Solved - z-axis not getting to end stop when homing

Hi guys,

Im building a prusa 2 from scratch, no kit, just by reading the guides on reprap.org and the bill of materials.
Sourced parts from all over at a fair price and cheaper than mostof the kits. Everything has gone fairly well.
Im using Marlin with ramps 1.4.
Ive got everything up and running with motors moving, bed and hot end heating.
Lcd display and controls are responding and controlled from my laptop.
Everything seems ready to go for me to go through the fine tuning.

But im stuck on getting the z axis to home to the z end stop.
X and y no problem after i made sure the motors were going in the right direction and id made the changes in the firmware config for normaly closed mechanical switches. I can repeat this as many times a i want and its reliable.

But if i try to home the z axis it counts down to zero and stops.
Z axis will move down when i tell it but it wont go down far enough to hit the end stop.
I can manually wind it down by hand and that position becomes the zero point and it wont go past it to the end stop.

I assume its got something stopping it going below what it thinks is home set in the config but i cant see anything.
Ive searched and read many, many posts and guides but cant find any similar problems to give me a clue.

Have i missed something really simple?

Thanks

Gordon

Edited 1 time(s). Last edit at 08/10/2014 04:58PM by gordonendersby.

Had a go again today with clear head. Long day yesterday.

I tried setting min_software_enstops = false
All this does is allow me to go past the end stop while i command the axis to move either through pronteface or the lcd menue.
Homeing the z axis will still not let the z-axis reach the z end stop.

Next tried reversing the endstop so that it would look for a stop at the top of travel.
This time homeing the z-axis it wouldnt move at all.

Ive attached my configuration.h

If anyones got any pointers id be grateful.

Thanks
Gordon

Ok, tried some more.

Got hold of the latest marlin from github.
In case there wad something wrong with the copy i got wih my ramps stuff.
Set it up and loaded it.
No change.

Still cant get the z axis to go down to the z end stop.
Pretty much stumped now.

Any help?

Gordon

Ive got a prusa i2 too. some things ive noticed differnt between your config file and mine:

I have endstop inverting set to false
I have commented out #define DISABLE_MAX_ENDSTOPS.
Also my steps per unit are differnt:
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,200.0*16/1.25,730}

have you measured how far Z moves when commanded?

Also have you tested the Z endstop? (Homing Z and then triggering the switch manually.)

Edited 3 time(s). Last edit at 08/10/2014 03:01PM by sprocket1597.

End Stops: Magnetic Hall Sensor, Auto level probe. Would an optical sensor be an improvement? [reprap.org]
Filament detection using an end stop. [forums.reprap.org]
some gotchas.. the steppers will not move in a negative direction if it thinks the min endstop for that axis is triggered. Which is why I like to get the endstops working first thing. Be very careful not to short the + pin to the - pin on the endstop connector. Shorting this kills most boards. [forums.reprap.org]
if you only have 3 endstops, you need to disable the max endstops, //#define DISABLE_MAX_ENDSTOPS
End Stop: Start with the M119 command to check your endstop wiring. If the switches are reading triggered when the carriages are not touching them, the printer will think that it is already homed and not move the carriages [forums.reprap.org]
Connecting end stop [reprap.org]
Wiring Diagram: Sometimes the parallel port's limit switch terminal will be signaled by the noise in the steppers’ wires. [solsylva.com]
Wiring limits and home switches [www.pminmo.com]
Unshielded twisted pair: End stop wiring [www.reprap.org]

Thanks for the comments.

Sprocket1597,
I wonder if the motor is turning and reaching the maximum number of steps and stopping before it gets to the switch?
I havnt yet done any of the fine tuning to set the distance to steps.
Thsts my next job after i get home set for all axis.
Ill look into that.

Ive tested all end stops and they are all working.
Also ive twisted the end stop wires, but also they arnt running with the motor wires.
No interferance that i can see.
I can trigger the stop manually and it stops the z-axis travel.

