Hotend assembly tutorial

[midget214]

Hi Guys,

I posted a step by step tutorial for assembling the hotend. Some steps have been taking from the official docs here in the forums. Experts, please leave comments/suggestions to improve the tutorial.

http://floorsctz.blog.com/2012/09/03/as ... nc-hotend/

Thanks

[Eric]

Very useful as an intro, as I haven't gotten to that part yet. Wouldn't wire strippers work even better than a knife for removing silicone from wire?

I'll be using ramps electronics, so I would think that a thermistor physically coming loose (unexpected sudden drop in temperature) would be detectable in software. Ditto for electrical issues (broken or shorted wire). If there isn't shutdown/alert code for those situations already, I may see about writing some when I have a working printer.

[tom10122]

most people use crimps instead of soldering the hotend as the solder can melt

[BrainSlugs83]

Disclaimer: I'm not an expert by any means at any of this stuff, but here's my $0.02.

For lead insulation, I just used kapton tape -- just lay it flat set the resistor lead across it, fold the tape in half -- then you can use a hobby knife or scissors (careful!) to cut the tape down to size.

I'll be using ramps electronics, so I would think that a thermistor physically coming loose (unexpected sudden drop in temperature) would be detectable in software. Ditto for electrical issues (broken or shorted wire). If there isn't shutdown/alert code for those situations already, I may see about writing some when I have a working printer.

I keep reading about how shorts will cause overheating, etc... -- doesn't make much sense to me -- if the temperature sensor shorts, then it will return a resistance value near zero -- which would mean that the hothead was already impossibly hot! Wouldn't the software automatically switch it off and wait for it to cool down?

As for if it comes loose -- well, that's an issue because the software will still be getting valid temperature readings -- how would it know the difference between a loose thermistor and a functioning one? (Unless you were doing running heat capacity calculations and suddenly noticed the heating capacity of the hothead went down dramatically -- but that could just indicate that the operator turned on a fan... -- same for measuring for downward temperature spikes, etc...)

I've read the best bet is to glue them in with a shitton of gasket maker and then wrap them in with a ton of kapton tape!

Also, you left out the part about cutting the "V" in the foil, it makes the resistors closer to cylindrical... and are you really supposed to glue the resistors in place? I can't budge mine just from screwing the hothead back together (though I have the H-1).

*You can use crimps or solder the resistor wires together. I decided to solder them.

How's that working out for you? I thought the solder would melt? Are you able to print ABS? What temps can you get it up to?

[Eric]

The math isn't beyond me, but it'll be easier to just do empirical testing to calibrate the numbers for the thermal mass of a particular setup. All the software needs to know is what the temperature/time curve is supposed to look like when the heater is on. If the thermistor isn't seeing the temperature rising at close to the expected rate during heater-on situations, then something is wrong! Similarly, if the sensed temperature of a hot end drops at an unbelievable rate (even with a fan), that's also a problem indicator.

[midget214]

I havn't printed with Abs yet, only pla, and so far the solder seems to hold out. I used lead free solder which in theory only melts at 280 and more. From what I understand abs melts at 250, so there is more or less a 30 degree "safe zone" - if you can call it that. Currently I am experimenting a bit (I have a spare hotend on hand if something happens anyway). Im sure Kapton Tape works well, but living in a country where all the cool stuff has to be imported, I have to make due with what I have available to me.

Lastly, the thermistor issue only becomes a real concern if you use a velleman board for temp control. The board relies purely on the reading of the thermistor. If it gets no reading it will keep heating up until your hotend is no more. This is where Ramps, printrboard etc has a great advantage.

I have had my printer for about 3 months but today is only the second day of printing. I ran into various issues along the way.

[jbinion]

A bit on the silly side but if you split the foil and wrap it around a pencil then wet the ends it will help keep the foil tight.

[tom10122]

I havn't printed with Abs yet, only pla, and so far the solder seems to hold out. I used lead free solder which in theory only melts at 280 and more. From what I understand abs melts at 250, so there is more or less a 30 degree "safe zone" - if you can call it that. Currently I am experimenting a bit (I have a spare hotend on hand if something happens anyway). Im sure Kapton Tape works well, but living in a country where all the cool stuff has to be imported, I have to make due with what I have available to me.

