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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Home switches - how useful, what is your set-up
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  1. #1
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    Home switches - how useful, what is your set-up

    How useful are home switches - if you have/use them what is your set-up and accuracy?

  2. #2
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    Re: Home switches - how useful, what is your set-up

    Home switches are used for two things.
    1) Setting soft limits, and
    2) Setting the worktable origin.

    For #1, the switch does not need to be particularly accurate. Pretty much any kind of switch will work.
    For #2, the switch needs to be as precise as you want your parts to be. (Unless your machine has servos with encoders, then you can use them for fine homing just like "real" industrial CNC machines do.)

    My desktop machine uses regular microswitches with levers. They are accurate to within 1mm or so, which is enough for setting soft limits.

  3. #3
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    Apr 2005
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    861

    Re: Home switches - how useful, what is your set-up

    I use cheap microswitches but rarely home my machine. Mainly they are a catch for when I get too close to the limits, I do not use soft limits. I sometimes home if I want to switch off mid-job and continue much later. In that case, these micro switches give me better than 0.05mm repeatability which is generally fine for what I do. You can get dedicated homing switches which are a lot better than this, if you need them.
    LongRat
    www.fulloption.co.uk

  4. #4
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    Re: Home switches - how useful, what is your set-up

    CitizenOfDreams has it, although I'd throw a wrinkle in there for #2 and add a #3.

    If you work - like many do on production line systems - by referencing your clamping system, vise or jig off the table of your machine, then referencing the part to the vise, and expect to throw your workpiece into the machine and hit "go" then those home switches better be bang on. If you work more on a part-by-part basis and are going to dial your workpiece in on each job with an edge finder or touch probe, then home switches and the machine coordinates zero don't really matter much at all - when you clock in your work offsets before the job that takes care of getting things lined up. In fact, if you don't care about soft limits then doing things this way you don't really need home switches at all.

    Machine zeroing on super accurate limit switches in combination with knowing your machine dimensions, accurately known offsets to fixtures which are in turn accurately modeled within your CAM environment can be a big time saver if you go to the trouble of setting it all up.

    #3 is that they give you a way to verify position - a way to check on a lighter machine whether any of your steppers have skipped steps. But this only works if the limit switch is accurate and repeatable to within less than half a step's worth of travel.

    I use cheap microswitches too, mostly for the sake of referencing the soft limits. I never really rely on saved workspace coordinate systems unless it's for a super rough "near enough" job.

  5. #5

    Re: Home switches - how useful, what is your set-up

    IMO in the long run decently repeatable home switches are absolutely mandatory. Lot's of good reasons are already posted, so I won't go into too much detail. Suffice it to say, they make lots of things not easier.

    I use ebay proximity sensor that work quite well. They cost something like $10 for 5 sensors. Maybe later I'll check them for repeatability with my dial indicator, but after a few years of running the machine I can tell you they are quite good. For example, I can run an A/B operation and generally it's hard to tell where they meet in the middle. Good enough for me.

  6. #6
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    Re: Home switches - how useful, what is your set-up

    Moto tech, any pictures of the mounting of the proximity(I assume induction?) Sensors. The difficulty I see is the sensor has to be at 90deg to the metal it is detecting so that the metal can pass over the sensor and the table/part can use all its travel but I assume this arrangement is poor for repeatability unlike like say if the metal was moving directly toward the top of the sensor but that could only be done for limit switches I think..

  7. #7
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    Re: Home switches - how useful, what is your set-up

    In Mach3 I just use the soft limits and seems to work well for now.
    For it to work properly though your table co-ordinates need to be right.

    Only issue is if you get missed steps (or you stall and get stuck which happens a lot on my X2) you lose table position and have to put it back in the right place again which can be a pain.

    If I had just home switches then it would be easier to put it back.
    As long as I don't stall and lose steps though I G28 at the end of the day before I switch off, Ref all home when I re-start it and the soft limits do their job.

  8. #8
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    Re: Home switches - how useful, what is your set-up

    Quote Originally Posted by dharmic View Post
    CitizenOfDreams has it, although I'd throw a wrinkle in there for #2 and add a #3.

    If you work - like many do on production line systems - by referencing your clamping system, vise or jig off the table of your machine, then referencing the part to the vise, and expect to throw your workpiece into the machine and hit "go" then those home switches better be bang on. If you work more on a part-by-part basis and are going to dial your workpiece in on each job with an edge finder or touch probe, then home switches and the machine coordinates zero don't really matter much at all - when you clock in your work offsets before the job that takes care of getting things lined up. In fact, if you don't care about soft limits then doing things this way you don't really need home switches at all.

    Machine zeroing on super accurate limit switches in combination with knowing your machine dimensions, accurately known offsets to fixtures which are in turn accurately modeled within your CAM environment can be a big time saver if you go to the trouble of setting it all up.

    #3 is that they give you a way to verify position - a way to check on a lighter machine whether any of your steppers have skipped steps. But this only works if the limit switch is accurate and repeatable to within less than half a step's worth of travel.

