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Newb - Machine Coordinate Confusion
« on: January 01, 2017, 12:19:10 PM »
I'm brand new to CNC and I am confused about what I might have wrong in my settings. I have the limit switches working well and when I press "Ref all home" the machine dutifully goes to a near corner and sets itself to zero for all 3 axis in the XYZ DROs respectively. However, when I then jog off the machine from that "zeroed" location my XYZ coordinates always read minus or negative values. I am working in mm so if I move off say 20mm from the zeroed machine coordinate "home" the X DRO will read -20. I assumed the problem must be that I simply needed to go to config>homing/limits and toggle the value in the reversed column but when I try that and then again hit the "ref all home" button the machine simply performs a 3-axis zero at the opposite corner of the machine, zeroes the DRO values and, again, any movement away from that position results in negative "minus" values in the X and Y DROs respectively.

I have no experience with CNC and assumed that this must be normal until now - that is, until I came to try and set the soft limit values which I am finding impossible because my Max value must always be LESS than my Min value. I assume I have something toggled or wired backwards - any help is appreciated. Thanks
Re: Newb - Machine Coordinate Confusion
« Reply #1 on: January 01, 2017, 12:28:00 PM »
Once you tick the reverse check you may need to hit the home negative check as well.
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.

Offline ger21

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Re: Newb - Machine Coordinate Confusion
« Reply #2 on: January 01, 2017, 04:10:16 PM »
Quote
until I came to try and set the soft limit values which I am finding impossible because my Max value must always be LESS than my Min value.

Even if the machine is backwards, softlimits will work, but Minimum must always be less than Maximum.

Before you reverse the axis, you need to make sure it's not already moving in the correct direction? WHen you jog off of the X axis switch, which direction are you moving?
What kind of machine is it? Moving table, or moving gantry?
Gerry

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http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Newb - Machine Coordinate Confusion
« Reply #3 on: January 01, 2017, 07:43:37 PM »
Thanks for the replies. I will try toggling the home negative tomorrow to see if that fixes it. It is a moving Gantry machine, I built a machine based off the Solsylva 18x24 aluminium framed router plans but I converted all to metric (being in the UK the parts were all metric) and I extended the bed size to approx 1400 x 900mm. I've never even seen a CNC before let alone operated one, but as a cabinetmaker it became evident I could really use one so I made one. It got complex because I did quite a few mods along the way - mechanically and electronically it all works very well - I am just trying to get my head around Mach3 so I can operate it more safely than merely working from zeroing from the workpiece. Therefore, being new to this, I am embarrassed to say that I have literally no idea which end is which or which direction of travel would be the correct one. The X axis is the long one, the one the gantry travels along (rack and pinion) and standing at the foot of the X axis (i.e. on the side of the gantry that houses the spindle) the machine seems to treat the Left as the bottom (correlates to the bottom of the mach3 screen preview), the right as the top and thus the far end as Left.  I have performed a few test cuts (went well) merely by zeroing to the material in the middle of the table and using a Z touch plate (hence how I know where Mach3 thinks the bottom and top of the machine is). My limit switches work well so I decided to test zeroing to the machine coordinates which it decided to do at the Top-Right of the table (Right end of the X in relation to the spindle). This set all axis to Zero in the machine coordinates but when I jogged the machine away from this zero point all axis went into negative numbers on the Mach3 DROs. That felt wrong for X and Y (though I did read it correct for Z which zeroes at the top of its travel) so I toggled to reverse direction for them both using the config>homing Limits screen. But, instead of fixing it, it simply changed the Zero position for the machine coordinates to the diagonal opposite corner of the machine (Bottom Left of the X axis according to Mach3). However, this didnt fix the problem with the negative numbers, because again when I moved the spindle away from the zero position the coordinates in the axis DRO in mach3 moved from zero to minus/negative values. I am curious as to what should be the top/bottom of the machine in relation to the spindle.

Offline ger21

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Re: Newb - Machine Coordinate Confusion
« Reply #4 on: January 02, 2017, 12:00:42 AM »
If you're standing at the foot of the machine, then the Y axis should be moving from left to right, correct?
If so, Y+ is to your left, and Y- to your right.
X+ is moving away from you, and X- towards you.
Generally, on a large machine like this, you stand on the side, where X+ is to the right, and Y+ moves away from you. This makes it much less confusing.
Now, where are you're home switches?
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Newb - Machine Coordinate Confusion
« Reply #5 on: January 02, 2017, 05:45:18 AM »
Thanks Gerry, it is good to finally know which way is up in the world CNC - and I am pleased to say I think I now have it all tickety-boo based on the instructions given. I'll be taking a marker pen to each corner so I dont get confused in future. Like I say, I have flipped the machine  a few times in trying to set machine coordinates by reversing directions in Mach3. So, based on your instructions. I am therefore assuming that x0,y0 should be at the front Right (which is where I started and more convenient for tool changes since the opposite corner is in a corner against a wall of the garage). Now, when I hit the "Ref all home" button on the Mach screen the spindle goes to the front/right of the machine (Z to the top), hits the limit switches, backs off about 1cm, zeroes and stops. Then, when I jog off from there the numbers now go into positive values so, for example, from X0,Y0 to x99, y99.

In addition, I have also now been able to set up soft limits which work well. I had assumed I would need to enter the "margin of error" distance from the limit switches but it appears Mach3 is doing this for me. Can this be adjusted?

In answer to where the limit switches are I have attached a photo of what the machine is now calling home (which I assume is correct )...

The machine stored in a small disused room at the back end of the garage (was an office in the 1970s) so its quite dingy and dark so I had to use a flash and cant really stand back far enough to get decent photos.  The first photo shows the machine in what it now thinks is home x0,y0,z0



Also some photos of where the limit switches are located:






I'm no engineer as you can see but it functions well and is by far the most complex thing I have ever made. Backlash is less than 0.10 of a mm.  Only downside of it is that you have to keep tightening bolts every so often and I dont trust those tiny limit switches as it is quite fast (maybe slightly too fast) and powerful (3.1nm but still quite a kick) and if there was a fault that gantry could fly off and really hurt you. I am already tempted to build a better one but I will run this for as long as I can so I can where improvements could be made.

Thankfully the soft limits now work - will those values persist when I power down or will I need to keep the PC running 24/7


(EDIT - forgot to post this)


By the way, I should mention, that I dont have separate home and limit switches - the same switches (2 on each axis) function as both limit and home switches, they are all wired NC in one loop so really operate as one 5v circuit with multiple switches. The Solsylva plans offer no instructions on electronics so its all cobbled together from a multitude of stuff I read and saw online.

« Last Edit: January 02, 2017, 05:57:27 AM by glynster »

Offline Davek0974

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Re: Newb - Machine Coordinate Confusion
« Reply #6 on: January 02, 2017, 07:54:46 AM »
Looks functional, nicely put together, well done on the build.

Re the axis flying off in the event of a switch fault - best solution is to fit hard stops, these may be plates, brackets, long bolts etc. Being a stepper drive system no harm will be done if the axis ploughs into a stop occasionally - mine has several times. Having the gantry fly off possibly with a running spindle and tool could be nasty as your instinct would be to try and catch it.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: Newb - Machine Coordinate Confusion
« Reply #7 on: January 02, 2017, 11:05:31 AM »
Hi, yeah that's a good point, I think on reflection I might try and grab it in the moment. I think I just about have enough space to affix some aluminium angle at both ends to clash with the V-bearings which should act as a dead stop. That sounds like a nice little project  8)