Configuring EMC2 for Limit and Home switches

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Y-Axis cable management

I didn't have the room for a nice cable-tray like I made for the X-axis.  A simpler approach was to use a scissors-type of assembly that just kept the cables neat, yet out-of-the-way.  I ran both the stepper cables and the router power through this arrangement.


At each joint of the scissor is a 3/8" OD nylon bushing, cut just slightly longer than the material thickness to avoid binding the joint when the nut is tightened on the screw.  Click on the image to see a larger version.  All 3 joints are made in a similar fashion, with the length of the nylon bushing and the 8-32 machine screw adjusted to fit the materials and washer thicknesses.

After the first test, I realized there was no good way to support the cables, so I made the 8-32 machine screws a bit longer and added a wire loom clamp between the nut and the last washer. I sized the clamp large enough to allow the cable to move freely.

It seems to work great.

Opto isolation board

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Z-axis homing & opto-isolation board

It is always uncomfortable bringing logic-level signals outside of the "box" and into the real world.  Any excess voltage can wipe-out your stepper controller board - and since the inputs are fairly high impedance, these lines are very susceptible to induced noise - especially from the nasty spikes caused during the driving of the stepper motors.
I designed a 5-channel opto-isolator board to keep the ugly outside world away from my HobbyCNC controller board.  I designed the board to run from around 12 volts, but I added a constant-current source to each input line.  This ensures 20ma flowing through the opto isolator LED.  The added benefit is I can add extra LED's to the 'chain' without affecting the signal and I can safely run the limit switch wiring through the same wiring harness as the stepper motor cables with no fear of interference.
I added a yellow LED on the board for each of the 5 inputs - this allows me to verify an input is working without needing to grab a voltmeter.  The constant current source also allows me to put another LED out where the work is done.
To complete the board is a green power LED and a fuse.  In the images, the opto chips are actually surface-mounted on the underside of the board - the one lit yellow LED is for the limit switches - this tells me all 6 limit switches are closed (good).

I created a special rig to set the z-axis home.  It uses an alligator clip and a precision brass 1/2" square bar.  I added an LED in the bar so I can confirm all is good before I press "home".  Any problem with this setup and the system will drive the tool into the workpiece - a real big issue if using small drills for PCBs.  The short video shows the Z axis home setup being tested to confirm continuity, then the video shows the opto board during the same test.

The new build - the base

I kept the base design similar to the original - using a torsion box design.  This provides a considerable amount of strength and rigidity with minimum mass.  It is important to have a very flat surface to assemble and glue-up the frame.  Even with all the care, I ended up in excess of 30 thousandths out of square.  This is excellent accuracy for a woodworking project, but it is not all that great for a milling machine.

Taking care at every step means less fine-tuning later.  Cut the components carefully, make sure to get the angles as square as possible.  Ensure the top (facing downward in these images) is flat-and-true against your flat surface.

Here is the finished torsion box.  I changed the design of the x-axis rails - both to provide extra strength and rigidity, and to get the x-axis rails inset just enough to keep them out of the way of most of the dust and debris created during milling.

Cutting Guide

I slept on the design - no changes.  Here is the cutting guide.  The whole router will fit neatly on a single 4x8 foot sheet of Baltic Birch 3/4" plywood ($64 USD).  I chose this plywood for a couple of reasons.  First it is a good looking wood.  It has a furniture-grade finish on both sides, no knots, no blemishes.  Second, it is made up of many more, thinner veneers.  On this website: www.leebarry.com is an excellent photo of "regular" 3/4 inch plywood next to the nice stuff.  More layers, better strength.  Also no ugly 'voids' in the inner veneers when you cut it.  Sand the edges, some polyurethane, and it's damn good looking.  3rd, I just like the idea of the CNC machine being made of wood.

Preparing for complete redesign

One learns so much from the "first time around".  I plan to take what I've learned, go a bit slower, use better materials (like 3/4 inch Baltic Birch plywood) and add the things I was missing - like limit switches and some better resistance to torque.  Here's the new design.  It's all on Google Sketchup in the event anyone wants a copy.  Just add a comment or send me an e-mail WoodWorkerB (at) gmail (dot) com.  Here's how the new design will look.

