Find 0,0 after lost steps

[rodm]

I ran a job last night and broke the cutter in aluminum and lost steps at the same time. As this was well into the job and I also didn't want to waste good material so I spent half an hour referencing X and Y to 0,0. Luckily the job had a straight cut parallel to both X and Y axes so I was able to zero the job back in. I then moved to various points that had already been cut and tested the cutter in a slot to make sure it was centred in the cut.

This was a pain and I am sure there is a method of establishing a 0,0 point easier so I am looking for suggestions. This is a common problem so would like to hear how others are doing it. Laser crosshairs and cameras would not have been any good because the cutter had already removed the 0,0 point on the job.
Thinking of something like homing the axes and then moving to the material and recording the material 0,0 reference from home position. A macro could be written to record the values on the screen.

[echnidna]

Don't you use a home position?

[Ch4iS]

Don't you use a home position?


was about to say this, if your workpiece didnt move I think home switches would work fine, easily and quickly find 0,0 again.

Then again Ive never used them so I am unsure if they would work or not.

[Greolt]

This is where the theoretical value of homing switches come into play.

I say theoretical because unless they are pretty accurate, they are not going to help much.

And of course unless you "home" before starting the job they will not help at all. I get lazy and rarely home the machine. :)

If you have those bases covered then when the incident has happened,

DON'T ZERO THE DROs, this will alter the G54 offset, you want that to stay intact.

Do a "Ref All" and then '"Goto Zero" This will return to the coordinates correct before the incident.

If you are like me and have no home switch on the Z axis then you still need to reset the Z zero height. Usually not a big deal.

After doing the manual reset as you did in aluminium, checking the cutter in the cut at different points, you will have got very close to spot on. Probably within a couple of thou.

It will need good home switches to achieve that sort of accuracy. Although even average ones would have made your process a bit quicker.

Greg

[rodm]

Yeah this is what I thought. The camera or laser cannot guarantee perfect accuracy and it looks like homing won't either. I did get it very close as you cannot see or feel a ridge between the two areas in the cut.

Apart from the inaccuracy of home switches there is the problem that your material is never set exactly to machine 0,0.

Was just thinking of a phsyical stop being put on the axes once you are at material 0,0,. It would have to be set and then flipped out of the way to account for outside cuts or negative moves. I might be going overboard as well because it happens only rarely and probably doesn't warrant a lot of work. Ideas?

[chrisb691]

What if you were to have a known reference point, at the other end of the bed. Say you machine a 1/4"(plus a smidgeon) hole at X0 Y450. Then you could put a 1/4" rod in your collet (not tightened), and jog until you can slide the rod into the hole easily. You could then set your DROs to 0 and 450, and the get to home from there. Z0 should be able to be reset from the work.

[simso]

Hey rod, regarding using the home position all the time, it will work, but will require some work on your behalf.

Firstly you would have to identify a spot on your cutting board that is "home" for all three axis's. Identify this as g53 code. home g53 x0,y0,z0 or whatever you want home to be

Then at the start of every job you would need to clock the side of the job and record this as your g54, then simply call up g54 as the workshift at the start of the job

Alternatively you could do what I do these days on big jobs,

I pick a section that will be scrap in the job, and the first G code is popping the cutter down at a known reference point usually for me its x10,y10,z1, then if something goes wrong I simply move the cutter back into its hole type 10 10 and 1 into xyz offsets and then continue the program

[rodm]

Chris,
This will only effectively home the machine to a know co-ordinate on the table and you would need to have a reference from there to the moounted job. I like the pin idea and am thinking spring loaded pin so it drags then drops in the hole.

Steve,
I can see you have been studying GCode for that machine centre. :2tsup:
Yeah I like your second idea (KISS is good) as it references the axes to the material. It needs to be quick and easy otherwise we slip back into slack mode and just start cutting the job.

Greg,
If I do a "run from here" will it re-establish the G54 in which case I would be able to zero or set other values into the DRO. In these instances I always go back in my gcode to a point before where the breakage happened.

[simso]

Hey rod, yeh here at home "kissing" the job in a scrap area works fine. At work there is no such thing as job 0,0,0, there all an offset from known home, example the corner of the job we identify as 0,0,0 at work is something like 347,600,-96, dependant on where you have it clamped down, and that figure changes subject to what tool is loaded up

[Greolt]

Rod

It all gets a bit hard to explain.

If you have never had home switches then you will never have had to think about machine coordinates.

Machine coordinates are always the distance from home switches and never change except when "referencing"

Work coordinates are what we always work in. Whenever you zero an axis you are changing the amount that the work coordinates are offset from the machine coordinates.

It would be advisable to watch the Artsoft video called "Coordinate Systems"

Don't get bogged down in G53 G54 G55 G56 etc.

