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Mach Discussion => General Mach Discussion => Topic started by: edmond on November 25, 2008, 12:00:12 AM

Title: setting a permanent home point
Post by: edmond on November 25, 2008, 12:00:12 AM
Is it possible if I can set a permanent home point in Mach3 so whenever I cut on my machine it will always start there pls let me know how I go about it Im asking this because I want to mill a big L on the one side of the table making it easier to line up material on the bed and therefore I need that permanent home point

Thanks :)
Title: Re: setting a permanent home point
Post by: HimyKabibble on November 25, 2008, 12:20:50 AM
That is the purpose of home switches.  Without home switches, you have to position the machine to your 'zero' point manually each time you turn it on, and zero the machine position DROs.

Regards,
Ray L.
Title: Re: setting a permanent home point
Post by: edmond on November 25, 2008, 06:09:22 AM
Hi Ray

Thanks for the reply.
So in theory it should go to the same point everytime I home it, but is there a setting I can use so I can set a permanent point say 10mm away from the zero home point, do I just tell it to drive off 10mm from the home switch or what.

Thanks
Title: Re: setting a permanent home point
Post by: Hood on November 25, 2008, 07:20:00 AM
Edmond
 I you close the controller down you really need to home your machine or chances are it will not go to the exact same point each time even if you have persistant DROs set. Now you dont have home switches but you can still home manually. What you want to do is jog to some sort of marks and then press Ref All button and you will now have a home position defined. How you make these marks and how you pick them up will depend how accurate you will be. Personally I would set up home switches, they are cheap and easy to install and saves all sorts of accuracy problems when trying to repeat a position day to day.
Hood
Title: Re: setting a permanent home point
Post by: Sam on November 25, 2008, 07:39:45 AM
After you install home switches, then yes, you can specify that "home" is anything you wish. Home doesn't have to be zero-zero.
Title: Re: setting a permanent home point
Post by: ger21 on November 25, 2008, 08:58:16 AM
Set the Home offset to -10, and your zero will be 10mm from the switch. Then, just home, and goto zero.
Title: Re: setting a permanent home point
Post by: edmond on November 25, 2008, 11:50:44 AM
Thanks guys for the help.
I will set up home switches this weekend will normal cheap NC microswitches work ok.

Title: Re: setting a permanent home point
Post by: Hood on November 25, 2008, 11:56:47 AM
yes but depends the accuracy you need. If you can shield from chips optical switches work well and are deadly accurate, an OPB 917B is around £5 here $8 or so.

Hood
Title: Re: setting a permanent home point
Post by: vlmarshall on December 28, 2008, 02:40:10 PM
Can you set up Mach so it homes in a set order; Z axis first, and then X and Y, so hitting the Home button doesn't cause a high-speed dive through everything on the table?
Title: Re: setting a permanent home point
Post by: Hood on December 28, 2008, 02:42:57 PM
The Ref All button is set to do that, it has Z first then Y then X then A if you have one. You can set it to any order you wish.
Hood
Title: Re: setting a permanent home point
Post by: vlmarshall on December 29, 2008, 06:10:58 PM
Ref All Home? It doesn't seem to do anything other than zero the DROs, and (I'll assume), set the machine's current position as Machine Home.

The 'GOTO Z' button causes strange jogging, I guess it's going back to Machine Home, but sometimes it just seems to head to a new location, and it NEVER moves Z first.
Title: Re: setting a permanent home point
Post by: Hood on December 29, 2008, 06:18:27 PM
Go To Z will move to your current offset zero position, if you have a safe Z height set up then it will go to that first then move X and Y to Zero then move the Z down to zero.
 Ref All button will set the position you are at as machine CoOrds zero if you do not have any Home switches set up, if you have home switches then it will do as I mentioned in the last post.
 What exactly are you wanting to do?
Hood
Title: Re: setting a permanent home point
Post by: vlmarshall on December 29, 2008, 06:33:24 PM
I guess I just need to stop trying to run this thing and get home switches installed in it.
I haven't really spent enough time learning Mach's oddities, I keep trying to get it to run like a Haas.
Nothing seems to work like I expect.
Title: Re: setting a permanent home point
Post by: Hood on December 29, 2008, 06:40:42 PM
You could probably get Mach to run like a Haas if you wanted to, you can quite easily add VB buttons to the screen and have all sorts of things happen.
Hood
Title: Re: setting a permanent home point
Post by: vlmarshall on December 29, 2008, 06:50:38 PM
I'm just used to having a tool offset page, and a work offset page, listing all of the offsets available and the distances from machine home for each of them.
I guess I'll figure out Mach eventually.

