One sided drive?

[irving2008]

Jeremy

If the gantry can be stiff enough to resist torsion on the XY-plane around the driven side in response to forces on the cutter then it can be done. What were you planning to make the gantry from?

ideally the drive should be outside the X-axis linear rails so that the turning moment due to the cutting forces moment acts primarily on the linear bearing and not on the leadscrew. With a cutting force of 50N (MDF or very light cuts in ali) at 300mm radius (assuming 600mm Y-rails) the turning moment is 15Nm.

By way of example, assuming 16mm fully supported rail on 40 x 30 x 3mm wall box sections 200mm spaced the deflection in the X-direction at the non-driven side will be ~.06mm (so .03mm at the cutter) and in the Y is .001mm. This shouldn't cause any material binding on the rails.

[Jeremy]

Thanks very much for that, Irving.

The gantry members will be two lengths of 2" square x 10g wall 6082-T6 alloy box, with SBR16 fully supported rails screwed to them, so it should be pretty rigid.

I'm thinking of something similar to the layout shown on that Durham Robotics link, with the leadscrew outside the rail, so it should be OK, with luck. The main reason for using this configuration is the reduction in machine height and a possible increase in overall stiffness, as the gantry doesn't need an under-table drive. It also means that I don't need to add the complexity of a double leadscrew arrangement.

Jeremy

[irving2008]

Well given that 50mm square 10g (3mm wall) box section is stiffer than the 40 x 30 x 3 I postulated this should be plenty stiff enough for your needs...

That calculation assumes rigid corner joints and a cross member at each end between the Y-rails of the same stiffness.

The other racking issue is where the cutting forces cause the non-driven upright to rotate in the vertical plane relative to the driven one. Obviously gets worse as the cutter rises above the table, so you need to ensure torsional stiffness of the gantry in the Y-Z plane.