Second CNC table build, here we go again....

[Robin Hewitt]

Every action has an equal and opposite reaction. If you apply 300N accelerating force to the cutting head, the gantry will push sideways with 300N.

[Davek0974]

Yes I can remember that from school ;)

But those 300N can be countered by applying gusset plates and ribs where needed, most tend to throw a slab of alu at it but that might not be totally needed i think.

[Robin Hewitt]

Or you could move the rails up closer to the gantry they support. The gantry only needs to be 2" above the bed, doesn't it?

[Davek0974]

In theory yes but my Z-axis needs a bit of clearance as its a pretty heavy built unit. I am trunk not to lift the rails - that was design idea one, but it means you do not have a clear open bed - you have rails either side which makes loading harder especially if juggling a bigger sheet on your own.

My high-rail option is sketched out earlier, it had no risers at all on the gantry - the beam was right down on the carriages.

[Davek0974]

Or you could move the rails up closer to the gantry they support. The gantry only needs to be 2" above the bed, doesn't it?

To add scale to my poor sketches, the bottom of the gantry beam is 140mm above the bed surface, not too bad??

[Davek0974]

Ok, stuff is on order.

The final result is 50x50x2 for the gantry beam and frame legs, 50x80x2 for the motion support/bed frame.

The final capacity is going to be the half sheet 1250x1250 / 4'x4' size.

Direct drive rack and pinion with a view to change to belt reduction drive or even ballscrews later on.

[JAZZCNC]

Good man thats what like to see no messing around.

[Davek0974]

Good man thats what like to see no messing around.

Oh I can mess around, to a point, then I just dive in and go for it.


The top box is the gantry beam, 50x50, the motor sits down the bottom on a plate that swivels on the point shown. It will be spring loaded but restricted so it cannot jump out of the rack and chew it up.

A couple of 75mm gusset plates under the beam on the inside and a rib or two on the outside should stiffen things up a fair bit.

Motors, controllers and rack arrived today :)