Intro: Flexible CNC Leadscrew Nut
This is my first 'structible so I decided to do something very simple yet helpful to the right people. I followed several very good Instructables on making your own CNC machine however, I ran into some trouble moving my tables using NEMA-17 stepper motors. These motors don't have a lot of torque and due to the difficulty of getting the leadscrew nut perfectly straight I ran into some issues with the leadscrew being difficult to turn. My solution was to create a mount for the leadscrew nut that could flex and conform to the path of least resistance on the leadscrew. The final product is a piece of rubber hose with a threaded sleeve pressed into it and mounted to my tables by two metal bars that clamp the hose in place when tightened down.
Step 1: The Original Leadscrew Nut
This is the original leadscrew nut mount. This made the tables very difficult to move because of the bind it put on the threads inside the nut due to its misalignment. I tried on several occasions to get the alignment just right however, nothing I did resulted in making it easier to turn the leadscrew.
Step 2: Hose
I used 4 inches of rubber hose with on ID of 3/8 in. Your application will most likely be different as I used 5/16 - 18 thread for my leadscrew for my CNC machine. Just make sure the ID is at least 1/16 in larger than the diameter of your leadscrew.
Step 3: Leadscrew Nut
I bought a coupling nut and cut it round using a lathe. I got lucky as once the nut was round, it fit snugly into the hose. It is not necessary to cut the nut round, just as long as you can press the nut into the piece of hose.
Step 4: Pressing the Nut Into the Hose
Hopefully you have some extra all thread from the leadscrew laying around, as you can thread the nut onto this and press it into the hose using a vice. I recommend using the all thread as a guide when pressing the nut into the hose by having the all thread run inside of the hose so that it prevents the hose from flexing. I pressed the nut in about an inch at a time; each time threading the all thread out another inch and tightening the vice until both ends for the all thread were touching the jaws of the vice. If your nut fits loosely in the hose then use a hose clamp to tighten the hose to the nut. I did not do this to mine however if I ever do encounter a situation where there is a high enough load against the leadscrew nut that it moves inside of the hose I will end up putting a hose clamp on it to prevent movement.
Step 5: Mounting Brackets
I had a lot of these 1 X 2 X 3/8 inch metal blocks so using two, I drilled a hole through the center the same diameter as the OD of the hose I was using, 3/4 in. After that I drilled two mounting holes on the thin side of the block. I then cut the blocks in half using a die grinder so that once placed on the tube, they would clamp down when the mounting bolts are tightened. The width of the cut allowed the blocks to clamp down firmly on the tube to prevent any sliding in the blocks.
Step 6: Installation and Final Assembly
The final assembly looks just like the first picture above. The next picture is the final assembly mounted to one of the tables and the last picture is just of the CNC machine I built using these. Right now I am using a 500 mW laser to burn wood however I plan on making a third axis and mounting a wood router to cut out shapes from wood. I am also using arduino with GRBL installed and easydriver stepper motor drivers. I use inkscape for making drawing and the laser engraver extension for making gcode files, which can be found on Instructable user Groover's pocket laser engraver Instructable, much thanks goes out to him as his Instructable was very helpful. Finally, I use Universal G code Sender to send the gcode to my arduino. Thanks for viewing, hopefully this can help some people on the track to building their own CNC machines. Like I stated earlier, this is my first Instructable so please don't be too critical however questions, comments, and advice are welcome. Thanks guys.