prints sliding on my bed?

Every one of my prints has been sliding mid print, and it's starting to bother me. The problem i presume is just the part curling, which everybody has, but i cannot for the life of me find any documentation on this problem either on the wiki or these forums. What basically happens is the printer will sometimes finish maybe 5 layers, or sometimes not even one, a few times it almost finished the part before slipping, and then it detaches from my print bed and slides around with my extruder. This happens both when my nozzle is within .02 inches of the bed, and when it's ridiculously high up (to the point that i can almost fit my pinky finger between Z0 and the bed)

when it slips early on the problem is very clearly curling, the whole part will be bent by 10-15 degrees sometimes, however what bothers me is a simple test cube i was printing a few days ago was maybe 4 layers from completion when out of the blue it slid.

I'm using repsnapper to control my mendel, and the only settings i've touched are temperature, extrusion speed, and a tiny bit of anti-ooze retraction.

has anybody else encountered this problem? and what's the solution short of setting up a heated bed? because while i do plan on that i can't for a while yet.

What kind of plastic are you using? What surface are you trying to print onto?

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I'm building it with Baling Wire

Hi there,

let me try:

I have had this problem for a short period of time.

Could it be because your layer thickness is set too small, and your flow rate / feed rate combination is too high? So there's too much plastic coming up but your extruder isn't rising the height it should be... so all that extra plastic is snagging on your extruder and pulling itself away from the print surface?

Tian Chang

Edited 1 time(s). Last edit at 02/03/2011 09:00AM by TianChang.

I should have elaborated more, I'm printing onto an aluminum bed which i've covered in kapton tape.

It's not heated in any way, and i'm using 4043D PLA.

I'll try messing with my feed rates and layer thickness some.

out of curiousity, what does changing the layer thickness modify in repsnapper? I mean the distance between your layers is defined largely by the size of your Z step isn't it, so the software can't have much control over that?

does it control the g-code generation, so that it makes the correct number of layers? if so my having the thickness set too low could definitely explain why my only successful test cube was taller than it should have been (IE, not a cube)

PLA and ABS only stick to Kapton when it is on a heated bed. For PLA on a cold bed you want 3M blue painter's tape

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[www.hydraraptor.blogspot.com]

Parker  Wrote:
> out of curiousity, what does changing the layer
> thickness modify in repsnapper? I mean the
> distance between your layers is defined largely by
> the size of your Z step isn't it, so the software
> can't have much control over that?
>
> does it control the g-code generation, so that it
> makes the correct number of layers? if so my
> having the thickness set too low could definitely
> explain why my only successful test cube was
> taller than it should have been (IE, not a cube)

It changes how far the head moves between layers, which in turn changes how many layers are generated. If your parts are taller than they should be, you need to change the Z_STEPS_PER_MM value in firmware.

hmm, I replaced my kapton with blue painter's tape, i don't know if it's M3.... i use it to mask things for spraypainting? it's sort of thin blue paper with tiny wrinkles on it?

anyway, what's the generally accepted distance between the tip of the nozzle and the bed? my feeler guages go up to .025 inches, but i think i have larger ones if that's too low.

currently i have it at about .0145, or .356 mm and i keep just getting large blobs of plastic. what happens is a tiny amount gets onto the side of the nozzle and then that drags through the previous line. not the layer below, but the adjacent line of infill in the same layer.

also, the way it gets stuck on the side is a mystery to me. when i extrude over my dump point, the filament pulls severely to one side sometimes. does molten PLA have enough surface tension to be causing this? i've noticed that very lightly sanding the end of my nozzle temporarily fixes it, which makes me believe there's a film of PLA over the front that's allowing surface tension.

If all that was unclear, i can post a video tomorrow.

The ideal nozzle height for the first layer is equal to the layer height. However, when using PLA on painter's tape you need it a bit lower to get it to stick. I would go for layer height - 0.1mm. That leaves a meniscus like ridge around the bottom of the object which can be scraped of with a knife.

Beware that with most extruders the distance when hot is much smaller that when cold because the extruder insulator expands about 0.25mm. If you calibrate with a feeler gauge then it has to be when it has been hot for a minute or two. With PLA that gets messy! I do a rough calibration when cold and then extrude an outline, measure how thick it is and adjust accordingly.

The way the filament comes out of the nozzle when in mid air doesn't make any difference, it is rarely straight. When it is being deposited the gap to bed/object is always less than the filament diameter so it compressed vertically and stretched horizontally as soon as it exits the nozzle. It doesn't get chance to go off to one side or curl.

Your symptoms sound like you might have too much flow rate, or the first layer height too low. Also PLA tends to ooze, so I always extrude a blob and a rectangle around the object to get the flow rate stabilised and remove any ooze that happens while the z-axis is descending slowly. I think somebody has done a plug-in for Skeinforge for this now.

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[www.hydraraptor.blogspot.com]

Quote
nophead
I think somebody has done a plug-in for Skeinforge for this now.

YES, Lenbok has it on Thingiverse and it works GREAT!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

hmmm, alright so i got the nozzle to an appropriate height (i just used feeler guages to get .271 mm and it seems to work pretty perfectly, so i'm sticking with that for now) and replaced my tape, now i can print drastically better, so on to some smaller problems.

has anybody worked with autodesk inventor and repsnapper in conjunction? Either inventor is exporting things far too small, or repsnapper is importing far too small.

soooo

what units does repsnapper use? I presume that .stl files don't contain unit specifications, just "this sphere is 30 units across, i dont care what units"

I can set inventor to use whatever units i like, however i'm not entirely sure it exports using those same units, it may be reverting to imperial when exporting, which would cause issue.

also, how big are the boxes on the grid in repsnapper? knowing that would greatly help in estimating how much these things are scaling.


edit: alright, i just measured my first test cube.... it's definitely inventor. my 40mm test cube came out 39.8 x 40.1 x 51 (due to incorrect layer thickness, also remedied quite well now)

so the new issue then, is to get inventor export settings just right.... i'll look around some autodesk forums.

Edited 1 time(s). Last edit at 02/06/2011 03:32PM by Parker .

In rep snapper under 'print' tab, jog your printer 10mm in every axis. measure it. if the distance is off then your scaling in firmware may need to be adjusted.

you can go here to calculate firmware settings
[reprap.org] (it still requires some mouse clicks to sort through.)

If your device is calibrated and everything related to distance travel is correct, then
the thickness of your printed walls may not be calculated correctly.

In rep-snapper look under 'definitions' tab. check the 'extruder material width' setting.

if you want to look at rep-snapper settings in detail, here is the manual for rep-snapper. [github.com]

good luck