Thread: Find 0,0 after lost steps

Don't you use a home position?

Originally Posted by echnidna

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.

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

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?

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.

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

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.
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.

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

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

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 ) , 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.

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

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

Thanks Greg

Br

Valther

Originally Posted by Greolt

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.