Problem -- limit switches shorting

[rusel]

Hi
I went and put limit switch (See thumbnail) on our mill, worked ok for little while
then started getting false signals. Found out that the coolant was shorting them out.
Question is is there a supplier of low cost water proof switches.
I would also like to get some home switches as well.

Russell

[Bubba]

I use a AAP2T51Z11 limit switch from Automation Direct. Got mine several years ago and use them as combination home and limit. To seal the wiring, I used some poly tubing from the hardware store and silicone rubber to seal it at the switch end.

As I remember, I paid about $12 a piece for these particular switches. They have been reliable and accurate for homing purposes as well of course as limit switches. They have several form factors, but this is the one I picked to work on my machine.

[Al_The_Man]

One of the best is the hermetically sealed Honeywell 914CE2-9 style.
They are pricey, but can be had on ebay often very cheap, Omron also make a version of them.
Al.

[rusel]

Thank for the info
Bubba
You use yours for a home switch. What accuracy do you get?

Al
They are price around $100au plus delivery. Will have a look on ebay. Would you use them for a home switch?

Russell

[Al_The_Man]

Originally Posted by rusel Al They are price around $100au plus delivery. Will have a look on ebay. Would you use them for a home switch? Russell

They have a micro switch internally so they should be accurate.
Al.

[Bubba]

As best I remember, I was looking at a deviation of less than .001" (0.0254 mm)and I am trying to be conservative here as this was setup several years ago.
The pdf file I have lists it as "0.01mm on the operating points at 1 million operations"

[Valen]

Just spoke to Russell (rusel) and he mentioned this thread to me, he's my father and we are both trying to get this conversion "just so" .
I looked at the datasheets for the switches you guys mentioned and the honeywell is .01mm and the automation direct limit switch is the same.
We are using .001mm glass scales on our mill for the servo loop. I know they are way overkill in terms of absolute accuracy but because we use them for the servo loop they need to be finer than if we were just using them for positioning, and it feels kinda wrong to not try to get the same resolution out of the home switch?

We are making our own tool length probe based on some of the designs we have seen on here and around the net and it seems to be getting ~.004 mm which isn't too bad for a prototype.
http://www.cnczone.com/forums/showthread.php?t=109146 so I was hoping there would be something off the shelf that would hit that sort of accuracy that didn't cost mega $.


A quick intro to our mill

I want to do a writeup on the build for it, what would be the best place on here for it?

[rusel]

Hi
Been think about this (ouch) I can get some of those limit switches that you guys suggested on one end of each axis, but on the other what if I made a home switch that has a limit switch in the same enclosure. Would that not be beautiful....... One mounting for both.

Russell

[wildwestpat]

Hi Russell

Can I suggest the electronic proximity switches used in the automation industry. There are several types both the physical arrangement for mounting as well as the technology used to 'sense'.

I have found these for sub $10 from china via ebay and been very pleased with them both interms of sensitivity and long term stability for use as 'home' switches. They interface easily to breakout boards PROVIDED you get the right polarity of switch.

Here is a link to the Ormon site as they have the best data sheets to give you an idea.

http://www.ia.omron.com/data_pdf/dat..._ds_csm446.pdf
OR
http://www.ia.omron.com/product/48.html

The main advantage is that these are fully waterproof - pick the sensing technology to suit the swarf / environmental crud that they will meet in your machine. Use some cunning to use only one switch per axis.

I use a wired in glass minature slow blow fuse as the limit switch of last resort and would avoid mechanical microswitches unless there are health and safety considerations which might require non electronic switching. (Safety switches are a complex subject and should not be confused with the other switching requirements.) My 'glass fuse breakers' are arranged so that the mill bed will smash the glass and break the wire which in the slow blow fuse is held by an internal spring which ensures a clean break in the circuit. The only care being to ensure that the metalwork of the machine does not form a continuity path accross the 'broken' fuse. I also made sure that the endo of travel approach speed / inertia were taken into account so that a runawway axis would be protected from a hard grounding.

Hope this gives an alternative view on switches and one that would sit well on your quality build.

Kind regards - Pat

[Bubba]

Russell,
I use 1 switch and trigger it from either side AND use it as a combination home/limit switch!
The problem with trying to have two switches in the same container is the fact that the controller will trip out on limit unless the home switch trips prior to the the limit switch! Using the home as limit scenario, allows using one switch to handle both features. All of the control programs that I am aware of allow this.

[rusel]

Thanks Pat for the info and I've had a look at the sites.
The problem I see with these sensors, if I have read them correctly, is there not that accurate, we are after 0.001 mm. Then there is the possible swaf interference
Please correct me if I am wrong

The glass limit switch sounds a little like calling the fire brigade I will have to think about that some more

Bubba
I was thinking of having some distance between the two switches.
Our system can handle the limit/home switch in one, but what I am after is a high accuracy for the home switch

Russell

[rusel]

This is just a general lay for discussion
When the red actuator is touched the two home plates move, where there is three contact in series running on very low voltage to stop arcing. This break the circuit and the pcb sends a home signal out.
The actuator can keep on moving then the limit switch is then switched.
Total mill move should be stopped by the hard stop before actuator reaches case end.
Thought, comments please

Russell