    I use cheap microswitches too, mostly for the sake of referencing the soft limits. I never really rely on saved workspace coordinate systems unless it's for a super rough "near enough" job.
    couldn't have said it better, although I went a different route. I spend money on some good switches. I run closed loop steppers and heaven forbid i ever loose steps my controller will stop motion automatically. I can reset the drive, rehome, and get right back to it. I have yet to scrap a part because of my machine (plenty of other reasons though, haha). It's just one less thing to have to worry about. Spend the money once, and never look back.

    It is also super handy to set the vice up once and as long as you don't take it off, you always have your reference edges set. Saves a bit of touch off time.

    These are the switches I run

  9. #9

    Re: Home switches - how useful, what is your set-up

    Quote Originally Posted by men8ifr View Post
    Moto tech, any pictures of the mounting of the proximity(I assume induction?) Sensors. The difficulty I see is the sensor has to be at 90deg to the metal it is detecting so that the metal can pass over the sensor and the table/part can use all its travel but I assume this arrangement is poor for repeatability unlike like say if the metal was moving directly toward the top of the sensor but that could only be done for limit switches I think..
    I run mine 90 degrees as you described. It doesn't seem to be an issue. I did experiment with various targets, but as long as the target was large enough and entering the sensing "window" they seem repeatable. I never made it to the shop last night, wife has night school the first three days of the week so I generally am hands on with my kid. I'll try to get out there this evening though.

    I use my limit switches as my homing switches. I have three total, they are not in series.

  10. #10
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    May 2015
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    Re: Home switches - how useful, what is your set-up

    Re-reading through all this, I'd just add: if you have to choose between a half decent touch probe for a couple hundred bucks vs the minimal cost but maximum mucking around of installing micrometer accurate limit switches, the touch probe is a better choice unless you're doing production line (many runs of the same job) work.

  11. #11
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    Re: Home switches - how useful, what is your set-up

    Quote Originally Posted by dharmic View Post
    Re-reading through all this, I'd just add: if you have to choose between a half decent touch probe for a couple hundred bucks vs the minimal cost but maximum mucking around of installing micrometer accurate limit switches, the touch probe is a better choice unless you're doing production line (many runs of the same job) work.
    This was my question (how useful are they) I'm guessing though they are useful if you are part way through a part and have to reset/continue where the edge that you originally referenced off does not exist, though reading what I wrote your suggestion would be re-reference off a machined edge which would almost certainly be more accurate with a decent touch probe...

    Or perhaps if accuracy is good (or good enough) it can continue the part without 2x tool changes to a probe?

    Hopefully some-one else will chime in what they use home switches for as I'm basically guessing here..

  12. #12
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    Re: Home switches - how useful, what is your set-up

    Quote Originally Posted by men8ifr View Post
    This was my question (how useful are they) I'm guessing though they are useful if you are part way through a part and have to reset/continue where the edge that you originally referenced off does not exist, though reading what I wrote your suggestion would be re-reference off a machined edge which would almost certainly be more accurate with a decent touch probe...
    what a hassle! Not only do you have to change the tool out for the probe, you'll also have to go back into your CAM software and reset your work offset to the new edge...repost...switch tools again. and they your still only going to repeat as well as your probe. Which lets be honest, even a nice Haimer is only good for a few thou. MAYBE half a thou if you have the tip really dialed in well. And of course this all assumes that your tools will repeat in Z height as well.

    Or..spend the money on good switches (which is still cheaper than a haimer). If something happens, rehome, rewind the program to a good point and go.

    I know 99% of us don't do any kind of production, but I think there is still value in your own personal time and anything I can do to put the burden onto the mill and make my life easy, I'll do.

  13. #13
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    Re: Home switches - how useful, what is your set-up

    My approach to the workplace zero probably comes from my time with manual machines using vices where everything changed from setup to setup. Touching off with a wobbler on the workpiece was how it was done, and how I still roll - just with an electronic edge finder. Ja, sure, the chance of skipping steppers and losing position fouls that approach somewhat but if your machine never skips, it doesn't matter.

    men8ifr - you got it. Hear that nasty noise of a tool getting bogged. Swear. Measure off the machined edge, calculate what the original work coordinate system's location would be for that and set it on the controller. No need to adjust CAM etc. And yes, it's a pain in the bum. But it certainly encourages you to get smart about feeds, speeds and depth of cut to avoid skipping steps And when it only happens once every few months it's quite bearable.

    CS900: What is this half a thou you're talking about lol? I'm going to assume that if someone is asking about the value of home switches that they either have none or they have rubbish ones (like me). In which case they're not looking at a machine capable of getting close to half a thou anyway. My machine came with a deck that deflected 1/16" under tool load, the new bed I made for it gets that down to about 0.1mm (what's that, .004"?) and so my much cheaper than a haimer probe is plenty good enough.

    I totally agree that having a well known home would be a time saver on the rare occasion of a lost position. Or if machine zero was workplace zero and went along with having a well known position of bed relative to home and fixtures relative to bed and accurately measured stock relative to fixtures and accurately positioned final part within the stock. You can see where I'm going with this, maybe, I haven't got the time/inclination/energy to dial all that in for the sake of odd jobs.

