Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Kristin D on September 06, 2008, 02:43:28 PM
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I am trying to figure out how and where to put home and/or limit switches on my Taig mill. The Z axis has a tee slot on one side where I can easily mount a home switch to home to just short of the mechanical top stop which is where I think that may belong. I can't really see the need for a lower limit as depending on the tool having a hard limit there is not going to keep me from crashing into the table, is that where the soft limits come in? Are soft limits set in the program coordinates or machine coordinates? For the Y axis I was thinking a switch mounted to the motor/leadscrew mounting plate will work and contact the movable slide, setting home as the furthest out position of the table. There is a pin fixed to the Y axis carriage that I can use to contact a switch mounted on the Table for my X home which I suppose should be table full right hand side for XY=0,0.
Does this make sense in the grand scheme of things, home would be table full right, full out toward the front and Z axis full up position? I am still figuring if I should use slotted opto sensors or microswitches so I really need to clear up my confusion with "Home" position before I can make the mountings and actuators or I might end up with a mirror image of what I need.
Once all this is done, if I have set fixture('s) say for engraving a plate I should be able to home the machine and either just load the program code or use the MDI to move to my X,Y zero position and run, that is my limited understanding.
Thanks,
Kristin
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I am trying to figure out how and where to put home and/or limit switches on my Taig mill. The Z axis has a tee slot on one side where I can easily mount a home switch to home to just short of the mechanical top stop which is where I think that may belong. I can't really see the need for a lower limit as depending on the tool having a hard limit there is not going to keep me from crashing into the table,
Personally I would also have a lower limit as it might save damage to the Z axis if for instance you never had a tool in and for some reason it went the wrong way and banged off the lower part of the ballscrew, maybe your motors would stall before any damage was done?
is that where the soft limits come in? Are soft limits set in the program coordinates or machine coordinates?
Softlimits are in machine coords, X and Y min and Z Max are 0 and X and Y Max and ZMin are the travel of these axis. (remembering Z Min is always a negative number)
For the Y axis I was thinking a switch mounted to the motor/leadscrew mounting plate will work and contact the movable slide, setting home as the furthest out position of the table. There is a pin fixed to the Y axis carriage that I can use to contact a switch mounted on the Table for my X home which I suppose should be table full right hand side for XY=0,0.
You can put the home switches wherever you want. Its easiest to think of the tool in relation to the work rather than the table movement. You really want to have your tool lower left and fully up in the home position, that would be table fully right and away from you and z fully up. If you chose to have the limits at the other extremes of X and Y you can still do it but you will need to set a “Home Off” value for these axis
Does this make sense in the grand scheme of things, home would be table full right, full out toward the front and Z axis full up position? I am still figuring if I should use slotted opto sensors or microswitches so I really need to clear up my confusion with "Home" position before I can make the mountings and actuators or I might end up with a mirror image of what I need.
As said above think of the tool but fully right and away from you for table is easiest to set up as you don’t have to worry about setting a Home Off value. If you use Optos and shield them in some way from much and swarf then you can mount the switch in the middle of the axis travel and have a flag either end that will break the light beam. Best if you can have the flag adjustable as it will allow you to fine tune. Z can be done in a similar fashion. You could also have a bar that runs the full length of an axis that blocks the opto and have slots cut in either end but that is not so adjustable.
Once all this is done, if I have set fixture('s) say for engraving a plate I should be able to home the machine and either just load the program code or use the MDI to move to my X,Y zero position and run, that is my limited understanding.
Thanks,
Kristin
If you keep the same work offset then yes
Hood
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Kristin,
I think you've got it pretty well figured out, and pretty much the way my knee mill is setup. I agree there seems little use to a Z "down" limit. I used microswitches, and feel that was a good choice. I seem to get pefect repeatability, to within well under 0.001", and they'll be less susceptible to damage from coolant/oil. If they do ever fail, replacements are as close as the nearest Radio Shack, for about $2 each.
Regards,
Ray L.
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Hood,
Thanks I knew one of my axis was the wrong way! I just was looking at table forward as mechanically it looked like the easy way out for switch mounting. If I put a limit on Z can that be wired in series with the home switches or would I need another input for limit switches (which I suppose I can wire all in series should I put X & Y limits too)? I am trying to wrap my head around the idea of a central switch and two flags, I can see it with using mechanical switches but the opto switches I have would lend themselves better to having the bar block them 99% of the time since they have a wide slot I could use .125" thick aluminum bar with adjustable apertures at the ends. Now the quandary is, how to set up the inputs active high or low so a failure will stop the machine. I know I saw something along those lines in one of the videos as to the preferred active state so it was "failsafe"
Kristin
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Kristin,
I think you've got it pretty well figured out, and pretty much the way my knee mill is setup. I agree there seems little use to a Z "down" limit. I used microswitches, and feel that was a good choice. I seem to get pefect repeatability, to within well under 0.001", and they'll be less susceptible to damage from coolant/oil. If they do ever fail, replacements are as close as the nearest Radio Shack, for about $2 each.
