In the first post in this CNC Router Skills series on
Origin Points, I emphasized how critical reference positions are for digital
woodworkers. When you’re working on a drawing in CAD, the origin point is at
the intersection of the X, Y and Z axis. All measurements — positive or
negative, begin at that point. By the numbers, that’s X=0,Y=0,and Z=0. It’s
from that position that the piece you’re cutting is positioned.
For accurate CNC Routers for
woodworking operation, Origin Points are extremely critical. Never more so,
than for digital woodworkers. The intersection of the X (red), the Y (green)
and the Z (blue) axises is the origin point.
The origin points on your CAD drawings and the material that
you’re cutting have to match. Several methods, tools and techniques make the
job easier.
As you’ll soon see, there’s a lot of
ways to do this. It’s a good practice to understand and be able to use a number
of techniques, even if you end up adopting only a few as your methods of
choice. The first challenge is setting the intersection of the X axis and the Y
axis on a board in relation to its position in your CAD drawing. We need to
establish an origin point on the corner of a board. There are a couple of
advantages to using a corner. For one thing, once you’ve found it, it can be
used as a reference point to accurately move your origin anywhere else you
might want to on the board. Second, if you’ve setup stops on the bed of your
CNC Router so that other boards will register to the same position, then you’ve
made it easy to mill multiple boards. For example, you could use four boards
and machine four table legs just as easy as one.
Because the wood boards we work with
usually have edges and corners, we’ve got a handy physical reference to work
with. Just like the intersection of the X and Y axis in your drawing, a corner
is just two edges intersecting at 90 degrees. That makes the corner of a board
a handy place to set your origin point.
The process is straight forward. Find
one edge, center. Find the other edge, center. Reset your machine to X=0, Y=0.
Though it sounds simple, it turns out to be an interesting challenge to
accurately put the center of your bit or mill over that edge. Fortunately, it’s
a well-known problem in the machinist world and a lot of thought has already
gone into this. The result is that there are several methods and tools to
choose from that deliver varying results. I have several on my list. Let’s have
a look.
Manual Methods
Use your eye. Sight along one side of a board and center the
bit.
By
Eye…
Look straight along one of the edges.
Get close to the corner of the board you’re cutting and line up your eye along
the edge and the center of the bit you’re using. Do the same for other axies.
With practice, you can get okay at this, but as you’d expect, this is just an
approximation and it’s not very accurate. If you have enough waste material
left on your board this might be good enough for a one off part. But, if you
need to repeat it may not be good enough. Here’s something better…
Using a known diameter bit, bring it to the edge of your
material until it just touches. Then raise the bit and move it one-half the
diameter of the bit to find the center.
By
Touch…
The idea is to move your bit right up
to the edge of the board you’re cutting until there’s no gap. This method can
work pretty well but it takes some time to make minute movements of your
spindle to get it just touching the edge.
Do this one axis at a time. The idea
here is to take advantage of a readily known measurement, the bit that’s in
your collet. A 1/4 “ or .250” bit for example. You move it along one axis until
by eye you’re close to the board. Then by moving .001” or .01mm at a time get
close to feel the bit’s just touching the board. You can check by rotating the
bit until you feel a tiny resistance. Once there, set the axis to zero. Raise
the bit above the board and then move 1/2 the diameter of the bit farther in.
In this case .125”. Then reset to zero. In practice, I find that this works
pretty well. But, I get even better results if I use a small flashlight behind
the bit to see the gap for final adjustments, or alternatively use a piece of
paper with a known thickness as a feeler gauge between the bit and edge. One
the paper moves when rotating the spindle by hand, you’re there.
Thanks to the machinist world, there
are tools designed for this specific job. Most are inexpensive and simple to
use.
Mechanical edge finders will move from their center position
once it touches and edge. Once it moves, you just need to raise it up and move
one-half the distance to find the center.
Use a Mechanical Edge Finder…
Edge finders are specialty tools that
you mount in your spindle or router that have a moveable piece held by a spring
that shifts slightly once you’re touched an edge. Just like the visual and
touch method, these tools also use a known offset based on the diameter of the
probe. Often this is .200 inches. Once you find an edge, then move .1 inches
and you’ve centered your bit. Edge finders come in mechanical form — where the
bottom of the finder jumps out once it touches and edge. And, electronic
versions where a LED light goes off once it touches. Unfortunately, the
electronic ones only work on metal. To run these make sure your RPM of you
spindle is set to the recommended speed. Typically this is 1,000 RPM. This may
not be possible if you use a router on your CNC Router. How well do these
probes work? With a little practice, pretty well, actually. Here are a few
examples…
Edge finders are not just for edges.
They can also be used for finding the center or hole. A task that comes up
frequently in digital woodworking. Here’s an example of how to do this…
Wigglers…
There are other types of mechanical
edge finders. One of the most interesting to use and watch are wigglers. Their
probes spin concentrically. Once they touch an edge they wiggle and spin around
dramatically. Just like offset edge finders they work well. Fun to watch in
action…
3D sensors…
Much revered in the machinist world are
the Haimer 3D sensors. Essentially, they’re super accurate calibrated dial
gauges that work in all three dimensions. As you’d expect with this kind of
precision German made instrument, they are expensive at $400-600 and up. The
results are typically within .002” to .004” accuracy. They are also very
versatile for calibration, tool setup and evaluating part accuracy.
On my wish list for fine-tuning a CNC Router and most of the fixed power tools
in my shop. Watch the videos below and you’ll see why.
Sometimes you want to set your origin point on
the center of a hole rather than on an edge of a board. There’s various methods
and other specialty tools available just for that purpose. Some of the above
tools can be used and there are mechanical center finders, but you also find
centers with an angled dial indicator or a centering microscope.
These tools and methods give you accurate
results. There are plenty of times when that level of accuracy is needed so
it’s important to have techniques and tools to help you find and set an origin
point. But, I’ve found that in working with a CNC Router day in and day out in
a woodworking shop that these processes can be a little slow. For that reason,
I regularly use a couple of quick techniques and new tools to find my edges.
I’ll get more into that in my next post on Origin Points.
As you can see, there’s a lot going on
when it comes to origin points and reference positions — in fact, entire books
have been written about this in the machinist world. This is about digital
drawings. This is about setting up the machine. This is about what you’re
machining. And, most of all, this is about methods of work and good practices.
If that sounds dull, I can assure you that it’s not. There are some incredible
benefits to using grids, jigs and fixtures based upon accurate zero points and
reference positions. With much to cover, I’ll come back to the topic often in
this first CNC
Skills Popular Woodworking series:
Origin Points. Below, I’ve already outlined several related topics that
you should know about, so I’ll be back soon.
This was a written well and simple to follow for those who do not know about CNC. We deal with used cnc machines and can help those who want to know the difference between a CNC mill and CNC lathe at www.cncmachines.net thanks for the article on the XYZ axis.
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