Lead screw the bigger the better?

Synapsis

I'm doing some upgrade on my z axis because I have artifacts like wooble. So I'm taking out the 4 rods
and replacing with linear guides I also want to change my two lead screw 8mm P1 which are connected to two
Nema 17 via couplers. I was wondering if I should go for something larger than 8mm like 10 or 12 mm lead screws like these:
Lead screw 12 mm DIN 103 Uni - Iso 2901-2902-2903-2904, tollerence 7e using oldham couplings.
Are even bigger like 16mm.
What are you thoughts
What are you using? any advice would be helpful.

thanks

fcwilt

Hi,

I have a Folger Tech FT-5 with twin 8mm leadscrews and quad 8mm round guide rods.

It prints as well as any printer I have seen.

I did change out the motor-to-rod couplings for this type:

https://www.amazon.com/gp/product/B078VT1QCK/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

The original ones were of this type:

https://www.amazon.com/gp/product/B01HBPHSII/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I don't know of any downside of larger rods other than the weight of the associated moving parts.

Frederick

deckingman

@synapsis The lead screws should only provide lift. The linear guides should prevent the build plate from moving in X or Y. The lead screws should not in any way act to constrain the bed from any X or Y movement - that is the job of the linear guides. Therefore, M8 lead screws will be more than adequate unless your bed or gantry weighs more than a medium sized family car.

frank26080115

Wobble could come from bad shaft couplings that are not concentric. The result is the leadscrew moving your bed in a lateral direction

(for flexible couplings, this might sound counterintuitive, but the closer the leadnut is to the coupling, the flexibility of the coupling doesn't help)

If you think about it... the thicker the leadscrew is, the worse this problem becomes

If possible, if I were you, I'd somehow get some stepper motors with integrated leadscrews, no couplings. My own printer uses some Tr8x8 from Pololu. E3D sells some that are Tr8x2, which have higher resolution and comes with a POM leadnut.

Also consider checking the stiffness of your linear rods. You want them to be a very hard steel that doesn't deflect, you want these to be thicker, not thicker leadscrews.

Synapsis

Thanks to all for the replys as you all suggested I will still use the 8 mm rods then and maybe by the motors with rods.
I'll let you know.
Thanks again