24 x 48 Rack and Pinion, or Leadscrew Machine
| A sturdy machine with a variety of options |
 This machine has its own set of plans; it is not included in the 5 Machine plan set. The machine was designed to be solid, inexpensive, simple to assemble and accurate for the cost. This was accomplished by using lumber yard materials with off the shelf drive components. Attributes include:
 Paper templates for a number of the gantry and carriage components are included. Left image. These can be cut and drilled with the stock. Their use greatly simplifies the construction process. ....................
This machine was designed to permit a number of options for the motion components and construction materials. This allows the machine to be customized. It is also designed to permit drop in upgrades; therefore, it can initially be built with cheap leadscrews and then be upgraded later. A chart in the manual lists the speeds and comparative costs of options from racks and pinions to Allthread and Acme as well as a ballscrew on the Y axis. This information is from actual tests on the many prototypes. Racks and pinions or leadscrews can be used with the X and Y axes. Racks permit long axes, and leadscrews can offer more precision and simpler construction.  Racks can be abutted to give infinite length. The X axis can be lengthened easily without the need to rework the other axes. The pinions cannot ratchet on this design; they are pressed into the racks as the cutting forces increase. Parts would have to bend before the pinions could skip teeth; the steppers will stall first. A pair of leadscrews can also be used on the X axis. The stepper to leadscrew coupling can be 1 long belt with 1 stepper; 2 short belts with 1 stepper, or 2 slaved steppers. These 3 options are addressed; also included are stepper mount templates and directions on scaling. The pulleys for the leadscrew to stepper connections were sized to be interchangeable; therefore, later upgrading to better quality leadscrews will not require reworking the belt sizes or stepper locations. Upgrading is simple. The gantry beam can be made of a 2 x 6 board as shown on the right, or with aluminum channel as shown at the top of the page. The carriage can be made of 1/2 inch plywood, or standard sizes of aluminum flat bar. The aluminum adds around $175 and gives a more solid machine which is capable of more aggressive cuts. The plans are written primarily for wood construction. However, the necessary modifications for the aluminum gantry and carriage are addressed with notes, images, templates, and a parts list. Most aluminum construction only requires that the flat bars be cut to length and drilled. There is no need to completely cut the aluminum components from larger stock. The image of the template above shows a plate being made from aluminum flat bar. The stock is cut to length and drilled. Parts are designed to be that simple. All rails are steel pipe; not conduit. This material is solid and can carry heavier loads. It can be upgraded to drill rod or similar. The bearings are 608 or 1603 bearings which are inexpensive and easily found. The X and Y pipe rail to support connections are simple and do not require thread tapping or channel cradles. The Z rails are also straightforward and solid with a minimum of components; they do require thread tapping for #8-32 screws. The 24 x 48 inch cutting area prototype described in the plans was sized to use stock sized materials efficiently. The gantry uses a 36 inch pinion axle (a steel rod) and/or a 36 inch leadscrew and/or a 24 inch rack. These options give a Y cutting distance of 24 inches. The X axis uses 48 inch racks and 60 inch pipe rails. These too are stock sizes and give a cutting distance of 48 inches. Directions are given for increasing the length to use standard 72 inch leadscrews. This machine was designed to permit multiple
options while remaining
home-shop friendly. It takes the lessens learned from the many other
machines built in this shop and combines them into a lean,
straightforward and solid product that can give good results with a
small budget.
The price of the table will vary according to the components used. Generally there are $250 of home center parts, and $125 in pulleys, belts and bearings. The prices of the leadscrews and leadnuts can range from a few dollars for Allthread to hundreds for Acme or ballscrews with quality leadnuts. $600 is a fair expectation for the basic table, not including the steppers, drives and power supply. The machines
were all designed to use the stepper and drive systems from Xylotex and
HobbyCNC. The recommended software is Mach3 or TurboCNC.
These suppliers work with the Do It Yourself market, and supply documentation and help forums for their products. Here is a short video. Templates include: Stepper Mounts for:
These plates support the bearings, steppers and gantry beam, and include the following versions.
Different template versions are supplied when wood and aluminum parts are not the same. The templates are actual size; their print scaling is good. Dimensions are printed on the templates for cross checking. Paper templates have proved to be easier to use than card-stock or plastic. The paper folds easily and can be creased for alignment. The plans for this machine are sold as a separate manual. They are not part of the 5 Plan set. |