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Re: Home and/or limit switch
« Reply #10 on: September 11, 2008, 11:31:09 AM »
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 :)

Offline jimpinder

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Re: Home and/or limit switch
« Reply #11 on: September 12, 2008, 03:59:57 AM »
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.




Not me driving the engine - I'm better looking.

Offline jimpinder

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Re: Home and/or limit switch
« Reply #12 on: September 12, 2008, 04:06:26 AM »
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$)
Not me driving the engine - I'm better looking.

Offline Hood

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Re: Home and/or limit switch
« Reply #13 on: September 12, 2008, 05:46:48 AM »
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
Re: Home and/or limit switch
« Reply #14 on: September 12, 2008, 07:42:12 AM »
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 :)

Offline jimpinder

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Re: Home and/or limit switch
« Reply #15 on: September 12, 2008, 02:59:55 PM »
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.

Not me driving the engine - I'm better looking.

Offline Hood

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Re: Home and/or limit switch
« Reply #16 on: September 12, 2008, 03:06:16 PM »
Your memory must still be pretty good though if you can remember what your reports said ;D
Hood
Re: Home and/or limit switch
« Reply #17 on: September 12, 2008, 04:11:29 PM »
It's probably the FREQUENCY of them that makes them memorable. :)
RC 8) (couldn't resist Jim)

Offline Kristin D

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Re: Home and/or limit switch
« Reply #18 on: September 15, 2008, 04:07:28 PM »
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

Online Chaoticone

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Re: Home and/or limit switch
« Reply #19 on: September 15, 2008, 04:25:18 PM »
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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