Plans, projects and how-to's for home machinists

CNC: Automatically find edges, hole centers and more with Mach 3

This article describes how you can use Mach 3, the popular CNC controller software, to automatically

  • Find the edges of your work piece (and therefore the corners)
  • Find the centers of holes and their diameter
  • Set your cutting tool at a known height above your work piece or table

What’s involved

This feature is very easy to implement and use and it will cost you almost nothing.  You don’t even need a licensed copy of Mach 3.  Here’s what you’ll need to do:

  • Download and install a free screenset for Mach 3 that has the buttons you’ll need to operate these features.  There are a number you can choose from.  Keep reading to find some of them.
  • Connect a wire to an unused input on your CNC controller board.  This is the circuit board your steppers motors are hooked up to.  You probably have a spare input unless you’ve used them all up for home or limit switches.  If so there is probably an inexpensive way to add more.  You may also have to add an inexpensive and easy-to-find capacitor if have a problem with electrical “noise.”  I didn’t have to.
  • Go into Mach 3 configuration menu for ports and pins and enable the “probe” and assign the pin you hooked your wire up to.  You might have to also change the “active low” setting from its default but that’s easy to determine and do.
  • Connect the other end of your wire to a touch plate.  If you’re working with wood or other non-conductive materials you’ll just need a flat straight piece of metal for finding edges.  There’s at least a few different kinds of probes and touch plates you can use to find the center of holes and their diameters.  One is simply a short straight piece of metal rod mounted in your spindle.  If you’re working with metal then your touch plate or probe will need to be electrically insulated from your work piece.  So it will require a little more effort to make one.

It took me only about 40 minutes to get it working on my mill, although that doesn’t include all the research I did first.  I also made a quick-and-dirty touch plate and I still need to make a couple of better ones.  I’ll be writing more about that later.

More details

“Erniebro” on CNCZone didn’t come up with the idea for an auto edge finder, but he deserves an enormous amount of thanks for publicizing this method and making it easy for others to start using it.  He designed the first screenset for adding this feature to Mach 3, made the video above, posted excellent instructions on CNCZone describing how to install it and patiently provided help and support for those who needed it.  Others have built upon his work and made improvements, but if you want to try this I suggest you start with ErnieBro’s instructions.

  • One of the first things you’re going to want to do is download Erniebro’s Mach 3 screenset.  I just want to let you know that if you’re NOT a registered member of CNCZone and logged in, you’ll get an error message that might make you think the file is no longer available.
  • There’s a very good chance you won’t have any problems getting your machine to work properly.  If you do there’s also a very good chance that someone else has had the same problem and you’ll find the solution in Erniebro’s forum thread.  Unfortunately, the thread has grown to almost 400 posts and it takes a lot of time to read them all (trust me, I’ve done it).  So I suggest you take advantage of the “Search this thread” link you’ll find near the top of each page, just above the messages on it. You’ll need to be logged in to use it.

Inexpensive and easy-to-make CNC scanner for duplicating parts

This is a very cool and extremely easy-to-make accessory that can turn a a CNC mill into a scanner which can be used to duplicate parts.  It uses an inexpensive USB webcam and some free software.  The camera mount is also super simple.  The video shows them simply taping the camera to a rod held in a collet.

The Bad News

You can test Tormach’s software for free but it’s pretty useless unless you buy the full version for $335.   The “shareware” version won’t let you save anything, so you can’t export your scan into a CAM program.  Which means you can’t actually use it to make a duplicate part or do anything else that is very useful.   Also, the video says your accuracy and resolution will depend on the web cam you use.  That sounds like you could use a $20 web cam but your results might not be very good.  Tormach describes the camera they sell, for $513 with a mount, as a USB microscope.  As you can see in the video, the camera is only a few inches from the part it’s scanning, so it appears you may need a camera that can focus at close distances.

I really wanted to try this out until I learned how crippled Tormach’s free software is and how unaffordable the full version is.  I even found a $12 web that would be easy to mount on my mill.  I don’t know how well it will work, but it has a focusing ring and it gets good reviews on Newegg (where it costs more).

This would be a nice accessory to have, but it’s not affordable and don’t see how I would use it much.

Wire Rack Attack!

This short video shows a simple low-cost method for organizing small reels of wire.  I found it on’s blog, which recently featured a couple of our articles.  One was Mikey’s contest winning essay and the other was Nate’s short article about some free plans for a Watt-style steam governor.

I’ve been working very hard lately at reorganizing my workshop and getting rid of stuff that I don’t need or rarely use.  I really need to make more space because I now have two lathes, two mills and a couple of friends who have been coming over to use them.

Tubalcain’s Lathe Bit Grinding Videos

Even though YouTube seems to have umpteen million videos about machining I’ve found very few that will you show how to grind HSS bits for a metal lathe.  And most of them show it being done on special grinders or with the help of jigs and accessories that most of us don’t have.  These four videos by Tubal Cain, the author of many books about machining and metalworking, are among the few I’ve found that will show you how to do it free-hand on the kind of grinder most home machinists have.  [This is not the same Tubal Cain who wrote more than 20 books and 200 articles about machining and model engineering.  That was the late Englishman T. D. Walshaw who used “Tubal Cain” as a pen name.  This “Tubalcain” appears to be a retired shop teacher living in Illinois. – Rob]

The videos are good, but not great because they’re too long.  “mrpete222” doesn’t get to actually showing you how to grind a bit until the fourth video.  During the first three he discusses the shapes and angles of the various kinds lathe bits using large wooden models that make it easier to see what he’s talking about.   He also discusses the tool bit holders used by older lathes, which hold bits at an angle so they don’t need back rake added to them.

I’ll admit I’m not real good at grinding lathe bits because I usually use carbide inserts.   But I did learn a lot from these videos including these two great suggestions:

  • Use lay-out dye and mark out the angles you need to grind.
  • Practice on mild-steel (keystock).  It’s cheaper and grinds faster.


Lathe Tool Bit Grinding Video #1 (10:46) – Right-hand turning tool, back rake & tool holders, angle of keenness

Lathe Tool Bit Grinding Video #2 (5:13) – Facing and universal turning tools

Lathe Tool Bit Grinding Video #3 (5:39) – 60-degree thread cutting bit

Lathe Tool Bit Grinding Video #4 (8:46) – Actual grinding of right-hand turning tool

Random Quote

The price of success is hard work, dedication to the job at hand, and the determination that whether we win or lose, we have applied the best of ourselves to the task at hand.

— Vince Lombardi