I want to make a 3 axis CNC (Computer Numerically Controlled) engraving tool for my workshop and I've pretty much completed the electronics side of the build (Arduino and EasyDriver based). I've looked at and experimented with a couple of different platforms for the CNC and I'm still experimenting and tinkering with different methods of driving the cutting tool.
I wanted to use a timing belt, pulleys and drive gears for my CNC tool, but I didn't find anything that was cheap enough along with being easily accessible (because I wanted about 12 drive gears), so I decided to make my own.
I was faced with a bit of a chicken and egg dilemma ... I needed a CNC router to make the parts for my CNC router/engraver. That is until I had a bit of a breakthrough moment. If I used the timing belt on the drive gear, it would be a perfect match for the timing belt. I let that thought soak in for a while until it was entirely obvious.
In this instructable, I'll tell you about making the Drive Gear.
- 7mm plywood (900mm x 650mm)
- 10mm pine stock (500mm x 50mm)
- 5mm 2GT timing belt (10m)
- 7mm dowel (500mm)
- 4 x 4G 12mm countersunk screws
- 1 x 4M 12mm countersunk bolt
- contact adhesive
- Drill Press
- 95mm (inner diameter) hole saw
- 27mm (inner diameter) hole saw
- 7mm drill bit
- countersink drill bit
- 2mm drill bit
Step 1: Make a Gear Blank and Hub
This is pretty simple ... mark out on your 7mm plywood piece where you want to cut
I made 8 blanks by marking out the width of the hole saw on the plywood and then using a try-square, I marked diagonal lines dividing the plywood into 2 rows of 4 x 100mm squares with the intersections of the diagonal lines marking the center of each square.
Using my large hole saw in a drill press, I then cut each of the plywood disks.
My hole-saw drill bit is 5mm diameter, so I then needed to increase the diameter of the center hole to the required 7mm using a 7mm drill bit.
Then, I made the hubs. The hubs are 27mm disks cut from the 10mm pine stock. Again, these were cut using the drill press.
I drilled 4 holes (in a square) through the hubs and drilled out a countersink with the countersink bit. This is so that the screws sit below the plane of the hub when attached.
I drilled a hole through the edge of the hub so that I could drive a set-screw (4M x 12mmm bolt) through the hub to secure the gear to the axle.
Then I drilled 4 corresponding holes into each of the 95mm disks so that I could attach the hub to the drive gear blank.
Step 2: True-ing the Disks
The hole saw leaves a fairly rough edge around the disk and the edge is not terribly straight, nor are all of the disks particularly equal in diameter. It is necessary to true the disks so that all of them are the same size and so that the outer diameter will be the right size for the 2GT belt ... the teeth have to be even or the joint between the two ends of the belt will either have a gap or will be too tight and your drive belt will skip or slip when in use.
To true the disks, I fitted a hub to 2 of the disks and then put all of the disks onto a 100mm dowel off-cut with the two hubbed disks at either end of the "stack". The set screw was tightened in the top and bottom hub to hold the disks to the dowel firmly.
The dowel was then put into the chuck of my drill press and I turned the drill on (as slowly as it will go).
Using a rasp, I smoothed the exposed edge of the spinning disks until I was happy with the diameter and finish. It's a good idea to have a piece of timing belt handy to measure and verify the disks diameter.
Finally, I used sandpaper and smoothed the exposed edge of the spinning disks so that they would better adhere to the timing belt.
Step 3: Varnish and Glue
I chose to varnish the disks so that the contact adhesive would make good contact. In my experience, contact adhesive doesn't adhere as well to undressed timber as it does to varnished timber. This is probably because the unvarnished timber tends to be filled with particles and dust making the contact less clean.
Anyway, I used a timber varnish and sealed the edge of the disks and, for appearance, varnished the rest of the disk. I fitted a 1/4" bolt through the hole with a washer on both sides into each of the disks, drilled a bunch of 1/4" holes into an off-cut piece of timber I had lying around and slotted the bolts into the timber. This meant that I could easily apply the varnish to the edge of the disk while rotating it so that I'd get a nice even varnish. I also varnished the top at the same time. When the varnish cured, I flipped the disk and repeated the operation on the bottom side (now facing up).
When the varnish on both sides had cured, I then spread a layer of contact adhesive on the underside of the timing belt and onto the edge of the disk. I left the contact adhesive until it became tacky and then applied the timing belt to the disk. I also used a rubber band to hold the timing belt to the disk until the contact adhesive cured.
Step 4: Done!
Now I have one completed ... I still need to complete the rest of them.
I need 8 drive gears of this size for the X and Y axis of the tool and 4 more smaller ones for the Z axis.
The neat thing about this method of making your own gears, pulleys, drive, etc. is that you can make them any diameter you want ... you can also make them elliptical or, indeed, any shape that you want. Composite gears are quite possible too!
Anyway, I hope that you enjoyed this instructable.