Lastly, the thermistor issue only becomes a real concern if you use a velleman board for temp control. The board relies purely on the reading of the thermistor. If it gets no reading it will keep heating up until your hotend is no more. This is where Ramps, printrboard etc has a great advantage.

I have had my printer for about 3 months but today is only the second day of printing. I ran into various issues along the way.

Actually I shorted my thermistor out on purpose and it didn't heat up at all for some reason.

[Eric]

I used lead free solder which in theory only melts at 280 and more.

Most of your lead-free solders are going to melt in the neighborhood of 220 C. 60/40 lead solder melts around 190 C, so it is better than that. 10/90 solder (90% lead) should get you up to that 280 C temperature, if you can still find any. Lead-free has done a number on the availability of the less common tin/lead blends.

If your solder joint wasn't an inch out from the actual hot end, you probably would have melted it already. It may still be ok when you do ABS...I guess you'll find out.

[BrainSlugs83]

Actually I shorted my thermistor out on purpose and it didn't heat up at all for some reason.

Of course, as I said, the lower* the resistance is, the hotter the board thinks the current temp is -- so a short (a resistance of zero), would think that your hot end was insanely hot already, and would thus switch it off.

(*: I don't know if this is true for all thermistors -- maybe some go in the other direction -- but on the ones I got from SeeMeCnc, lower resistances indicate a higher temperature.)

[johnoly99]

Hey guys, thought Id chime in quick. Most if not all firmwares have a MIN and MAX extruder and bed temp. If you set those within your temp range, and while printing a thermistor pops out, and reported temp drops below that temp, it will shut down. That takes care of the thermistor popping out problem.

[Polygonhell]

The problem with that John is that if the thermister "pops" out it just reads ambient and the firmwares min/max doesn't protect you from a meltdown.
That particular case is relatively obvious if you watch the temperature in pronterface or repetier, since it's usually only an issue after re-assembly.
The more difficult one to catch and the one that cost me my first hot end is where the thermister creeps out while running, what happens is the thermister slowly reads lower and lower, and the board pumps in more and more power until you smell or see the peek melting or it bursts into flames.

Firmware min/max only really protects against a short, a broken wire or a user setting the temperature explicitly too high.

[johnoly99]

Polygon, if you normally print at 225c, and set your min to 220c and max to 230c, it should catch it fairly quickly. Granted, a narrow range doesnt leave a lot of room for "tweaking" things, but like all safety mechanisms, you gotta weigh risk vs. reward. I personally dont use it that close, mine are min 195 max 250, and knock on wood i havnt ever lost a hotend, but i take extra care when assembling them, maybe overkill even.

[drew]

John, Do you have a description of how you go about adding overkill when you assemble your hot ends? I melted mine last weekend and will probably be assembling one that's in the mail this weekend.

Not sure why mine melted. By the time the smell got bad enough for me to check it out, the nozzle end of the hot end was dangling by the wires and the thermistor wasn't in the hole anymore. I'm thinking of wrapping things up with kapton as a precaution.

Drew

[Polygonhell]

Polygon, if you normally print at 225c, and set your min to 220c and max to 230c, it should catch it fairly quickly. Granted, a narrow range doesnt leave a lot of room for "tweaking" things, but like all safety mechanisms, you gotta weigh risk vs. reward. I personally dont use it that close, mine are min 195 max 250, and knock on wood i havnt ever lost a hotend, but i take extra care when assembling them, maybe overkill even.

Actually when I lost my hot end the temperature in repetier looked constant right up to it melting.
The issue was the thermistor creeping out of the hole in the Hotend, not fast enough for the heater not to keep up.
I guess min temperature might catch it if it popped out but it's really designed to detect a disconnected thermistor and is generally set below ambient, since you can't jog or do anything while the temperature is below min temp (at least in Marlin).

[flink]

Hey, thanks for the instructions. I'm finishing off my h1.1 today and after checking square once more, I'll be wiring things up and learning how to make it all run. I wasn't sure how everything went together for the hotend.