On our routers we just use Machine coordinates (G53) and Work coordinates (G54)

Worry about the rest when you start mass production and have several fixed job fixtures on your table.

Regarding home switches, the ones I use are very accurate and consistently return exactly to the same spot according to my dial indicator. Less than a thou.

A lot use cheap micro switches. If you use proper limit switches they can be very good and I believe better than any spring loaded pin system. :)

Greg

[rodm]

Thanks Greg,
With my new machine I am going to go with quality rather than economy so it will have smoothstepper, digispeed (got those from Peter :2tsup:) , Geckos, linear supply and bob. I have to fit homing switches because I will have twin ballscrews on X. I have not got any yet so what do you recommend - photoelectric or proximity. Obviously I struggle with the electronics but I am like a dog at a bone and keep trying until it works. If you could PM me any retailers or suggestions it would be good.

I know what you are saying about the hole and pin method as it took some very fine adjustment to get my machine alligned last night. I ran the spindle and moved the axes manually until it just rubbed on the cut line. All up it probably took half an hour and lots of reference points to get it spot on.

Homing and then using an offset is the right way to do it as you point out.

Had a run on jobs lately and had a ball tonight doing three jobs in acrylic. Some bending with the heat gun was invloved so that was fun also - never done that before. Can't show any of these as they have people's names on them. After cutting aluminum for four days it makes a welcome change to cut acrylic at 2m/min and very little cutter noise. I've been Dumster diving for acrylic and have heaps of it now.

[elevalther]

G´day folks

I ´m still new here on the wwf, but I would like if any know where it is possible to get information to build your own 3d cnc machine

Where to get the step motors
where to get the motor driver/controller or drawings + component list
where to get the soft ware if it dosn´t follow with the motor driver/controller
Which cad
and at the end how to use it


Br

Valther

[Greolt]

Valther

I suggest you go to CNCzone and do a lot of reading. Look at pictures too.

They even have a Spanish section.

http://www.cnczone.com/forums/

Greg

[elevalther]

Thanks Greg

Br

Valther

[WillyInBris]

Rod

A lot use cheap micro switches. If you use proper limit switches they can be very good and I believe better than any spring loaded pin system. :)

Greg

I am just using the cheap switches and they work ok I would rather get some decent switches got any links Greg?

I just home and run my job off that if something gos South I can home again and its spot on when I rerun my job.

[Greolt]

I am just using the cheap switches and they work ok I would rather get some decent switches got any links Greg?

I just home and run my job off that if something gos South I can home again and its spot on when I rerun my job.

I have often heard reports that micro switches do not give consistent accurate homing.

However if you are getting repeatability that you are happy with then stay with them. :)

Search this ebay number for what I am using, 360102764246

This seller has a range of limits that seem reasonably priced.

What I have done is mount the switch on the moving axis and activate it with a ramp at each end of travel. Less switches.

Greg

[elevalther]

Dear WillyInBris

Thanks a lot for your information for the CNC suppliers, I have only had short time to browse though on a few of the links.

At the moment I´m totally new to the subject, I would hesitate to transfer any suppliers with interests if I will find any.

Br

Valther

[epineh]

I have often heard reports that micro switches do not give consistent accurate homing.


Hi Greg, I have heard both for and against, but as it turns out I have them on my machine but have not tried them for accuracy, I might give them a go and report. I think it would depend a lot on how they are mounted and make contact, some limits are mounted so the moving part of the machine kinda slides across the face while others push the lever directly, which is how mine are. The only problem with mine is if the axis isn't stopped in time it kinda rams into the limit and bends the lever and other fun things (ask me how I know :) )

I had lots of fun while setting up my machine for homing, my setup detects the limit, moves off it then moves slowly again until the limit is tripped then rapids 5mm (or whatever you set it) off the limit. If the value is set in the wrong direction it kinda goes another 5mm into the limit switch, not the best result...at least they are cheap, lol

Cheers.

Russell.

[rodm]

Hi Russell,
Welcome to the Ubeaut forum. :2tsup:
There are a few of the old Zoners over here. We are slowly getting more threads and attracting more interested in CNC. Going by the views on the threads there are a lot lurking which means they are interested so hopefully we will become a good reference in time.
Anyway it is good you have found us and I know you are a wealth of information on that mumbo jumbo electronics stuff and home fabricated machines.

Anyway back on topic I ordered some of the limit switches Greg referred to and am still deciding on front on or side trigger. Front on trigger is easier to adjust than side on but as you say more prone to crushing. I have to work out a way to get adjustment on the side on fixing.

[WillyInBris]

The only problem with mine is if the axis isn't stopped in time it kinda rams into the limit and bends the lever and other fun things (ask me how I know :) )



lol Yep been and done that as well I broke a couple of switches as well by the time the switches has sent the instruction to stop its gone too blody far so I basically just use them for homing and find the accureacy is spot on and that keeps me well.

