nozzle height from bed

hello all,
I have now got my machine - a prusa explorer from 3dstuffmaker people.
i have brought the nozzle down (with little -.1 z steps) to the bed and checked with paper that it is .2 all around the place. So thats good.
Then i slide the z limit switch up to the z cradle (ie. to set z zero position or z home) and tighted with screwdriver.
But then when i do a Z home (from software - pointerface) it reverse up a bit (it reverse a little when it hits any of the limits).
So now i'm 3 or 4mm above the bed not .2 (see picture - has reversed up a couple of mm from the very bottom).
I need to be .2 to print don't I??
Can readjust the limiter again but would be guessing a bit.
Thought I could -Z.1 down again keeping track of how many mm it is and then add this as a G1 statment before printing. Does that
sound right or is there a simpler way.
Thanks in advance for any help you can provide.
Regards,
Roger.

umm have i placed this in the wrong forum
roger

You need your home as close above the surface as possible without scratching it anywhere. Firmware should not allow positions deeper then z-endstop, so no you can't go to -1 but have to move the endstop so z-home is just above the bed. If your bed is already leveled you can do the following:

1. Move endstop down so you can as low as needed with tiny steps
2. Use the M119 command to question the endstop status. Change position of endstop until it starts triggering the endstop. Iterate until satisfied.
3. Home z to test if you succeeded.

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thanks repetier
i end up manually moving the end stop untill i got it pretty close then adjusted the bed

can u please point me in the direction of a post or doc that steps thru getting the print going
i have got the nozzle moving around and .2 from the bed
have got some plastic to flow with a temp of 210 and rate of 30mm/min
not sure if this is normal
and would like to know how to set up all the other variable to get it going - sure this has been asked many times
regards,
roger

It's best to use a sheet of paper as a feeler gauge between the nozzle and the bed surface. Most paper are around 0.1 mm thick. After homing the z, pull the paper. If it won't move or there's too much resistance, then you're too close and you need to raise the endstop a bit. If the paper moves without any resistance, it's obviously too far and you need to lower the endstop. When you can move the paper with a slight resistance, you're good to go. You can home a couple of times after that to make sure.

Note that you need to do this with your bed heated to operating temperature, if you are heating your bed, and your nozzle at temperature for about 5 minutes to allow for components to expand.

Roger, it sounds like a problem with the software.

Usually a software will run the axis to the home, then back off a couple of mm, then return to home again at a much lower speed. This ensures that the axis is just at home, and has not overshot due to the inertia of the carriage (Remember that while limit switches prevent the motor from turning in the direction of the switch, they cannot instantly stop movement!). From what you've explained, the software is "forgetting" to tell the machine to return the home the second time.

I would try deleting and reinstalling Pronterface.

Failing that, you can always adjust the Z-offset feature that is in Slic3r, located under Printer Settings -> General. That will automatically offset your generated Gcode however much you wish. This would functionally do the same thing as manually adding your G1 statement to the beginning of every Gcode. Make sure you specify that the Z-offset you want is negative.

Hope this helps!

Quote

I would try deleting and reinstalling Pronterface.

This won't fix the problem. Homing is performed at the firmware level, and not by Pronterface. Pronterface just sends a G-code,"G28 Z0" to home just the z axis for instance, and the firmware executes the command.

Also, repetier already pointed out that you can't go to negative offset (below the endstop) with most firmware unless you modify the firmware to ignore the endstop which is dangerous as it can lead to the nozzle crashing on the bed.

rogerw Wrote:
-------------------------------------------------------
> can u please point me in the direction of a post
> or doc that steps thru getting the print going

The next crucial step is proper calibration.
RichRap always writes great articles and this one is one of his best. There is another version of it at his richrap.com site.
Also have a read of nophead's blog which is generally regarded to be one of the most authoritative around.

thanks evryone lots of info here to digest - need to do some work around the house today or my wife will kill me - is quite adictive this little printer.
at some point during my blurry night the z nozzle all changed and scrapped thru my
yellow tape so need to get some more. (or print around the hole).
i am swapping from ponterface to repitier at the moment to figure out which i prefer so must have buggered something up.
i will try to start again and see exactly what is happen for other beginners - think it is important.

on that note is there any way for me to set up a 'ships log' of all the (many) problems i encounter - preferrable in this forum somehow - so that other new people can learn (eg.. i was supplied with a 2.5m usb cable and gave me error until i used a 1.4m usb cable). would like to do a step by step thing.
i would refer the ships log back to where i got help like this post.

perhaps this all ready exists or maybe i need to set up a seprate web page somewhere - does any one have thought on this - if it needs to be external from this forum then does any one know a free place to put it.

i have met a few people who have just given up because they could not get things ptrinting - would like to help them out if possible

hey look how confident my daughter is of me getting this going (not)

brnrd Wrote:
-------------------------------------------------------
> Also, repetier already pointed out that you can't
> go to negative offset (below the endstop) with
> most firmware unless you modify the firmware to
> ignore the endstop which is dangerous as it can
> lead to the nozzle crashing on the bed.


