One ring to rule them all?

[routercnc]

Hi Rufe0

These are my thoughts for a machine like that -

1. Double gantry, as per your drawing, and the machine I linked to, and MechMate:



and Jonathans machine a while back-
http://www.mycncuk.com/threads/6484-...strong-machine


2. Box Z, as per the link machine and Jonathans using 4 rails on the Z

3. Twin ballscrews on the X,Y and Z axis to avoid racking and allow the bearings to be close to maximise travel. Z twin ballscrew is to help with lifting the weight of the 1m axis, plus keep the loading central to the spindle.

4. Hiwin rails all round, 20mm or bigger.

5. Height adjustable bed with vertical rails at each corner -
Manually
or hydraulic using 1 ton bottle jack in the centre
or ballscrews
Which ever option you must be able to 'lock it down' before cutting - like you would lock a quill or lathe saddle once in position. Maybe thick angle brackets around the edge to nip up and hold it fast.

The alternative to height adjustable bed is to use bedplate mounting blocks (scroll mid/bottom):
http://cnzbzg.en.alibaba.com/product...eers_cube.html


6. Spindle(s) capable of high speed medium torque [alum, wood], plus very low speed high torque [steel]. Maybe via a single spindle linked to a separate cartridge spindle with pulley drive to give different ratios.

7. Automatic Tool Changer (air powered), optionally with ATC carousel.


In terms of your calculations the bending stiffness calc is straightforward (load one beam then half the deflection for 2) but that only accounts for the Z axis weight and the plunge stiffness. For the sections you are talking about (200x100x8) etc this will no problem for simple bending. However, where you will come unstuck is having enough torsional stiffness when cutting in X (gantry moving forward or back), especially at 1m extension. I don't think hand calcs would be possible on a double beam in torsion so you need an FEA program if you want to work it out. I notice Fusion360 has FEA built in and this is 'free' so worth a look. This will give you deflections once you have learned how to use the CAD part of the software.