During the conversation following my original post on the MakerBot support forum, CodeRage suggested using cartridge heaters. I asked Eks about that and he said something along the lines of “Damn straight! We used ’em all over the place! Just do it!”
CodeRage plans to retrofit his MK5 head with a pair of 230 V 150 W heaters running at 120 V to get a total of 75 W. I have qualms about running line voltage around the extruder head, but it’s certainly a better solution than toasting power resistors.
The trouble with 1/2-inch models is that they don’t fit conveniently on the Thermal Core. I’d make an adapter block with a hole for the heater and two holes for the existing cap screws, but the screws don’t quite pass around a half-inch cartridge heater.
He suggested 1/8-inch heaters from Sun Electric Heater Company, which look like just the ticket except that they’re nigh onto 40 bucks a pop. Ouch.
High Temp Industries [Edit: new link 2013-12-27] has 1/4-inch heaters for under $20 that will fit in the space available. If I understand the configuration options, you can even get 12 V 30 W heaters (the same power as the existing resistors) with a 1000 °F (call it 500 °C) temperature rating.
So I think what’s needed is to get some of those heaters, machine blocks to hold them on each side of the Core, and see how that works. The heaters will fit between the resistor screw holes and the Core is just about exactly 1 inch long. What’s not to like?
This might work… except for the fact that HTI has a $150 minimum order, which is somewhat off-putting even for me. Anybody up for a group buy of ten cartridge heaters?
Note that if you swap in some cartridge heaters, you really should do the separate +12 V supply Extruder Controller hack described there.
[Update: Zach @ MBI has ordered a stack of cartridge heaters for their internal testing (he promises to send me some), plans a retrofit kit, and may become a retail source for the heaters. He reports the lead time to get heaters in bulk is something over two weeks, which is a lot longer than I expected.
In light of that, I will hold the “group order” until I have a better handle on what’s needed to retrofit cartridge heaters into the existing MK5 head, how they’ll actually work, and what PID loop retuning may be required. Once I know more about all that, we can proceed.
Having MBI handle the ordering & shipping makes sense to me!]
The Smell of Molten Projects in the Morning 
Put me down for two cartridge heaters… I’d be shocked if you couldn’t get enough people to give this a try. Contact me if you can’t… My Cupcake should arrive on Tuesday :-)
– Steven Ciciora
I’m in! Count me for two as well :)
Have you considered using a single higher wattage cartridge heater? It would bring the overall cost down of upgrading from the current resistor configuration.
I would also be interested in joining a group order.
a single higher wattage cartridge heater
The thermal resistance from resistor-to-Core is around 1 C / W, which means a 60 W heater would run at nearly 300 C. That’s scary-hot next to the plywood Z platform and below the acrylic Extruder Frame; I can think of plenty of ways that might go wrong in a hurry!
A pair of 30 W heaters that duplicate the thermal performance of the existing resistors seems like a better idea. A single 30 W heater should work, although the warm-up time is much longer, and I have some numbers on that situation that I must write up.
I’ll take two as well. Sounds like a worthy upgrade.
Saw the Square ones they mention in the catalog, really nice stuff!
I am going to build my MK5 this week as is and retrofit later :)
Thanks for finding the supplier!
retrofit later :)
That’s entirely reasonable; many folks are running the stock setup with complete success.
As I said before, electrically insulate the thermocouple from the Thermal Core and add a ground wire, so if a resistor blows you won’t lose the Extruder Controller, too.
Not sure why I am so fascinated by your experiments since I don’t have a makerbot of any sort, but I guess I might get one sometime. Anyway, if all you want to do is run tests with different cartridge heaters there is always ebay http://bit.ly/e5CfZU
It’s the same fascination we all have with a horrible automobile collision: you can’t help but rubberneck as you drive by, while thinking “Dang, I’m glad that’s not me over there!”
And the trouble with eBay is that I need a specific heater: 1/4 inch diameter, 1 inch long, 30 W. I sifted through their listings a while ago and came up dry…
Love your website. Thanks for all of the hard work. After reading about your search for inexpensive heaters, I came across my old Weller battery operated soldering gun. The heating element is built into the replaceable tip, and it runs on 6V DC. It’s rated for temperatures up to 950 F. The replacement tips retail for 9 to 10 dollars each. I bet they could be purchased for cheaper in bulk quantities. The resistance of the tip element is 5 ohms. The handle delivers 6V from 4 “AA” batteries, and it heats up fast. The connector looks like an RCA type plug and very amenable to hacking.
Here’s a fact sheet from the manufacturer:
http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=037103221551
The tips just pull right off for replacement.
This might let you avoid the problem of running 110V through the makerbot. Also because the tips are basically cylindrical in profile, it would (in theory) be super easy to attach to the thermal core. Take a small block of aluminum, drill holes for the mounting screws, do the machinists’ cut/clamp/drill technique and you’ll have a mount that will hold the soldering tip super tight without the risk of crushing the tip if the installer accidentally over tightens the mounting screws. You might have to develop some kind of fail-safe to shut down the heater in the event of “stuck in on position” error (getting the thermal core to 800+ degrees F would be a really bad day for the makerbot).
Not sure if any of this is feasible, but I saw that tiny, self-contained, 6V, 950 degree heater and thought you might have use of it. Best regards, and thanks again for a great website.
Fes
tiny, self-contained, 6V, 950 degree heater
The keyword there is tiny: it’s designed to deliver pinpoint heat, rather than create a bulk temperature rise. The instructions say 8 and 11 W, but that sounds optimistic to me…
The MK5 head requires about 25 W to maintain 220 C, two or three times more than the soldering iron tip can provide. Yes, you could over-power it, just like the resistors, but then you’re headed down the same path that got us here.
It’s certainly a difficult problem and I’m not sure I have the right answer, either!
Thanks for the good words; I’m trying to document enough of my experiments that other folks will know what works and what doesn’t.