[DistortedDesign]

I have keling 425oz steppers (they are the uni so induct is high 6.8) with keling 4030 drivers, and 36v power. I have a joes 2008 cnc. I just noticed how heavy my z axis carrage is. With the router it is 14.5 lbs. I am using a acme 2 start 5 tpi screw. Am i going to have problems moving that around? What should i set micro step to ?

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[Bartos]

From my calculations you will get following parameters (in metric units)

Fmax=1320 N at the screw
um/step = 3,13um (at 8 microsteps)
max acc = 4 [m/s^2] - assuming steel screw l=300mm and d=16mm; and safety factor of 2 - that is you won't use more than 660N for acceleration (but torque is dropping at higher RPM so you might need to adjust according to the curve of your motor)
And you need around 100W power supply capable of providing 2A current per stepper motor (assuming max RPM=500 - thus max speed = 2,5 m/min 98 IPM)
At least in theory, form my calculations.
Whether it is enough or not, that's up to you.

[DistortedDesign]

I will be suppling 2.8 amps. Not sure if that took the weight of the z axis in mind? I guess i can put a torque wrench on it and see how many pounds it takes to move.

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[ger21]

It should have no trouble lifting 14 lbs.

[Dylwad]

It should have no trouble lifting 14 lbs.

+1 my z axis with a water cooled spindle is probably twice as heavy with smaller steppers and the same acme screws and it was never an issue.

Your machine should end up with enough force on all axes to do some serious damage to a stray finger or hand in the wrong place at the wrong time.

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[Bartos]

Not sure if that took the weight of the z axis in mind? I guess i can put a torque wrench on it and see how many pounds it takes to move.

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If you mean what I think, then...gravity exerts force of around 60N on the Z axis assembly and that is around 10% of the force avilable so (assuming my loggic is correct)
going down you will have max acceleration of 4,4 [m/s^2] (+10%) - due to the help of gravity
going up - max acc of 3,6 [m/s^2] (-10%) - because you need to fight the gravity

However, since your voltage is not very high and inductance is quite high this might be a smaller problem then lost of torque at higher PRM
Regards

[DistortedDesign]

Thanks everyone! Z seemed really heavy but i dont have a reference point. I was just worried my steppers wouldn't lift it.

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[Bartos]

Its not heavy - it's actually very light. What you don't see is that Screw Equivalent Mass is around 50 lbs and Motor Equivalent Mass is around 250 lbs. If screw and motor were mass-less you would have max acc of 100 m/s^2 and that would give you virtually instantaneously speed of 100 IMP.

You didn't specify what diameter is your screw and what length.
Also, if you can find motor's moment of inertia in datasheet, that would help to give you more precise numbers

[Bartos]

Its not heavy - it's actually very light. What you don't see is that Screw Equivalent Mass is around 50 lbs and Motor Equivalent Mass is around 250 lbs. If screw and motor were mass-less you would have max acc of 100 m/s^2 and that would give you virtually instantaneously speed of 100 IMP.

You didn't specify what diameter is your screw and what length.
Also, if you can find motor's moment of inertia in datasheet, that would help to give you more precise numbers

[DistortedDesign]

Screw is 1/2" and 36" long, 2 start 5 tpi.

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[DistortedDesign]

Screw is 1/2" and 36" long, 2 start 5 tpi.

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[James Newton]

Worse comes to worse, you can always add a pully to the top of the Z axis mount and hang a weight pulling the z head UP. But Bartos is right; it's not going to have a huge effect.

[DistortedDesign]

Since i am using a 5 tpi screw shouldn't i be able to run the z at 1/4 step and get close to the same resolution as the other axis running 1/8 step with a 2 tpi screw? Running at 1/4 would give me more torque than at 1/8, or am off?

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[ger21]

Don't use microstepping to increase resolution. It's mainly used to get smoother running motors, and reduced risk of resonance.
You really shouldn't see much difference in torque between 1/8 and 1/4 microstepping.

[victorofga]

if it is acme screw, I would suggest more tpi... like 6 or 8 because within use the dust will make noticeable friction, and the motor originally could handle it, it will become not sufficient for 3d cuts..
that is where the most stress occur..

but all is this just my 02...

[H500]

14 lb is nearly weightless. Most of your energy will be lost to friction. My SX3 head weighs about 120 lb. My 280 oz-in motor can reliably lift it upward at 80-100ipm using 5tpi ballscrews.