[RicknBeachcrest]

I have my machine calibrated, I've got limit switches installed and working, and am ready to move on to the next step. I just gotta figure out what that is. I've been watching the videos from ArtSoft.
ArtSoft USA - Video Tutorials

I get the idea that I need home switches to set soft limits? I definitely like the idea of Mach stopping the machine before it hits the limit switch.

I've kind of got the idea for a methodology of milling something, but feel there are a lot of holes in my understanding, that only doing it will help.

So I got to wondering how important are home switches?

Thanks.
Rick

[Trotline]

If you've installed your Limit switches, you're closer than you may realize to having a Homing system in place. Mach3 is capable of using the same switch as both a Home and a Limit trigger. Check out section 4.5.3 (4-14) of the Mach3 manual for the details of this setup.


Luke

[CitizenOfDreams]

I use homing switches and software limits. Saves me one switch per axis.

[DonFrambach]

Homing switches are extremely convenient for my small router.

I initially set up the switches on my small router as limit switches but found that I would occasionally set up a job to cut outside of my machine's cutting area thus triggering a limit condition (which would usually ruin my work piece and could waste lots of time)

My switches still function as limits (and once saved my system from damage when I had a bearing failure that caused lost steps). Therefore, I strongly advise you to have physical limit switches on your system even if you use Mach 3's soft limits!

It was easy configure the x-, y-, and z up switches as home switches through Mach 3 while keeping them as limit switches too.

Now, I start my machine, activate Mach 3's homing routine, load my project and, with soft limits set, I can immediately see (on the Mach 3 preview screen) that the project will or will not fit into my machine's cutting area.

My current switches are simple mechanical switches so my initial home location can vary a little bit. I've just purchase (but not yet installed) proximity switches which I hope will allow me to cut part of a project, turn my system off for the night, and resume cutting the same project the next day.

[Bubba]

I use multiple fixtures (Gread G53, G54, G55,.......) and need to have the fixed reference that homing provides. The offsets to the other fixtures are fixed so when I home, I know where everything is.

[whateg01]

Your poll lacks a response for "No, but I wish I did." Having seen the home/limit switches in use, I wish I did have them for some operations. I don't think they are always necessary, but they are certainly useful. I am contemplating whether it is worth it on my plasma cutter, but I am thinking of adding them to my mill.

Dave

[robedney]

I'm adding limit/home switches shortly -- just go them delivered. One thing not mentioned so far about having home switches:

Most of us are working with steppers that don't have encoding feedback. In other words, Mach3 keeps track of where the cutting head is on the basis of where it started. If anything goes wrong (missed steps), Mach3 no longer has an accurate fix on location -- but thinks it does.

So, having physical home switches means that at the start of each job you can "home" the machine to the switches and check the coordinates in the Mach3 window. If they are not zeroes all around, you've missed steps at some point and can re-zero the machine. By the way, limit switches can share duty as home switches, but that basically means running the machine all the way to a preselected corner to home it. You can also have limit switches and separate homing switches, which allows you to home to zero in the center of the table -- saving time particularly on a machine with a large bed.

[RicknBeachcrest]

Thanks to everyone who responded. I'm sure, just as everyone uses a different machine, everyone has a different way of running a job.

My inexperienced idea of running a job (without home switches) would be to jog the spindle to the corner of a fixture (which would be a known distance from the piece to be milled) and reference all. Then start cycle from there. The down side is that to be accurate, I would have to jog to the corner each time a new piece was put into the fixture. I can see using home switches would greatly simplify this procedure.

I've wired all 5 limit switches in series so as to only use one input on the Gecko G540. The limit switches are just simple lever switches so their repeatability is questionable. My plan for home switches was to make some hall effect switches using the most excellent guide provided by Roman.
http://www.cnczone.com/forums/open_s...e_easy-74.html

I was planning on wiring each home (X and Y axis) to a separate input on the G540 which would allow them to home simultaneously.

I guess I am getting a little anxious to stop building this machine and start milling some wood and was looking for an excuse.

Rick

[DonFrambach]

...

I've wired all 5 limit switches in series so as to only use one input on the Gecko G540.

...

That's the way I wired my switches to my G540. Yes my machine takes a little longer to home because it only moves one axis at a time. But I usually home only once a day so I don't find the slower homing to be a hardship.

Don

[ben_mtl]

hint so homing is not that long at startup : make a "prepare for shut-down" button somewhere on your screen that moves your axis close to the homing switches, you just hit it before closing Mach3/computer while you put your jacket on... that way you only have 1in to travel on each axis when homing the next morning.

[DonFrambach]

hint so homing is not that long at startup : make a "prepare for shut-down" button somewhere on your screen that moves your axis close to the homing switches, you just hit it before closing Mach3/computer while you put your jacket on... that way you only have 1in to travel on each axis when homing the next morning.

Great idea! Thanks!!

