[AndrewBond]

Hi Guys,

Thought I'd share with you my new Y&Z axis design, I've ordered the bits so should know some time next week if its a winner...

Anyway heres the details,

BOTH axes are rack & pinion drive, module 1 with a 30 tooth pinion.

Drive is from 4nm NEMA 34 stepper motors on both axes, currently its direct drive but i have allowed for the installation of 3:1 reduction via a planetary or belt rive gearbox.

The extrusion profile is bosh rexroth 40x120.

Hiwin 15mm Bearing rails.

Chassis folded 3mm Mild Steel.

Z axis is counter balanced with a variable force gas strut, to stop it falling.

This is intended for a large format. (10x5)

PS. I know your all going to say that ball screws are better for the z but I was trying to keep everything low profile and simple.

Anyway let me know your thoughts.

[CarveOne]

I like the way you have the Z axis motor and rack. It does simplify things and places the rack at center of the Z axis, as a lead screw would normally be located, instead of off to one side of the Z assembly. Nice.

CarveOne

[jjobezo]

Can you explain the advantage of using the profile for the Z axis as opposed to using a plate?

[CarveOne]

Can you explain the advantage of using the profile for the Z axis as opposed to using a plate?

The profile is potentially stiffer, and it allows easier mounting of anything that is attached to it. That doesn't mean that there are no drawbacks or compromises from using profiles. It's just a decision to be made as to how you want to build the Z axis for your own particular needs.

CarveOne

[AndrewBond]

Carveone has pretty much covered it,

One of the other main reasons is that I have no facility to machine or get a plate machined andthe profile comes cut to length. It also allows for mounting dust extractors and coolant systems into the T-Slot without me having to plan for it right now (lazy I know).

T-Slots also mean any error in the hole positions for the rack and rails is not a problem.

[jsheerin]

I'd be worried about the stiffness of your 3mm steel parts. Perhaps you've done calculations that show it will be okay though.

Have you thought about any provisions for spring loading the pinion into the rack to reduce backlash?

[AndrewBond]

I ran a few simulations in solid works but the 3mm carriage is formed out of one piece with relatively large radii bends, once formed it is welded in to form a "box" I'm confident that coupled with the points where its fixed to the bearings this should be stiff enough, If not I can always up it to 5mm, but I'd rather not over engineer..

Spring loading, the Y axis is sprung into the rack to allow for any backlash and possible undulation in the rack/wear.

As for the Z axis, this is moving over a relatively short distance (175mm) so currently the motor is going to be fixed and the the gas strut should take up any potential backlash by pushing the rack up against the teeth, I hope that makes sense?

Andrew

[jsheerin]

Typically you'd set the gas strut so it had enough force to balance the z axis against gravity but not press it upwards. Otherwise your motor will be having to overcome that upward force when it moves the z axis down. You could accomplish the same thing by leaving the gas strut off and letting gravity provide preload, although it might not be enough preload to perform well. With the short run you might be able to just adjust the engagement of the pinion to the rack and solidly bolt it in place and it would be okay.

[AndrewBond]

Are there any negative effects from the motor having to overcome the upward force of the strut apart from wear on the motor?

I chose this over a gravity preload mainly so that when the power is removed the axis does not drop and I dont have to incorporate a brake.

Thanks for your input btw.

Regards

Andrew

[jsheerin]

I wouldn't think wear on the motor would be an issue. I would worry about the motor having enough torque to accelerate the axis and produce the force necessary for cutting. That can all be calculated though (how much force is available from the motor).

[AndrewBond]

Pictures...