January 18, 2021

Yet another gantry cnc design

2 min read
Hey guys! After acquiring of chinese 3018 CNC and playing around it little bit (installing...

Hey guys!

After acquiring of chinese 3018 CNC and playing around it little bit (installing new 500W 100V 12,000 RPM Spindle, limit switches, more stiff springs in anti-backlash mechanism, etc) I started to think about rebuilding it from scratch. I honestly don’t know why those chinese engineers have put the axis with the longest travel (X) on the gantry. They could easily design X travel of 180 mm and Y travel (table itself) of 300 mm without breaking the bank, thus making the gantry much stiffer. But they’ve chosen more floppy way and as the result whole Z carriage has a play of 2-5 mm just by twisting it by hand, let alone cutting.
(However, I managed to get good result on the PCB making side of things though). But I wanna be able to cut & mill aluminum and for this some changes HAVE to be done.

Let’s start with basic specs for the new machine:

Small table top footprint.
Gantry type – fixed (for more rigidity).
X travel – 180 mm.
Y travel – 300 mm.
Z travel – 95 mm.
Table – Z carriage clearance – 125 mm (for accommodating using of 4-th axis with 100 mm chuck or basic 3" milling vise with height of 70 mm).

Spindle.
Two options can be installed:
a) 500W 100VDC 12,000 RPM air cooled spindle with diameter of 50 mm (0.49 Nm).
b) 800W 220VAC 24,000 RPM water cooled spindle with diameter of 65 mm (0.33 Nm).

After several design iterations I came up with following hardware:

X axis (gantry):
2xHGR15 280mm rails. 2xHGH15CA blocks;
SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Belt driven;
Bearings – motor side – fixed, FK10. Opposite side – supported, FF10;
Motor – NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver – HSS57.

Y axis (table):
2xHGR15 420mm rails. 4xHGW15CA blocks;
SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Direct coupled;
Bearings – motor side – fixed, FK10. Opposite side – supported, FF10;
Motor – NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver – HSS57.

Z axis:
2xHGR15 160mm rails. 2xHGH15CA blocks;
SFU1204 ball screw (4 mm pitch, 10 mm minor diameter). Direct coupled;
Bearings – motor side – fixed, FK10. Opposite side – supported, FF10;
Motor – NEMA23 57HSE2N-D25 closed-loop stepper, 4.2A, 2Nm torque. Driver – HSS57.

Structure materials:
Aluminum profiles (20×40, 20×60, 20×80, 40×40).
Structural steel plates with thickness of 8 and 10 mm.
Connection type – bolted.

Several screenshots of the inventor project in the current state using 3018 original table (belt and pulleys for X axis are not yet added to the model):

So, what do you think about the design? What aspects could be improved for milling light metals?
Would steel plate give enough rigidity or better stick to the full aluminum structure?
Thank you!

Happy New Year!
Phil.

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