Some say that necessity is the mother of all invention, and I'd have to agree with them. When we decided to start MakerBot and launch a complete 3D printer kit for under a grand I knew we had a lot of work cut out for us. Transitioning the RepRap technology from a research project to something that is a product presents many challenges. One of my main tasks was preparing the Plastruder MK3 for production.
I had been developing the 3rd generation extruder as part of RepRap for a while and it worked great. However, there were parts of the process that just weren't suited for a DIY kit at all. The main problem was attaching the nichrome wire and thermistor to the heater barrel so you can accurately control the temperature. For years (literally) we've been attaching the nichrome wire to the heater barrel with some form of high temperature cement: first JBweld, then with fire cement and stove cement. The latest revisions for doing this all work, but I didn't like them.
Why? Because they are horribly messy. Stove cement is an awful, black compound that stains and is probably toxic as hell. Fire cement only comes in 55lb bags. Stove cement only comes in giant 5 oz tubes. All you need is a tiny amount of this stuff to insulate and bond the nichrome. Plus, it is a very delicate process to wrap the nichrome and then apply the goop the whole time hoping that you don't jiggle it the wrong way and have everything fall apart. If some of it gets in your extruder nozzle? Game over. Oh, did I mention that you have to let it sit OVERNIGHT to fully cure? You're all fired up to build your extruder and WHAM! Instant timeout.
So, what did I do? Well, aside from the intial panic, I decided to try about 10 different techniques and go with the best one. I tried all the various forms and techniques for dealing with high temperature cement when I stumbled upon this blog entry by Limor Fried of Adafruit fame. Something there sparked my eye: it was here use of the Kapton tape. Up until now I had not even heard of it, and maybe its the same for you as well.
After doing a few hours of research on it and realizing it was PERFECT for what I wanted, I quickly ordered a tiny little roll from McMaster for $4. As soon as I got it, I built a heater barrel assembly from it. It took me 15 minutes and I was able to use it right away. It was the fastest and easiest extruder build I had ever done. Usually when I built extruder barrels, I had to use some sort of tape to hold down the leads while I build it anyway. With Kapton tape, I didn't have to remove them and they simply became an integral part of the extruder itself.
Wow, that turned out to be longer than I thought. I managed to find a good supplier of Kapton tape so you can get it from the MakerBot store, and it will be a part of our upcoming Plastruder MK3 Kit which will start shipping Monday.
Nice find!
ReplyDeleteTwo things though:
I bought fire cement, and it came in much smaller than a 55 lb bag - a little 2 cup plastic pail.
Also - I can't quite tell from your picture, but do you really have tape rated only up to 500F directly against a heating element (nichrome wire)? I mean, the nozzle doesn't get above 260C/500F, but something that's glowing red-orange is going to have a surface temperature on the order of 1000-2000F. :o
A good source of Kapton Tape is Deal Extreme. ~$3 USD (depending on width) including shipping to anywhere in the world. http://www.dealextreme.com/products.dx/category.404~search.tape
ReplyDeleteLet me try that URL again: http://tinyurl.com/d7fz4x
ReplyDeleteThey have lot's of other good deals on tools as well.
This is something i found in my gluegun once i opened it. (The kapton tape that is)
ReplyDeleteI would've gotten a picture, but i don't know where it is now (i moved recently), anyway, it was wrapped around the cables that went into the heater barrel, wondering what it was.
I don't know what wire or heating element is used in it though, will try to find out.
Thanks a lot for sharing! :)
Do be careful - kapton doesn't seem to melt as much as catch on fire, which would be kind of inconvenient.
ReplyDeleteHas anyone tried a high-temp adhesive such as Silicone Gasket maker? This one (or an equivalent) should be fairly easy to find:
ReplyDeletehttp://tinyurl.com/dlrwee
That one is rated to 650F (343C). There are even higher-temp versions available, though they're probably harder to find. This one is rated to 371C or 700F:
http://tinyurl.com/csxy88
The same company also sells a 'metal repair compound' for repairing car exhaust systems. It "gets stronger with heat up to 2000°F." It can also be drilled, sanded, and tapped after curing, so it seems like it would be an ideal candidate for the extruder. Not sure how easy it is to find, though.
http://tinyurl.com/d8vvoe
Why not bore a recess for the thermistor to sit in? You should get better thermal contact.
ReplyDeletepoll junkie: may people have been using adhesives such as those, but as i wrote in the post, they are a real pain in the arse to use. nothing wrong with them, just hassle.
ReplyDeletecharles p: you can absolutely do that. it works just fine without the hole and there's less chance of messing up a machined nozzle.
This also seems useful tape:
ReplyDeletehttp://www.rescuetape.com/videos/latitudes-attitudes.html
Temp. tolerance seems a little low, though (260'C). Otherwise, it's still very useful for other applications.