Regards,
Ray L.
Ray,
So at home position where is your table? Full right and out or Full right and in?
Kristin
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Kristin,
Home position is with the table full right and out, which I believe is the most common place. But, you can put it anywhere you like, even in the middle of the table if you like (but then you can't use the same switches for home and limits). It really makes no difference where home is, as long as *you* know where it is.
Regards,
Ray L.
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Well that works for me as I mentioned it is easier mechanically to mount the switch that way and also gets the table clear of the spindle for setting parts. Then all I need (haha ALL!) to do is set up the work offset, I can feel the brain hemorrhage coming on already. ::)
Kristin
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If you have Home in a place other than lower left fully up (tool in relation to table) then you will need to set up a Home Off distance for that axis so that the Machine Coordinates are zeroed to lower left fully up.
As Ray says if you use home positions other than axis extremes then you will need seperate Hom and Limit switches for each axis. If you have the switches at the extremes you can use the same switch for each axis.
Depends on your switches whether you can connect all in series, I have 3 inputs to Mach on the machine I use optos on, not tried connecting in series.
On my other machines I have good quality HoneyWell plunger switches and my homing looks for the switch then looks for the index from my motors encoder then backs off a preset amount of encoder counts. This is only possible with either drives that can do this or Eds BOB (No longer made I believe :( ) but may also be a feature in the SmoothStepper in the future.
Hood
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If you have Home in a place other than lower left fully up (tool in relation to table) then you will need to set up a Home Off distance for that axis so that the Machine Coordinates are zeroed to lower left fully up.
As Ray says if you use home positions other than axis extremes then you will need seperate Hom and Limit switches for each axis. If you have the switches at the extremes you can use the same switch for each axis.
Depends on your switches whether you can connect all in series, I have 3 inputs to Mach on the machine I use optos on, not tried connecting in series.
On my other machines I have good quality HoneyWell plunger switches and my homing looks for the switch then looks for the index from my motors encoder then backs off a preset amount of encoder counts. This is only possible with either drives that can do this or Eds BOB (No longer made I believe :( ) but may also be a feature in the SmoothStepper in the future.
Hood
Many stepper drivers also have a "Phase 0" output that can be used the same way, switch resolution permitting.
Regards,
Ray L.
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OK,
I think I have it, going to set up the home switches, wire them is series N.C. and get moving. I have 5 inputs on the controler card 10,11,12,13 &15 and a second port if I run out of inputs/outputs so that is not a big problem using seperate I/O for everything. Really not planning on making this too complex (Famous last words) I do want to add spindle motor control and perhaps a coolant output but I am sure I'll find another one or two things like the spindle speed if I swap to a variable speed drive.
Kristin
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Spindle control is pretty easy and by implication so is coolant control. Of course the cheaty way is to have the coolant pump in series with your spindle motor (if you don't use reverse) and switch it out if you want to cut dry. I didn't think of this, put in software control and the computer runs the whole thing.
A quick opto-isolator circuit will drive a small 5v coil relay, and the relay, if selected for its contact properties and isolation values, will drive a hefty 3-phase contactor with no gripes. While we're here, mobile phone chargers power relays and opto circuits very nicely :)
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You have obviously been giving it a lot of thought and your last post was one where the light had switched on.
I'll dim it down (a bit) but it might help you even more.
The limit and home switches on Mach3 can all be daisy chained together and used through one input. Use them normally closed as you were going to do, but wire from the pin input through the first switch, then the second, third and so on and then to the supply. In this case ANY switch opening triggers a high input to the pin (i.e. the 0v wire is interrupted and the pull up resistor on the input takes the pin to 5v. (If you are going through a BOB, this might be the other way round).
Does this matter that all are on one wire!!
No - all limits and home switches are shown as using the same pin in your Config/Ports and Pins, and Mach 3 sorts out which one it needs at the time. Limit switches clearly don't matter - a limit is a limit, and should be obvious from the position of the table. The home switches are normally limit switches, BUT, when homing, Mach 3 changes the configuration to suit homing. It knows which axis is homing, and when the signal is received, applies it to that axis.