  14. #14

    Re: Home switches - how useful, what is your set-up

    Quote Originally Posted by CS900 View Post
    what a hassle! Not only do you have to change the tool out for the probe, you'll also have to go back into your CAM software and reset your work offset to the new edge...repost...switch tools again. and they your still only going to repeat as well as your probe. Which lets be honest, even a nice Haimer is only good for a few thou. MAYBE half a thou if you have the tip really dialed in well. And of course this all assumes that your tools will repeat in Z height as well.

    Or..spend the money on good switches (which is still cheaper than a haimer). If something happens, rehome, rewind the program to a good point and go.

    I know 99% of us don't do any kind of production, but I think there is still value in your own personal time and anything I can do to put the burden onto the mill and make my life easy, I'll do.
    I couldn't agree more with this post.

    I also can't imagine having to touch tools off every tool change, and without homing switches there's simply no scenario for stored tool length offsets. I have something like 25 tools that I regularly use. I just load the required tool and hit go.

    Also in that when doing CAM i pretty often plan to use the corner of my vise for a lot of setups the only axis I need to probe is in Z, again without decent home switches that would be impossible.

    Even with eBay switches the repeatability is good enough to do this type of stuff. It seems silly to not.

  15. #15
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    Re: Home switches - how useful, what is your set-up

    WTF are you guys on about. Touch off every tool change? Changing CAM zeroes because of skip? Do you even know how WCSs work?

    Find a zero. It could be your machine home. It could be the corner of your workpiece. It could be your elbow. It doesn't gorram matter, as long as it finds your part. Run your program. If you stuffed up on your feeds and speeds, deal with it. If it's via a micron accurate homing, great, you've saved yourself a whole minute of tool swaps and probing. If you don't do it often, it really doesn't matter.

    Caveat: This said after a half bottle of whiskey on a Friday night after a really long week from someone who's learned one way of doing things that works for them and, whilst acknowledging the advantages of accurate homing, still struggles to justify the pain of adding it vs the pain of not having it.

  16. #16

    Re: Home switches - how useful, what is your set-up

    Whats your tool length compensation relative to?

  17. #17
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    Re: Home switches - how useful, what is your set-up

    dharmic, I see where you're coming from and maybe I hold myself and my mill to a higher standard than most. I've put a lot of effort into making sure my mill can repeat withing a few thenths. I'm well aware this is overkill for most hobby work, but there is no reason these small machine can't be accurate. It's super nice to program a part, let it run and be within +/-.001 almost every time. I also subscribe to the old metrology rule of thumb that your equipment should be 10X better than the tolerances your trying to meet.

    That said, I'm well aware of how work offsets work. If you zero off your stock, then machine the reference edges off, you're up sh*t creek if your mill looses position without home switches. I suppose you could always use the vice edge or some other reference on the mill as your zero point, but then you have to make sure you position the work piece correctly relative to that feature. I'm way too lazy to put myself thru that if it's not loaded against a vice jaw edge.

    Bottom line, we are all just trying to answer the OP original question. I place a high level of importance on repeatability and accuracy, so my home switches reflect that. If you're ok repeating to +/-.004 then by all means get a cheap micro switch. No problems with that at all. But in the end limit switches can help you save time, your part, and your machine. For the minimal cost and effort to install them, my personal opinion is that it's worth it.

  18. #18
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    Re: Home switches - how useful, what is your set-up

    Sorry, even I cringed reading my last post just now. It seemed a lot more light hearted and a lot less like mactec last night.

    @CL_MotoTech: I misread your comment about each tool change. Again, I'm operating under the assumption that if the limit switches are rubbish or nonexistent then it's most likely a machine that doesn't have things like accuracy, stability, interchangeable tool holders - I'm picturing my cheapo router or little manual mill which have something like an ER collet in the spindle. Or am I making too big an assumption? Do you get machines with toolholders etc that still use microswitch home stops?

    @CS900: I'm not arguing with you anymore, thank you for helping me see things in a different light. Life with trustworthy homing / machine zeroing would be easier and nicer - something I've never denied - but I'm starting to see just how much nicer. Life without it is still surviveable, I probably won't go to the effort on my current gear, but if I get another machine at some point I think good homing switches will likely be on the shopping list

  19. #19

    Re: Home switches - how useful, what is your set-up

    No worries man, I love me some bourbon so no judgement here.

    I have a g0704 (BF20) that I converted to CNC. It uses R8 collets, I use mostly set screw and ER type holders. I also use a gage line type macro to measure my tools against a electronic tool height setter. This relies on the limit switches and homing routines and generates great repeatability.

    I'd say I have no more than $50 in my setup. Again, I have a hard time understanding why you should skip this on anything other than the cheapest machine. To keep it in perspective, a stock G0704 is like $800 or something. Despite the literal thousands I have spent to get my machine to the point that it is now, the proximity sensors used for homing/limits were absolutely one of the best upgrades.

  20. #20
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    Re: Home switches - how useful, what is your set-up

    I have (hopefully) a SwissMak on the way, when it finally arrives I'll be remembering this thread to build some decent homing switches in from the get go. Thanks, chaps!

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