I am well aware of that. Since Roger said that his nozzle is hitting the endstop and then backing off, however, there is no reason why he could not be able to push the z back down to it's limit with the offset. He doesn't need to go below his endstop, he needs to move to his endstop.

If homing occurs at a firmware level, then he should reinstall his firmware. Since it occurs on all axes, it sounds more like a problem with the programming than with the hardware.

I don't know of a way of setting up a log barring opening up a text file and just making notes of what you've done and tried.

brnrd Wrote:
-------------------------------------------------------
> It's best to use a sheet of paper as a feeler
> gauge between the nozzle and the bed surface. Most
> paper are around 0.1 mm thick. After homing the z,
> pull the paper. If it won't move or there's too
> much resistance, then you're too close and you
> need to raise the endstop a bit. If the paper
> moves without any resistance, it's obviously too
> far and you need to lower the endstop. When you
> can move the paper with a slight resistance,
> you're good to go. You can home a couple of times
> after that to make sure.
>
> Note that you need to do this with your bed heated
> to operating temperature, if you are heating your
> bed, and your nozzle at temperature for about 5
> minutes to allow for components to expand.

He hit it in the head

That is exactly the method I use.

Quote

If homing occurs at a firmware level, then he should reinstall his firmware. Since it occurs on all axes, it sounds more like a problem with the programming than with the hardware.

His method of setting the bed clearance is wrong. He just need to do it correctly. The method I described is what I learned from this forum and how a lot of people do it.

Specifically, the right way is to move the endstop, home, measure the clearance, adjust and repeat. The way he's doing it which is to jog the nozzle down to the right clearance and then move the endstop up to meet it won't work. I'm not sure if using the M119 to check the status of the endstop would produce the same result as the firmware when it homes the z axis.

Edited 2 time(s). Last edit at 11/04/2012 01:07AM by brnrd.

hello all - thanks everybody for your input.

was ineterested in pomeroyB post that the nozzle will hit the endstop, rewind and then wind back again.

i watched closely and it is doing this (so think the poterface software is ok).

my confusion (which has lead all of u astray i'm afraid) is in my expression 'it hit the endstop'.

I thought it phyically 'hit' the endstop (ie. that it was a mechanically or physcial thing).

But it 'stops' the 3 or 4 mm before the physical end ie. the gap in the photo IS the end stop amount.

Sorry for all that gents(?) i don't know much about electronics so it is obviously some electrical or magnetic thing that stops
it at the 3 or 4 mm above the physical bottom.

(i moved the stopper hard up against the silver pin as I thought THAT was z0 ie. the physical bottom).

SO.... i will try to set up the gap as described above. It seemed weird to me (without any proper instructions) that i would have to move the stopper (ie. unscrew, move, tighten) when we are talking fractions of mms.

Also thanks for the links, I also know about the Wiki calibration thing so will continue on.
Thanks again,
Roger,
PS. So how does the stopper work??

In your photo it looks like an optical sensor - an infrared LED in one side and a detector in the other, with an opaque shutter such as a piece of metal that moves down between the two.

thanks richgain, makes perfect sense.(is so small i can't actually see it)

this thing [www.thingiverse.com] looks like that gadget to help level the bed
(if only i could print one).
seriously thought I have levelled it now and was not as hard as i though (now that i actually had the confidence as i knew that thats what i was suppose to do).
left the screw in the endstop just tight/loose enough that i could twirl the end stop from side to side and gently up/down. then test with paper,
repeat, and then finally tighten up properly.

thanks again everybody -

regards,
roger

Hey Roger,

You have got it. I have just finished the assembly of my Prusa (3DStuffmaker) and am in the process of making my first prints.

I too struggled in the begining but think I have now understood it. I tighten the end stop screws, so that I can move them with a bit of friction. Slowly and steadily I move it by a faction and test the home button till I get 0.2mm (folded paper) height.

