SO3 Stronger springs for Z axis for Kress 1040 spindle?

Hi all,

with the standard springs for the Z axis that came with my SO3, the Z axis sags about 2 cm down if my spindle is mounted. The spindle is a Kress 1040 that more people have used successfully if I look into the forum. Is that a particular problem with my springs or do other people have the same issue? Is there documentation about the standard springs that would allow the selection of a stronger replacement spring?

Best regards,

The Springs are a commodity part (EDIT: described as 2.25in to 6.25in Extension Spring and you can source similar springs at the hardware store.

Alternately. clip a few loops off.

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Did anyone ever find out if there were strong/more suitable springs?

Hey Luke, do you have an equivalent of McMaster Carr over your way? Should be a matter of finding the specs on the original spring, then going up in wire diameter, maybe buy an assortment of varying wire diameters till you find the balancing act you’re looking for? Looked in the BoM in the ShapeOKO wiki and it only describes it as “2.25in to 6.25in Extension Spring”, but you could probably put a caliper on them to find the actual wire gauge. I get for stock on my August 2016 XXL:

in inches 0.0048 (as read with my calipers, and it matches the rest)
wire gauge 40
in mm 0.1219

Note I think somewhere in the evolution of the SO3 C3D changed these to something lighter, but not sure, maybe @WillAdams can chime in.


Nah I wish we did.

I bought a mixed pack off amazon but they were way too week. Over ordered one more set from them with a hope. All others I can find are from China, problem is that’s a 3 week wait and £3 a spring.

I’ve measured mine they are 1.1mm gauge wire but I’m unsure on how they are measured. Chinese listings on eBay don’t give much detail…

They don’t have a selection in the local hardware store? They’re usually used to close doors.

The uks take on a hardware store is a joke. Any type of spring would be deamed specialist, they’d tell you to throw it out and buy a new appliance.

There might be specialist spring suppliers online in the UK, buying 2 springs might be difficult mind…

If you’re in London check in at


Springs are typically wire gauge and material I believe:

The higher the number the thinner the wire, mine comes to 40, yours sounds like a 41. I’m not expert, but that seems right. When was your SO3 made? I remember some discussion about lighter springs in later machines, but I don’t know exactly when, or to what they were changed.


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I have two things to say on this:

  1. making a spring is about as easy as it gets. Measure the wire on the spring you have, and buy a length of music wire in the same or next size from a hobby store. Use a piece of tube, rod, or even a wood dowel about 20% smaller than you want the inside diameter of the spring to be, clamp up in a vise and wind away by hand. Give yourself two extra turns for the ends on an extension spring and about 4 extra turns to waste at the ends when hand winding.

  2. Are you sure you need it? The motor does the least work when the balance (neutral) point is at about half way. The motor does half load to lift to the top and half load to push to the bottom. If the neutral point is at the top, the motor pushes full load to get to the bottom. Ideal is a very long (or effectively so) spring with a low K, so that the change in force is small over the travel to minimize force needed at the ends of travel.


Unfortunately I’m not close to London.

I got the next set from amazon and they were no good. I am wondering about rubber bands at this point too.

Yes they are definitely needed. With the 2.2kw spindle and standard springs it rests on the bed…

At this point, one begins to consider whether one should also shift to an Acme screw. Would that be an option?

Not a bad shout, where can I get find one in the UK?

Or a counterweight? If you google “cnc counterweight,” you can find some images and information about counterweighting for the weight of a spindle. Could be something as simple as a cable and weight, with a pulley mounted to the ceiling.

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Maybe a robotics specialty house?

I put together a B.O.M. for a design I sketched up (it’s pretty obvious, and I lost the sketch) here: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable

Mounting Plate for Nema17 or Nema23 — use a pair to mount the motor at the top of the plate: Mounting bracket for stepper motors - RobotDigg

ACME Threaded Z-axis Nema23 Stepper — mounting the nut looks as if it will need a custom part ACME lead screw threaded Nema23 Stepper - RobotDigg

KP08 Pillow Block — would probably need to cut a slot in the bottom of the plate KP08 Pillow Block for 8mm shaft - RobotDigg

I’d definitely try @cgallery’s idea of a counterweight first though — negative of course is doubling the mass involved, but I think the motors would have the torque to cope w/ it.

More I think about it, the counterweight has to be mounted to the Z-axis, otherwise you’re complicating X/Y movement.

I think that is what Will is alluding to in his last paragraph. Good catch, Will.

I have one on order -

This one is setup for XCarve, but Joe is including an adapter plate for a bolt on installation to the SO3. He is also drilling out holes for my stock SO3 spindle mount. Mine arrives next Tuesday, so once I have it installed I will do a review. It is getting rave reviews on the Inventables Forum.


@cgallery - I have thought about counter weights but it then makes the logistics and the way the machine handles much more complicated.

I actually had a mini breakthrough last night. In my pack of 200 springs from amazon they offered no more springy-ness than the original, however they were held the diameter - as a result I can double them up without hitting the x extrusions like the original, which gives me much more confidence in running the machine (which I’m yet to do).

Currently I have 4 in place (2 each side) and it supports the spindle in a neutral way - it doesn’t pull up but doesn’t fall down much either. I might add an additional spring or 2, I will post pictures this evening.

@dtilton71 - I’d love one of those (love is a strong word) but it’s currently out of budget since I spent all this months pay on the spindle…

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