Trouble printing PLA bushings

I've been printing for a couple of weeks now with fairly good results. I have added a hot bed to avoid warping. I am still reluctant to print many objects at once as one failed print usually ruins the rest. Having said that, I just can't get prusa pla bushings to print. Each time I try it seems to fail right from the start. I've tried lifting the head a bit and lowering it a bit (from the .5mm location). Any else have similar problems ?? Does anyone ever polish the tip of the hot end to keep the filament from sticking to it ?

Edited 1 time(s). Last edit at 01/16/2012 04:46PM by HereIgoAgain.

I use a PTFE coated nozzel which allow you to clean any material off easily. When the extruder is operating properly there is no real benifit from the coating. So I'd say that polishing won't help but nothing prevents you from giving it a try.

When your extruder is operating properly material flows freely from it and it doesn't have a tendency to curl back.

Since my mendel has a single belt Z axis drivce which allow me to easily adjust it during the start of the print - skirt. There is no connection between that gap and the materials tendency to curl back. Too high and the material won't stick. Too low and nothing will come out eventually leading to material build up in the drive teeth, which causes further slippage.

I had a problem with filament curling back on itself. This started after many print jobs failed from the filament slipping out to one side of the hobbing in the extruder. It seems that erratic feed through the extruder caused a build up of something - I suspect thermally degraded filament - on or in the tip, which encouraged the filament to curl back on itself. The problem went away when cleaned the tip in acetone and fitted a hobbed bolt with a deeper groove to make the extrusion rate more reliable.

it might be worth looking at the hobbed bolt for any buildup after things go bad. Look for buildup in the grooves. I had an intersting exchange somewhere on this forum where someone recommended using an M4 tap instead of an M3 The problem with an M3 is that the grooves are shallower and tend to build up. I've been using an M3 for a long time with success but I'm putting considerable force on the filiment from the bearing. My extruder is made out of steel. Anyway per Tony's lead, buildup causes lack of forward push which would result in curl.

Can you elaborate a bit on what is different with your attempts to print PLA bushings compared to other successful prints? That is, what are the characteristics of your "successful" prints (part size, wall thickness, filament, etc) that are significantly different to your "failed" attempts to print PLA bushings?

One thought - you may have more success if you attempt to print a batch of 4 or 6 PLA bushings at once, rather than one at a time - the bushings are quite small parts and only take a few seconds to print each layer, so if you are only printing one, the previous layer will still be partially molten when the print head moves back for the next layer. Printing 4 at once allows each layer to cool a bit before the new layer starts. (Or else modify your settings to allow the hot end to pause to cool between layers, if you really want to only print one at a time.)

Hope this helps!

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Follow my Mendel Prusa build here: [julianh72.blogspot.com]

Well I have to say, this one has me confused. I followed everyone's advice, cleaned my hobbled bolt (it was dirty) , took the hot end apart and cleaned everything but still I can't print. This after many perfect prints. I have included a link to a video I made. the first 6 seconds seems to show it all...why the filament keeps shooting up to the hot end and getting everything stuck, I just can't figure out.

[youtu.be]

I assume you are starting and stopping the extruder several times? In which case I can't see any problem.

Whether the filament curls upwards or comes out straight into mid air is irrelevant when you are printing. The first layer height is always less than the filament diameter, so the filament gets squashed between the bed and the nozzle and has then no opportunity to curl up as long as it sticks to the bed.

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[www.hydraraptor.blogspot.com]

Go figure. I cleaned the glass with ammonia and lowered the head a bit more and everything now works again. Thanks nophead sometimes I think we just need some reinforcement.!!