Thus all your inputs are on one wire, meaning you have four other inputs. I know you said you had a spare port, but why use it if you don't have to - it is just something else to fiddle with. You will need other inputs for spindle control etc.
I think Hood said that the position of your home switches does not matter, my apologies if it was someone else.
The idea of Home switches is not for your benefit, it is for the machines benefit, so the machine knows where it is. It keeps track of all movement in "Machine Co-ordinates". When you home the axis, each axis moves to the switch in turn and zeros the machine code DRO (if you have auto zero turned on). Machine Co-ordinates are displayed when the machine code button light is lit.
Machine Code is of no use for work. The zero position could be anywhere and certainly not where your program starts. For this you need a convenient position on your table, many have a workpiece holder, or similar jig so the work is always in the same place. Milling programs normally have 0,0 on the bottom left of the table (but not always) and Z0 is with the cutter resting on the work.
If (in machine co-ordinates) you jog to this start location, when you get there, note the DRO's. Switch to "Program Co-ordinates" (Press the Machine Co-ords button and the light will go out). Zero the Program Co-ordinates DRO's (These will set to zero, Machine Co-ordinates will not, except when homing).
Your machine is now in a position to start work.
If you noted your Machine Co-ordinates, then this is the offset for that particular start point (or for that particular program), and if you check the Config/Fixtures table, you will find the co-ordinates have been entered in the G54 position (G54 being the default offset if no other is selected).
There are about 255 other offset slots - G55 G56 G57 G58 and G59P7 through to G59P255 or something. You can enter offsets into the table directly, or, if you select the offset first, when you zero the Program Co-ordinates it will be entered automatically. If you include that offset in your program, then the machine will automatically go to the correct position for that program. So all you do is home your machine and run the program.
A bit of a faf if you are doing a one off, but if you are doing a lot, or it is something you do a few of at different times, you can see the benefit. The only thing you must not do after you have entered an offset is zero the program co-ordinates (unless you mean to do so) because this changes the co-ordinates of the selected offset - and you will have to set up again (unless you have it written down).
Jim.
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To Blue Pinnacle -
Try using a Darlington array chip. These are normally 18 pin packages 0v, supply voltage (which can be quite high to suit the load) and eight pair of input/output conveniently arranged across the chip from each other.
They can be driven directly from the computer output - and when sent high, the output side sinks to 0v. Each pin can sink 1/2 amp and you can double up input/outputs to drive what current you want.
Best of all the are cheap (less than £1 or 2$)
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Jim, not sure if it was me that said that regarding the position of the home switches and I am too lazy to go read again. However is doesnt matter where your home switches are located as you can use a Home Off distance to tell Mach your position of Home in coomparison to your axis travel. For instance on my lathe it has a front toolpost and rear turret, If I were to home at the extent of the X axis one of these would be past centre of axis (chuck centre) and this could be very dodgy as tools sticking out in all directions would be sure to smack into something. My Home switch for the X is at a position such that X axis is centred, ie Turret and Toolpost are equally spaced from the centre line. Now also because this is a lathe I wish to have my zero position at centre of the chuck so I set up a Home Off distance to make my zero position on centre for my Master tool and then all tools in the post and turret are referenced to this.
If you are thinking for a mill then some people prefer to have the machine home so that the Y axis moves towards them so that loading stock is easier (closer without having to Jog) This would however mean that the axis is working arse for t** as Y+ would be the opposite way that it should be. To overcome this you set a Home Off distance for the Y axis. As an example if your Y axis had 12" travel then the Home off Distance would be 12 so when you homed the Machine CoOrds would show that the axis is at 12Inch and zero would be correct in relation to normal conventions.
Adding to that some people have vast travels and it might suit them better to have Home switches nearer the centre of the travel, again a Home Off distance would put coords back to the way they should be :)
Hood
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Jim - good call, mine uses DIP16 packaged darlington phototransistors (ISP845X). Four isolation channels per chip and 5KV isolation. nice sharp switch-on with very little forward current required, ideal for a first stage from one's LPT. And like you say, very cheap :)
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Thanks Blue -
Hood -
Yes - I haven't used the Home off feature before becasue of my laser type detectors for homing, and I have one which homes the lathe without any large movement away from the centre, which as you say, is x0.
Ah Well - there's always something on this bl**** program to swot up on - I'll have to look at that, now, I suppose.
