[momus_cnc]

So, the plans just show a couple of photos of how to mount the X and Y limit switches, and don't show any photos of Z switches at all. Frankly, it is because I hadn't fully resolved where to put them or how to mount them, so it temporarily got avoided. I had rigged up some brackets, but they looked so bad that I never even photographed them. Every once in a while someone would email me wondering where to put their Z switches, and I kept saying “it's coming soon.” A few months ago I finally got around to trying to figure out where to put them. I designed some brackets, started cutting them out of some aluminum plate, and promptly ran into a problem with one of my stepper motors. So I finally got around to getting my new G540 and Keling stepper motors wired up, and got some new brackets cut.

The G-code is posted below. So is a DXF file with a drawing of the parts.

The first photo below shows the brackets cut out of a plate of 3/16” 6061 aluminum. The brackets for all 6 switches (2 for each axis) are nested together into one 4” x 6” area. The parts are held together as they are cut with partial thickness tabs. All plunges into the material are with helical ramp moves. The new G540 performed flawlessly, and the surface finish on the milled edges was very nice.

The next photo shows the parts after separating them and removing the tabs with a file.

Next is the Z-minus bracket and switch. This is designed to be adjustable. How I intend to use it is to lower the Z axis until the tip of the end mill just touches the surface of the spoilboard (or whatever lowest point I anticipate cutting to), slide the bracket down until the switch is just triggered, and then slide it back up .050”-.060” or so. In this position it will trip if the tool cuts into the spoilboard by more than the .050”-.060”, which is a more than I use for breakthrough out of the backside of my parts. So this switch will trip if something goes wrong and the Z attempts to plunge too deep toward the table.

The next photo is of the Z-plus switch. It has a little adjustability, to allow getting it just where it needs to be to get full Z+ travel. This one will do double duty as the homing switch for the Z axis. As will be apparent in the photos to come, it is a fairly tight fit, so a little bit of material needed to be removed off the back for clearance where it would just touch the motor coupling.

The two switches are wired in series. The leads will eventually be going into some shielded cable, but for now they are installed with some haphazard test wiring back to the G540.

OK, next photo shows them in the installed positions. The Z-minus is the upper one, and the Z-plus is the lower. They are mounted to the moving axis and trip against carriage parts, so that is why the Z-plus ends up being lower than the minus. Both of these mount to existing studs, so no modifications are necessary if the machine has been built to plan.

Next photo is the Z-minus in the tripped position.

Last photo is the Z-plus approaching its tripped position during a homing procedure.

Both switches have been working great so far, and it nice to finally be able to home the Z axis. I still need to install the new X and Y brackets, but they are basically nicer versions of the crude ones that are shown in the plans. I'll post some photos when I get around to installing them.

A few notes on the G-code. USE AT YOUR OWN RISK. It is programmed with the following parameters, most of which are also noted on the attached PDF drawing:

Z zero is at top of stock.
Z-minus direction is toward the bed.
Use 1/4” end mill.
3/16” thick stock. If using a slightly different thickness, adjust your Z zero position to compensate, so that the tab thickness will remain the same. (i.e. make sure your Z zero is .1875" above the spoilboard)
All tabs are ramped, and entry plunges are helical ramped. Make sure that IJ mode is SET TO INCREMENTAL in the settings. Otherwise weird things will happen at these helical moves.
The parts are tabbed together, but there are a couple of little areas of stock between the parts that will be cut loose and not held down. Not an ideal situation, so BE VERY CAREFUL.
There is a small safe zone at each corner to hold down the stock.
You will need to drill the 2 mounting holes for the switches by hand.
The switches I used are a standard micro-switch that they carry at Radio Shack. I'll see if I can dig up a part number.
If I recall correctly, each pass steps down .020”, and the feed rate was 15ipm (the latter can obviously be overridden in Mach3.)

-Bob