I’ve really enjoyed this little CNC machine I bought earlier this year. It’s been a good learning experience and I’ve been able to make some things that I just couldn’t make using a 3D printer. CNC machines offer greater material choices and precision, but are also harder to use than 3D printers. It’s a whole different world compared to 3D printing.
I bought my machine for about $1200 (with shipping) off of ebay from a company in China. For that price I got a small 4 axis machine (3 axis plus rotary axis), ball screws for good precision, a controller box, and a couple of bits to get started. Hard to beat the price, and I expected some inadequacies in the product. I’ve been able to identify some not so good qualities in the machine and made improvements and enhancements which I’ll preview here.
Here’s a photo of the machine, post-enhancement. I’ve swapped out the spindle motor, leveled the table, and added a camera to allow me to make more precise parts. The camera is essential for lining up the work piece again after it has been moved, like when it’s flipped over to machine the back side. I also added a wireless MPG (manual pulse generator) for controlling the machine during setup and operation. That alone is a big improvement to the process and is well worth it.
Naturally, the new spindle motor didn’t “just fit” onto the existing machine. It was off by a millimeter or so in motor diameter and also in a couple of the mounting holes. I chose to make a new mounting bracket for the motor using my 3D printer. The bracket is certainly not as strong as the machined aluminum one that came with the motor, but seems very adequate for this machine. Because of the larger size of the motor, I had to change the configuration a little for the motor mount, and I made a new cable chain on the 3D printer to route the wires for spindle motor power and USB camera connection. I added a new, dedicated bench power supply for the spindle motor which is a big improvement over the spindle motor speed control that came with the unit. Actually the spindle motor control that came with the unit as part of the controller was pretty cheesy and burned out twice. The motor wasn’t so good either, and sometimes made noise like the bearings were not very good, including a loud vibration in the motor whenever much of a lateral load was placed on it. It would squeal pretty loud.
It’s so much nicer to use this machine now. I’ve still got some learning to do and experience to gain. I’d hardly consider myself a machinist but at least I can make some things I didn’t have the means to make before by myself.
Here’s a picture of the machine in its original state.
Original CNC machine configuration.
In upcoming articles I’ll provide a little more detail on these enhancements. Stay tuned!
Today I’ll show the first test of the CNC vacuum plate, but first we’ve got a little bit of work left to do to make the top part. You may recall that I likened it to an air hockey table, but instead of forcing air out of the holes, we’ll draw air down through the holes with a vacuum pump.
Here’s my top plate being drilled with an array of holes. Again, remember that if you use extruded acrylic, you’re likely to have a lot of problems while machining or drilling it because the plastic melts and gets stuck on the bit and also leaves rough edges. Cast acrylic chips away nicely.
Drilling holes in the top acrylic plate.
The next step for me was to make an adapter to go from the vacuum hose to the cavity at the end of the base plate. I won’t go into a lot of detail here but what I did was make the adapter on the 3D printer because it was faster than machining one. 3D printed objects made with the FDM process (using a spool of plastic filament) are usually fairly porous (not airtight) so I’ll use some glue and/or tape to improve the seal and fill up the pores at least well enough for it to function.
Adapter being printed on a small 3D printer.
Finally, putting it all together, it’s looking pretty good!
On the left you can see the hose adapter. My little air hockey table is sitting on top of the base plate. I’ve temporarily fastened the top to the base with a few spots of glue and tape around the edges for a seal. Later I’ll make a more permanent seal after seeing that it works ok.
First test. It works!
For the first test I’ve connected a pretty strong vacuum pump that’s designed for applying vacuum to air conditioning systems to remove all of the refrigerant, air, and moisture. I doubt this is necessary and I’ve seen others use shop-vacs. This was just convenient for me and gives me a chance to see how much leakage there is in my system. I know that with this pump I should be able to get over 29 inches of vacuum, but as you might be able to see, I’m only getting about 14 inches on this test, and sometimes as little as 7 or 8 inches. I’ve got some leaks, probably mostly in that area where the hose adapter sits. You can see I’ve taped over unused holes since the 6 x 6 inch board doesn’t cover the whole area. Imperfections (like board warping) in the pcb also contribute to leaks. As it turns out, 7 inches of vacuum seems to hold it pretty well. I had to apply a lot of force to move it by hand. It was stuck very well.
I hope you’ve enjoyed seeing this and it’s been a fun and useful project. Later on I’ll show some other improvements to the CNC machine itself and refinement of this fixture that allows greater precision when making circuit boards on a machine like this.
Let’s move on to the next part of building the CNC vacuum plate: machining the base. You may recall from the last post that the base was to be machined from a 1 inch thick piece of cast acrylic material. The base will have channels that allow air to be drawn through a top plate that has an array of holes. From there, the air will be drawn out of the vacuum plate and into a vacuum pump that has adequate suction to hold the work piece in place.
Below is a photo of the base being machined. I’m using a flat end mill to carve out the channels and the area at the end where a vacuum connection will be made.
These small desktop CNC machines usually handle bits that have a 1/8 inch shank, and as it turns out, just about all of the bits I’ve found that have a 1/8 inch shank have a cutting width of no more than 1/8 inch. I did manage to find a 1/4 inch drill at one site, and I’ve found some “deep reach” bits that have a longer than typical bit length and cutting depth. It just means that it’ll take a bit longer than it would with larger bits because more passes will need to be made.
Finished base part, all cleaned up. Beautiful!
Next, we’ll make a top plate which will have all of the holes in it, connect vacuum, and see how it works!