Just spent the day fitting a dremel type unit on the mill spindle, to have a go at cutting copper clad circuit boards. It was a fine idea - a holder went up the mill spindle apeture with an arm on holding the dremel. I though it a great idea, until I fitted it and realised I had no way of locking the spindle, and it wagged about like a dogs tail. So I had to fit a stabaliser, which had to fasten on a post , which had .....
I used to get reports at school - ideas good, execution careless !! Now the ideas are getting careless as well.
See you later
Jim.
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Your memory must still be pretty good though if you can remember what your reports said ;D
Hood
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It's probably the FREQUENCY of them that makes them memorable. :)
RC 8) (couldn't resist Jim)
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After several false starts, waiting on parts etc. I finally got the limit switches mounted on my Taig mill, N.C., wired in series, figured out the basic settings so the quill goes to the top, table full left and full out. Now the question is how do I set the offsets to reflect where "program" coordinates really are? I am thinking I need to enter something like -9.5X and -4.5Y to tell Mach where I want my start point to be. Same goes for soft limits, I'd like to set up so the machine can't back the table all the way out of the leadscrew nut also.
Now that the switches are there another question comes to mind, if I am right up on the switch and jog into it what happens? Do I crush the switch or does Mach prevent that? Once the switch is opened can I back away or will it be a PIA? I can post my config file if needed.
Kristin :o
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Krisitn, Post your config and a picture of you machine. You ever heard of the 3 finger rule? That will get you sorted as to which directions are + and -.
Brett
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Brett,
Can't seem to get the network connection to work right now for the XLS and my usb drive gave up the ghost a while back, however here is a bad picture of where the switches are mounted. The X & Y switches are mounted off the rectangular motor mounts and contact the stationary bed of the machine (aluminum casting that the arrow is pointing left at the x home area) the Z axis switch is up top and contacts a accuator mounted on the spindle slide. Think I already figured out the crash factor, set the Y -- limit and ran into the switch and had to power down to manualy back off the switch.
Kristin
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Ok first thing is you can set AutoLimit Override, that will allow you to back off a hit limit switch but be aware that you can jog the wrong way so be careful :)
Easiest way is to have the home switches for X at the left hand end of the table for X, and for Y at the column, Z is at the top. If you do it this way then setting up Softlimits is easy, you enter zero for X and Y Min and Z Max, then X and Y Max and Z Min is the distance of travel on each axis.
If you have the limits at the other extremes of the axis you still set the Min and Max for each axis the same but you have to enter a Home Off distance for each axis. The reason for this is you want Mach to know that when your tool is at the corner of the table I have marked it is the X and Y zero position.
Hood
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Oh Also remember Z Min will be a negative number.
Hood
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I also meant to say, try to mount your switches in a manner so that physical smashing isn't possible.
Brett
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OK,
Think I have it(famous last words!) Where is "autolimit overide" general config? I would have done otherwise but there reall is not any other places to mount switches so I guess I will have too set up the offsets.
Kristin
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Think its on the settings page, been a while since I looked at the standard screen so may be on Diagnostics but its one or the other.
Hood
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Hood,
Yup was on the "settings" page and I was able to overun the switches by .010 and not crash! ;D
Got all three axis figured out and zero'd with the "safe limit" keeping from crushing any now, Wonder if I should go buy Igor a Glock like Brett's Chimp, good lab assistants are hard to find but I wonder if armed lab assistants are worth having, normaly I am the only one armed in the shop and it would be a pity to loose that advntage! Perhaps a super soaker and I'll just leave a power panel open! :D
Kristin
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Glad you got it sorted Kristin- :)
I also meant to say, try to mount your switches in a manner so that physical smashing isn't possible.
Brett
Unfortunately I was mounting my 3rd limit switch (Y axis) while remembering this so I'll be redoing my Z and X axis at some point in time. If I crash, I have backup switches, lol!
By the way, since I'm hoping to setup for coolant or mist in the future, what small limit switches can I use for that application? These (limit switches in general) aren't all sealed are they?
Thanks,
Dave
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I use these http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0335081 on the lathe for limits and home switches, they are accurate and waterproof but fairly large and expensive. For homing on the lathe I use the servo drives as they home to the index, what happens is the drive starts homing until it hits the switch, it then backs off until it sees the Index pulse from my encoder and then sends a signal to Mach to say its homed.
I have these switches http://www.rapidonline.com/Electronic-Components/Switches/Microswitches/IP67-Microswitch/74548 on the turret and toolp[ost on my lathe, they seem to be pretty good as far as being coolant proof and are certainly accurate enough for the toolpost and turret but never =measured for use as limits.