The new design provides additional strength (due to material selection), higher quality assembly practices, recessed lower bearing races (to hopefully minimize the amount of crap that gets on the bearings).

I am considering incorporating small brushes on the bearings to keep them somewhat clean.

I will "tear apart" the drawing and create my cutting guide.  I plan to start cutting and assembly this weekend.

Recent addition - a UPS

Simply plugging in my welder caused a power glitch in the middle of routing a PC Board - the glitch caused the computer to re-boot.  I was not happy.  I decided to purchase a Uninterpretable Power Supply from APC.  It only provides 10 minutes of backup - but that's plenty to make it through the occasional power glitch and even the careless tripping over the power cord.  I have both my CPU and monitor powered via the UPS.  The mongo power supply for the Steppers can ride through powerline glitches with ease.

I also isolation-routed another PCB, this one a simple linear-regulated 12VDC power supply to drive the case fans.  I was much more comfortable with Eagle CAD this time around.  I set up the raw PCB, hit "GO" and came back 45 minutes later to have it all perfectly done.  Sweet!

Upgrading Ubuntu & EMC2

This weekend I upgraded from Ubuntu 8.0.4 to Ubuntu 10.04 & EMC2_2.4.4 Release.  The install went without a problem.  However, I couldn't get the steppers to move.  I recall having parallel port configuration issues the first time.  I wasted 4 good hours of shop-time with no success.  Then the proper information turned-on the light for me, and all is working well.  This page on HAL drivers did it for me.  I mistakenly thought the "in" and "out" parallel port settings meant the parallel port was installed (in) or not (out).  Since I was using an add-in parallel port, I was attempting to set parallel port 2 as the port to drive the steppers.  Wrong.

The "in" and "out" refer to the signal directions of the parallel port (I wanted "out").   Here's a hint how to find the address for your parallel port setting (the 'stuff' after the "0x").

The cable track

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New Router Table as-is

Here's how the stand looks so far. Only two drawers, but it covers the basics. I've got the keyboard/mouse tray and computer/control electronics. I left room around the router table for an eventual plastic cover to control dust and noise.

A large challenge was mounting the monitor - I wanted it convenient, but not in the way of the plastic dust cover. I decided to mount the monitor on top of an extra length of steel pole I had around. Consider using a heavy-duty closet pole from Home Depot. You need to make sure that the power and video cables will fit through the tube first!

Monitor Mount: I made the monitor mount from a couple of scraps of plywood. The bottom and middle parts are bored-through with a 1.5 inch hole (the same diameter as the support tube). The top hole is a 1/4 inch smaller. This design allows the cables to be fed through the center of the tube and for the monitor to spin 90 degrees so it's out of the way during storage. There is a similar block under the surface of the table to support the tube.

Electronics Drawer: The drawer is roomy enough to hold the computer, power supply for the steppers and the stepper electronics. I added a master "mains" switch and a switch to control the router to the front panel. Also a big "stop" switch (Rockler) at knee height - for those times when things don't go as planned.
Hitting "stop" kills power to the router and to the stepper motors. A pair of filtered, computer case fans provide positive pressure to (hopefully) keep dust out of the drawer. An aluminum cover sits over the drawer.

New CNC Router table

I need to re-build my CNC router from scratch - taking into account all I learned during the first build. I decided to start with a stable, portable stand that would house the computer and electronics in a clean, safe space. I went with a simple MDF carcass with drawers. The computer drawer would contain all the electronics and would be positive-pressurized via two filtered case fans.

I can provide the sketchup drawings for the stand and the cutting guide if you're interested. Just drop me an email at woodworkerb [at] gmail [dot] com. The core case is built and the electronics installed. Not all the drawers are made yet, but that's coming - I am tired of leaving tools & such laying on the router table - just begging for trouble.