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View Full Version : Home switches and limit switches.



ynneb
04-04-2004, 04:28 AM
I know that a limit switch says not to drive past a certain point, and a home switch say here is zero.
What i was wondering was, does the home switch get mangled in order for the limit to be activated?
Is it possible for the limit switch to be the same switch as the home switch? Does my qusetion make sense?

ger21
04-04-2004, 09:02 AM
Usually, if you have both a home and limit switch, the home swith is activated with a ramp-type block so it can slide past it without damaging or rippin it right off. Whether you can use a single switch for both home and limits, it depends on your control software, but I think you usually can. Get back to reading that Mach 2 manual, it should be in there. :D

Swede
04-08-2004, 10:41 AM
On my system, the home and limit switch are one and the same. When seeking home, the table slowly drives and trips the limit switch. It then reverses and backs off the switch a software-set distance, and that point then becomes home.

It's not hard to set up a switch which will not get mangled. You can mount a roller-equipped micro-switch. A cam can drive right by the switch, tripping it, and riding right over the lever to continue on without harm.

Here's an example - note the round cam on the ballnut. It trips the switch with ease, but can also drive past the switch without harm. The roller lever on the microswitch depresses another 0.1" or so past the point where it is electrically actuated.

Bloy2004
04-08-2004, 10:53 AM
ok Swede! That's how i'll be hooking in switches on my machine..
Thanks for the photo!
By the way..I like that lubrication fitting you have incorporated into your drive screw/nut housing!

Swede
04-08-2004, 02:40 PM
Grease zerk - I wish I could take credit for it, but that grease zerk is stock on this particular THK ballscrew. If I had more patience when I built my mill, I would have tied all of the zerks together and created a one-shot lube system. As it is now, I have to lubricate, hmmm lets see

... 13 grease zerks! The good news is that with all the wipers and protective flanges and stuff built into ballscrews and THK linear bearings, they stay pretty clean and retain grease well.

On the switches - You'll want to make them easily adjustable. I found that as I add stuff to a table (like a vise which overhangs) I wanted to reset the switches to prevent crashing, and when they are buried inside the machine and hard to adjust, it is a real pain!

Best of luck.

Bloy2004
04-08-2004, 06:32 PM
a way around this, according to a fellow named Ballendo, suggested I hook into the home/limit switch series with a stereo phone jack for plugging in an extra moveable switch... that is for each individual series of switches....
...so if there is no room for adjustment, maybe this is the way to go....
I believe he was refering to a Mach2 setup.....can't recall everything.....
....but I certainly like the "over-ride/cam idea and the way you presented it above......