I've got another one coming - a small stepper motor with an 8mm lead length. If that doesn't work I might try a ball screw, and then possibly give up on attempting a threaded rod style actuator. The problem is the smaller you go with the thread and motor, the less likely it is to find a longer lead length. And ball screws are expensive!

You quote in your 1st post you have a one of these. https://www.omc-stepperonline.com/n...-0-03937-lead-length-100mm-8e11s0504sc5-100rs
What is the issue with the one you quote?
Lead screw:
POM (polyoxymethylene) nuts are known for their low friction and self-lubricating properties. They are commonly used in applications where high precision and low noise are required, such as in medical equipment and laboratory instruments. POM nuts also have good chemical resistance and can withstand high temperatures

 

You might consider using halfnuts to disengage the slide from the lead screw.
I could be spring loaded to disengage with a lever to slide and reengage when released.
https://www.answers.com/Q/What_is_half-nut_mechanism
https://thehabitofwoodworking.com/2024/what-is-a-half-nut-on-a-lathe/

Thank you @DNA Robotics - an idea I hadn't even thought of. However I'll be swapping between using the actuator with no force and force very quickly so not sure it will be right here. I'll still explore though.

 

I should add, the quality versions have a built in preload in the ball nut to reduce any backlash down to zero as close as possible.

From my research, the more preload in a ball screw = greater inherent friction. Does this translate to the real world in your opinion or have I got this wrong?

 

You quote in your 1st post you have a one of these. https://www.omc-stepperonline.com/n...-0-03937-lead-length-100mm-8e11s0504sc5-100rs
What is the issue with the one you quote?
Lead screw:
POM (polyoxymethylene) nuts are known for their low friction and self-lubricating properties. They are commonly used in applications where high precision and low noise are required, such as in medical equipment and laboratory instruments. POM nuts also have good chemical resistance and can withstand high temperatures

I haven't received it yet. NEMA 8 are much less common to come by than the bigger brothers that are more common in CNCs etc. It's shipping.

After I bought that (in haste) I did more research, especially re: lead length. I am already assuming that setup in the original link won't work for my scenario, but I'll know for sure when it turns up at my door.

 

Because you are all so overwhelmingly helpful, I'll add in here:

Any advice from real world experience on the least friction guides and bearings?

Namely:
- Linear guide styles (ball spline, rail etc. Needs to be silent, frictionless and small, less than 150mm long, no more than 20 or 30mm wide)
- Pillow block bearing (or something similar for 4mm rod)

 

Does the stepper motor move the slide in both directions or only one?
Is there much resistance against movement?

 

Any advice from real world experience on the least friction guides and bearings?
Namely:
- Linear guide styles (ball spline, rail etc. Needs to be silent, frictionless and small, less than 150mm long, no more than 20 or 30mm wide)
- Pillow block bearing (or something similar for 4mm rod)

Have you checked out the Misumi CAT/site?
They have just about everything in this area.
https://us.misumi-ec.com/misumi-configurable-solution/