[manualmachinist]

How good is the repeatability of the various home limit switches people use for their mill? I cant imagine the cheap clicker switches being very repeatable, or even the hall effect or optical ones couldnt be that great. Are we talking about +/-0.3mm error generally?

This matters I guess because you might have various things located based on the mill coordinate, such as your vices dialed in a certain fixed location, or your tool change relies on the position of the tools etc.

Whats the best home switch to use for best reliability and repeatability?

[Bubba]

Way back when I first setup my home/limit switches, I too was concerned about the repeatability of the mechanical switches that I used.
On the Z axis, I have an optical interrupter type of switch that I salvaged out of a copier or printer. I made 10 passes at homing and moving to a fixed point to see what the repeatability was. In these 10 passes, I averaged a difference of .00029" (0.0073mm) so as far as I am concerned, there is no problem with that.
On the X and Y axis, I used some mechanical switches (AAP series miniature DIN limit switches) which are supposed to have a repeat accuracy of "0.01mm on the operating points at 1 million operations"
In my testing using the same type of operation as above, I got results on the order of .0018" (.046mm) on the X and .0009" (.023mm) on the Y axis.
These test were run using my finest .0005" DTI of dubious origin:})

On my router, I used Hall effect switches and remember getting excellent results but I cannot find the spreadsheet where I saved the data. These switches were based on the thread by RomanLini here on the zone http://www.cnczone.com/forums/open_s...made_easy.html
and used 1/8"dia x1/16" thick magnets of ebay.

Hope this helps

[ger21]

Roman's testing of his hall effect switches showed that his were repeatable to better than .02mm.
http://www.cnczone.com/forums/open_s...made_easy.html

[Analias]

How good is the repeatability of the various home limit switches people use for their mill? I cant imagine the cheap clicker switches being very repeatable, or even the hall effect or optical ones couldnt be that great. Are we talking about +/-0.3mm error generally?

With my CRP-4848, I am seeing 0.01" variance in my homing with simple roller micro switches. I notice it has a lot to do with the speed at which I approach the micro switch. I would expect this is due to the momentum of the gantry. The faster I approach the switch, the longer the it takes to stop, and the further up I am on the switch. I solved that by having the homing process back off the switch and re-approach it at a much lower speed.

Although, I would expect that shouldn't matter if you are homing your machine and zeroing your work. I was pleasantly surprised to see .002" variance when testing repeatablity off of the X and Y faces of my spindle mount at rapid speeds.

[Drools]

What is the best way (procedure) to measure this?
I have HP optical switches on my big machine and romans SS441s on my small machine. I would do a few tests if I had a detailed procedure to measure it and I would be willing to post the results.
I also have 3 new Allen-Bradly 871C-A5N18-R3 (sans harness) prox switches I was going to use but the 40-250VAC input made me decide to leave them in the drawer. However I suspect they would be the best solution.

[ssutton]

Using hall effect switches and homing at < 20 ipm repeatability is around +-.05".

The trick for me was SLOW homing speed, before that +- .025". When I power up the machine I turn off soft limits and then manually rapid to close to home position, then home and then re-enable soft limits.

[kevincnc]

The best? I have been able to get within .001" repeatability with inductive prox sensors, thru-beam (slot sensors), and sealed mechanical plunge-roller switches that are made to be home or limit switches commonly used on CNC metal working machines. What kind of accuracy are you looking for? The backlash in your mechanics and homing speed will be a big factor. What is your definition of a cheap clicker switch? My mill uses a (super chaep) mini snap-action cam roller switch to home to and I'm pretty sure it's within a thou or two.

[kevincnc]

What is the best way (procedure) to measure this?
I have HP optical switches on my big machine and romans SS441s on my small machine. I would do a few tests if I had a detailed procedure to measure it and I would be willing to post the results.
I also have 3 new Allen-Bradly 871C-A5N18-R3 (sans harness) prox switches I was going to use but the 40-250VAC input made me decide to leave them in the drawer. However I suspect they would be the best solution.

1) Home your machine, set up a dail indicator to zero
2) Jog off the axis, and re-home
3) Note the indicator reading, and repeat #2 &3

You might need to ignore the first couple readings until the indicator settles in.

[skray775]

Proximity switches from DMM tech.

Proximity switch testing - YouTube