A
Computer for CNC
Lead-screw Conversion
Stepper Motors
Controller
Breakout Board
Pendant
Relay Box
CNC Rotary Table
Tooling Plate
E-Stop switch disassembled. The switch is a NC momentary &
the button contains the latching mechanism.
It mounts through a ⅞" mounting-plate hole where the button bayonets into the
bracket to hold the switch.
The two screws then pull the button's base against the mounting
plate.
Left-side E-Stop shown. Also, note the two leveling shims under the mill's
feet.
Right-side E-Stop shown. The two, bench-mounted
normally-closed (NC) E-Stop switches are connected in series to
LPT1 pin 13 input of the
breakout board. A pressed
E-Stop causes the breakout board to pull all LPT1 outputs to ground.
The breakout board uses a resistor to pull the pin high (and low). If no
breakout board, use a pull-up resistor on the input pin.
Mach3 E-Stop input setup.
LPT1 INPUTS are 10, 11, 12, 13, 15 &
LPT1 OUTPUTS are 1-9, 14, 16, 17.
Limit/Home Switches
One-piece, mirror image, ±Y-axis limit switch L-brackets. The slots & pivoting mechanism allow position adjustments.
Two, 4-40 screws hold each switch. The plate is threaded for the pivot screw. Switch holes are #5
counter
bored.
Used the small rotary table to
mill the short arched slot for the pivoting-switch adjustment.
±Y-axis limit switch brackets shown temporarily mounted on
the
milled & tapped
side of the Taig carriage.
SS,
6-32 cap-head screws & washers hold the brackets.
The +X switch will be located in the middle area.
Front, +Y-axis limit switch shown tripped. The extended hex nut
acts as a small handle for making
the adjustments.
The notch by the roller eliminates any possible bracket interference & allows small
swarf to drop through.
The switches ride along the smooth, extruded lower area surface of the Taig's
carriage & trip off the front or back edges.
The bracket protects the switches that are tucked-up underneath the table
to reduce the effects of swarf.
I considered a knurled thumb nut but decided it was best to be able to lightly
(3/16") wrench
tighten to hold the settings better.
The X-axis switch rollers are released for normal operation & depressed at the
± limits.
The Y-axis switch rollers are depressed for normal operation & released at the
± limits.
The Z-axis switch roller is released for normal operation & depressed at the
upper limit.
All switches were wired in series to be closed during normal operation &
opened at the limits.
Rear, minus Y-axis limit switch shown tripped.
Milling the +X-axis limit switch adjustment plate.
+X-axis limit
switch adjustable bracket. The switch roller-lever is characteristically loose & can
move from side-to-side.
The notch by the roller eliminates any possible
interference.
The switch plate is held by two, 4-40 counter sink flat-head
screws on the bottom of the bracket.
I changed sides to locate the switch more central to the table (lower swarf
effects).
The table lead screw bearing plate trips (depresses) the +X limit switch.
Minus X-axis limit-switch bracket bolted to the bottom of the
carriage gib retaining plate.
The steel retaining plate was drilled & tapped for two, 10-32 screws.
The switch adjustment plate is, as all others, held by two, 4-40 screws.
Minus X-axis switch adjustment plate.
Centered underneath the table to protect from metal swarf.
A fabricated (left) table end-plate trips the limit switch.
Protruding Z-axis gib adjustment screw head reduces +Z travel
range.
Used a 7/16" end mill to relieve an area of the bearing block to allow room for the
gib adjustment-screw head.
The relieved area allows an increase of +Z by 0.3" (but
it can vary according to gib
adjustment).
Milling the short, curved slot for the +Z limit switch plate.
Vertical adjustment slot sized for 10-32 screws.
The counter bore not really needed, here.
Drilled & tapped 50%,
10-32 threads to mount the +Z switch bracket & cable strain relief clamp.
+Z limit switch trips off the top edge of the box-slide assembly. -Z limit is controlled via software.
The electrically shielded
limit-switch cable starts here, at the +Z. Note cable clamp for strain relief.
From the +Z switch, the cable connects to -X limit switch &
then it loops under the carriage.
The cable is tied through a hole to the bracket for strain
relief.
From under the carriage, the cable then connects to the +X & ±Y limit switches &
continues to the breakout box Molex connector.
Used shielded, Teflon-sheathed wiring, protected with cable wrap.
The cable is tied through a hole to the bracket for strain relief.
Spade connectors proved too bulky so I hard-wired all connections. The switches
are easily removed via their screws.
All used & unused switch lugs are shrink-wrapped to prevent metal chips from
shorting out the circuit.
The cable terminates with a
4-pin Molex that plugs into the
breakout box. All shielding
is connected to the stepper-side power supply ground. See the
schematic.
Mach3 home/limits setup:
LPT1 & pin#10 is the
input. I wired
the shielding to the stepper-side ground of the
breakout board.
Under Settings Alt6 Tab, enable (green on) the Auto
Limit Over Ride so you can reset the E-Stop & then jog off the limit switch.
In the menu under Configuration &
Motor Home/SoftLimits, there are additional
settings.
See Mach3 Mill Manual, page 4-8.
The 305oz-in steppers are relatively strong & easily jammed the lead screw
quite tightly at the mechanical end-of-travel.
The installation of the limit switches eliminated this problem plus it added the
axes homing capability.
The wide range of switch adjustability afforded by the bracket design made the
limit-trip setup quick & easy.
A
Computer for CNC
Lead-screw Conversion
Stepper Motors
Controller
Breakout Board
Pendant
Relay Box
CNC Rotary Table
Tooling Plate