How to mount limit switches?


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    Default How to mount limit switches?

    So I got a new Taig mill last week and so far have got the steppers mounted and running and the basic setup in Mach3 is done. Now I'm trying to mount some limit switches and am having a hard time figuring out where to put them. I've looked on line and see some people are doing some serious mods to the machine just to mount their switches. I was hoping some of you have some simple implementations that you could share that don't require any drilling and taping of the machine itself.

    I'm only looking to mount 3 to home/limit the machine and use soft limits for the opposing directions.

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  2. #2

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    Hmmm, I recommend just skipping the limit switches. They seemed like a useful thing to me when I first started with a CNC mill but I quickly realized I did not need them and really can't come up with a way I could use them if I had installed them at this point. The reason is that every Gcode you generate in CAM will be setup to zero off of a corner or sides of stock material and so knowing home won't help much. Also with every tool change, z height changes so manual setups are already a given. Maybe one application would be to zero on stock and then move to home and record the offset from zero, providing a handy reference point for when something goes wrong and the original zero references are missing from previous machining. Even then though, a 1-2-3 block mounted to the table would suffice and be more accurate I suspect.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by desktoplathes View Post
    Hmmm, I recommend just skipping the limit switches. They seemed like a useful thing to me when I first started with a CNC mill but I quickly realized I did not need them and really can't come up with a way I could use them if I had installed them at this point. The reason is that every Gcode you generate in CAM will be setup to zero off of a corner or sides of stock material and so knowing home won't help much. Also with every tool change, z height changes so manual setups are already a given. Maybe one application would be to zero on stock and then move to home and record the offset from zero, providing a handy reference point for when something goes wrong and the original zero references are missing from previous machining. Even then though, a 1-2-3 block mounted to the table would suffice and be more accurate I suspect.
    That, having chucks, magnetic vices or jigs set in a specific place and so on make limit switches essential. Also not having your machine try and feed your X or Y through the end of a machine

    We have a chuck and magnetic vice set up on most of our metal cutting machines.
    Using centre as orientation for the chuck and bottom left for the vices means all we have to do to start a new job is pick up the Z on the material and copy/paste X and Y position in for orientation/reference (the machine has a tool changer and tool length sensor so picking up te Z is only for the initial setup, even if 12 tools are used to complete a job).

    Anyway, you have a power failure or power spike 8 hours into a job without a home position, throw the material away and start again.
    Precision and a perfectly aligned and centred job every single time.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by MT_Pockets View Post
    So I got a new Taig mill last week and so far have got the steppers mounted and running and the basic setup in Mach3 is done. Now I'm trying to mount some limit switches and am having a hard time figuring out where to put them. I've looked on line and see some people are doing some serious mods to the machine just to mount their switches. I was hoping some of you have some simple implementations that you could share that don't require any drilling and taping of the machine itself.

    I'm only looking to mount 3 to home/limit the machine and use soft limits for the opposing directions.
    What type of limit switches are they?
    Snap action you may need to modify the machine a bit, Proximity switches will work fine with a bit of double sided tape to hole them in place



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    Default Re: How to mount limit switches?

    Quote Originally Posted by desktoplathes View Post
    Hmmm, I recommend just skipping the limit switches. They seemed like a useful thing to me when I first started with a CNC mill but I quickly realized I did not need them and really can't come up with a way I could use them if I had installed them at this point. The reason is that every Gcode you generate in CAM will be setup to zero off of a corner or sides of stock material and so knowing home won't help much. Also with every tool change, z height changes so manual setups are already a given. Maybe one application would be to zero on stock and then move to home and record the offset from zero, providing a handy reference point for when something goes wrong and the original zero references are missing from previous machining. Even then though, a 1-2-3 block mounted to the table would suffice and be more accurate I suspect.
    Limit switches and home switches are two different things. I agree with you regarding home switches, I find them pretty useless, but limit switches are there to prevent disasters, to prevent you running your machine into the edges or the top. Limit switch on Z -- is pointless since tool length is different, so you must allow the Z to run pretty low, practically down to table, but Z ++ is useful since you never want to raise Z more than that the maximum, so there is a top limit.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by SeanLe View Post
    What type of limit switches are they?
    Snap action you may need to modify the machine a bit, Proximity switches will work fine with a bit of double sided tape to hole them in place
    I wouldn't trust double sided tape or any glue for limit switches, even less for home positions... but it is an idea for people who are afraid of drilling and tapping.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by A_Camera View Post
    I wouldn't trust double sided tape or any glue for limit switches, even less for home positions... but it is an idea for people who are afraid of drilling and tapping.
    If there is plenty oil or other lubrication they can come off but with proximity switches not actually touching anywhere to "switch" they can last for years with a bit of tape



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    Default Re: How to mount limit switches?

