CNC Router: Mantis Build Update 3 – Movement!

Well, I promised, like two weeks ago that I would have a big update for you complete with videos now that my Mantis PCB Engraver is done – sorry the Thanksgiving holiday got in the way. I think it was worth the wait.

Before I get too far into that I want to draw all of my readers attention to a most helpful eBay seller of CNC goodies – carolbrent. This seller has an eBay store – Hubbard CNC – that is chock full of CNC equipment, parts, pieces, doodads, tools, videos, manuals, and way more! The HY-TB3DV-M 3-axis driver board I chose is a fairly common Chinese board with a so-so reputation – mostly that the Toshiba driver chips (TB6560 chips) are very susceptible to back EMF, the documentation is poor, and the typical eBay seller not too helpful. Well, I chose to buy mine from Hubbard CNC almost exclusively because this guy knows CNC and has gone above an beyond with this particular board in that he personally tests each one and videos it for you and includes that on a CD along with excellent documentation, a Mach 3 XML setup file, and a basic setup video. This is indicative of the type of helpful service you get from carolbrent. I started having problems with the first driver board I received and emailed Hubbard CNC with the bad news – any other eBay seller would have told me “too bad” , but carolbrent was excellent enough to meet me halfway on the cost for a replacement board which I felt was more than fair even though, in most of these cases, the problem is “operator error” and despite the fact that he had given me a video showing me that the board was working when it left his shop. As it turns out, and this is a “gotcha” of using this particular board so here is a warning to anyone using this board – DO NOT UNPLUG THE DRIVER BOARD FROM THE POWER SUPPLY WHILE THE STEPPER MOTORS ARE ENERGIZED OR YOU WILL FRY A DRIVER CHIP! Other than this, the board is great! You have to understand the capabilities and limitations of the board and there really is no better way to do so and alleviate the headaches many other people have gotten when purchasing this board from some other eBay seller by purchasing it from Hubbard CNC (carolbrent). He has some excellent diagnostic CNC tools as well but I am going to devote a future post to some of the neat yet inexpensive tools that are out there for working with homemade CNC machines. Anyrate, I just wanted to mention the driver board I am using for my Mantis and the best source on eBay for it.

As I told you before, I blew out my PCI parallel port card (hey another warning – DO NOT PLUG OR UNPLUG YOUR DRIVER BOARD FROM THE PARALLEL PORT WHILE THE PC IS ON OR YOU TOO MAY BLOW OUT YOUR PARALLEL PORT) in my desktop computer and none of my other computers or laptops had a parallel port so I ended up borrowing a laptop from TrackHacker.com member/contributor and colleague JT to start testing out the Mantis electronics. I was fortunate that his laptop already had the Mach2 CNC control software installed as well as CamBam for generating g-code from geometry. I did discover another “gotcha” while working with Mach2 and Mach3 on my desktop before I fried the parallel port card – you have to run the “OCXDriverTest.exe” in the Mach2/Mach3 install directory first BEFORE running Mach for the first time or, regardless of whether you have the correct parallel port address setup in the Ports & Pins menu of Mach or not, it will not run your machine until you do so. Doh! I really should read the software documentation first. Well, I setup my Mantis and JT’s laptop on my kitchen island as my workshop was too cluttered and I thought the kitchen setup would demonstrate the small size and portable nature of the Mantis admirably. Everybody, particularly my wife and JT has been dying for me to get this little machine moving (and cutting).

So without further blustering from me, here is the first video of me jogging the tables of my Mantis CNC PC Board Engraver around:

I thought that was pretty neat considering all of the troubles I had with this project. I am still in the process of learning CNC and control software which I think makes the Mantis a more compelling project really since – if I can do it, anybody can! As you can see from the video, jogging the machine around with a joystick is pretty neat. My kids thought so too – my son ( the family video game expert) particularly thought so. He loved jogging the machine all around using the joystick but soon taught me a valuable lesson – you need to have limit switches installed or else setup virtual limit switches in Mach or you WILL damage you’re machine. My son jogged the x-axis all the way over when I had the soft limits turned off in Mach (you can tell from the sound of the steppers in the above video that they were on when I recorded the video) and slammed the x-axis against the side of the Mantis. He didn’t realize this was a problem and kept trying to push the x-axis in that direction and the force eventually popped the x-axis stepper motor off the Mantis (remember I epoxied all of my stepper motors in place) and I lost an entire day while I waited for the epoxy to cure the motor back in place. Doh! I decided to use CamBam to create a very simple g-code for me to try parsing with Mach2 and get my Mantis moving around in a more useful and typical manner.

Here is a video of my Mantis CNC PC Board Router running through a simple g-code:

Well that is a little more practical I suppose, yet probably a bit more boring since I’m not actually cutting anything yet for fear of damaging my machine. I did learn that creating g-code, even simple g-code, is not the most intuitive process and I still have a lot to learn. I still have to get a grasp on all of the terminology – perhaps I should spend more time reading documentation and cruising the CNC forums but I got impatient during the build and I wanted to jump into creating things with my Mantis as soon as possible. Unfortunately I found out that I really do have a lot to learn about CNC – whether it’s the terminology and processes or knowing when your equipment is messing up. I couldn’t for the life of me get my z-axis to zero properly and behave in a repeatable manner. It seemed like no matter where I zeroed the z-axis on, it would never return there but more than once. I kept zeroing the z-axis with the very point of an engraving bit installed in the Mantis just touching the copper of a blank PCB and then trying to execute my basic “circle in a rectangle” g-code and found myself cutting straight through the blank PC board right into my y-axis table. Fortunately it wasn’t too deep. I did this a couple of times. One other “gotcha” I discovered here is you need some way of manually jogging the z-axis but you can’t use a handwheel mounted to the rear shaft of a dual shaft stepper motor because of the location of the z-axis stepper. I suppose you could cut extra length on your z-axis threaded rod and fix a handwheel at the top but it will always spin when the z-axis table is jogging up and down. Don’t lean over it with a necktie while you’re machining something! Well, I kept playing around and THOUGHT I had the z-axis figured out as demonstrated by my next video and tried cutting my basic g-code with some funny results. Take a look:

Doh! I was inclined to blame my self for this as I said in the video and to some degree that’s true but, as it turns out, after extensive testing of my Mantis by JT, it was discovered that my driver board had problems with the z-axis. It kept losing it’s position which is why I could never get it to return to the same spot repeatably. JT changed the settings in Mach2 to swap the x and the z axes around and the problem seemed to go away. Perhaps the gravity exerted on the z-axis was playing a part. Not sure but JT was able to get the z-axis working predictably and repeatably. He also found that I had the y-axis reversed.

Well, that brings us up to date with the project. I have subsequently received my PCI parallel port card for my desktop and went through a weekend of hell trying to get it and Windows 7 to play nice – I eventually won – and have setup my Mantis in it’s permanent place on my desk next to my PC. I plan on doing some more testing and cutting over the next week so I will be posting those results as well. Check back soon!

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