A Cheap Compact Linear Motion Slide
Introduction: A Cheap Compact Linear Motion Slide
A "linear motion slide" allows precise positioning along precisely one axis of motion.
This Instructable will show how to build a usefully stiff and precise linear motion slide from very low cost materials, mainly 1/8" hardboard & 6 mm rod, and access to a laser cutter.
As configured in the lead photo, the slide uses a wheel on a screw to reduce tangential motion at the edge of the wheel to linear motion of the slide by about 100:1, turning small human motions into tiny slide movements. The video below shows the photo model used for most of this 'ible repeatedly returning to within ±5 μm (indicated) of a set position — while carrying a 30 lb weight (± 2/10,000 inch; 14 kg). [1]
Stackable
If one axis of motion is good, two must be better! Two copies of the example configuration stack together trivially, one across the other, for precise 2D positioning. Stick them together with your favorite double-stick tape, hot-melt glue, Blu Tack®, etc. Other configuration options include more elaborately matching surfaces with tabs for fastening a pair of slides together. The video below shows mostly the 2D action of the 3-axis application that spawned this design. (stepper motor option introduced below)
Telescopic
More often the moving part of a slide runs on bushings/bearings that have some fixed span in the direction of motion. Wider span gives greater rigidity but reduces range of motion within a given overall dimension. Narrower span allows wider range of motion but reduces rigidity. A telescoping design like this turns that range-rigidity trade-off into a run-time option: greater rigidity within limited range, or longer throw if you can accept less rigidity. I'm happy to add that this design turned out much more rigid at full extension than I expected!
This Instructable
This 'ible got huge. How much you end up reading will depend on what you want to make. Reading straight through about half of it will show how to build the example in the lead photo with the white mug. 226
The rest describes variations on that theme.
Steps 1-38 may be all you need. They show how to build the photo example. This part includes the core sliding mechanism shared by all other variations. While mechanically simple, the core could be kind of a “bar bet” puzzle to put together without any guidance. This section uses lots of steps and pictures to walk through an assembly sequence that I hope can take you straight to a good result on the first try. The flag "※" marks notes about what might change when building a different variation.
“Variations” include swapping the hand-crank leadscrew for a stepper motor + leadscrew assembly. Actually, this design started as a powered slide and the manual variation was an idea for dividing the basic slide design from the details of putting a motor in it.
Steps 40-52 show what stepper motor fits, how to prepare it, and how to make a spring that you will need. Then that part will send you back to the first part to build a slide while showing where to fit the motor into the process.
Step 55 describes options for “accessorizing” a slide with features for attaching it to something, or something to it, or two slides together for 2D motion.
The last section introduces real live danger by showing how to assemble and use a clamp for holding a Dremel-like rotary tool.
I've tried to make this 'ible complete enough to follow from a cold start without booby traps or puzzles to solve. That probably means both over-detailed and still under-detailed. If building a second or more slides, your process may evolve. There is no warranty to void by doing something differently.
Feedback, Please?
This is the cheapest way to build a comparably capable device that I know of, and I hope it will enable/encourage someone to find other applications and improvements. Please give it a try and share how it goes.
[1] Yeah, mixed units throughout. Sorry, but metric bearings and UNC threads. No Mars landings will be attempted. 226