purpose of z axis gas spring

[boblee]

Hi Everyone
I've visited this site from time to time and drooled over the mechmate design .
I'm thinking of building and have a question concerning the z-axis gas spring .
what is it's function or purpose ?
Thanks
Bob

[MetalHead]

It acts as the counter weight for the z axis. If it is not there the full weight of the parts would be felt against the motor. Think of a draw bridge balance.

[boblee]

Makes sense
Does it affect backlash in any way?

[MetalHead]

No it does not.

[riesvantwisk]

Bob,

the side effect of having such a gas spring is that your hight will be set more accurately and your Z axis will move more smooth.

The reason for this is that a stepper motor uses micro stepping and if a stepper motor is in a micro step, then it will loose strength as well. When the full weight is on the stepper motor, the stepper motor will go back (give or take) in a full step position because it doesn't have enough torque to hold it into a micro step.

You will see that if you have no gas-spring and you move your Z up and down, you will only get full-step accuracy. Top of my head, that was 1/3 of a mm in my case.

[buuk]

Hi,

I have one more question about the gas spring. Is the gas spring extended in its normal (free/rest) state? As this would mean that when moving the Z gantry up, you would have to lift both the weigth of the slide, router, etc. + the pressure of the spring...

Thanks in advance,
Luc

[riesvantwisk]

Luc,

the normal position of the gas-spring would be extended so it pushes against gravity.
So it counter balances the wight of your spindle and your Z axis so your Z stepper doesn't have to work so hard.

Also, when you buy your gas-spring, make sure it doesn't counter banker perfectly, but always have so push again or for gravity so your rack+pinion always make good contact

[Gerald D]

When the z-slide is up then the spring is extended....when the z-slide is down then the spring is compressed.

The bottom of the gas spring is fixed to the y-car, the top of the gas spring is fixed to the z-slide.

[buuk]

Thanks for your quick replies.

I was thinking correctly about the forces, but made a mistake in which part was moving... stupid of me. But such things happen after a long day at work. Excuse me for this question...

Thanks anyway!
Luc