Introducing the New CNC Machine


This is the CNC router that I’ve been working on for the last two months; the first one I’ve ever worked on. It’s a 4×8 PRT Alpha from Shopbot, and we bought it used, which means that it’s the older model, but it did come all wired up. That means that we got it up and running quickly, but it also means that I don’t really know what I’m doing when I have to find a wiring issue. If I’d wired all the connections from scratch, I might actually remember what things are. As it is, I find that I have to talk to tech support about once a week.

All in all, I’m pretty happy with this machine. In function, price, and capability, it sits somewhere between a DIY hobbyist tool and full-fledged production machine. It’s cheap (for what it is), and you are expected to be pretty handy with a multimeter and machine code to keep it working (I am not handy with these things). There is no hand-holding or helpful software wizards or internal digital diagnostic checks on this machine. On the other hand, it is a sturdy steel table equipped with fast and powerful stepper motors and a 4hp spindle that can do a lot of serious work.


Here are a few “starting-out” lessons I’ve learned that seem really obvious in hindsight. As you might guess, these are trial and error kinda lessons:

  • After you have leveled the table, make sure the spindle is still plumbed vertical.
  • After you have squared the table, square the gantry also.
  • If the proximity sensors aren’t working right, check for shorts all along the entire cable before re-writing the whole XY zeroing procedure in the software.

All of these half-completed tasks introduced glitches that were deeply mysterious at the time. It’s also important to ground every single part of everything. This is a very analog machine. Even static electricity will quickly introduce noise that a digital system might reject, but will be enough to throw off inputs or trip switches in the control box.


But, now that I’ve been messing with it for a while, I think I’m at least part of the way up the learning curve. We’re cutting lots of usable parts for T-Rex Arms, parts that are actually shipping to customers, and experimenting with parts for several different future projects. I’ll be posting more about what I’m learning and doing with it, and I’d love to hear any input on what I should be doing differently, or any questions about other things that we’re working out.

  1. That’s great, Isaac! Your tenacity will pay off . . . I look forward to seeing what you can create on this machine 10 years from now!

    - Chad Roach
  2. It’s amazing what these tools can do now with the assistance of computer tech.I have a freind in the business and he was demonstrating what some of the smaller desktop versions are even capable of. Amazing. His company is

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