Mk4 Nozzle Change Frustration
I've just completed my first attempt at changing from the OE 0.4 nozzle to a 0.25 nozzle. Not a pleasant experience. The copper bit of the 0.25 nozzle is 0.02 mm larger than the OE nozzle and has a burr on the upper edge. It will not seat all the way into the heat sink. Dressing the burr and polishing the copper gets it further, at which point it jams in the heat sink and won't budge. Broke the tube getting it out. Reverted back to the OE nozzle which slides right in.
Also tried switching to a 0.60 nozzle just on principle, it is closer to fitting than the 0.25, but still not right. Having been burned once, I did not try too hard on this one and reverted again. Once again, the OE nozzle slid right in.
I'm not even going to mention the cable management problems as they seem to have been covered elsewhere.
Are replacement nozzles known to be difficult to apply? Is there some magic lubricant required? None was mentioned in the instructions.
RE: Mk4 Nozzle Change Frustration
I only have the Obxidian 0.6 nozzle and the brass 0.4 nozzle so I can't comment on the quality of the other nozzles. However, I recommend using this clamp (and wrench) for nozzle change, it's a total game changer: https://www.printables.com/model/624027-mk4-nextruder-nozzle-change-heater-block-clamp
Do you actually need to insert it all the way including the last 0.2mm? There isn't anything that it needs to bump up against inside the extruder, just needs to be located so the thumbscrews can lock in the small notches on the nozzle, right?
RE:
It should be a slip fit without lubricant. I would contact Prusa and find out what the nominal size and tolerance is for the hole in the heat sink and the copper shaft on the tips Ask what they are being QC checked to. If out of spec, send them back.
I think that part is 4mm. .02mm could be the difference between a slip fit and not fitting. Out of round could also be the problem. On an application this size, .02mm would be the total tolerance range in my opinion. For the shaft, something like 4mm +0-.02mm would be my thinking. There are manufacturing standards for slip fits based on size.
RE: Mk4 Nozzle Change Frustration
@mhacker - Thanks for the tip on the clamp. It looks like it will save me having to grow another hand.
RE: Mk4 Nozzle Change Frustration
@vhubbard - The original 0.40 nozzle just slides in without drama. Both the 0.25 and 0.60 jam before getting near the depth the 0.40 achieves easily.
I'll try talking to Prusa. Maybe they got a bad batch.
RE: Mk4 Nozzle Change Frustration
I had the same issue. A nozzle didn't fit. I didn't want to use force and do more damage I just contacted support. After back and forth a bit (sending pictures so they can confirm I wasn't doing anything stupid), they send a new nozzle, which did fit perfectly.
Remember, things should just work fine. If they don't, it's probably something going on where support can help.
RE: Mk4 Nozzle Change Frustration
I haven't had the nozzle fit problem, but I think something is a little off in the mechanical design of the nextruder. The thumbscrews hold the nozzle in place via the features in the nozzle (and some pressure on the tube), but the ultimate insert stop is a printed piece up near the gears. In my case, the top of the stainless tube is pressed against the printed piece. While that's certainly good in terms of preventing flexible filament from squishing out in an un-wanted location, I suspect this leads to some inconsistency in load cell readings since the force on the nozzle bypasses the loadcell to some degree.