A2,
End stops were set up tested and working before i moved a motor.
X and y end stops are spot on and reached on the x and y axis.
Doesnt matter what type of sensor im using for the end stop. Its not getting anywhere near it.
Ive been using M119 shows end stops are working correctly.
They arnt getting triggered by noise, as above wires are twisted unshielded.
Already disabled max endstops. See config file attached above.

So my end stops work, i can lower the z axis but only to z=0. But when i give the command to home the z-axis it will not get low enough to reach the z end stop and set the z home on the end stop.

Gordon

Edited 1 time(s). Last edit at 08/10/2014 03:28PM by gordonendersby.

The travel is set by Z_MAX_LENGTH. So if the steps per mm are wrong then it might no go the distance.

your current Z steps per mm are "200.0*8/3" or 533.3, mine is 2560.

can you manually position it just above the bed (10mm) and then home Z?

Edited 3 time(s). Last edit at 08/10/2014 04:06PM by sprocket1597.

I can wind it down by hand and that is then z=0 when i turn the machine on.
So yes i can manually set the home position.

Just tried setting the position of the z axis just above z=0. Z=8.
With the z axis just above the switch.
Then gave the home command via the lcd.
So it should have moved as far a before down the z axis.
But it still stopped when z=0 and didnt reach the switch.
So doesnt look like steps per mm isnt the problem after all.
I will need to set this up soon but its not causing this problem.

As i see it. The home command should ignore whatever the current co-ordinates are and travel to the end stop switch and set that as zero.
But my printer when homing the z axis has a software stop that triggers when it thinks its reached home at z=0. Not when it reaches the switch.

Getting a bit frustrated here.
Spent about 6 hours on this z axis problem so far.

Gordon

What about homing it over usb?

And yes the homing comand will make it go and find the new 0. Im wondering if the lcd is just sending it to Z0 instead of actually homing.

Edited 1 time(s). Last edit at 08/10/2014 04:26PM by sprocket1597.

Ive only gone and sorted it!.
Thanks for all the help it gave me the inspiration and clues to solve it.

As expexcted something silly, but non intuitive.

Id set invert_z-dir to true as my z was going up rather than down.
Even though the comments said for mendel set to false.
What i should have done is turn the plugs around on the ramps board to compensate.

But because all my other pins were the right way round and doing what they should do.
I assumed i needed to invert the z access.
And the logic in the firmware would compensate. But it didnt.

Bad assumption and now its working and homing the z-axis.

So in summary.
For mendel do not invert z axis but turn the plugs round if your z-access is going in the wrong direction.
Hopefully this will help anyone who makes the same mistake.

Thanks again.
Gordon

Glad you got it sorted!

Funny thing is Ive also got invert Z dir. probably for the same reason, to have all the plugs round the same way.

Looks prettier like that doesnt it.
I didnt want to swap it round as it just looked wrong having one set reversed.

Just before i turned everything off i tried it again for sanity via the lcd control.
Guess what, it went up instead of down when i selected home.
But id being fiddling with the plugs again so it may be a loose connection in the plug.
I dont like those pin connections they should be proper locking plugs and sockets.
Id tinned the wires and properly crimped them.
Im going to put a spot of hot glue on them to hold them secure when ive got it right.

Was working from pronteface, ill look into that tomorrow.
But at least i have some homing working.

Gordon.

Hello Geeks,

I am using Marlin 1.1.0 RC8 and I have a problem with homing my Z axis. X and Y homing works fine but when I give Home Z signal, the Z axis moves up and down in 10 mm range and when i press limit switch manually, it stops.

I have separated and twisted cables of limit switch from Z Motor cables. Still the problem persist. Please guide.

when M119 is given, it shows Z as Open initially and then triggered when i press the lever manually.

I guess this is a problem of noise but not able to find out from where it is getting generated.

can it be a problem with marlin RC8?