I don't know how to program in VB.
Title: Re: setting a permanent home point
Post by: Hood on December 29, 2008, 06:52:58 PM
I don't know how to program in VB.
Neither do I but I muddle through when the need arises :)
Hood
Title: Re: setting a permanent home point
Post by: edvaness on December 29, 2008, 08:40:38 PM
H  :D :D D,

Youve been "muddling" pretty good from what I've seen.  ;)

Ed   :D
Title: Re: setting a permanent home point
Post by: HimyKabibble on December 29, 2008, 09:24:38 PM
I guess I just need to stop trying to run this thing and get home switches installed in it.
I haven't really spent enough time learning Mach's oddities, I keep trying to get it to run like a Haas.
Nothing seems to work like I expect.


If you don't understand how Mach deals with Home, zeros, and the different coordinate systems, adding home switches is not going to make it any less mysterious.  You *really* need to understand how Mach does these things to make good use of it.  Once you do, adding home switches may, or may not, add value for you.  I used my two machines for years with no home switches.  Now that I have them, I like them, but they are a convenience, not a necessity.

Regards,
Ray L.
Title: Re: setting a permanent home point
Post by: vlmarshall on December 29, 2008, 10:13:18 PM
Yeah, I don't know what Mach is doing with the offsets. Since they have no steady Machine Zero to reference from, I feel like I'm getting different results with the offset buttons every time I hit one.
My earlier problem was that I thought the button marked "GOTO Z" was trying to return the mill to Machine Home.

The 'Abnormal Condition' blinking light is annoying, the edgefinder diagram on the offsets page seems like a waste of space, as are the TWO Tool Offset buttons with 'Gauge Block Height' settings. Those last two features seem like they're aimed at non-machinists.
I'd rather have the Work Offset and Tool Offset lists onscreen.

Title: Re: setting a permanent home point
Post by: edvaness on December 30, 2008, 12:36:30 AM
vlmarshal,

Go with the home switches like Hood suggest. With home switches your work coordinates will be right on ,day after day.
Most VMC's won't do anything until they're homed. AND, They can prevent DISASTERS.  >:(
My opinion, home  (limit)  switch's are as important as an E-stop.

Ed
Title: Re: setting a permanent home point
Post by: vlmarshall on December 30, 2008, 06:16:53 AM
My opinion, home  (limit)  switch's are as important as an E-stop.

Thanks, that's my opinion too. Although, in this case, the disaster would be a small one, this is just a tiny little Sherline.
Still, I haven't really looked at Mach's homing setup yet, because I can't apply it to anything. I'll get to the switches this week.
Title: Re: setting a permanent home point
Post by: jimpinder on December 30, 2008, 09:54:53 AM
There are several posts on the forum about this.

The machine keeps it's position in machine co-ordinates. These are displayed on the DRO's when the machine co-ordinates button is pressed and the led surround is lit.  In theory, the only way to zero the machine co-ordinates is to have homing switches and home the machine. However, when Mach was written, if you do not have home switches and they are not activated on the Ports and Pins, RefAll Home will zero them anywhere. You could, therefore, as Hood says, place your table in any position and home the machine co-ordinates. How accurate this would be depends on you.

The "home" position is probably no good for machining, and certainly will not be the start position of your GCode Program. For this you use offstes - G54 to G58 and then another 250 or so under G59 - plenty to go at.

The idea is that you wake up in the morning, and in a stupor, press the RefAllHome button. The machine then moves to it's "home" position. So the machine is now happy - it knows where it is. As Hood says, you cannot rely on it being in the same state as when you switched it off.

Having now woken up, for the first run, you then need to jog your table to the 0.0.0 position of your program. If you input G55 on the MDI line, then change to the program co-ordinates (by pressing the machine co-ordinates button - the led goes out) and zero each axis individually, then G55 is set to the start co-ordinates of your program. You can check this on Config/Fixtures. Run your program.

The next time, before you start, insert a G55 command in your GCode at the begining, followed by a G0 X0Y0Z0.

Start up, and "home" the machine. Run the program, and the first thing it will do is get the offset from the table, then move to the X0Y0Z0 position of the program, and then run the program.

The offset table is saved when you close down, and reactivated when you start up, so once set up, it can be used as many times as you want.

If your case, with a fixed position for your work piece, once "home" switches are fitted, the rest is easy.
As Hood says, optical switches are probably better than fixed mechanical switches. I use lasers shining onto detectors, and these are accurate to several 1/10ths of a thou, and have the advantage - if I accidentally overrun doing something manually, I don't plough through them.

Jim Pinder





Title: Re: setting a permanent home point
Post by: HimyKabibble on December 30, 2008, 11:47:30 AM
Yeah, I don't know what Mach is doing with the offsets. Since they have no steady Machine Zero to reference from, I feel like I'm getting different results with the offset buttons every time I hit one.
My earlier problem was that I thought the button marked "GOTO Z" was trying to return the mill to Machine Home.

