Supported linear rail can be quite expensive, at over $100 per rail per meter, not including shipping. An alternative support was theorized using 3/8″ threaded rod, drilled, tapped and screwed into the rail. Today it was assembled and tested, and has now been confirmed as a valid lower cost linear rail/bearing solution. This following method required no precision equipment other than a straight edge.
To facilitate handling as well as semi-accurate drilling and tapping, a 2×4 was notched approximately 90 degrees to carry the 25mm rail. Strapping was placed across the rail and screwed on either side to firmly fix it.
With rail securely nestled in groove, it was then marked every 12cm, center-drilled for alignment, drilled to 5/16″ and tapped to 3/8″. The drilling was performed with a vise in the drill press, tapping was done with the cordless drill and was finished up by hand with a blunt tap. No taps we’re harmed, maimed or mangled in the process, a localized anesthetic consisting mainly of 10w30 was used for the tapping process.
After blind tapping, the 3/8″ threaded rod was cut to 14cm lengths and the cut ends were sanded to remove burs. A pair of wrenches and a double nut was used to apply ample torque in securing the threaded rod into the linear shaft. With the threaded hole being tapered, some thread deformation occurred to make for a very solid fit.
With the rails assembled, the focus then shifted to the body of the Y-axis. A pair of thick walled 1.5″ steel square channel were drilled every 12cm to match the increments in the rails. A pair of 3/4″ MDF sheets were also prepared, that along with the channel, form a torsion box structure making up the Y-axis. As MDF is of sandwich construction, 1.5″ fender washers were used as force spreaders to prevent critical surface deformation (cracks around washers). With pressure the fender washers visibility deformed to apply a concave gradient.
A single rail was bolted to the torsion box frame and adjusts were made with the straight edge of a level until no light could be seen between the level and the rail. The Z-axis carriage was then added to align the second rail. As the carriage rode from one end to the other, the second rail was tightened down to make for a parallel linear system. No further adjusts were required, as seen in the following video the carriage rides smoothly end to end and without bind.
The last step is to seal the MDF from absorption of moisture for dimensional stability. Weather permitting, this will be done with some epoxy based garage floor paint. In perspective, this is one of three axis’ making up the CNC Gantry Router project.