    Quote Originally Posted by A_Camera View Post
    Limit switches and home switches are two different things. I agree with you regarding home switches, I find them pretty useless, but limit switches are there to prevent disasters, to prevent you running your machine into the edges or the top. Limit switch on Z -- is pointless since tool length is different, so you must allow the Z to run pretty low, practically down to table, but Z ++ is useful since you never want to raise Z more than that the maximum, so there is a top limit.
    On a big machine I would agree, but I've never got around to fitting them on the Taig. It just stalls when you hit the end stop, and comes out of the nut if you go too far the other way.
    Yes it can be useful to have a home stop if you are configuring a particular set up, and using a probe as a tool touch off helps ensure tool change alignment, but limit switched are of little use when you have jobs on with clamps and the like which need avoiding, one just has to take care and jog around the obstacles manually at times. What I keep looking at is a 'three axis probe' which can bolt to the table and act as 'home' for the tool tip. Most of the jigs I use have a home position which one sets manually and just return to between pieces, and ensuring there are no missed steps would be nice ... but most of the time it's too late if the cutter has hit are hard patch in the work.

    I've currently got the Taig closed loop on the machine, so it trips the power when the motors stall anyway. That is perhaps one of the good features of the closed loop, and the 'home box' would then reset to start the same job again, but invariably it starts tripping after a few perfect pieces and the offset affects the final finish. I bit more more from a bipolar driver is more practical in daily use.

    Lester Caine - G8HFL
    http://medw.co.uk - Home of electronics for the Model Engineer


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    Default Re: How to mount limit switches?

    I consider homing switches a necessity, especially if you're part way through a part and god-forbid you lose position or otherwise jam something up and have to re-locate your part in order to resume cutting. I would definitely finangle something in they IMO



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    Default Re: How to mount limit switches?

    For me, limit switches are a necessity, especially when using Mach3. I've had a lot of issues with Mach3 interpreting G28 and G54 commands and have found that when the machine is homed there's a far greater chance of things not crashing.

    I've been working on fabing up some mounts out of some 1/16in thick aluminum stock. I'll post pics when I'm done.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by DubMFG View Post
    I consider homing switches a necessity, especially if you're part way through a part and god-forbid you lose position or otherwise jam something up and have to re-locate your part in order to resume cutting. I would definitely finangle something in they IMO
    For me limit switches are absolute must. Home switches are not useful because I don't have a home. Home = X,Y,Z zero and that depends on what I am doing, but it is always somewhere on the work material. If I end up in a situation you describe I just set the "home" i.e. X,Y,Z zero, again and restart the job from there. Limit switches prevent me from causing accidentally damage to my machine, so they are definitely a must.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by A_Camera View Post
    For me limit switches are absolute must. Home switches are not useful because I don't have a home. Home = X,Y,Z zero and that depends on what I am doing, but it is always somewhere on the work material. If I end up in a situation you describe I just set the "home" i.e. X,Y,Z zero, again and restart the job from there. Limit switches prevent me from causing accidentally damage to my machine, so they are definitely a must.
    You don't understand homing then. The home position is the machine home and all other work coordinates are based off of that position. If my machine loses position, I can re-home and have everything back ready to run in about 10 seconds.

    Do you use G54-G59 work offsets?



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    Default Re: How to mount limit switches?

    Quote Originally Posted by 109jb View Post
    You don't understand homing then. The home position is the machine home and all other work coordinates are based off of that position. If my machine loses position, I can re-home and have everything back ready to run in about 10 seconds.

    Do you use G54-G59 work offsets?
    Indeed I know what it is, but like I said, I am not having ANY need for such position. My machine does not lose position, and if it would, it would not help me at all since I don't use ANY fixed point as reference. To be able to use it you must know the EXACT position of your work piece as well as the top or bottom of it and that is in my case totally impossible. Of course, if it helps you in any way, I am not saying you should not have it, just that I don't have it and don't care to have one because I don't have ANY use for a fixed home position. Limit switches are totally different, I have those and also have use for them.

    No, I don't use G54-G59 offsets.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by A_Camera View Post
    Indeed I know what it is, but like I said, I am not having ANY need for such position. My machine does not lose position, and if it would, it would not help me at all since I don't use ANY fixed point as reference. To be able to use it you must know the EXACT position of your work piece as well as the top or bottom of it and that is in my case totally impossible. Of course, if it helps you in any way, I am not saying you should not have it, just that I don't have it and don't care to have one because I don't have ANY use for a fixed home position. Limit switches are totally different, I have those and also have use for them.

    No, I don't use G54-G59 offsets.

    Not using G54-G59 offsets is your problem. As I said, you don't understand the home position, and not using G54-G59 you are probably using G92 which is used in a totally incorrect way by most people that use it.

    If you have home switches then the home machine position is repeatable, and then the G54-G59 offsets are exactly that. They are offsets from the machine home position and those offsets are saved even if the machine is powered down. G92 is not saved, so if you zero your machine using G92, then you do lose position. If you use G54-G59 then once the machine is homed, the zero position is also reset to exactly where it was before.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by 109jb View Post
    Not using G54-G59 offsets is your problem. As I said, you don't understand the home position, and not using G54-G59 you are probably using G92 which is used in a totally incorrect way by most people that use it.

