Years: 2016 - Today
Time: >3000 hours
Skills: Welding, Metal Cutting, Electronics
Cost: $7356
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CNC Hybrid Router-Mill
I designed and built the Rigid Router CNC machine from scratch.
My unique design maximizes rigidity by translating the entire gantry up and down to minimize the force path between the spindle and workpiece at any Z position. I designed with strong-but-economical materials like hot-rolled steel C channel for structural rigidity and decent overall straightness. I avoided welding where it would release internal stresses and cause warpage.
Most CNC routers can only cut wood. The Rigid Router easily cuts aluminum like a mill. I'm looking forward to seeing if it can cut steel. It's also a hybrid because the table has both a rigid steel bedplate and wooden area to use for softer and larger materials.
Tech Specs
Cutting Envelope = 4’x5’x1′ (1220x1530x300 mm).
Spindle Power = 4 HP (3 kW)
Translation = Ballscrews + Ball Nuts and Linear Bearings
Axis Drives = 5x Clearpath Servos - CPM-SDSK-3411S-RLN
Controller = MASSO G2 - HTG-5A1S Mill controller (5 Axis)
Total Weight = 2100 lbs. (944 kg)
Rigid Router is so rigid because the entire gantry (yellow) slides on the Z axis. Other CNC machines have a fixed-height gantry, and the spindle extends down to the work piece. This extension behaves like a diving board, which is terrible for accurate machining - especially harder/stiffer materials.
Rigid Router continuously maintains the shortest possible force path between the cutting head and the work piece. When Z height is low, the entire gantry is very close to the table. Fortunately most of my metal cutting is on shorter stock, so this design benefit is quite useful.
The gantry and spindle (yellow + red) together weigh 330 lbs. (150 kg). Because the gantry must frequently raise and lower, and ideally do so quickly, I installed 2 gas struts, each with capacity of 150 lbf to offset the weight and reduce loading on the Z-axis servos and ballscrews.
I retrofitted belts to link left and right ballscrew rotations for both the Z axis (above) and the Y axis (below). This was a correction to my original design in which I assumed that the servos would remember their locations when the machine was turned off. Without the belt linkage, the left and right sides of the gantry would sometimes fall (slowly) at different rates and cause misalignment with respect to the table along the X axis travel.
As for linking the two Y-axis ballscrews, I found that they would lose synchronization for a few reasons. When both of the high-end ClearPath servos are powered on and operating properly, their motions match perfectly. Internal rotational encoders ensure extreme precision, but when powered off, they forget where they are, and small forces can cause the left and right sides to move with respect to each other.
These belts are not elegant, but they do work well. In the future, or if I build another Rigid Router, I would use a single bicycle chain between the two ballscrews, and I would drive the chain via a shaft in the center. Tuning and setup is much easier with a single (larger) servo/stepper driving each axis. I did leave that option open on both belt arrangements - I could still add servos to the open shafts in the centers.
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DESIGN
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