Two question and a problem

Question !: How far above the printer bed should the extruder nozzle be while printing or for "Z" home?

Question 2: What causes occasional blobs while printing (using PLA, 0.35 nozzle, calibrated extruder)

Problem: My extruder (Wades type) stops extruding after a short period. Filament is not moving, all looked OK when opened up i.e. filament intact minimal plastic on hobbed bolt (what a pain getting at the filament, a hinged exruder is on my printing agenda). I was formerly printing at 195 - 200C but was getting some blobs, so thought perhaps a lower extruding temp would help, so dropped tems to 185C which seems to be the usual temp mentioned on the forum. If however the material is not soft enough in my extruder this could likely cause output to stop and filament to stop moving because the hobbed bolt is now spinning on filament instead of driving due to insufficient temp and flow.
Perhaps my extruder temp is reading incorrectly and I should not use it as gospel. Perhaps a 10degree drop was too much.
At least those are my guesses based on what I have learned about this whole process.

Any comments, suggestions, or corrections to my understanding?

Thanks,

Bob

How far above the printer bed should the extruder nozzle be while printing or for "Z" home?

Answer: about a little higher than the thickness of a sheet of paper. You want it down as far as it can go without actually dragging on the surface. In some instances this will not be possibly, however the idea is that the x/y does not loose position while z axis is at zero and x/y moves. Keep in mind the first layer will raise the z height before print.

What causes occasional blobs while printing (using PLA, 0.35 nozzle, calibrated extruder)
Answer. This is hard to pinpoint because several things cause it. What happens is for various reasons the area that is being printed is double or triple dosed with the filament from the hot end. Either a stutter, a lack of motion in x/y, or a slow change in z height, or lack of proper flow, or z height change. There are several reasons. You will want to start by watching the motion of your machine when it happens.

As for your extruder. Never believe the extruder temp. It is +/- 5 deg c! If set correctly. Just set it where the feedstock flows and works at the speed you want to print at reliably. On the high end of temp range you need to worry about pla crystallizing, on the low end you need to worry that it does not melt fast enough to push thru extruder. Likely now your hobbled bolt is filled with plastic and no longer effective. Take a nail and place bolt under hot water, and peel the plastic out of the teeth. I would recommend also turning motor current down further on e axis to have it stall out so you don’t strip feedstock. If motor stalls a lot then raise temp to make it easier to push feedstock thru.



hope it helps, hopefully many others will reply and aid in to help you with your issues.....

Hi James,

Once again thanks for the advice. Slowly improving, results getting better.

Sure is great that you and others so freely offer your expertise!

Bob