Fixed z axis to gantry design

[routercnc]

The fixed gantry would benefit from stiffening in the fore/aft direction. Start at the top of the gantry in each corner and run a brace down to the front or rear corner of the machine. If you look at this machine from the side you would see the gantry sticking up from the base with little support.

If you go with only 1 ballscrew on Z then there is the risk of racking when cutting off centre. Imagine doing a plunge cut at one side of the table, the Z axis will try to rotate, possibly bind the bearings, but certainly loose some accuracy. To combat this you have to space the bearings apart (vertically) but then you start to limit Z travel, or have a much taller gantry and this then needs to be braced still further.

Small ballscrews at this length are not that expensive on e-bay, and you can use a single motor as per the design in the picture to save costs on two motors & stepper drivers.

[Lachlan]

That makes sense, I will use two ballscrews on the z axis and brace the sides of the gantry front to back.

[Robin Hewitt]

Loved the movie, someone has actually sat down and thought about it rather than following the herd.
The gantry connects to the bed. Presumably linear blocks are screwed to the gantry, linear rails are screwed to the bed.
If you want to add dead weight to cancel out vibration, by all means bolt the gantry to the building.
Maybe I an missing something, but I don't see any need for bracing because the bed does not reference anything apart from the gantry.
Cutting steel badly indicates that it might cut aluminium alloy reasonably well

[routercnc]

Hi Robin,

What I meant by bracing was if you view the machine from the side the 'bed' is effectively a capital "L" shape, with the stiffness of the vertical part dictated by the stiffness at the joint to the horizontal part. Better to join the top of the L to the front of the L to form a complete triangle.

[Robin Hewitt]

But the horizontal part should be a mere decorative trim. It shouldn't connect to anything

Edit: It does have a purpose, it stops you putting your tea cup where it will get knocked over

[JAZZCNC]

But the horizontal part should be a mere decorative trim. It shouldn't connect to anything

Edit: It does have a purpose, it stops you putting your tea cup where it will get knocked over

How do you work that out then.? It's the foundation of the whole machine and what the Fixed Gantry connects too. Rob is correct in that the Fixed Gantry would benifit from bracing to form a triangle rather than just being a tall pillow.!

Regards twin screws on Z axis then 100% needed and it would fail badly without them. Personally if your only cutting aluminium then I would stay with 5mm pitch has you won't require the extra speed 10mm gives but you will benifit form the extra torque and resolution 5mm gives. Even geared 2:1 so doubling the Torque/resolution 5mm pitch will easily give higher feeds than are required for aluminium.

If your thinking about cutting woods/plastics then go with 10mm pitch.

[Robin Hewitt]

How do you work that out then.? It's the foundation of the whole machine and what the Fixed Gantry connects too.

At first glance you might think that, but the foundation of the machine is actually the rectangular gantry.
Everything refers to the gantry, that is why it is such a rigid design. The overhangs are minimalized.
Okay, you need something to support it so it doesn't fall over, but a strut? Does that not detract from the beautiful simplicity of the design? That tower in Pisa would get a lot more benefit from a strut than this, but it doesn't mean you should fit one. I mean, how gauche