18 x 24 x 5 V Bearing Machine
A Simple and Solid CNC Router Table
- V bearings
- Supported steel rails
- Aluminum body
- Wooden table bed
- Leadscrews, racks and pinions
- Stock sized components
- Fast and accurate
- Efficient material use
- Straightforward construction
This machine is made of stock sizes of aluminum, steel and wood, which are cut to length and drilled. This simplifies construction and reduces cost.
The axes are supported by V bearings that ride steel rails. This gives stable travel for fast and accurate cuts.
The gantry is driven with pinions on racks, and the carriage and Z axis are driven with leadscrews. Racks and pinions are fast, and leadscrews are simple.
Modular DesignAs shown above, the machine can easily be disassembled for storage.
The modular design also permits the axes to be exchanged with other ones. For example, a second longer table bed could use the same gantry and Z axis assemblies.
The machine can be removed from its wooden base so it can cut large stock.
Individual legs can be removed to fit oddly sized stock.
Building CostThe cost for this machine's components, not including the router and stepper-drive package is ~$600. This roughly breaks down as follows:
Aluminum and steel ~$110
Racks and pinions ~$80
Pulleys, belts, leadscrews, etc. ~$145
The remainder is hardware and wood. These are inch sized components.
Stepper and drive packages start at $250
Trim routers start at $80.
SpeedsNEMA 23 steppers move each axis. This is a standard size that is available in many stepper and drive packages.
When moved with 269 oz.in. steppers driven by Geckodrive's 201 drives, the rack axis can rapid over 1000 inches per minute, and the leadscrew axes can move over 600 ipm.
Less powerful drives and steppers, such as HobbyCNC's 200 oz.in. kit, can move the machine at ~200 ipm.
The machine uses a trim router. Its power is compatible with the aluminum construction and the popular steppers and drives.
Scaling NotesThis machine has a footprint of 26 x 30 inches. It was designed to use off the shelf stock in standard lengths. The 2 foot gantry beam gives a cutting width of 18 inches. The 2 foot racks give a 24 inch cutting length. The Z travel is over 5 inches. These can be enlarged.
The rack axis can be made longer. The limitations are the length of the rails used with the V bearings, and the solidity of the bed. Racks can be abutted for virtually infinite length.
For the gantry axis, a 4 inch beam up to 3 feet long has served well on other trim router machines that have been built here. Longer beams flex with aggressive cutting, which permits more chatter. A 36 inch beam will give 30 inches of carriage travel.
Replacing the 4 inch channel beam with 5 or 6 inch channel stock will require multiple alterations, which are not addressed in the plans.
The Z axis can be made longer by increasing the length of the Z channel, the Z rails, and the leadscrew. The legs can be made higher to allow more Z travel. Chatter will increase the farther the router bit is from the support of the gantry and carriage.
The machines have been pushed hard to find the weak links.
Generally, the NEMA 23 steppers, the trim router, and the aluminum all fail in the same range of forces.
An overly aggressive cut will either stall a stepper, stall the trim router, or tear the stock from chatter caused by the machine flexing.
Upgrading one element without upgrading all of the others will not greatly improve performance.
Using a Larger RouterA larger router has been tested on this machine. The machine will flex before the router is pushed to its stalling point. However, a larger router can still be useful because of its longer life, and its ability to use a wider variety of bits.
The weight of a large router will cause fast leadscrews, such as 2 turn per inch, to back-drive on the Z axis when the stepper is disabled. This can be remedied by using a five or more turn per inch leadscrew on the Z.
Supplier NotesThis machine is sized in imperial units because it is built of inch sized components from USA suppliers.
The suppliers' international shipping varies. Metric substitutions will require alterations to the machine's design, which are not addressed in the plans.
Pulleys and belts are available from a variety of suppliers including mcmaster.com and sdp-si.com. Their inventories change regularly and it may be necessary to shop among these to find a match that is currently available. The plan's materials list mentions a number of options that will work for the pulleys and belts. There is more information on the Pulleys page.
Onlinemetals.com is the supplier for the aluminum. Their smaller steel stock has arrived bent, so it is recommended to buy it locally. The steel is usually available from homecenters.
Dumpstercnc.com sells leadnut components. The multi-start screws are not standardized so it is necessary to use the brands that the components are made to match. For example, all 3/8-8-4-2 leadscrews are not the same. Many of dumpstercnc’s components are for mcmaster.com leadscrews. Roton.com sells leadscrews and leadnuts, but their other offerings are limited.
The racks and their pinion-spur gears are from mcmaster.com. There is more information about racks on the Drive Systems page.
The R6 and R8 bearings are standard sizes and are available from a number of suppliers. Skatebearings.com and vxb.com sell online. The V bearings are from vxb.com.
The above vendors work with the Do It Yourself market and have help forums and documentation.
The Digital Download page gives more information about downloading the plans.
These plans are also in the five plans bundle, which includes the 10x9, 13x13, 18x24, 25x25 and 24x48.