nozzle jam

Hi, I'm using 3mm PLA filament but when I try to extrude it the nozzle gets jammed.I guessed that the PLA expands a little when heated so I expanded my nozzle so the inner diameter is about 3.5mm but it still gets jammed. Is there anything I can do about this? Does ABS expand less? or do I just have to go down to 1.75mm filament?

If you are looking for a solution you need to fully describe the design of your hot end, probably the whole extruder. No one would be able to tell that 1/2mm clearance causes jamming.

Here's what i do to narrow down the problem:

remove the hot end and extrude filament, use a fish scale to measure the extrusion force. pla needs ~12lbs of force to extrude. If your extruder is not producing >12lbs of force tighten the springs.

set the hot end up on the bench without the extruder attached. bring it up to temperature and try extruding filament by hand. This should be EASY. If it's not, try increasing the temperature (i use 200 - 215 C for PLA). If that doesn't work, you'll need to redesign your hot end.

ABS does expand less, but it's better to correct the problem. PLA expands at a lower temperature than it liquifies at, so what's probably happening is that the heat from your nozzle is creeping up far enough that the PLA farther up is getting hot, expanding, and causing a blockage. What hot end are you using? Cooling the barrel or upper part of your hot end with a fan is always a good idea and is likely to pretty dramatically improve issues such as these. Also, the tension on your extruder's idler may not be enough, causing it to not have enough force in feeding the filament.

I had this happening all of the sudden mid print, after several prints with no problems. The extruder motor was going forward a bit then started skipping and even jumped backwards sometimes. I first thought the extruder driver decided to quit so I replaced it ... to no avail.

Next was logically the hotend itself, I took it apart and cleaned it as thorough as I could, it's a 0.35 mm j-head. I did found some clogged PLA in there but I don't think this was the cause.

Lastly I remembered to have a look at the hobbed bolt, it's teeth were all clogged up :/

I think this caused my issues so have a look at that, I can't confirm yet as my hotend is still in pieces ... hopefully tonight I'll be able to test.

Thanks for all the advice, I'm using a Wades extruder and the nozzle set from bilbycnc.com. I shortened the barrel by about 1cm and its working now. Thanks again.