Thread: Find 0,0 after lost steps

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

Originally Posted by Greolt

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.

Hi Russell,
Welcome to the Ubeaut forum.
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.

Originally Posted by epineh

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.

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 NOThesitate to transfer any suppliers with interests if I will find any.

Sorry Willylnbris for the mistake

Br

Valther

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 ? "

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.

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.

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

Cheers.

Russell.

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.

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

Russell.

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

Originally Posted by WillyInBris

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?

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.