    If you have home switches then the home machine position is repeatable, and then the G54-G59 offsets are exactly that. They are offsets from the machine home position and those offsets are saved even if the machine is powered down. G92 is not saved, so if you zero your machine using G92, then you do lose position. If you use G54-G59 then once the machine is homed, the zero position is also reset to exactly where it was before.
    It is YOU who don't understand why I don't need a home position. Remember that not everybody is having your needs, your machine or your requirements. It is totally and utterly impossible for me to have a home position because it would be totally useless for me. If you don't understand that, well, that's your problem not mine. I know exactly how those offsets work and what a home position is, but believe me, I have no use for those at all and I have no problems at all with losing positions.

    You have no clue about what I use my machine for and have no imagination why I can't and won't need those offsets.

    BTW, no, I also don't use G92.



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    Default Re: How to mount limit switches?

    So basically you are recommending not having home switches when you use your machine contrary to the vast majority of CNC users, and you recommend this without even explaining your use. How about explaining your use so that others can understand instead of just saying home switches are useless . When you make a recommendation yet use the machine unlike others you do a disservice if you don't explain. I still fully believe that you don't understand offsets, homing or the use of them. In a previous post you said:

    Home = X,Y,Z zero and that depends on what I am doing, but it is always somewhere on the work material.
    Well Home DOES NOT equal X,Y,Z zero on the part. That is part zero and not machine zero and not the machine home position.

    From the above,t you do zero somehow on the part you are making. Well so do I and that is not the home position of the machine. The home position is simply a repeatable position for all of the axes of the machine and has nothing to do with the part being made, My home position is with the Z fully up, and the table fully aft and to the left, but the machine home position can actually be anywhere. My part is never located to that position and this still leads me to believe you have no clue about how homing works, or about how work offsets operate. You always use at least one work offset and usually G54.



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    Default Re: How to mount limit switches?

    Quote Originally Posted by 109jb View Post
    So basically you are recommending not having home switches when you use your machine contrary to the vast majority of CNC users, and you recommend this without even explaining your use. How about explaining your use so that others can understand instead of just saying home switches are useless . When you make a recommendation yet use the machine unlike others you do a disservice if you don't explain. I still fully believe that you don't understand offsets, homing or the use of them. In a previous post you said:



    Well Home DOES NOT equal X,Y,Z zero on the part. That is part zero and not machine zero and not the machine home position.

    From the above,t you do zero somehow on the part you are making. Well so do I and that is not the home position of the machine. The home position is simply a repeatable position for all of the axes of the machine and has nothing to do with the part being made, My home position is with the Z fully up, and the table fully aft and to the left, but the machine home position can actually be anywhere. My part is never located to that position and this still leads me to believe you have no clue about how homing works, or about how work offsets operate. You always use at least one work offset and usually G54.
    I am not recommending anything. I only say how I have and use my machine and what I have and not have use for. My needs I know better than you think, and definitely better than you do. For ME home is X,Y,Z zero on the part. I use no real home position because I have no use for that. Period. I have nothing more to say about the subject. Bye.



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    Default Re: How to mount limit switches?

    Well, its been a while and haven't been able to post pictures of my homing switches as I've been really busy making parts with my new mill (actually I just forgot). I decided to keep it simple and mounted three switches, one for each axis, with some 1 x 1/16in aluminum bar stock. I'm using soft limits after the machine is homed. I've homed the machine about a two dozen times now and they work pretty well and mounting the switches required no tapping or drilling of the machine.

    One thing to note, is the y-switch is in the normally open position. When it slides off of the edge it opens up to NC.

    The last pic is of my machine set up in the walk in closet of my apartment, don't tell my landlord!

    Attached Thumbnails Attached Thumbnails How to mount limit switches?-wp_20161120_20_39_47_rich-jpg   How to mount limit switches?-wp_20161120_20_40_22_rich-jpg   How to mount limit switches?-wp_20161120_20_38_31_rich-jpg   How to mount limit switches?-wp_20161120_20_38_19_rich-jpg  



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    Default Re: How to mount limit switches?

    Quote Originally Posted by MT_Pockets View Post

    One thing to note, is the y-switch is in the normally open position. When it slides off of the edge it opens up to NC.
    Be careful with that sort of installation... what happens if your wire breaks or you get a lose connection...? Nothing. The Y continues off the edge until it hits the floor or something else nasty will happen.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: How to mount limit switches?

    Quote Originally Posted by A_Camera View Post
    For me limit switches are absolute must. Home switches are not useful because I don't have a home. Home = X,Y,Z zero and that depends on what I am doing, but it is always somewhere on the work material. If I end up in a situation you describe I just set the "home" i.e. X,Y,Z zero, again and restart the job from there. Limit switches prevent me from causing accidentally damage to my machine, so they are definitely a must.
    There are as many ways to do things as there are folks that do them. Thant being said. you can avoid G54 commands and homing switches by simply using an exact spot on your vise or the actual work material as your "0". location. If you need to start the run again from some point in the program, Mach 3 will allow you to do that quite easily. I am not saying G offsets are right or wrong....but I find the more simple things can be done, the better. Dan



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How to mount limit switches?

How to mount limit switches?