Shopping Cart

FREE shipping for the E3 CNC Router in the continental US


Credit Card Badges

3D Printer high grip string drive

Posted by Bob Wood on
3D Printer high grip string drive

I have designed and built several CNC routers and added CNC to a Grizzly desktop mill. They all had one thing in common: that is ACME threaded rods for precise movements. Once I decided to build my first 3D printer I knew I would not need the force carrying acme screw, so I looked into belts and strings. Belts seemed to be an obvious choice, but they do have some issues. For me, they do not seem to be a cost effective way of moving the small mass of an extruder. I purchased some braided fishing string and started designing. At first, I used the common method of drilling a hole thru the steel or plastic coupler, then wrapping 8 to 10 turns for each direction. This works, but the sting takes up too much room axially. Fuel line or rubber hoses work well for a few printed parts but wear quickly as the string constantly is making small cuts into the rubber surface.  I have a 4th axis on my Bridgeport mill, so I make a “threaded” v-groove aluminum coupler. It worked better, but the grooves with the bit I had were too wide to grip well. This got me thinking… what if I used a threaded rod. What groove angle would I need for a given string diameter? From there, it was pretty simple. I settled on a 7/16-20 threaded rod with 0.54mm string diameter. It has an awesome grip with only 3 to 4 turns, and it is fairly simple to make on the lathe.  Recently, I received some customer feedback which stated “I was admittedly somewhat skeptical of the fishing line and screw ‘high grip’ drives. But holy s!#t, they work extremely well, and I find totally silent.”There might be other combinations that will work, and it would be easy to try a few just by taking your string to the hardware store and wrapping it around a few bolts.

The next issue to solve is how to keep the string tight? It makes sense that we should use a fishing knot since we are using fishing string. I watched several YouTube videos and found a knot that does not creep. It is named the Uni-knot. Ensuring that I kept the design simple and cost effective, I decided to try nylon zip ties to keep the string tight. They have several features that make them the right choice. First, they have a hole so that it is simple to tie a knot. Second, they lock into place and are designed to lock into position. Third, with 2 of these ties one can make an adjustable tensioning string drive for a 3D printer, Laser engraver,  or any other low mass CNC machine movement. And lastly, they are cost effective. I use the 40 lbs zip ties, and I have a video on YouTube that shows a working model, or you can download the manual.

Older Post Newer Post