[elevalther]

Dear WillyInBris

Thanks a lot for your information for the CNC suppliers, I have only had short time to browse though on a few of the links.

At the moment I´m totally new to the subject, I would :2tsup:NOT:2tsup:hesitate to transfer any suppliers with interests if I will find any.

Sorry Willylnbris for the mistake

Br

Valther

[epineh]

Hey Rod, I was trudging through my subscribed threads and thought I would add to this one, my friend who does a lot of work on large VMC's for a living uses a method that sounds really good, I will use it on my next build and see how it goes.

The idea is to have an "AND" gate using your homing switch with the index pulse on your servo encoder, the idea is that both have to be logic on, 1 or 0 whatever your setup is for the machine to be homed, makes sense as unless the homing switch is on for a huge amount of time the home position will only be in one spot, and be really accurate.

I know what you are thinking, "but what if I am using inferior steppers and not servo's ? " :D

You could still put encoders on your steppers, though it would be a little overkill, I guess if there is a need...

I have changed my setup methods from when I first started, I was using DeskCNC and as Greg mentioned I would just move to a position and zero what I wanted or enter a value with no machine coordinates whatsoever. This worked fine and I never had a problem.

These days I use EMC and it is setup similar to the bigger machines as in you really need to home the machine first before you start doing anything. At first I hated this and tried to get away without doing it, but once I started (and actually installed some limit/home switches) it is pretty good. My red machine really isn't good enough to bother doing the encoder/homing switch thing and the good ol micro switches work well enough for my needs, but as I intend to try doing some lithoplanes with the new machine it would be nice to be able to pick up on a job that was 10 hours into a 12 hour job that got interrupted by power failure or whatever.

I will do some tests once I get it working and let you know the results...though it may take a little while, the new machine is just a couple of basic parts at the moment...but they are shiny :)

Cheers.

Russell.

[rodm]

I work with positioning the job then re-setting the axes to zero. It does make sense with homing and using an offset. I can see the merit in what you are saying and will give it a go.

[epineh]

Hi Rod, I guess it is really the same thing but done differently, I don't use Mach so I don't know how it would look for you, but with EMC once your machine is homed it draws a red box, the dimensions of your machine's cutting area. The cool thing about it is that if a job you are doing will make the machine try go out of its travel EMC will let you know as soon as you load the G-Code.

Also it will stop jogging if you reach the end of travel, and I have it setup so this is about 5 or 10mm before the limit/homing switch. This is really not usable for Z as different cutters will almost always hit the table before it runs out of travel, though it is handy for the top clearence over a job.

I can only speak about what I use and with EMC all I do is jog to where I want my 0,0 and press "touch off" , this uses a fixture offset (default G54) and off I go, but the advantage is that EMC knows the machine boundary's and won't let me try run off the end, I do need all the help I can get :) I know Mach would also do all the above as well.

Any Hoo, the main thing I wanted to mention was the encoder index pulse/homing switch idea, I class myself as a beginner as far as running these things go and don't want to give the impression of trying to tell anybody what to do, after all I do tend to blow things up every now and then :D

Cheers.

Russell.

[rodm]

Hi Russell,
Yeah Mach3 has all the soft limits etc. Glad you revived this thread as I will do something about it soon.
I am busy catching up on a few jobs and then enclosing my carport so I can get Morphy out of the weather. The rails have surface rust on them so it is important to house the machine before some permanent damage is done. Too many jobs and not enough hours in the day lately.

[epineh]

Yeah always too many jobs...I don't even have power to my shed yet. :) Well not permanently anyway.

Russell.

[Frankmc]

Hi Guys

Way back.... when i was wiring + commissioning cnc laser cutting machines we had to setup the home positions..Very similar to what Russell has described.....When the axis was homing and it hit the microswitch it would then move off in the opposite direction until it detected the index pulse of the encoder...this distance was shown on the screen...I cant recall the exact figures but it was related to the lead screw pitch...if this distance was less than a certain percentange you had to add an offset (i think it was the lead screw pitchadded ) to the homing position and this was now the home position....Hope that makes some sense...I think the idea was it might be possible to miss the index pulse if homing switch was triggered closely followed by the index pulse....

HTH
Frank

[niall]

I am just using the cheap switches and they work ok I would rather get some decent switches got any links Greg?

I just home and run my job off that if something gos South I can home again and its spot on when I rerun my job.

When i worked for a company making cnc machines there was a home postion
set up in the software ,so at any time you broke a cutting tool or just
wanted to start a new job the first thing you did was send the machine to home...0.0.0
postion.. Why arnt you guys starting at a known postion?

[John H]

It would have to be a hardware solution (switches) to find home after you lost steps. If it is pure software then the software looses where it is when the steps are lost.