Limit Switch Mounting Methods

[dgates80]

For general discussion, what techniques and methods have ya'll come up with for mounting limit and home switches?

For example, using a typical roller microswitch, do you have a little ramp? are they set up so that machine inertia / overtravel won't run into the switch or are they in the line of fire?

I am seriously looking at the magnetic hall effect sensor based limit and home switch setup from the , though clearly this is not a workable soloution for those that machine ferrus materials, magnets and iron or steel ships do not play well together. For me though, for whom the typipcal materials incluse wood, plastic, and aluminum, hopefully won't be a problem.

[Al_The_Man]

I am seriously looking at the magnetic hall effect sensor based limit and home switch setup from the , though clearly this is not a workable soloution for those that machine ferrus materials, magnets and iron or steel ships do not play well together.

There are non-magnetic hall effect sensors available, these only require a ferrous metal flag.
And although generally more expensive, non-ferrous metal hall effect detectors are also out there.
Al.

[wcarrothers1]

I use the roller type switches for most stuff and just attach a strip of alum that has a ramp built into it. Also has a slot which alows me to screw it down and adjust back and forth.

Basicly how ever you mount the switch you of course want to mount so somehting else would smash and stop the machine before the switch would be crushed. Some of my micro switches are just the metal bar/tab type and that is bent to hit the stop but if over travels it will just compress the bend in the metal tab of the micro switch before the machine hardwware would hit the hard stop. In those cases adjustment might be as smiple as bending the home swith tab out a little farther then then point where the over travel switch would trigger.

My new machine will probably be setup so the switche possition is adjustiable rather then the ramp it ingages.

Personaly I stick with mechanical switches. Just my preference. In my case I could see triggering an optical sensor on accident and not know or explain why it triggered (ya sorta know if you trigger a micro switch with your shirt sleave on accident..hehe but did I block that optic?.)

Standard micro switches have been plenty accurate for me, my old school cnc bridgeport uses them.

b.

[wildwestpat]

Hi dgates80

The choice of limit switch technology is set by the budget as well as the possible contaminants the switch will have to operate under.

Setting aside the simple non sealed microswitch which can be had for $2 or less complete with lever or roller actuator. The actuator is there to protect the switch from over travel as well as improving the sensitivity of the basic switch. (This why the roller is used with a ramp with the switch operating prior to the roler reaching the end of the ramp. Obviously the ramp reduces sensitivity as well as giving some repeatability problems due to dirt. The basic microswitch has its own repeatability accuracy.) For applications where fouling with dust or liquids are a possibility these switches are unsuitable. The long term operation would require some provision for adjustment as well as replacement of the microswitch dependent upon the quality of the switch used.

For the price of a sealed microswitch with it associated roller or lever mechanism there are other possibly much better switches available to act as limit switches offering both stable operation and long term life.

There are several technologies commercially available.

Optical - These use a vane to obstruct a beam of light (IR is common) or rely on a mirror and can be effective as DIY projects as the electronics are available at low cost and the sealing is easy to arrange as well as fully sealed units ready for bolting on to your machine. Cost of the light sensor electronics might be $5 and the ready to go version arrounf $15 - do a seatch on ebay for optical proximity sensors.

Magnetic - There are two types those that use a permanent magnet and those that use the disturbance of a high frequency oscilating magnetic field. The technology and application restrictions are very different:-

Magnetic - "Hall Effect" and simple reed switch. Both use a permanent magnet and are best avoided if the machine is to cut magnetic materials. The reed switch is possibly the lowest cost limit switch and the reeds are available encapsulated in either plastic or metal cases to ease mounting. "Hall Effect" semiconductor detectors are available for DIY sensors if that is your route.

Inductive proximity sensors - these use a high frequency oscillator to produce a high frequency alternating magnetic field. The frequency of the oscillating field is changed by the approach of a vane made of any type of metal. Good sensitivity is obtainable and the repeatability over time is excellent. These switches are available for interfacing to most common interface electronics. They are available housed in either 12 mm bolts or oblong blocks with two mounting holes fully sealed and with an indicator led that shows the switch state. (The indicator is of dubious value but does ease setting up where multiple axis are connected to the same electronic input.) Typical costs are $15 and are common on ebay - search on proximity switch.

Older machines will often use fully sealed microswitches where the switch is housed in a nice metal enclosure with cable sealing and a seal on the actuating plunger. However these cost more than the all electronic versions outlined above. However there is a Health and Safety risk assesment that may require that the safety limit is achieved with non electronic switches or devices. Where Health and Safety is concerned local requirements will dictate what is safe and what is not so if the machine will be used by others or with others in the vacinity advice becomes necessary.

Hope this helps - regards Pat