scraping on filled layers

Hi,

I'm having problems with my extruder head making contact with filled layers. Usually this only occurs with the bottom most layer when doing the infill. If I raise my z home any higher I'm unable to place supports so I don't think that's my problem. When it does the completely filled layers it seems to be putting down more plastic then it accounts for so when it tries to sweep to a far side it drags the head through the current layer. This causes problems on large objects when the layer is already semi hard as it will desync the location. I do see this when I'm making an object with near 100% infill in every layer. I've calibrated my E steps (via telling it to extrude a distance and measuring the actual) and I've used SFACT's calibration objects to adjust the packing density. I'm not sure what to try to fix this other then redoing the calibration (which I've tried several times). I've already kind of tried fudging my calibration numbers to put down less plastic but it feels like there should be a real solution.

I'm printing with a prusa mendel (SAE) in pla on blue tape. I'm using SFACT to slice and printrun to host.

Hey Zarquon, I don't have much advice, but just wanted to chime in to say I have the same problem. I have gone through calibration a few times (finding errors I made last time each time I do it), and seem to have a pretty good E steps and packing density now. In the Infill plugin (I think) there is a parameter for extra spacing between infill lines. It's sort of described in coasterman's calibration set, but I think it's talking about settings that were in Skeinforge, but were changed in SFACT. I have tried that and it does improve the situation some, but like you I feel like there must be a better way.

I've been poking at this a bit more and my current conclusions is that I only have a 'normal' amount of scrapping but my x stepper driver is not providing enough current which causes even a little bit of resistance to misalign the layers. This happens even if I turn the current all the way up via the trimpot but the motor doesn't make any noise or get warm so I think the stepper driver is defective. Switching my X and E drivers causes this problem to (seem to?) go away but now my E misses steps obviously. I ordered a replacement Pololu driver to test but it arrived DOA.

Edited 1 time(s). Last edit at 12/29/2011 04:36PM by Zarquon.

Zarquon,
I would re-calibrate the amount of plastic coming out of your extruder. The problem may be that you are simply putting too much plastic down. I have had that happen to me before, and then the nozzle would catch on the plastic once it cooled.

Try increasing your filament backing density by .2(lower is more extrusion), or, if that doesn't help, try decreasing your infill solidity by .2.

I've also had the thought that if the X and Y axis steps may make a difference, because if the X or Y doesn't move far enough it would result in overlap of the plastic, even if the amount SFACT expects is extruded.

Do you have all of the other things in your setup correct? I had something similar and it was because I was using a .35 nozzle, but slicing it for a .5 one. I could see the filament diameter (as measured with calipers) also doing something similar.