The usefulness of limit switches

Software FireControl
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I saw someone write here a while back that the only point of limit switches was to be able to home the machine at the end of the day. I’d like to shed some light on this.

The limit switches allow you to operate based off a consistent 0,0 location. Upon homing, you can work from the same spot every time. Index your material off of a jig, and make the home location your work zero, and you can resume a cut without material loss if you encounter an error. Even if the torch snags a tip up and moves the sheet, you can re index, home, and start your file from the line of code the error occurred on.

Even more, let’s say you started your cut in the middle of the table with an unknown relative 0 like a madman (which I do all the time) and fire control freezes after a pause to fix a tip up. Well, I wrote down the machine coordinates, and the work coordinates, then subtracted them from each other to find the machine 0 I had started with. This ended up being X11.378, Y-1.355. Now, because I could not just type that into fire control, I had to use a combination of continuous jogging and 1/16 steps to get it to those coordinates to set my work zero where it had been. Luckily my material never shifted. I couldn’t get it dead on, but I was within .002 of each. Resumed my cut and you cannot tell I lost my zero and restarted in the middle. Took about 5 minutes to get back to zero and save the cut.

In the future, if I need to start a cut in the middle of the table on some scrap, I’ll probably move the torch from home by 1 inch increments then position the sheet accordingly to make it easier to get back to my exact work zero based on machine coordinates.

Firecontrol rarely gives me issues, I believe this was just a fluke from me pausing right as the torch was about to fire. Otherwise, every other pause worked fine, and I run firecontrol off a tiny cheap stick pc. Yes the limit switches kill a tiny bit of your workspace, but your table stays dialed in. Depends on what this ability to salvage a cut is worth to you. If you’re doing a giant sheets of tons of parts or huge signs, then the limit switches can pay themselves in one salvaged cut.

Happy cutting.

Just getting primed, 16g mild steel. Hypertherm 45xp with fine cuts, book specs.

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Thanks for the input Jon… I’ve had my limit switches sitting here for a couple of months and just haven’t gotten around to doing the install(I know, big job right?) LOL… I think I’ll let it warm up just a big and go ahead and do it… Nobody says I have to run them all the time anyhow right??

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That’s true. You can disable them, but you may have to move them to gain back the cutting space. Mine don’t give me any problems though.

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For me the biggest advantage to using limit switches has been Firecontrol knowing the exact work envelope. It really helps to position my work zero and get the part where I want it without having to guess or do a lot of jogging to see where the right, left, top and bottom extremes are.

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You got me on that. I should note that was a discussion with someone that was having a number of issues with their setup with their system and getting a number of errors. I believe my quote was: “The only advantage that the limit switches have added is the convenience at the end of the day to press “Home” and it travels to that position and raises the torch.”

I should have said the “only advantage that I have found” since I have not had very complicated pieces and none that spanned past the area of the table.

I believe Langmuir’s original idea was for indexing so you are exactly right. There are some exceptionally valued purposes for the limit switches.

Having said that, yesterday I got no less than 7 warnings while I set up to cut three different pieces. I finally went into the settings, told the machine I did not have the limit switches and had a great time.
At the end of the day, I turned the limit switches back on and “Homed” the machine and put it away.

I do thank you for not dragging me through the mud for my ignorance. And you made a stellar presentation for the value of the switches.

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@brownfox
Jon…as usual you post pictures of the most amazing work!..and of course sound advice…

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I have same issues with the limit switches. I’d rather spend my time cutting old school than mess with it right now. Very unstable, very disappointed.

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I don’t know what you guys are doing to have so many problems with the switches.

I did, however, have an error when using home as my work zero. It looked like a wire from IHS got between the carriage and switch and caused a premature alarm. For now I’ll step 1/16 off home.

Thanks @toolboy ! Retirement present for my coworker whose place I took.

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Are you updated to the latest version of firecontrol? I get warnings but they don’t require me to interact with them. If they did, I’d probably toss the limit switches as well.

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BTW I like your Isiah 68 piece.

I have a Pro table.

I have latest version of firmware v1.3ls and Firecontrol v21.1.5, ran reset and restarted…

After setting soft limits the homing routine runs but never reaches one or the other switch or neither. If it reaches one (whichever it is closest to) it will touch off there and stop on the other. Visualizer shows at 0:0 top left corner but cutter isin middle of the table.

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Exactly. They are like nagging messages. I am fully updated and I can click on the “x” and make them go away. They happen every time I bring in a new gcode and as soon as I mark the program origin and zero my axis then I get a dark gray workspace that makes me know that everything is fine. I cancel the message and cut as usual.

The part that really annoyed me on Saturday is that I wanted to trim about 20 inches off the end of the sheet. The torch was as far to the left as the limit switch would allow. I set firecontrol to generate a line along the x-axis of 48 inches. I already knew that the metal was closer to 49. It threw a hard code that stopped firecontrol from even generating the line. I then turned off the limit switches, same location, and asked it to generate the line. No problem. It cut 48 inches and did not hit the bolt heads. I fully expected to hear a bang. But nothing. It was the end of a long day in a 35 to 40 degree garage.

Now I know you will say that my soft limits need to be adjusted but I will say I spent a considerable time adjusting them within the nearest 0.01 so that it did not collide with anything. The problem seems to be the reaction to the limit switch activation. It hits the switch and then backs off. There is a fully 3/16 of an inch that I lose on the left side. Once it backs off, it is not even touching the switch at all. I could probably adjust that switch and get back about up to an 1/8". I might do that.

I appreciate you reaching out. And, I do know they have value and at some point, I will like their ability to relocate a spot. What I have installed since the limit switches was a straight edge. I have found this to be more valuable for quick placement of a sheet. My only reluctance to show this is that someone deserves credit and I don’t remember who posted their bracket design. If they send me a message, I will edit this post with their name. (It might have been @DnKFab but I could not find it.) Here is the straight edge. I found this 1x1 steel tube on a Sunday, in a small hardware store where I live! I found that it is rigid enough to span the 40 some inches, with only two mounting brackets, and stick up high enough but not too high.

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In closing, I was not disputing your success and value that you found with the switches. You do great work and love the message of your piece.

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No problem, I didn’t think you were being negative at all. I was just trying to see if you are having to clear every alert.

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