While it may be dumb, I want to let you know what I stuffed up: my home position (see my post on Home position)

Some more tips that I am following for adjustment of the printer:

1. Check the print bed level using a level gauge - Adjust the screws
2. If Print bed is level and you are experiencing an uneven gap between nozzle and print bed it may be due to problem in leveling X axis - check the level on the X axis both lateral and medial - see the photos - you can adjust any unevenness by rotating on Z axis motor and/or by adjusting the frame bolts on top
3. As you have bought the printer from 3Dstuffmaker (As I did), please apply some form of lubrication on Z threaded rods- very soon you will experience a jam on one of them and they will out of position very soon. Came across at very early stages and applied some grease on the threaded rods.


Let us all know how you go.

Dinesh

I might be weird, but i like to do things the other way around.
My Z axis limit switch is at the top (max), not bottom (min).

Here's how my Z calibration procedure goes:
1) i home Z to maximum
2) i do G1 Z10 to get the head a cm or so above the bed
3) i jog down until the nozzle touches the bed (easy to see thanks to glass surface and LED lighting on the gantry)
4) i jog up by 0.1
5) i do G92 Z0

With some forethought, it's much more flexible and faster than having the limit switch at the bottom and adjusting the stop:
- G1 Z10 and G92 Z0 are assigned to custom buttons in Pronterface
- it's easier to do a few jogs from Pronterface than fiddle with a stop all the time
- after you nail it down and zero in, the initial move can be much closer than Z10, so you only need a jog or two in 0.1 increments before a print

Downside:
- if you don't pay attention, you can crash the head (not that dramatic if your bed has springs and the Z steppers current is limited so they stall)

That seems to be a lot of manual prep before each print. There's really no need to fiddle with the stop all the time. Once you adjust you z endstop at z=0, you don't need to keep doing it again. I print without having to readjust the z endstop unless something breaks or if I change something in the printer that affects the bed clearance.

If there is no need to fiddle with the stop all the time, there is no need to do all the steps i've outlined either.
If the height is always the same, you can do the same G1 Zxx command every time, followed by G92 Z0.
Which means you can just add it to the startup G code.

Difference being that, if you need to adjust it for whatever reason, you change one number.

Compared to fiddling with the endstop physically.
So there really is no reason to do it the way most people do it (which is to have a minimum end stop).

The problem with the endstop at max is that there's a large distance between your endstop position and the bed surface. If your endstop is located at 100 mm, even a change of 0.01 % in this distance would have a large effect on your bed clearance. So, it's less likely that your G1 Zxx command would be reproducible.

If you're getting variations of 0.01% on regular basis, *while doing the calibration*, then you're likely to have more problems with your printer (or its design) than the endstop at max

The layer thicknesses in your prints will be off kilter, for one.
I won't even start on things like binding (if you're getting such variations during a print, it's more than likely they won't be symmetric) or wobble.

hello everyone,

orcinus - thanks for your post
am a bit scared to be moving things around at the moment and not really up on my g codes - perhaps will do this at a later stage
certainly like the idea of not moving the z stop manually.
i have that many lumps and bumps in my kaptan tape now that i am hooking my nozzle on it frequenlty which seems to bugger up all
the leveling so i have to start again.
anyway am printing the reprap calibration small cube (in one corner of the plate that i have stuffed up) and will post some questions.

3eality:
yes we have spoken before - think u realise that now
yes the z axis does make a ugly noise every once and a while so will put some sewing machine oil on or something thanks.
in regards to your x axis being wrong - mine looked completely in reverse to the instruction and would have put it on in reverse if I could have figured out how to do it !!!
have pretty much given up on the support from stuffmakers and am working thru reprap calibration with the help of all of the above.

roger.

Quote

If you're getting variations of 0.01% on regular basis, *while doing the calibration*, then you're likely to have more problems with your printer (or its design) than the endstop at max

I meant anytime after the calibration. Also, I meant 0.1% which is 0.1 mm for a 100 mm distance. Anyway, since the endstop is attached to the smooth rod, I agree that it doesn't make much difference if it's on top or the bottom. The linear expansion coefficient of steel is the only factor that I can think off that would affect clearance more with a top endstop than with a bottom endstop and this is insignificant. But there are two main disadvantages of having the endstop at the top of z. As you pointed out, if you're not careful, your nozzle will crash into the nozzle which can be a a minor or major disaster depending on how the x-carriage and bed are fixed. The other is that it takes longer to move the carriage from the endstop position to the bottom of the bed before starting a print. There doesn't seem to be any advantages to this method while requiring more changes to slic3r and the way the host (pronterface) is used.

I actually do a combination of both methods. My endstop is on the bottom, but it is 2mm or so above the bed. I have a homing command, and then a g92 z1.7 command in my startup script. The switch easily has 3 or 4 mm between actuation and the point where it actually gets damaged.
That way i can swap beds and only have to change the gcode. I could see this working much better with optos, in fact.