The 'Abnormal Condition' blinking light is annoying, the edgefinder diagram on the offsets page seems like a waste of space, as are the TWO Tool Offset buttons with 'Gauge Block Height' settings. Those last two features seem like they're aimed at non-machinists.
I'd rather have the Work Offset and Tool Offset lists onscreen.



When you do "Go To Z", it send all axes to their *user* coordinate zero positions.  This has nothing to do with the machine coordinates, and it makes no difference whatsoever where machine zero is.  Machine zero is useful *only* for referencing a vise, fixture, etc. to an absolute position on the machine, so you can quickly and accurately return the user coordinate zero to an exact physical location on the machine after a power loss, position loss, etc.  It is a convenience that saves setup time.  Nothing more.  Once you're actually machining, unless you're writing some very "incorrect" G-code, the location of user coordinate zero relative to the machine coordinate zero is totally irrelevent.  All your G-code should be working only within the user coordinate system(s) as defined by one or more of the fixture offsets (G54-G59).

Regards,
Ray L.
Title: Re: setting a permanent home point
Post by: softselect on December 30, 2008, 04:08:20 PM
My opinion, home  (limit)  switch's are as important as an E-stop.

Thanks, that's my opinion too. Although, in this case, the disaster would be a small one, this is just a tiny little Sherline.
Still, I haven't really looked at Mach's homing setup yet, because I can't apply it to anything. I'll get to the switches this week.

If you don't have home switches YET and you using steppers, simply place a dowel pin between a stop and the table and jog till it jams and the motor slips, do this in the same place everytime for all axis and press reference all
this proves to be repeatable to within 1 motor step size
Fit a clock and try it, you will be surprised
PS when the motor starts slipping stop movement within a second or so (try to keep this time the same and use the same slow jog every time)
thanks Friedrich
Title: Re: setting a permanent home point
Post by: edvaness on December 30, 2008, 04:46:21 PM
softselect,

NO-NO-NO-NO    :o :o

YOU DO WHAT?

Ed










Title: Re: setting a permanent home point
Post by: HimyKabibble on December 30, 2008, 05:10:23 PM
My opinion, home  (limit)  switch's are as important as an E-stop.

Thanks, that's my opinion too. Although, in this case, the disaster would be a small one, this is just a tiny little Sherline.
Still, I haven't really looked at Mach's homing setup yet, because I can't apply it to anything. I'll get to the switches this week.

If you don't have home switches YET and you using steppers, simply place a dowel pin between a stop and the table and jog till it jams and the motor slips, do this in the same place everytime for all axis and press reference all
this proves to be repeatable to within 1 motor step size
Fit a clock and try it, you will be surprised
PS when the motor starts slipping stop movement within a second or so (try to keep this time the same and use the same slow jog every time)
thanks Friedrich

On my machine, that would result in a lot of sheared-off dowel pins, or worse.....

Regards,
Ray L.
Title: Re: setting a permanent home point
Post by: softselect on December 30, 2008, 05:23:27 PM
It was actually a suggestion i found somewere on the net related to Sherline and Tiag micromills, with small motors that you can actually stop by hand without ripping all the skin off ;), it would be dangerous on big strong systems that can break things. :o
i should have said it was aimed at MICROMILLS
Title: Re: setting a permanent home point
Post by: vlmarshall on December 30, 2008, 06:26:51 PM
Well, thanks for all of the suggestions.
I gotta say, though, I know how Machine coordinates work in the real world, most of my problem has been caused my my not reading Mach's instruction manual.
Clearly, 15 years worth of 'I know what I'm doing' isn't helping. :D

The other day I hit the 'GOTO Z' button accidentally, and the mill ran back to the home coodinates I'd set at the same time I'd set G54. Unfamiliar with Mach's single-DRO offset page, I've just been homing the machine AND setting a work offset at the same time.
Anyway, as the machine moved, I noticed that it positioned X and Y first, and then Z, which, for a homing function, would be backwards, and potentially disasterous.
Since then, I've learned that the GOTO Z is just heading to Work zero, and the positioning of Z last makes complete sense in THAT case.
Still, it's a button I'll remove when I start experimenting with VB.
Again, thanks to everyone for your help. :D
Title: Re: setting a permanent home point
Post by: HimyKabibble on December 30, 2008, 08:26:15 PM
GoToZ will first move Z to the "safe" height, then move Y to zero, then move X to zero, then finally move Z to zero.

Regards,
Ray L.
Title: Re: setting a permanent home point
Post by: Hood on December 30, 2008, 08:28:47 PM
Ray, it will only move the Z first if a safe Z is set up then on mine it moves X and Y together, does yours move seperately?
Hood
Title: Re: setting a permanent home point
Post by: HimyKabibble on December 30, 2008, 10:50:47 PM
Hood,
   You're right, as usual.  X & Y do move together, once it's gone to safe Z.

Regards,
Ray L.