Back in Part 1, we introduced the basics and started building the electronics. In Part 2, we finished up the controller and started building our machine. Today we complete our unholy marriage of cutting boards and dot matrix printers in Part 3 of How-To: Build your own CNC machine. Good luck.
Last time we showed you the completed base, with the first axis. The screw drive turns easily and there's very little play in the motion of the table.
The design of the upper axis is simple, but is the most difficult to execute. Originally we hoped to use a pair of the small sliders, but binding was an issue so we redesigned it to use a large printer slider at the base. Ultimately, the binding was caused by the nut and threaded rod we were using. Swapping them out solved our problems.
A simple tower constructed of three pieces forms the basis for the rest of the machine. The tower will be mounted to the outer edges of the base. This allows greater side to side movement to maximize the usable area on the table.The center piece of from the same cut as the bottom of the base. To drill the two sides evenly, we screwed them together and drill the mounting holes with the drill press. One the first screw was in, we drilled the rest one at a time.
The center slider is the most complex to build. Each piece is visible here. We used our usual trick of screwing the opposite pieces together in order to align the holes for the slide and the threaded rod. The brass slider and long hex nut were pressed into the plastic with our bench vise. This technique seems to work well, but alignment is critical!
To effectively deal with the minimum space, we had to get tricky. There just isn't enough room in the carrier to mount bearings for the Z axis. Instead, we pressed bushings into the plastic with our vise. Then we added a washer and a lock nut to the threaded rod at the top and bottom of the carrier. Careful tweaking with a pair of wrenches made for very little play. Just how long this setup will stay tight is in question so we'll have to keep an eye on it as we break in the machine.
This slide and carrier were salvaged from an old Okidata printer. We decided to use it to smooth out the action for the Y axis.
We whipped out the drum sander attachment on our dremel tool and contoured the plastic on the bottom so we could mount the printer slide without compromising the integrity of the cast metal.
Once the slide was mounted, we marked and drilled the mounting holes for each axis. Once the slides are set up, we'll use some screws to lock them in place.
Once things start coming together, they'll get extra frustrating as you begin aligning the slides and drive screws. I took us a while to narrow down that the source of binding was the drive screw and nut combination. We'd overlooked them initially because they worked very, very well in the other cases.
Once each axis has been constructed, we needed a carrier for the rotating tool. We picked up a flexible dremel shaft and created a simple mount for it. The flexible shaft will reduce vibration. The dremel version has the nice button for locking rotation -- far less frustrating to use than the off-brand tools.
We used a couple of tricks to achieve a nice fit. The strips were cut first, then screwed together with some space to spare. Then we drilled the plastic with a starter hole and used the dremel tool to taper and round out the holes until the fit was perfect.
Motor mounts are dependent on the motors you've ended up with. If you're lucky, you'll salvage some motor mount brackets. Creative mounting can be achieved by using new or salvaged pulley systems.
Limit switches are very helpful for keeping your machine from self destructing. A switch is placed at the limit of each axis and wired in parallel. When the carrier or table contacts one, the circuit is closed and the controller signals the computer. Lever switches like these are ideal, or you can salvage some of the exposed contact switches from printers. The main danger of either switch is fouling caused by debris from your work project. Covering the switch with a bit of latex glove or balloon can help prevent problems later on.
Now that you've got all the bits of information you'll need to build your machine, lets get into some actual software to make the machine work.
KCam - Probably the easiest software to set up and configure, KCam is great for testing out your machine. It ran just fine on our Windows XP laptop. The drawback has to do with the method that Windows uses to access the parallel port. Because of this limitation, the machine won't run as smoothly as it really can.
EMC Linux - Some dedicated individuals maintain EMC and actually produce a stripped down, brain dead install of Linux just for running EMC. It doesn't take much of a machine to run, so it's great for dedicating an old machine just to run your CNC machine. Add a network card and you can operate and send jobs to the machine remotely. It's not too bad to install, but expect to spend some time figuring out the quirks.
Now, what you've all been waiting for... the machine in action! The bit is another tungsten carbide bit from Drill Bit City. (Oh, how we love them.)
If you've gotten this far, congratulations are an order! Oh, and then you should already expect to spend some time troubleshooting your creation. Don't be upset if everything doesn't work perfectly! (Or if you end up ripping all apart and starting all over...)