I am looking for the best type of axis homing switch. Is it proximity, micro switch or light/laser beam switch? Any ideas anyone?
Microswitches are great and work very well.
If you want to protect everything from dust, you may want a hall-effect sensor with a magnet.
@Arthur_Wolf So in your opinion micro switches are good enough? I am dubious about there positioning repeat ability. Well I could try them out for a while as they are easy enough to swap out later.
@Robert_Ritchie You can find their repeatability in their datasheet, they are usually very good, and you can find some for which it’s even better ( at a cost ).
They are what most everybody uses.
There are also proximity sensors. They are pretty cheap and work without a magnet. They just need metal. Beware that most of them need minimum 6v to work. Repeatability is also good on them.
@Robert_Ritchie
Software compensates for switch deficiency with seeking routines. Which is to say that the designers of CNC control software are also aware of the issue.
@Paul_Frederick Having worked with electrical control systems for many years I am concerned with the accuracy of homing using micro switches. Although, so far the micro switches seem to perform very well. I am also hesitant to use proximity sensors. So guess what? I am developing an ultra precise and reliable homing system that will incorporate the micro switches as maximum travel limits and a special type of closed loop optical switch that will deliver exact positioning. I will share this freely with everyone as soon as I test it. “Laser Light Pistols” because it is the 21st century.
@Robert_Ritchie
You might want to read this to gain a greater understanding of how involved homing is in the software http://linuxcnc.org/docs/html/config/ini_homing.html
Your switches don’t matter nearly as much as you may think that they do.
@Robert_Ritchie I use the Metrol touch switches(CS-series).
http://toolsensor.com/switch/
Although they’re more expensive than Reed micro-switches, reproducibility is good.
How much accuracy is required?
@Sumito_Oda Yes I like these I had a look at them they are incredible. Accuracy should be plus or minus 0.25 micron, but a micron would do to start with. I am looking at making my own from laser emitter and light receiver through a dual slit alignment filter.
Regarding laser @Robert_Ritchie . You should consider dust. I would stick to mechanical or proximity for this reason alone.
@Henrik_Larsen I watched your profiling video so I realize you speak with experience. Being an experimenter I will try several methods and I will take your comments on board when considering different methods.
I should say that i havn’t tried proximity sensors myself but have one that i can experiment accuracy with. I’ll one day make a jig with an arduino and some stepper and rods and wheels to test it. I don’t know when i get around to test it. …
@Henrik_Larsen I used lots of proximity sensors in industrial applications and they do work but I can not say for sure what there accuracy is when you go sub-millimeter. I am also considering making my own touch switches from ruthenium/silver alloy with stainless steel actuator rods and crystal insulators. I know you may think this extreme but that is what I am aiming for extreme accuracy so my machine could be micron accurate. Cost is minimal about $10.00 and I have estimated $1 for the silver/ ruthenium contacts. Years ago I made contacts from pure silver for a large industrial contactor. I can get my motors down to 3 pulses per micron.
@Robert_Ritchie
Yes but can you control the temperature of your lead screws? They will expand as they heat up. What do you plan on making where you need that kind of accuracy anyways?
@Paul_Frederick Yes I am aware of thermal expansion and things like modulus of elasticity. Yes I can regulate the temperature and have planned my working temp envelope. I want to make tiny micro machinery almost nano but not quite. Good news today is my Auto tool zero probe works well. I am just concerned with structural deformation of micro switches over time and here I have through discussion picked up many tips and good advice.
Thats pretty extreme @Robert_Ritchie and not a typical DIY environment. It would be nice to see your work 
Wouldn’t one best zero with respect to the stock or item you work on. The homing switches are typical mechanical far from the working position and thus add to inaccuracy. I just use homing to initialize the machine position after having it turned off.
Unless you aim on very acurately positioned fixtures. But then you would have another problem with fixture accuracy or what ?
@Robert_Ritchie
If you are working on the micron scale then you are making micro-machines. Some folks go for miniaturization. I am at the opposite end of the scale. I like big stuff. thousandths of an inch is too fiddly for me. So I am the wrong guy to talk to about microns. If I can’t measure it with a ruler it shouldn’t matter to me then either.
@Paul_Frederick Most CNC machines are accurate to 1/50th mm or 20 microns. So in saying that we are already talking microns. The professional manufacturers can do repetitively down to a micron so I should be able to also. Lets see how good I can get it.
@Henrik_Larsen You are 100% correct homing is relative to the starting position. Yes I will have to add edge and centering probes to my machine and reference from the work piece starting position. A friend would like me to build a machine about 4 times bigger than the one I have just built (for cutting Granite) and if we can get the accuracy down to 1 micron for him then the benefits are great time savings in the polishing stages. Also I am building this machine in my shed so to achieve that sort of accuracy would be of great personal satisfaction. I would like to machine exotic materials like Gold and Silver etc.