Hot Ends and Other Important Bits

2022-02-28 21:00 by Jonathan Buford (comments: 0)

Hot Ends and Other Important Bits


Yes, that is my finger in that picture. The little wire thingy is a 0.5mm drill bit. Finally was able to get started on building the hot ends for the MakiBox. Got working on the new lathe and found that the frame had cracked so that everything was not held in alignment. So, four hours later, I had a replacement and started over where I was this afternoon. Hong Kong is pretty cool that way, you just run over to the store that sells machines and tell them the first one isn't working.

So, I've done a lot of fine work machining before, but each kind is a little different. I started with making a couple of different tips, one out of brass and another out of stainless steel.

I started first with 1.75mm filament sizes so that I can test it first. If it looks like everything works well with this size, we will just go with it for now.

So, tomorrow will be a day of attempting to not burn myself with hot plastic, metal, or any combination of the two. 




Florian Horsch responded:
Good luck with everything! Regarding hot fingers: It's really useful to have a small silicone mat around - saved me quite some skin recently ;)
amramsey responded:
Looking good. You might have troubles with the stainless steel though as its thermal transfer isn't great. Aluminum might be an option instead?
Jonathan Buford responded:

Yep, thinking Aluminum with anodized coating might do the trick. Steel might work if it is thin enough, as the conductivity should mostly be an issue with thicker pieces. With steel, we can make it quite thin.

Jonathan Buford responded:

I'm using that for the hot end to surround it. It is the material used in laptops, comes in a sheet, so easy to die cut during production. And cheap.

ipeerbhai (Twitter) responded:
Hi Jon,

Here's some experience from my RepRap that may help your design. I have the makergear .5 brass hot end, and have owned a reprap Prsua for over a year now. Brass wears over time pushing PLA. My filament hole is now .69. I've probably pushed about 1.5 Kilos through to date, Ultimachine 3mm PLA. You notice it over time, as your print quality goes down over time. I never use ABS, as I don't have a heated print bed. I don't know if ABS will dissolve/wear hot brass.

I've wrapped nichrome for the RepRap hot end. It's no fun. Also, replacing hot ends is a problem. I've broken a hot end before -- threads got clogged with back-flow, nichrome wire broke when the hot-end mount failed under load. Replacing isn't too hard with the Wades, but expensive!

Have you thought of a cartridge heater? I think you could take a transistor or resistor and use it as a heat source. A transistor may actually work better than a resistor, as many transistors have known resistance/temperature curves, and you may be able to both use it as a heat source, and as a temperature measure.

Anyway, exciting progress! These videos are a great way to keep us all informed!

Jonathan Buford responded:

I'm leaning towards the nichrome approach, as I can productize it easier, have more consistent output, and it will be more compact. Keep in mind that I will be setting up a production process for these, so they can be a bit difficult for one offs, but easy with some jigs and tools.

That is an interesting thought about the transistor. Also, thanks for sharing about your experience with the brass wearing, I hadn't thought about that aspect yet, and I've not had to do a teardown of our RepRap to rebuild the nozzle. I will plan to do a RepRap conversion design once I have the new hot end and drive finished. It will be cool to get another 100mm or so travel out of the z Axis.

KNSRail (Twitter) responded:
just a thought, why not try a stainless steel with a brass core, this way you get the high thermal transfer of the brass without the worry of the extrusion hole warping or misshaping over time, plus from what I have learned so far about 3D printing having the extrusion cooling soon after coming out of the extruder helps prevent warping and makes bridging easier and cleaner, it could also give the extruder a cleaner and neater look. IMHO
Jonathan Buford responded:
Hi Karl,

That could be interesting, a press fit stainless tube with the correct ID for output would be pretty consistent. I'll have to do some experimentation.

Evan responded:
How much is the hot end itself likely to cost? If it's only a little bit ($10 or so) then it might be easier to just sell new ones rather than trying to design it to last for years.

In many other manufacturing processes (mills, lathes, drills, etc) it's accepted that the cutting bit will wear out and have to be replaced. Why should the head in a 3D printer be expected to last the life of the printer? If you can swap the hot end over for a new one in five minutes every five spools of plastic, that's probably preferable to spending hours dismantling and cleaning the old hot end. Of course, if you were printing something where tolerances weren't critical then you could also get away with using one of the old hot ends, just like people do with worn out milling bits.

Jonathan Buford responded:
Aiming for something in that range, as you say, fully assembled. Shipping would be excessively cheap. Gotta wait and see what the costing comes in at for the final design.


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