Struggling with a BFB Rapman Extruder

Okay, the nichrome wire has broken, the thermistor has broken three times, the board fried, so this thing is getting to be a bit of a pain. I just want to get it working. Any tips for macgyvering a nichrome wire into a heat-resistant sleeve using a butt-splice and a pocketknife?

A double knot should do it. ;-)

A bit more sophisticated: put both ends into something like this, after removing the insulation:



A reliable solution: buy a meter of new wire. One or two dollars.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Well it's joining nichrome wire with normal stranded wire. And then I'm supposed to slide this siny heatproof sleeve over it. And I have tried those things. That was the most recent attempt.

Also, if it doesn't work, would anyone be willing to buy an unfinished, but never used, mostly assembled Rapman 3.1 (soder Kit) with the most recent of the circuit boards attached for $950 (subject to change if I get it working...) so I can buy a makerbot?

I found it easiest to tie the nichrome to stranded wire using a double sheet bend, then just twist the loose ends around each other. There's no crimp or anything, and it's held up just fine through many, many extruder rebuilds.

what about the thermistors? Those things are cruel and unusual punishment and impossible to work with!

I agree with you about the thermistor wires, I must have broken them 2 or 3 times during assembly. I ended up with an ugly looking hot end, but I'm happy as long as it works.

BfB does sell preassembled hot ends here: [bitsfrombytes.com]

(There is a drop down menu). Cost is 80 GBP (plus shipping I imagine), but it might just be worth it to save yourself the trouble.

I'm as broke as a smartcar in a road accident. I have about 34 cents to my name. I'm going for quick and dirty here... and do not TWSS me!

Figured out a way to make a false thermistor, as a series of resistors in parallel. However, I need to know what temperature the rapman software says it's at when it starts to print, so that I can calculate the resistance for the second resistor. Or...I need to know the resistance of a thermistor at whatever that temperature is.

Why don't you just use a variable resistor and watch the display of the temperature as you adjust it?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

That's what BFB told me to do as well, except with a potentiometer. It's a good idea though... as soon as I get cash I'll try it.
I'd also appreciate solutions for the real thermistor though, if anyone has success or failure stories they'd like to share.

If you're in a pinch and want a potentiometer, connect one end of a pencil lead to 5v, other end to earth, and slide a crocodile clip along it, and connect this to the analog in pin. This is a bit hacky, but exactly the same as inside a potentiometer. Don't have a pencil lead? Use a pot of salty water instead. I rarely have the right parts on hand :p

using any 200K thermistor works fairly well. RT curve does not match but you will be in the +-5C range (real - shown temperature). If you don't have 200K NTC, you can use 2 100K thermistors (attach them both to the print head) and you will have similar precision. Using the pot will make calculating temperature from the display'd one pretty hard. I tried with bunch of different 100K and 200K NTC's and the results were good. (I used to run 2 extruders with honeywell 135-104LAG-J01 ( [uk.farnell.com] ) 0.3GBP on farnell - it is 100K NTC so i used 2 of them to get 200K on 25C. The RT curve is close to the 204GT BFB extruders use (204GT is more expensive btw - the company that makes them sell's only 100pcs pack and for 150$ so 1.5$ per piece on that large volume is much more expensive then the honeywell one - the only difference is that 204GT is "bead" and 104LAG is "axial" - so you cannot put the 104LAG into the small hole on the extruder but have to attach it on the side of the heat barrel)

Got the pot rigged up, and it accepts it beautifully. For anyone wondering, radioshack sells these 100k Ohm pots that are awesome. It now melts and extrudes, well...to a degree. I warm it up for about 5-7 minutes, to the point where it's oozing a little bit of plastic, and that the plastic curls up around the fire cement. I then turn the pot up to around 107 C, where the machine then responds by printing a test raft (the current only file I have). It prints about half (more if I warm it up longer, less if I warm it up shorter) then the print volume really thins down. And it all comes up from the print bed (which I sanded with 240 grit...). The hot end is very sparsely fire cemented, in that I have some nichrome showing on one side... and I also have some sort of opaque rubber cylinder-y tube thing. COuld I have excluded a part or skimped on the fire cement?

I cracked the sparse layer of existing fire cement off, put on a more minimal layer, and am trying the silicone insulator. THe extruder does not function in print mode, meaning the gears spaz out and click, and it doesn't seem to get as hot. Suggestions?

It may have been a stepper motor wiring fault, as I jiggled the extruder connecter and it doesn't click. It also doesn't seem to get as hot anymore though. Please, can I get a little help?

hi i just want to do that.. maybe you can help me.
i cant get a useful temp reading (always stays 1.045°C) in ReplicatorG when i hang this BFB Hotend to the Makerbots Extruder controller board 3.6.

I double checked with multimeter and i think its a 200k thermistor inside. Sadly the guys from BFB didnt wanted to send me more informations. No Openscource... so i dont get the beta value nor PID settings.

Strangely i now get same wrong temp reading out of my original makerbot thermistor.. and its also not broken.