Two types of 3D printer owners

[Dave_Sohlstrom]

Well there are two types of 3D printer owners. Those that are going to have a hot end melt down and those that have had a hot end melt down.

I am now a member of the latter group. Here are the photos to prove it. Second print of the day, first went fine. I was about 15mm into a 50+mm high print and Murphy struck. I was on the internet in the shop with the printer running at my right shoulder. Look over and this is what I find. temp is around 650F. Emergency shut down.

[img]http://i132.photobucket.com/albums/q3/D ... 0_1243.jpg[/img]


[img]http://i132.photobucket.com/albums/q3/D ... 0_1244.jpg[/img]


[img]http://i132.photobucket.com/albums/q3/D ... 0_1245.jpg[/img]


[img]http://i132.photobucket.com/albums/q3/D ... 0_1246.jpg[/img]


[img]http://i132.photobucket.com/albums/q3/D ... 0_1247.jpg[/img]

Now I have to rebuild the hot end but I can still use the machine in CNC router mode.

[michaellatif]

What happened? Did the thermistor come loose?

[Dave_Sohlstrom]

Best guess yes. It was out of it's hole by the time I got it shut down so my thought is it came out during the print and away the temp went. I was running at 99IPM

[Polygonhell]

To say I used a bit more silicon on my second hot end would be a significant understatement.
I think what caused my first one to work itself loose was constantly removing the hot end to clear PLA jams.

[mhackney]

Welcome to the elite crowd Dave! You are in good company. Thermistor pull out is probably the primary contributor to this. On my rebuilt hot end I siliconed the thermistor in place and when that cured, I made a wrap with Kapton tape between the thermistor leads to insure it won't fall out. I think the RepRapers all wrap their hot ends in Kapton, there's probably a reason for that!

Cheers,
Michael

[michaellatif]

Welcome to the elite crowd Dave! You are in good company. Thermistor pull out is probably the primary contributor to this. On my rebuilt hot end I siliconed the thermistor in place and when that cured, I made a wrap with Kapton tape between the thermistor leads to insure it won't fall out. I think the RepRapers all wrap their hot ends in Kapton, there's probably a reason for that!

Cheers,
Michael

Yep, I wrap my extruder in kapton for two main reasons. One, keeps all the critical components (thermistor) from coming loose. Second, it makes for easy cleanup/maintenance of the extruder, you are bound to get filament stuck to your extruder.

[Dave_Sohlstrom]

Well I am using Alibre 3D CAD right now to design a new hot end. I have some very nice .5" copper bus bar and lots of brass and bronze. I going to make the lower part out of the copper with holes for the heater to go in and a deeper hole for the thermistor. If my new dual temp controller ever shows up I will change over to a bolt on thermocouple. I will silver solder a brass upper end to screw on to the PEEK tube.

[Leeway]

I use a J head hot end. I have only had to take it apart once early on when I had a leak. I don't think it was assembled tight enough when I received it. I haven't had any trouble with it since. It came wrapped in Kapton and I rewrapped it after the fix. It is pretty nice as a solution. Comes off easy when wanted, but otherwise stays in place very well.
Kind of amazing to have a tape that does this job so well. I can see why they charge what they do for it.
Hope you get er going quickly.

I too am fiddleing with my own hot end design. Mainly using brass pipe fittings initially.
I am sure other hot end designers have been down this road before, but they may have left a path untravelled.
It will be interesting to see what we all can come up with.
Hot ends aren't that cheap, so can't keep too many on hand for emergencies.
I do have spare resistor and thermistor, but those are the cheap parts.

[TKL]

Just mount a bimetalic thermoswitch like this one, turning off at 250 Deg. C

http://dk.rs-online.com/web/p/termostater/2282529/

[Dave_Sohlstrom]

Good idea will have to see if I can find one on this side of the pond.

[Dave_Sohlstrom]

I've been working on my new hot end. I have some new nozzles that are in USPS never never land. Here are some photos of the work so far. The wire you see coming off the bottom is a thermocouple that will be used if I ever get the dual temp controller I ordered. There is a hole for a thermister and a thermocouple temp probe on the other side. Bottom piece is 1/2" copper bus bar with a brass adapter silver soldered on.

[img]http://i132.photobucket.com/albums/q3/D ... 0_0311.jpg[/img]

[img]http://i132.photobucket.com/albums/q3/D ... 0_0312.jpg[/img]

[img]http://i132.photobucket.com/albums/q3/D ... 0_0313.jpg[/img]

[mhackney]

Looks great Dave. Looking forward to seeing how it works!

Cheers,
Michael

[michaellatif]

Looks nice Dave! I like the copper and brass colors, I bet the copper will change color with time and usage.

[Leeway]

That does look good. I am trying to design one myself just to save a bit of cash on what seems to be a fairly simple part. I ordered some small brass air and gas fittings and some thin and thick wall nipples to try to come up with something. I also have some of the plastic PTFE insert tube.

Let me ask you why you went with Peek for the top part rather than brass, aluminum or copper?
Most of the hot ends I have seen use that there and I suspect it might be for heat dissipation. Just guessing of course, but I know you would not want high heat translated up to the mount because most of those are printed plastic as well.

I am hoping that with an aluminum mount for the hotend, that may dissipate the heat well enough not to melt the extruder. I haven't had time to do any of the work yet. Did buy some tiny drill bits. My first task is to determine how to hold those secure in my lathe.

[Dave_Sohlstrom]

I have noted that the plastic mounting plate already has some signs of heat. I tried to think of a way to change out the PEEK but I was unable to figure a way to keep the heat away from the plastic parts so just went with Steve's design. I do have threaded holes available that I can attach a heat shield to so even less heat goes up.

[michaellatif]

PEEK is mainly used as an insulator in this scenario. It helps limit the amount of heat transferred from the extruder to the mounts and rest of the carriage.

[Dave_Sohlstrom]

Mike I agree. I could not think of a material that would do a better job so I kept the PEEK. Who in the group knows the temp that PEEK starts to soften and melt. I do know it melts real well at 650F.

[Leeway]

Thanks for confirming what I suspected, guys. Here is the Peek WIKI.
http://en.wikipedia.org/wiki/PEEK

It has the temp range there.

So the biggest issue for me will be heat dissipation at the hot end mounting point. I'll get to thinking on that one. Look forward to seeing your results, Dave.

[Dave_Sohlstrom]

interesting the wiki says it melts at 662F so I guess my temp probe reading around 650 was close. Kind of hard to tell with the panic of getting it shut down.

[mhackney]

Like most polymers, PEEK does not have a discrete melting point. Many factors influence the polymer when it is synthesized that have an effect on MP. A ceramic material might be a good option. There are millable ceramics that do not melt and are good thermal insulators. I haven't investigated them for awhile but it might be worth looking in to.

cheers,
Michael

[@CiDG]

That really stinks, Dave. I really like the new hot end you're building!

The second time I powered up my printer, I stepped out of the room to do something and I smelled something hot. I ran back in and while it hadn't melted or gotten distressed, there wasn't any good reason for it to have gotten so hot. I shut down and turned my thermostat down as far as possible (just a few degrees rotation, as I am running a 10 Ohm resistor). I powered up again and I have never had a problem again. I am concerned the velleman may not be the best setup for regulating temp without some sort of overheat alarm or an emergency shutoff relay.

[Leeway]

Here is another interesting link or Wiki about DIY hot ends if you haven't seen it. Some interesting info there.

http://reprap.org/wiki/DIY_Direct_hot_end