Advice on FUBAR hot end UM2+ refurbish

[gdog 4]

Hopefully I have all the correct part names now, so I'm posting this up seeking advice and hoping there are many here who have experience with clogged / burned heater block / nozzle / isolator / etc. who faced a similar dilemma and will pass along their insights to me:

 

First some background - I got an UM2+ from my local library.  It had earned something of a reputation for clogged nozzles and they have an UM3 with the print cores I guess they like better so... it got dumped in the "recycle" bin where I rescued it.   The hot end is a hot mess.  Nozzle was hopelessly clogged and burned.  Parts were missing  (see photo) - nowhere to be found was the 9.4mm spacer that should have been pushing the TFM coupler down in the isolator  (the spacer I'm referring to is what used to be a spring in the UM2).   The TFM coupler was kind of rattling around taking a ride on the filament.  Also missing were 2 of the ISO 7380 M3x4 bolts that connect the fan shroud to the hot end (i.e., there were only two of those bolts rather than 4 and things was "wiggling" a bit).   In the process of disassembling the head, I pulled the thermistor/temp sensor off at the wire, as the probe was welded in the olson block and wouldn't break free even under a heat gun.  Lost of charring and burned carbon deposits all over the olson block.  Had to use vice grips on the isolator (also welded into the heat block) to get it loose and may have smushed it a bit.  Out of the middle of the block between the isolator and the nozzle ends, I found a PLA plug/multi-color sandwich about 2-3mm thick, with leftover junk from at least 4 different clogs fix the problem- evidenced by the colors in the plug.  The amazing thing... the last color printed by the machine was silver (from the nozzle clog and a cut off piece in the bowden tube), and so somehow that silver just mashed right through the pink and green glob.   I suspect after the head was disassembled and the spacer + 2 screws were lost, what was going on is that when the nozzle would clog, the library would, maybe after the atomic pull didn't work, sensibly enough, just get a new nozzle, wrench off the old one, put on the new one, and try to print without really inspecting the condition in there...  that's my hunch.

 

So hopefully that was an entertaining read... now to the advice part.  Given the condition of all this mess, I weighing to just go out and buy the complete hot end assembly (assuming I can find it).  That means replacing fans, plates, heater probe and other stuff I don't need... but that might be near end of life anyway.   One of the main reasons I'm going in that direction is that I can't seem to find anywhere to buy the 2 missing screws - other than getting a box of 1000 that I don't even know for sure are the right ones as I'm not a master of ISO jargon, nor can I find the spacer for sale by itself or with the isolator (which looks like were sold together in a "pack" but it seems to be out of stock wherever I've seen it).  Being something of a dumpster diver, I'm kinda working on a low budget here. 

 

So I had a couple other thoughts -- one was to get the 2 to 2+ upgrade kit that would contain most of what I need in the hot end....

 

Another idea would be to go back and use a spring in the assembly like was done with the UM2 originally. 

 

That gave me another idea - getting either a complete print head assembly for the UM2 (no plus) or a hot end replacement assembly - those seem to be easier to find and cheaper than the UM2+ "hot end pack".  If you can go from a UM2 to a UM2+, then why not go backwards from a UM2+ to a UM2.... I don't need to change nozzles much, I'm not going to be printing with boron-composite filaments, and even so I could always swap in an Olsen block eventually with removable nozzle later on if it turns into a hassle but then I would presumably need to find the spacer somewhere unless I keep the PTFE coupler and don't use a TFM coupler (?) 

 

Ironically one part of this assembly that looks immaculately un-damaged is the consumable the TMF coupler! 

 

Also, a couple of more questions: 

1) I've seen some dual extrusion "upgrade" heads for the UM2+ that seem to be less expensive than the single extrusion basic 2+ kit.  I assume that because they don't really work well and/or require other upgrades in addition to be able to actually get them to work.  But if I got one of those any only use one side / one nozzle / one filament, is there any particular reason why that wouldn't work? 

 

2) is it OK to use in this machine a cheaper 6mm bolt end, .040 nozzle that I can pick up at my local micro-center?  

 

3) the spec on the temperature sensor says "PL100B glassfiber".   If it's a PL100 sensor, then the temperature map range should be what the machine expects, so do I need the glassfiber insulation?  And if so, where can I get "glassfiber" high temp wire without paying a big markup?

 

Anyway I suppose the "right" thing to do for an aspiring maker is to take the specs for the spacer from github and go to a machine shop and have the spacer milled, then re-tap the holes in the plate to fit four randomly available "tiny" screws I can get at the hardware store for the fan shroud.  But that seems kinda like way too involved and as I mentioned I'm on a dumpster diver budget.  🙂

 

Pics below: (L/top) TFM coupler rattling loose in print head; (R/bottom) A tasty clog sandwich... don't leave this in your hot end because a new nozzle won't last long if you do!

 

 

Edited January 16, 2022 by gdog

[gdog 4]

I think this question of whether to get the complete print head assembly is moot, as I've been searching around, come up empty, and am about to give up looking.  This is P/N 225864 for the UM 2+ connect.

 

Anyway, they have the spacer for sale at fbrc8.com, and so the trouble in parting it piecemeal seems to be figuring out where to get the screws that hold the fan shroud.  Anybody know if those M3x4 screws are fine or coarse thread pitch?

 

BTW... seems that few suppliers uses those part numbers, which is kinda frustrating.  And then there's the issue of different part numbers for the same thing... like the glass build plate for the 2-series, which seems to have gotten a new part number for each Model 2 variant.

Edited January 18, 2022 by gdog

[geert_2 556]

Except for cameras, microscopes and similar special equipment, people rarely use fine metric threads, because the coarse thread is already quite fine. So any "M3" should be a standard coarse M3 thread, if not explicitly indicated otherwise. If it is a fine thread, then it would say: "M3 Fine", or "M3 F", "MF3" and/or give the pitch "M3 x 0.35mm" or "M3-0.35", or something like that. I don't know what the official notation is, but I have seen all of these. Not to be confused with "M3 x 20mm" in which 20mm is the length of the screw (including head in countersunk screws, without head in standard heads).

 

If no pitch is mentioned, standard is M3 with 0.5mm pitch.

 

Can't you find those M3x4 screws in a hobby hardware shop? I think it is a quite common size. Or else, maybe take a longer M3 screw and cut off a bit?

 

[LePaul 312]

Your local hardware store or if you have a hobby store, should have metric.  Where are you located?  If in the states, I've found some at Lowes and Home Depot, usually phillips head and not as nice as the stock hardware.

 

[gdog 4]

5 hours ago, LePaul said:

Your local hardware store or if you have a hobby store, should have metric.  Where are you located?  If in the states, I've found some at Lowes and Home Depot, usually phillips head and not as nice as the stock hardware.

 

I didn't see anyt M3x4, but if I'm now reasonably sure it's M3-.50 then I don't mind having a go at buying a longer screw and cutting it down to 4mm.  Just have to find the cutters I have buried somewhere that does that.

 

In the meantime, I got the other parts on order... will report something back if I can get it working!

 

[geert_2 556]

If you would have a Dremel or similar tool, and a cutting disk, you can cut screws with that disk.

 

[gdog 4]

Home Despot had the screws in with phillips head in 2mm length... so all set.  Surprisingly that also had spacers that looked like they might work in that gap between the TMF thing and the head top plate... however they were all in Imperial measurements and I didn't have my slide rule with me to convert.  (Plus already ordered from online place)