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replaced extruder fan: X axis too short now  

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draeath
(@draeath)
Active Member
replaced extruder fan: X axis too short now

I'm getting resettled after leaving my MK3S printer unused for a good amount of time. In the far past, I replaced the noctua extruder fan with one that pushed more air but ran faster (I'd rather avoid heat creep, at the expense of noise).

That all worked and continues to work fine. The problem is that if I try to run a belt test or self-test now, the printer fails with "Selftest error! Please check axis length" for the X axis, and I can see the fan screw contacting the left threaded Z rod.

The printer can home just fine, with plenty of space to spare. The lost length is not actually important, it seems? The original noctua fan apparently had the screw bore shoulder sunk in so it's clearance was effectively lower. I've tried to simulate that by drilling out the outer face of the fan holes, but I can't go any further without risking the burrs from contacting the fan blades. I'd also prefer not to have to replace the fan with an original noctua - I really find managing the extruder wiring a huge pain in the rear.

Is there any way I can work around this without patching my firmware or tweaking my EEPROM (wherever the axis length is stored, I haven't checked)? I've patched the firmware before (I've actually had a PR accepted a while back!!) so that's not something I'm unwilling to do if there's no other option... but the problem then becomes how to figure out what the right value would be to replace the original with.

Posted : 30/09/2022 4:25 am
Neophyl
(@neophyl)
Famed Member
RE: replaced extruder fan: X axis too short now

That’s one of the most tight areas and your screw heads are simply in the way. Hard to tell from your pics but you could try using countersunk m3 screws on those back ones so they don’t hit the printer. Or you could grind the cap heads down possibly. A physical option will almost certainly be much easier than messing with the firmware. 
I also recall seeing printed ducts on thingiverse that allowed mounting of the fan offset to get around the problem when people fitted different fans. 

Posted : 30/09/2022 5:15 am
draeath
(@draeath)
Active Member
Topic starter answered:
RE: replaced extruder fan: X axis too short now

I may have to go the way of the grinder, then. The duct is a good idea, but I assume I won't have enough slack on the fan cable for it and I *really* do not want to take the extruder cabling apart 😀

The thing is, I only have a dremel. I believe I can pull it off with the bits I have, but it'll be tricky. We'll see. Honestly, I was thinking of trying this already and your suggestion kind of bumps the idea up in the list, so to speak.

Thanks for the ideas!

Posted : 30/09/2022 5:37 am
Neophyl
(@neophyl)
Famed Member
RE: replaced extruder fan: X axis too short now

Yeah the mk3 wiring is a pain to work with.  Which is why when I rebuilt my extruder last time (a geared ratio one) I also fitted connectors to all the cables except the pinda.  I can change my fans, thermistor, heater cartridges etc without touching the rest of the bundle.  Was worth the extra effort.

You can get fan extension cables, they sell them for pc builds which might be an option too.  Would save you having to touch the wiring at the moment and would be plug and play.

Posted : 30/09/2022 6:23 am
Diem
 Diem
(@diem)
Famed Member

Low profile M3 screws are available, they are specialised parts so search online.

Cheerio,

Posted : 30/09/2022 2:46 pm
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