On the Cheap: Supported Linear Rail…

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.

11 Responses to “On the Cheap: Supported Linear Rail…

  • Hi,
    What kind of linear bearing is it on the carriage?

    Regards OEP

  • how much force do u supposes this could take?

    ps: love your project. would be awesome to make a 5 axis machine based off of this.

  • I have no idea of the actual force/stiffness yet.
    When I get my hands on a dial indicator, I will measure deflection under load and calculate stiffness.

    With the supports being short and frequent, the intended target is to be able to cut aluminum.
    For a production machine, this has a required stiffness starting around 20,000 lbs/inch.

    The X axis is now assembled and the machine has a coat of paint, I will post an update soon!

  • Just use regular epoxy to seal the board. Two part epoxies should be part of any workshop; plenty of uses and has a shelf life of years. To thin it down to get it to soak in you can mix in a little denatured alcohol.

    http://www.shopmaninc.com/epoxy.html

  • Just what I was looking for. But i have one question. What type of material is the original round rail?

  • Precision ground round…

  • Thanks for sharing. Where did you source your “precision ground round”?

  • hola .
    I respect you work men ,you are so smart.
    I think on this idea before ,but see this ready made, is very good.
    congratulations!
    a question;where did you get the rails?
    thank you!

  • Hi,
    I’ve tried several times to drill a harden rod, suitable for shafts but it was impossible. No drill or center drill can drill through hardened steel. Not even a lathe can turn it properly unless I have annealed the shaft first. Normal carbide tools do not even scratch the shaft before annealing.
    You don’t show any pictures of your drilling. I guess that either your rods are not hardened but then they will not last even a month since the linear bearings will damage them or you have come up with a method that I am not aware of. Can you show some pictures of your technique and explain further how you perform the drilling?

  • Yeah, they’re probably not hardened rails. Silver steel rods are ground to pretty tight tolerances and can be machined easily, and hardened to 64HRC. And the stuff is pretty inexpensive, so that’s probably what he’s using.

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