprised by the results even if you see obvious wobbles in your z-axis lifting rods.

That is what I thought it was long ago. Then I did a simple test with a cube. One i printed at .2, the other i printed at .197 something that was calculated, and the other calculation around .21.... And they turned out the exact same. The tops of my threaded rods move at least 1.5 cm while it rotates so I thought this was a major problem. [www.robotdigg.com] This is the lead screw I was planning on buying. One thing I am concerned is that my smooth rods are 8mm too, I remember people saying you want the threaded rods to be thinner? So that they don't counter the path of the smooth rod. Should this be a concern?

When you upgrade to the TR8 lead-screws, they should be dead-straight and their thickness, relative to your smooth rods, shouldn't be a factor. If you were going to stick with threaded rod, I would say upgrade the smooth rods to 10mm or 12mm to better constrain their movement. I can say from experience that those Robotdigg nuts will work well. I use them on my Taz clone along with their steppers with integrated threaded rod. That setup eliminates the coupling between the motor and screw and is as smooth as butter.