Z axis spindle too heavy for Nema 23

Hi all, I've run my home built cnc machine for approximately 8 years. I use Nema 23, Mach 3, Gecko g540, 5 start acme screws on linear rails.
I've never had a problem till now. I have been using cheap air cooled spindles but keep wearing them out. Inner bearings keep going bad.
I just upgraded to a 80mm liquid cooled 110v spindle but now it it too heavy for z axis to lift without stalling. I've slowed it way down but no luck.

How do I overcome this? I don't think gecko will drive a nema 34 and I don't know how else to connect to mach 3 if not all going through the same driver board.

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Originally Posted by MP40cal

Hi all, I've run my home built cnc machine for approximately 8 years. I use Nema 23, Mach 3, Gecko g540, 5 start acme screws on linear rails.
I've never had a problem till now. I have been using cheap air cooled spindles but keep wearing them out. Inner bearings keep going bad.
I just upgraded to a 80mm liquid cooled 110v spindle but now it it too heavy for z axis to lift without stalling. I've slowed it way down but no luck.

How do I overcome this? I don't think gecko will drive a nema 34 and I don't know how else to connect to mach 3 if not all going through the same driver board.

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Your 5 start acme screw is most likely the biggest part of the problem

Hi MP - As MC says you will need to change the pitch of your Z axis screw and nut. What is the pitch of the current screw? Typically 5mm is a good pitch for a Z axis and a N23 motor with a 5mm will easily lift and support that sort of spindle. Peter

Thanks all, my screw is a 1/2" 5 start. I will try and change that, thank you.

You can also add a counter weight for spindle or use a air cylinder like on your car hood to offset the spindle weight. This reduces the load on Z axis motor

I thought about counter weights but I think in the long run it'll be better to change up the lead screw.

I am now wondering (after I just ordered one), can I run two different screws with Mach 3?

Meaning, X and Y will run on 1/2 5 start acme screw. Z will be on a 16mm x 5mm pitch screw.

From Amazon...
300mm/11.81 inch Ball Screw RM/SFU1605 (Diameter 16mm, Pitch 5mm) with Metal Ball Screw Nut and BK/BF End Supports for DIY CNC Machine and 3D Printer

Hi,

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You can also add a counter weight for spindle or use a air cylinder like on your car hood to offset the spindle weight.

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Yes, this would work but it doesn't cure the acceleration problem. Even if the mass is balanced there is still the higher absolute mass to accelerate and the higher the potential acceleration the
better the toolpath following. Using a finer pitch screw will help, it may reduce the top speed of the axis but increase the acceleration.

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I am now wondering (after I just ordered one), can I run two different screws with Mach 3?

Meaning, X and Y will run on 1/2 5 start acme screw. Z will be on a 16mm x 5mm pitch screw.

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Yes, no problems. In Mach3, and indeed most other CNC software, you put in a value 'steps per unit' for each axis, say the number of stepper motor steps in one inch of travel.
That number accounts for such variables as ballscrew pitch and microstepping regime. X,Y,Z need not have identical 'steps per unit' values.

Craig

I've only ever been able to cut 20 inches per minute because my Y axis would stall out. If I can keep that I'll be happy. I have even thought about researching how to use servo motors instead of stepper motors but right now I have projects lined up so I can't redo it all for time sake.

I'm just frustrated because it seems these nema 23 are strong but weak at the same time.

Hi,
servos are great. Funnily enough they tend to have less torque than a stepper motor of the same size, but they retain that torque right up to rated speed whereas stepper reduces torque BIGTIME as the speed increases.
Over all servos 'eat any stepper ever made'. Clearpath are a common choice for people whom don't know anything about servos because they are nearly as simple to set up as steppers, unfortunately
they are expensive for their power output, have poor resolution encoders, and vastly diminished IO by compared to Delta (Taiwanese brand made in China) or DMM (Cnadian brand made in China), the competition.

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I'm just frustrated because it seems these nema 23 are strong but weak at the same time.

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I would guess that your steppers have high inductance, a common fault with steppers made for new customers whom may not know all the pitfalls.

In particular ALL steppers lose torque the faster they go. The critical specification that determines how bad that degradation is is winding inductance.
A 23 size stepper of low inductance, say 1.5mH, will have about 40% of its torque still remaining at 1000rpm. Such steppers are sort after, tend to be high current types and aren't cheap.
A more common 23 size stepper but 6.8mH will have about 5% of its torque remaining at 1000rpm. These steppers are 'like an arsehole....everyones got one'.

The classic method to (attempt) overcome winding inductance is to use a high voltage driver and power supply. The current norm amongst high performance stepper drivers is 80VDC and an 80VDC supply.
If you have a cheap driver whats the bet is 24V or 36V, and that will make ANY stepper as slow as a wet week.

Craig

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Originally Posted by MP40cal

I've only ever been able to cut 20 inches per minute because my Y axis would stall out. If I can keep that I'll be happy. I have even thought about researching how to use servo motors instead of stepper motors but right now I have projects lined up so I can't redo it all for time sake.

I'm just frustrated because it seems these nema 23 are strong but weak at the same time.

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The problem is the 5 Start screws if you did a 2:1 timing belt drive that would help on the Y axis you may need 3:1 your 5 start screw is probably doing 1" travel per rev you can measure this and see what you are getting, you would need a lot of torque to use the 5 start screws

Either do as Mactec suggests with the belt reduction or replace the screws/nuts with a slower one, particularly on the Z-axis, which will probably be easier.