[vtx1029]

I use homing switches and software limits. Saves me one switch per axis.

Same here. I don't use any real limit switches only software limits.

[LeeWay]

I use them on my plasma cutter and my 3D printer. I use them to keep the slaved axis squared up on my plasma and the little printer came with them, so I used them. I will soon be putting them on my router too. I don't have them on my lathe or home made mill. I ordered a new Torus and I think it will come with them.

[DonFrambach]

I use homing switches and software limits. Saves me one switch per axis.

Same here. I don't use any real limit switches only software limits.

I think omitting limit switches is a dangerous. If you lose steps, your machine won't recognize a software limit and you could have a crash. My machine lost steps when one of its bearings failed and the Y axis flew off to the Y+ side. Since I had a limit switch, I did not crash my machine and only had to replace the failed bearing.

Here's a link to that episode: http://www.cnczone.com/forums/diy_cn...ml#post1014407

[LeeWay]

While homing switches have their place on a lot of different type machines for different reasons, I think limit switches are the same. I feel that on a stepper driven machine, it is far more important to have good solid hard stops. Homes are beneficial and limits are nice. On a servo system, I think all three are required though. They are far more likely to tear something up in a crash.
Besides hard stops, homes and limits, I think a charge pump signal is also ranked as a priority. If the machine gets into a runaway situation where Mach 3 is not responding, limits and homes will not help at all. An estop just wired into Mach 3 pins won't either. A charge pump signal will stop it though as well as an estop that is wired to both Mach 3 pins and to the BOB or drives.

Just my thoughts on it. Rules a regulations vary, so if it is in a commercial shop, all of the above are required on all cnc machines.

[Devastator]

Your poll lacks a response for "No, but I wish I did."

My thoughts exactly.

[BanduraMaker]

When I built my machine, I included limit/home switches from the get-go. I'm using purchased hall effect switches, one per axis, with two magnets; one on each end of each axis. I installed the magnets very close to but still a smidge away from the hard stops.

Once I had this done and my spindle tramed and square, I made some aluminum corner/ fence blanks and positioned them so that they stuck into my cutting area just a little bit. I then homed my machine and cut the face of the fence at 0,0. I now have a repeatable 0,0 position on my table.

I use fixtures for most everything. When I machine a new fixture, I butt it up against the fence and then cut it after homing. If I'm not using a fixture, I've machine 1" spacer blocks so that I can hold down work at a known distance from my 0,0. Now, every time I switch fixtures or whatever, I simply type in the offset or choose the offset that I designed into the fixture.

If I didn't have home switches, I'd already have wasted countless hours of my life.

When it comes time to re-tram my spindle, or remove and replace the table, or bump a magnet or whatever, I simply re-mount my fence "in" a little and re-cut my 0,0 point.

p.s. I copied this idea from Ger. - Excellent advice!

[adprinter]

I originally wired limit switches at each end of travel for each axis on my machine. But after some use, realized that the only switches which were really needed were the home switches. (Which I had already set up as the -Y, -X, and +Z limit switches). However, by sharing the same switches (I.E. -Limit/Home switch) in Mach3's logic, a "Limit Switch Triggered" error would always occur during Homing operations. Even though Mach3 is supposed to be smart enough to realize the switch "Should" be triggered during machine homing. I never could get it to function correctly, so I disabled the -Y, -X, and +Z limits in Mach3's logic. (and enabled ONLY the Home Switches wired to the same address).

Doing it in this way, Mach3 actually is smart enough to differentiate between a Limit Switch Triggered, and Home Switch triggered during a Homing operation. If the Homing Switches get triggered at any other time (I.E. during a cutting operation, instead of machine homing operation) they are sensed by Mach3 as a "Limit Switch Triggered" condition. Since the limit switches are wired in series, for both ends of travel on each axis, one has to pay attention to WHICH SWITCH gets triggered in an actual "Limit Switch Triggered" error condition. A simple glance at the machine makes this a simple process.

I had a problem with my machine losing steps on the Z axis, (or at least I THOUGHT SO at the time- turned out to be loose mounting bolts on the Z axis lead screw nut assembly) and came up with a solution which involved the use of a -Z limit switch. For more on this, see my article in the Winter Edition of Digital Machinist Magazine.

[RicknBeachcrest]

I just finished my hall effect homing switches. These things work great. I am getting repeatability of less .001" and most times it is .0005". I highly recommend them. They're cheap, accurate and kind of fun to put together. (Not only that but I got to use my router to make the acrylic housing for them.) I just need to silicone the magnets onto the bracket and this will be a done deal. See my build thread for a little more info.

http://www.cnczone.com/forums/cnc_wo...ter_build.html

[BanduraMaker]

Your poll lacks a response for "No, but I wish I did." [snippity] but I am thinking of adding them to my mill.

No need to wish - in the time you spent thinking about adding them, you could have added them