Hood
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Dave, i use prox switches. There is no contact, they repeat accuratley, and coolant doesn't bother them. You can get some that will sense only certain materials as well. That comes in handy at work on our robot cells. If it is an Alum. cell, we get ones that can only see steel and use steel targets. You can get PNP or NPN and 2 wire NO and NC. Here is a link to an example. http://web4.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Inductive_Proximity_Sensors/8mm_Round_(AE_Series)/Standard_Sensing_Distance_(AE1_Series)/AE1-AN-1A
Brett
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Kirsten -
To swing back onto the post, so to speak (although with that chimpanzee firing at me I am not so sure). I covered this in an earlier reply.
If you have your homing switches fitted, and they are working, then to set your offsets up takes only a moment.
Home your machine. If you have set "Auto Zero" on Config/Homing Limits, then your machine should home, and all the DRO's should go to zero - when looking at Machine Co-ordinates (the machine co-ordinates button should be lit). You cannot zero machine co-ordinates any other way except by homing (now you have the switches set up and working).
If you press the Machine Co-ordinates button, the led will go out, and your DROs will now display Program Co-ordinates. This may or may not be the same display. If it is not displaying 0,0,0 like the Machine Co-ordinates, then zero them, using the buttons at the side of the display.
Type in your MDI line "G54". This is the default offset. Mach 3 (and all other machines) keep track of their position in Machine Co-ordinates, but to make the display more recognisable to we mere mortals, it adds an offset to the display so that we can associate it with the program we are using. G54 is the default offset, and should be selected at all times when not actually running a program.
Jog your machine to the start point or 0,0,0 of your program. The Machine Co-ordinates will change, and the Program Co-ordinates will follow, but when you get to the correct position, zero the Program Co-ordinates.
If you check the Machine Co-ordinates, you will see that they have not changed, and the difference between the two is the offset.
If you check in Config/Fixtures you will see that G54 has changed - and now reflects the offset.
You can do this with the other offsets G55 - G58, G59P7 to G59P255.
The idea is that you include the offset in your program, at the beginning, so that when you switch on, you "home" the machine - so it knows where it is. If you then run the program, the offset will be read in, and the machine will move to the correct position for that program. Each program might have it's own offset, or sevral programs might share the same offset, if they start at the same point - e.g. work is set in the same position each time.
DO NOT zero your Program Co-ordinates while the program is running. It will automatically change the offsets. Only zero the Co-ordinates when setting up.
If you go to Config/General config - bottom right hand corner, you will see a box "Copy G54 from G59.253 on Startup"
If you want your machine to start in the same position on start up, then enter where you want the machine, and enter the offset in G59.253. This wil be copied into G54 and if you then go to 0,0,0 the machine will always move to the same place. If you are running a program, this does not matter, because once you run the program it will have it's own offset, which will over-ride G54.
Offsets do not accumulate, they are individual, and only one is in operation at one time. (However, Tool offsets then accumulate on machine offsets)
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You cannot zero machine co-ordinates any other way except by homing (now you have the switches set up and working).
Actually you can, I use to zero the machine coordinates when I didn't have home switches by going to the diagnostics tab and entering "0" and then hit the send to DRO button and it will zero out where your table may be -
Conventional or not, it worked for my application at the time ;)
Dave
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Dave, never tried that but that was a roundabout way of doing things ;D
If you didnt have Home switches configured pressing the Ref All button would have set your machine coords to zero :) (of course AutoZero would have had to be configured previously in Homing and limits)
Hood
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Looking at the TurnSilverBlue.lset, the Program, Machine and Part coords don't work like they do in the other screens.
You can ZERO the Program and the Machine coords but not the Part coords.
Can someone please verify that I'm seeing this correctly ?
Maybe the buttons are mislabeled/configured.
RC
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Dave, never tried that but that was a roundabout way of doing things
If you didnt have Home switches configured pressing the Ref All button would have set your machine coords to zero (of course AutoZero would have had to be configured previously in Homing and limits)
Hood
You have to remember that, believe it or not, I knew less back then than I do now. :D
I watched the videos for Mach 3 and saw that reference to hit the ref all button but my Z axis would start to move and there were no switches at the time so I just never did that again because I didn't understand the software at the time. So I kept fooling around in the diagnostics page and figured that "zeroing Mach coords" out. As long as I "homed" my machine before turning it off, it would be the same the next time I fired her up.
Unfortunately if I hit an E stop for any reason, it had to be reset. :P
Good times........ :D
Dave