source of home/limit switches

[phantomcow2]

I dont entirely understand how limit switches work and what types there are. So are there any good online stores that have various types of switches that I can look through and hopefully learn?

[PEU]

I won this auction: http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7546658549, and planning to install them this week. Switches are super sturdy.


Pablo

[phantomcow2]

So ebay has a section just for limit switches, that is helpful.
Would switches like these be sufficient for a small milling machine?
http://cgi.ebay.com/10-Honeywell-Mic...QQcmdZViewItem

[widgitmaster]

http://www.mpja.com/listitems.asp?dept=64&main=117

http://www.alltronics.com/switches.htm

http://www.action-electronics.com/gcmicro.htm

http://www.surplussales.com/Switches/SWPressMic-4.html

http://www.electronicsurplus.com/dictionary/cat2105.htm

http://www.sciplus.com/category.cfm?subsection=14

[Al_The_Man]

I would consider those too fragile for exposed conditions, one of the best I have found is Honeywell 914CE series, they are hermetically sealed and come wired with a 12ft sealed cable, they are compact with a roller actuator and they can be stacked easily.
There is an Omron equivalent also and they come up on ebay regularly.
Al.

[phantomcow2]

THanks for the links.
So basically you mount switch where you need it to be mounted, and mount some other contact where ever you need the axis end on the table iutself, so the mounted piece hits the switch.
What about something like this guy did?
http://www.balbots.com/article_info.php?articles_id=10
He ysed hall effect sensors. THe part # he gives for digi key shows about 1 dollar each.

[widgitmaster]

Here is an example of how I used one micro-switch to limit the travel in both directions of the x-axis
The springs keep the trip pin in the center, there is a little divit in the pin where the limit switch sits, it is normally open, and is grounded on contact.
Eric

[philba]

I'm a cnc newbie (though not to electronics). I've always wondered why people use contact sensors for limit switches. It seems like you need to carefully tune the location of the switch to prevent over-travel from smashing it. I would think a Hall Effect switch (using a magnet), photo interruptor or other contactless switch/sensor would be less prone to damage.

This isn't an oblique criticism - I would really like to understand this issue.

[ger21]

A lot of machines use ramps to activate the switches, so the machine will slide right past the switch without hurting it.

[philba]

Originally Posted by ger21 A lot of machines use ramps to activate the switches, so the machine will slide right past the switch without hurting it.

That makes sense, seems a little trickier to make, though.

What about over travel? I'm not yet done with my first machine but am at the point of trying to figure out where the Limit (home, too, I think) should be. I assume it's specific to my machine but I don't want to be over conservative yet want to make sure the carriage stops before it smacks a hard limit. Figuring that out is a real puzzle to me. Guess I'll make it adjustable - I've got a bunch of photo interruptors that I'll try first.

[phantomcow2]

I was htinking that a mechanical switch could break or something, which is why the hall effect system like i posted a link to appeals to me. The only thing is, i dont know how to put it all together to work with my HobbyCNC board.

[ger21]

One thing to keep in mind, if you're worried about switches getting broken. If you're using Mach3, you set up soft limits (software limit switches) just inside your limit switches, and the machine should never hit the switches. The switches then become basically backup switches, just in case. of a Mach3 error.