Metal CNC Machine

This machine was designed to address the problems with the trial machine.

The X rails were placed near the gantry beam to reduce gantry end-plate flex.
The under table leadscrew was removed, and racks and pinions were used on the ends of the gantry to prevent racking.
The X and Y rails were supported, and the Z axis used fixed bearings with moving rails.
The rails and racks were placed above the work surface so the chips would fall away from the mechanical components.
Gantry made of aluminum End Fixity of leadscrew
The gantry is made of aluminum tube, angle and flat bar.

 The Y leadscrew is supported by a pair of bearings that are spaced a few inches apart. This greatly reduces leadscrew whip.
Welded X frame Gantry on X axis
The table bed just welded. The bed is a discrete unit which is connected to the chassis with adjustable mounts. These allow the bed to be leveled relative to the router's travel. The gantry on the X chassis. The gantry weighs 80 lbs and rolls easily. The bearings are adjustable and allow proper tensioning.
aligning rack Pinion on rack
Though the rack is already installed, this shows how the rack was aligned when butt-jointed. A short piece of rack was clamped into the two meeting pieces. This made the job manageable and the results are accurate. The rack ends before the rail does; if the limits fail the pinions freewheel.  The rack was placed upside-down above the pinion so the dust would fall away from it.
Pinion Tensioner Gear reduction for rack and pinion
The pinion is pulled upward into the rack with a spring loaded bearing block. The rod coupler adjusts the spring's tension.
The rack version of the 24x48 table eliminates this complexity with a much simpler system.
 Gearing on X axis. Servos turn much faster than steppers, and require a more complex gearing system for the pinions. The compound pulley system shown above gives a ratio of 13.8 motor turns per inch of gantry movement. The steppers in the 24x48 table do not require this level of complexity.
Z axis Bearings on pipes
The servo's belt is adjusted by a moving plate.
The bearings for the X and Y axes are based on the system derived earlier. This is overkill on the gantry.
The tables in the plans use simpler systems that are stable and are more easily adjusted.
Z top Z axis
The X bearings from the trial table were recycled into the Z axis. The system in the plans is greatly simplified and does not require welding.
 The Z carriage on the gantry. The moving pipe with fixed bearing system has served well.
Metal CNC machine Metal Machine
The table moved to its own room. Stock can be moved directly from the truck to the table.
The control box can be seen on the back of the computer cabinet.
 The tee slots from the trial table were reused. The slotted table can be removed for deeper stock.
Hold down clamps slide in the slots.
The table was lined with tempered hardboard on the sides and MDF on the bed. This contains the chips.
Side of Z axis Adapter for Dremel
The router mount can be removed from the spindle plate by loosening a few nuts. This permits other tools to be used such as the circular saw shown below. An adapter for the Dremel fits into the router clamp and vac system.
It also allows access to the shaft lock for bit removal.
It is made of copper fittings and DWV plumbing pipe.
Saw bracket on Z axis Saw on Z axis
A bracket for an old circular saw was welded together. This made the table handy for cuts that would be difficult to do with a table saw or by hand.



The saw body cannot swivel so cuts can only be made in the X direction.
Z's height and Y's positioning are still functional, so rabbets and dadoes are possible.
There are no plans for this machine. It was designed on the fly as it was built; all drawings were back of the envelope quality, not CAD.
Though it works well enough, there are a few features that I would do differently.

The gantry was made of ¼ x 6 inch flat bar and angle. 6 x ~½ inch thick channel as used on the 24x48 would have made construction easier and more solid. This size stock was chosen for the 24x48 because it was the thickest channel sold by onlinemetals.com.

The gantry ends were made of square tubing; flat plate as used on the 24x48 is solid and easier to attach to the gantry beam, and it is easier for motor mounting.

The racks are on the inside of the supporting rails of this metal machine, and as a result they collect dust.
The 24x48 places the racks farther from the cutting area to address the dust problem.

The motor that moves the gantry on this metal machine is behind and below the gantry. This should be higher as it is on the 24x48 to keep the motor farther away from dust.

The square steel tubing has served well, as has the adjustable height bed.

I like having the rails above the work surface, rather than below as is often done on flying gantry machines. This makes the gantry simpler and less prone to rocking.
The ends of the machine are open, so it is seldom necessary to lift stock over the rails, though bending over the rails during set-ups can be rough on the back.



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