Most home-built cnc machines use a driver program such as Mach3, which is what I will be using in this guide. I’m also going to be using CAM software called MASTERCAM, which has a post-processor in it for generating G-code compatible with Mach3. For those of you that have Mastercam but don’t know where to find a compatible g-code post-processor for Mach3, I found mine here (this is the link for downloading the file):
For the sake of keeping things simple, This guide will show you how to make a #25 1”, 11 tooth sprocket. If you want to make a different sized sprocket, you can use this guide as a basis on how to construct your sprocket.
This guide will only show you how to make the sprockets with a cnc mill/router that uses Mach3 driver software. The process is pretty straightforward, though, so using this guide with other cnc mills/routers should simply require small adjustments to the process to work properly.
This guide will not show you how to create the 3d part on solidworks. If you want to know how to do that, here’s a great link that helped me:
Note: you must at least have a cnc mill/router AND a metalworking lathe (preferably a cnc type). You could try using a woodworking lathe, but I advise you only do that if you plan to make wooden sprockets with far less precision.
I AM NOT RESPONSIBLE NOR LIABLE FOR ANYTHING THAT HAPPENS IF YOU DECIDE TO USE THIS GUIDE! REMEMBER TO USE COMMON SENSE AND GENERAL SAFETY PRECAUTIONS WHEN OPERATING MACHINERY AT ALL TIMES!
Step 1: Tools/Materials Needed
-A CNC mill/router that uses Mach3, and has a vise for holding the stock.
-A 1/8” cutting diameter end mill and a ¼” cutting diameter end mill
-A CNC lathe with manual control OR a metalworking lathe
-A Drill press
-A ½” diameter drill bit with a tapered end. For extra precision, use a counter-boring/step drill bit with a small diameter of ¼” and large diameter of 1/2”. You can also use a ½” drill bit countersink that attaches to a ¼” drill bit. Using these REALLY HELPS and makes a huge difference in the quality of your sprocket.
-A hand saw AND a hacksaw (or a jigsaw with both wood and metal cutting blades)
-A 1/8” drill bit (Size can vary as it is simply for predrilling the holes for the screws)
-One 1-1/4” diameter aluminum rod (length must be at least ¾”)
-One 2”x3”x0.75” block of wood (Block 1)
-one 1”x3”x0.75” block of wood (block 2) (size can vary as long as it is 0.75” thick and at least 2-1/2” long)
-Two 1-1/2” screws (size can vary as long as they are ½” longer than the width of the 2nd block of wood on the list.)
-Mach3 licensed version
-Mastercam with a Mach3 post-processor (optional)
-A 3D CAD program such as Solidworks (optional)
Step 2: Part 1: Creating the G-code Files for the Sprocket
If you plan on making your own custom sprocket, then make sure you tell the CAM software to ONLY cut the outside teeth of the sprocket. It should look something like the toolpath in the picture.
Step 3: Part 2: Making the Sprocket Blank
1) Cut a ¾” long segment out of your 1-1/4” aluminum rod and place it in the lathe chuck and tighten it.
2) Flatten the end of the piece first, then take it out of the chuck and reinsert it with the flat end facing the chuck. Now flatten the other side of the piece.
3) Gently cut down the outside of the rod blank until it is ½” diameter and 0.37” long. This will be the arbor.
4) Flip the piece around so the arbor is facing the chuck and gently gut down the outside of the blank until it is 1” in diameter. Then machine the end so the 1” diameter end is 0.16” in length.
5) Bore a ¼” hole into the center of the blank. You could use a drill press for this part, but I highly recommend you do it on the lathe, as this significantly increases the precision of the hole.
You should now have a sprocket blank that looks like the one in the picture.
Step 4: Part 3: Making the Sprocket Template
2) Predrill 2 holes using your 1/8” drill bit, each being ½” on either side of the center of block 2, as shown in the picture.
3) Insert the screws in each hole.
4) Make sure to mark the top side of your template. This side will be facing up when you begin milling your sprocket.
This should be plain and simple. The end of the template will fit up against the chuck on your cnc and will hold the blank sprocket piece in place.
Step 5: Part 4: Setting the Origin Coordinates on Your CNC
2) Place your blank template in the CNC vise the ends fit snuggly with ends of the vise, and then tighten. Make sure that you place the template face side up.
3) Insert the ¼” end mill into your machine and position it directly over the center of the template, then move it down by 1” in the x axis.
4) Turn on the mill and gently lower the z axis to make a ¼” hole that is about ¼” deep. DO NOT MOVE THE X AND Y DIRECTION WHEN YOU DO THIS.
5) Slightly raise the z axis until the end mill is no longer in the hole and turn off the spindle. Now click on both the 0 x axis and 0 y axis buttons on mach3 (they are circled in orange on the picure.)
Take your template out, but keep the origin coordinates where they are. Your template should now look like the one in the picture.
Step 6: Part 5: Finishing the Template
2) Secure your piece in a vise and, using a saw or jigsaw, cut all the way down the center of block 1 (as shown in the picture). Make sure your cut goes through the ½” hole you made in step 1, and don’t cut into block 2.
If done correctly, your template should now look like the one in the picture. The two screws should now be supporting each half of block 2 in place.
Step 7: Part 6: Milling Your Sprocket
2) Place your template top side up in the CNC vise so the ends of the template fit snug up against the ends of the vise and tighten greatly (but not too much). The amount you tighten is crucial for keeping the sprocket blank in place while it is being milled.
3) Replace the ¼” end mill with the 1/8” end mill. Don’t worry about length, as it will be corrected in step 4.
4) Move the y-axis ¼” from the center origin and gently lower the z axis until the tip of the 1/8” end mill is touching the top of the sprocket blank. Click on the 0 z axis button on Mach3 (circled in red), but DON’T press the 0 y axis or 0 x axis buttons (circled in orange in the picture). If you do, you may have to start all over!
5) Raise the z axis slightly, and start the spindle. It is highly recommended that you spray a cutting fluid (WD-40 works too, but not recommended) on the blank if your machine doesn’t have an automatic cutting fluid dispenser.
6) Click on Cycle Start to start the program, and wait until your CNC mill has finished milling the sprocket. If something happens, make sure you press the emergency stop immediately (or press the space button on your computer keyboard). Don’t worry if you have to the axis; as long as your sprocket blank stays in place, you will be able to automatically go to the last known position of your sequence before resuming the cycle.
7) Once your CNC mill has finished the cycle, turn off the spindle (raise the z axis if you have to) and remove the template. Wash it down with water until most of the debris is gone and remove your finished sprocket from the template.
Congratz! You’re finally done!