Trying to Understand Z Axis Rigitity

[bense (Ben S)]

I am not questioning that a longer Z axis will loose rigidity. I am trying to understand why.

Is that distance from the cutter to the Z axis bearings? If so, does that mean I could build a large Z, but when I needed accuracy I could raise my workpiece?

Thanks

Ben

[scrounge79 (Marion J. Makarewicz)]

@bense

I could raise my workpiece

That in fact has been suggested, either have a spoil board that you can take out or drop for thicker materials or raise the material so the lever action of a long Z axis is minimized for most of use. The ability to drop the bed seems a better option because you aren’t dealing with long corner tubes which could introduce flex.

Here’s how I have been thinking about it.

Three of many considerations for establishing z height: 1. If you are doubling as a printer too, folks want more Z, but that compromises rigidity for milling. 2. To work on thicker piece of material, but since endmills are going only 20mm depth before collet interference, that does mean that you aren’t going to be cutting material thicker than that in normal cases. 3. Carving the surface of thicker material, like a cutting board. In that case, it would be better to have a drop center with a removable spoil board since you aren’t going all the way through.

Z axis height adjustable legs or drop bed

If I want to use this machine mostly for 2.5 d cutting on 1 inch hardwood, but at times need a 3d printer, can i make the Z axis 8 inches but with short legs and replace them with longer legs when needed or a drop center table and still be able to have a ridged system. Or just make two setups and keep one dedicated to s specific task?

Question about Z axis height and accuracy

The FAQ says smaller is better for all axis for better accuracy. For some projects I have, I need at least 24" x 24" for XY for routing, so I have to try to make that work at least. For routing, I wouldn’t need much height, since I am mostly planning to just cut out of plywood, as I think most people do, but I’d like to keep my options open for 3D printing. When having a higher Z axis, I assume the reduction of accuracy increases further away the spindle hangs down from the gantry, and also f…

[jamiek (Jamie)]

@bense

Is that distance from the cutter to the Z axis bearings? If so, does that mean I could build a large Z, but when I needed accuracy I could raise my workpiece?

Yes. The two things that get worse with higher Z is the tilt of the Z axis away from vertical and the flex of the four legs at the corners. The flex of the legs is much smaller and is insignificant. This is good news because it means propping up the workpiece gives you a rigid machine. If the legs bent a lot then you would need a different workaround.

[elektroschrauber (Thomas)]

That’s exactly what i do experience with a 3kg watercooled spindle even the height of m z-axis (legs) is only around 6" which sould give me more flexibility when (for example) cutting/milling foam.
It’s slightly tilted and the weight of the spindle makes it more worse …