In the world of RepRap, all-metal hotends have been a big deal lately.
Do you really need one?
On the one hand, they promise the ability to print in amazing new and exotic, high temperature materials with seemingly unlimited posibilities.
They also serve to calm the nerves of those (myself included) who have had the unfortunate experience of looking over at your printer, only to discover that you have inadvertently gathered field data on the melting point of PEEK, PTFE, or some other polymer. Maybe you’ve been lucky enough to salvage the brass parts after the puddle of goo has finally cooled, maybe not.
So why have we been making hotends out of plastic anyway? Couldn’t we use a metal tube and call it good?
Well, it turns out there are some problems with that approach, which are beyond the scope of this article, but suffice it to say that nearly all of them could be largely solved by using a PTFE (commonly known as Teflon) liner. This keeps the filament pathway smooth, sealed and unobstructed, and provides a very low-friction pathway to allow filament to proceed, even if it is a little bit oversized or oddly shaped.
The problem still arises, though, that there is a crucial piece of the hotend that is temperature-limited: PTFE generally has a maximum operating temperature of around 260 degrees C.
Enter the current generation of the all-metal hotend.
There are now a number of new and promising all-metal hotends on the market. Most of them do a really good job printing in ABS. A lot of them, though, are subject to mild to severe jamming when printing in PLA (some designs actually do a fantastic job of printing in PLA, but not many). For some folks this is fine, but I find PLA to be way too useful to give up, unless I was getting something REALLY good in return.
Losing out on PLA is not the only price of admission, of course. As I write this, an all-metal hotend will separate you from somewhere between 150% and 200% more of your hard-earned currency when compared with a PTFE lined hotend.
So, what exactly do you get for twice the cash and the potential loss of PLA?
Not long ago, I had a brand new, high-performing all-metal hotend in my hot little hand, and I wanted to see just what it could do. So I went to one of my favorite filament suppliers, Makergeeks.com, to see just what kinds of new, wonderful, and exotic materials were now available to me. At that time, my experience had been limited to ABS, PLA, and a couple of rolls of Taulman Nylon.
Of course, what I found is the only current, common printing material that needs to be extruded significantly hotter than ABS is polycarbonate, which is usually extruded at around 300 degrees C. It also generally costs more than twice as much as ABS or PLA.
I am currently waiting for a spool of PC to arrive, and I look forward to sharing my experience printing with it, but that’s for another post.
So, for up to twice the price, you get to print in polycarbonate.
Is that all?
Well, no. The lack of a polymer liner does have some significant maintenance implications. An all-metal hotend can be removed and dropped whole into a container of solvent for a deep cleaning, or even heated with a torch if need be.
There is also the possibility that an all-metal (or even a “mostly metal”) hotend can allow for faster printing. The idea is that the metallic construction can withstand higher internal pressure, so the extruder can then stuff filament into the hotend more quickly, giving a higher rate of extrusion. This, of course, assumes that the hotend is mounted in a printer which is otherwise mechanically capable of printing quickly enough.
So do you need an all-metal hotend?
If you see a need to print in polycarbonate, then yes, you do.
If not, you’ve got a decision to make. If you’ve got a solid, robust printer that can move the carriage around very quickly, the notion of easy recovery from a disaster-level jam appeals to you, and the price doesn’t turn you off, then an all-metal hotend is well worth looking into.