Stepper driver current/settings etc--my Z won't lift

Quick break down:
4’ x 4’ table using 25.4mm DOM steel rails,
500W spindle
z-steppers are Nema 17 17HD48002H-22B Stepper Motors-- 1.7 A, 0.59 Nm, 84 oz/in
control board SKR v1.4 with 2209’s set at 800ma (default), 24V power supply. Each stepper has its own stepper driver so no splitting of voltage or current.

everything else standard.

Issue: my z-steppers won’t lift the gantry without a little help.

Before I start tinkering does anyone see a smoking gun there as to why? I’m assuming the amperage settings to the motors are too low? I don’t want to raise them to max and risk blowing something out if that’s not the solution.

No smoking gun, but it is unlikely that raising the current will be the ultimate solution to your problem. There are lots of LowRiders built with stock settings and heavier routers/spindles that don’t have your problem, so upping the current significantly is the last thing you should try.

Be sure you are not using both ZMA and ZMB plugs for your Z azis. These two plugs share a stepper driver in parallel and therefore do divide the current.

Mechanical binding is a common reason for Z lift problems. I don’t own a LowRider, so I cannot give you specifics on how to troubleshoot the problem, but it is covered a number of times in the topics on the forum.

The V1 maintained firmware set the current at 900ma RMS. This small difference is unlikely to have much impact on your problem.

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Just to make sure. Some boards have two Z ports. You shouldn’t be using the second one if you have separate drivers configured.

Also, make sure the leadscrew are lubed and the leadscrew nuts aren’t misaligned. Removing a screw or two and leaving just one will let it line itself up with the leadscrew. A good sign the friction is low enough is if the gantry falls on its own.

If you have a 1 start leadscrew, it will never fall on its own, but you need to reduce the speed.

Adjusting the current up is a good choice. The drivers need a fan to keep cool. If the motors get above about 50C, then the mounts can deform. That’s usually the upper limit.

Check the alignment of the Z axis.

A few things that come to mind:

  • The XZ pieces should have the lattice part towards the router side. While you can assemble it the other way around, the motor does not then cleanly align with the Z nuts on the Y plates. This misalignment causes more friction than we like.

  • Lubricate the Z screws. A little of that silicone grease makes a huge difference.

  • Check that the Z axis tubes are properly seated in the XZ caps. There should be a gap between the clamp pieces and the main body. Check that those clamps are right side up. I’ve seen one where the clamps were upside down, causing alignment issues. (The bottom of the part as printed should face upwards, there’s a small lip inside to brace against the top of the Z tube.)

  • Leave a little slack for the Z nut to wobble a bit. Being mounted too rigidly doesn’t help things.

Well I’m embarrased to say, thats exacyly what I did LOL. Once I moved the Z2 plug over to the proper port, it worked as expected–thanks for the really quick responses everyone!

(and I lubed those lead screws while I was at it–they did sound rather dry…so thanks for that reminder as well!)