View Full Version : The best solution for limit / home switches on a mill is .....what ?

29-05-2010, 10:47 AM

First of all I'm new to CNC so be gentle with me !!

I'm converting a small milling machine to CNC, and having trouble deciding what type of limit / home switches to use and where to locate them.

I'm going to use Mach 3 software, the 10amp stepper drivers from Routout CNC, and I want to cut steel on the mill.

I guess reed switches are not the best as the magnets will cause problems with steel swarf....or am I wrong here ?

There is also a possiblity I may cut some small wood parts on the mill so perpaps an optical system isn't too good either ?

I guess this leaves microswitces but which type to choose ? Normally closed normally open, button, lever, lever roller etc etc.... and also where is best to locate them....on the table and use flexible connections or fixed to the bed ?

Also if microswithes are the answer, where is best to buy them in the U.K ?

Any ideas much appreciated.

Cheers Nick.

Robin Hewitt
29-05-2010, 01:38 PM
Hi Nick

If you hit a limit switch on a cnc mill the part is probably going in the bin, so we never hit limit switches, they are surplus to requirement :heehee:

So any limit switches fitted are actually homing switches and your only priority is repeatability. It must always switch at the same position. Reed switches can't do it. Microswitches with rollers allow the tool to pass by but the lever costs you precision. You don't want to ram into a solidly fixed microswitch because you will have enough driving force to crush it flat. Best way to fit a microswitch is to spring something in to it holding the pip down, then have the slide hit that something allowing the pip to rise. Microswitches always have change over contacts so NO/NC is a permanent option.

If the G00 fast feed isn't ultra quick, waiting while the tool winds all the way to the end and back is a pain, so a moveable switch is good for the X.

OTOH, do you really need them? Pretty useless on a round column mill. Pretty useless unless you are mass producing with a fixed jig to hold the job. Positioning switches might be useful if you had a whoopsy and lost position, but you do your best to avoid that.

A Z switch could be handy for tool changes, but there are simpler solutions.