Lead screw upgrade

[adamfilip]

Can anyone recommend a precision Ground Lead Screw or ballscrew and Nut that I could purchase that I could swap in for the existing Threaded rods on the makerfarm i3v 12"
ideally same diameter

[printbus]

I could have missed them, but when I looked into this before your last lead screw thread, the smallest I was finding were 8mm.

[sniffle]

depending on the pitch you may have to swap the X motors to a geared X motor to have enough torque to be able to lift the X carriage

[printbus]

Most know that I nitpick and analyze the core of these printers to no end...

The existing Z motors theoretically *should* have the ability to drive the Z axis faster, especially after reducing the microstepping ratio from 1/16 to say 1/4 (which I have done). Reducing microstepping has two benefits. There's a limit to how many step commands Marlin can and will process in window of time, and the default 4000 steps per mm feed is already a pretty heavy number of step commands. Reducing microstepping reduces the number of step commands required, or conversely, for the same number of step commands more rotation can be obtained. Increased microstepping comes at a loss in torque; reducing the amount of microstepping should provide more torque. There's a precision loss with reducing microstepping, but to date no one has challenged my position that we don't need 0.250 micrometer precision in the z-axis (1mm/4000 steps per mm).

In practice, however, I have found the Z motors can't be driven to the theoretical maximum on my 8-inch printer, likely because they just don't have the torque to do it. Yeah, setting Z up with little acceleration might help but that detracts from the speed increase we're shooting for. When I ran into that block, I dropped pursuit of M6 or M8 threaded rod upgrades, and certainly the lead screw thought.

The x-carriage is surprisingly heavy. I'm surprised by it every time I have the z-nuts disengaged. The 10 and 12 inch printers will be even heavier. The longer lead on lead screws is going to make things worse. Not only are the narrower lead screws hard to find, they're also typically "4-start" threads and you have (IIRC) 8mm per rotation lead. From the motor perspective, there's a big difference between moving the x-carriage 0.8mm per rotation with the M5 rods and 8mm per rotation with the lead screws. Find a 5mm lead screw with no more than 2 thread starts and I'm on board. Well, I'd give it some serious thought.

Like sniffle said, before you know it you're looking at geared motors to deal with the torque. The other option I've pondered is actually adding a counterweight for the X-axis. That's not really all that far fetched - put pulleys at the top of the frame, looping lines from the X-carriage over the pulleys to some fishing weight lead ballast on the back of the frame...

[sniffle]

Considering most of us are printing at either .2 or .3 mm layer height, inluded with the geared torque that gearing is also how we regain that precision for moving those small movements.

[adamfilip]

I need to replace one of my z rods as its now bent, so I would like to take the opportunity to switch to a 3-4mm lead screw or ball screw if budget permits

1mm per rotation preferred
But I'm willing to look into geared steppers to achieve better precision

[printbus]

no one has challenged my position that we don't need 250 micrometer precision in the z-axis (1mm/4000 steps per mm).

Wait. I forgot the conversion from millimeters to meters. The Z axis resolution is actually 250 nanometers per step.

[adamfilip]

http://www.mcmaster.com/#precision-a...screws/=vtnouc

[adamfilip]

Thoughts on this lead screw
http://www.mcmaster.com/#6642k11/=vtockj
comes in 18" lengths

and either these nuts
http://www.mcmaster.com/#6642k31/=vtoeev

or these nuts
http://www.mcmaster.com/#6642k21/=vtoexq

Each rotation is 1/41.7" = .02398" = .609mm

[brochapman]

For what its worth I did this mod http://www.thingiverse.com/thing:449341 and have had much better z axis movements and resolution. I originally got two 12" acme threaded rods and that greatly reduced the z height, I have since purchased a 36" piece and cut it down to the same length as the stock threaded rods.

I know this is not a precision lead screw but it works really well for me.