Limit switch

The Oracle

The Oracle

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Would anybody, have a suggestion or information on what switches they’re using for the limit switch inputs something that’s relatively impervious to flood coolant❓

Thanks,
Lynn M.
 
My Tormach mill came with microswitch limit switches. They have a plunger with a roller on the end which contacts a ramp and are relatively immune to flood coolant. However, I found them to be less accurate than desired for use as a homing switch so I devised my own optical homing sensors. The OEM had a repeatability of around =/- .0025. The optical system is =/-.0001".

The Grizzly G0755 mill uses mechanical switches in conjunction with spring loaded plungers. The spring loaded feature permits overruns without hard crashes. The parts could be ordered as replacement parts. The actual switch is located in a housing and should also be relatively immune to flood coolant.

If reproducible homing isn't required, either of these mechanical systems should be suitable.
 
RJSakowski said:
My Tormach mill came with microswitch limit switches. They have a plunger with a roller on the end which contacts a ramp and are relatively immune to flood coolant. However, I found them to be less accurate than desired for use as a homing switch so I devised my own optical homing sensors. The OEM had a repeatability of around =/- .0025. The optical system is =/-.0001".

The Grizzly G0755 mill uses mechanical switches in conjunction with spring loaded plungers. The spring loaded feature permits overruns without hard crashes. The parts could be ordered as replacement parts. The actual switch is located in a housing and should also be relatively immune to flood coolant.

If reproducible homing isn't required, either of these mechanical systems should be suitable.
Click to expand...
The optical homing sensors that you came up with if you could share what you ended up doing, that would be fantastic repeatability on your system versus microswitches is far superior.

Thanks,
Lynn M.
 
The Oracle said:
The optical homing sensors that you came up with if you could share what you ended up doing, that would be fantastic repeatability on your system versus microswitches is far superior.

Thanks,
Lynn M.
Click to expand...
I had done a write up some time in the distant past. There is a fairly complete discussion of the project on CNC Zone. https://www.cnczone.com/forums/torm...ng-proximity-sensors-tormach-pathpilot-2.html I also have a full set of documentation on Dropbox.

The modification is by no means plug & play. To get the required sensitivity, I used a special optoisolator and designed my own optics and electronics. The system has been in operation for more than ten years and t date there have only been three failures. One was a component failure; another had to do with coolant getting into one of the optointerupter windows after some prolonged heavy usage. That was clear up with a blast of compressed air and a redesign of the shield corrected the problem. The third occurred recently when I was using the mill for some wood work and a lot of fine dist was generated. Again, a blast of compressed air solved the problem.

I left the OEM limit switches intact as a backup. Should the optical system fail to properly home for some reason, it will hit the mechanical switches some .040" in back of them. PathPilot has a feature in that once the system is homed, it knows where the the limits are and will never exceed them, even traversing at rapid speed so it has been literally years since my mechanical switches have been activated.
 
Last edited:
The Oracle said:
Would anybody, have a suggestion or information on what switches they’re using for the limit switch inputs something that’s relatively impervious to flood coolant❓

Thanks,
Lynn M.
Click to expand...
$114 at Grainger. I've used many of these in another life and found them to be high quality.
Main product photo


HONEYWELL MICRO SWITCH General Purpose Limit Switch: 1NC/1NO, 15A @ 600V, 2A @ 250V, Top, Surface​

Item 12U161
Mfr. Model BZE6-2RN

Product Details​

Catalog Page262
Limit Switch StyleGeneral Purpose Limit Switch
Basic Actuator Style - Limit SwitchPlunger
Actuator Style - Limit SwitchPlunger
Actuator Location - Limit SwitchTop
AC Contact Rating - Limit Switch15A @ 600V
DC Contact Rating - Limit Switch2A @ 250V
Contact Form- Switches1NC/1NO
Actuator Length - Limit Switch0.97 in
Body Height - Limit Switch1.75 in
Body Width - Limit Switch3.04 in
Body Depth - Limit Switch1 in
Boot Sealed Actuator - Limit SwitchYes
Mounting - Limit SwitchSurface
Body Style - Limit SwitchMiniature
NEMA Rating1; 3; 4
Wiring Entry1/2 in NPT
Electrical ConnectionScrew Terminals
IP Rating66
MovementRelease Force 0.25 lb min
TravelDifferential Travel 0.0004 in to 0.0020 in; Maximum Pretravel 0.078 in; Minimum Over Travel 0.219 in
Operating Temp. Range-25° to 160°F
Mounting Hole Pattern - Limit Switch2 Hole Horizontal
Mounting Hole Spacing - Limit Switch1.00 in
Mounting Hole - Limit Switch(2) 0.22 in dia
Stem Thread - Limit SwitchNo Stem
Body MaterialZinc Die Cast
StandardsCSA; UL
UNSPSC39121509
Country of OriginUSA (subject to change)
 
Inductive proximity switches are often used and there are harsh environment and stainless steel sealed type that can be used in corrosive environments. They have a high level of repeatability (typically better than 0.001" in the applications I use them for as a limit switch). There are also a host of sealed mechanical switches. I prefer to use them in a a NC configuration and go open when triggered, as well as use a redundant mechanical switch in series. This way if there is any damage to the wiring/switch they would normally go open. You also can also use snap type limit switches, which are more repeatable. Some examples below. One other factor is the orientation of the sensor/switch and speed of movement of the approaching object and how fast it will stop once the limit switch is triggered. If a switch is in the direct path of the moving object it may not have enough stroke/detection time and be damaged. So you either need a longer stroke switch, use some form of roller cam, or use a detection device that is perpendicular to the moving object.

 
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