This is an alternative extruder hot-end design for the makerbot, though it may work for other 3d printers as well. The big advantage is that it does not require an insulator (usually PTFE or PEEK), which causes problems for some (or perhaps many). Instead, a stack of washers and nuts is used as a heatsink to reduce the temperature.It worked really, really well for me, no more stalled extruders, stuck filaments, half-way prints. It heats up rapidly less than 1 minute from 25 to 220 degC), and I haven't had any problems with it (yet..). I've only printed ABS so far, so I have no idea if it will work with other materials. My original version used an aluminum heatsink (bottom image), but I thought that might be a bit hard for others to duplicate, so I built this one. Works just as well, just looks a little less fancy.You'll need a small fan, stainless steel M6 bolt as well as a stack of M6 nuts and 25mm M6 fender washers in addition to asome components from a standard makerbot extruder.1 - Cut the M6 bolt to 65 mm length. Make sure the ends are flush, use a lathe if possible.2 - drill a 3.2 mm hole in the bolt, all the way through. You'll likely go through a few bolts and drill bits before you have something good. Take your time. Slower is better. If you don't have a lathe, use the "afghan lathe" method or a drill press. (Check instructions at bottom how to use a drill press for this). Note: This is fairly hard to do nicely. You'll probably have to drill from both sides, with the risk that the holes won't align up properly. If that happens, you could use a larger drill to enlarge the hole at the cool end, to make sure the filament feeds through well. I got it right at the first try, but I was using a lathe. Get a few extra bolts and spare drills before you start. Or go to a local workshop and ask if they can get it done for you.3 - Create a thermal barrier by reducing the diameter of the bolt to 4.8 mm, over 10 mm length, starting 10 mm from the bottom end. Check the images (IMG_1744) for details. You can do this on a lathe, or simply with a file.4 - Nozzle: (IMG 1740) cut the makerbot nozzle in height, leave around 5mm of height for the hexagonal part. Make sure the end is flush.5 - Heater: (Img_1745) I decided to make it separate so it can be removed or exchanged easily. Cut the threaded insert to about 5-7 mm length. Make sure the end is flush. Wrap the nichrome around it and fix with kapton tape. (refer to the standard makerbot extruder instructions if you\'ve never done this before). Start wrapping in the middle, then up and down a few times to make sure the nichrome doesn't easily slide off.If you can't find a threaded insert, use something else that has M6 thread and an outer diameter of about 8mm. Brass is probably the best.6 - Heatsink: The washers are just a little too large to fit in-between the M4 bolts that nurmally hold the extruder. Cut some notches in the washers to make them fit.7 - Assembly: Screw the heater onto the low end, followed by the nozzle. Tighten the nozzle first, then tighten the heater against the nozzle. The heater should sit tight to the nozzle. If there is a gap between the heater and nozzle, it will be harder to transfer the heat to the nozzle. It may still work, though. (img_1748)create a stack of M6 bolts and washers, include the MK4 retainer washer is at the bottom. Tighten everything well. Make sure the notches in the washers are aligned with the holes in the MK4 retainer washer. (IMG_1756)Don't forget the thermistor and the insulating blanket. (IMG_1758)Mount everything with the M4 bolts that came with yoru standard MK4 extruder. Check the length of the bolts, you may want to use a few washers to make sure you don't break the plastic housing.Last (but not least): use a fan to cool the heatsink It may work without, but if it heats up too much, you may break your extruder housing. You can mount the fan on the extruder platform with a dab of hot glue.Drilling the 3.2mm hole with a drill pressYou should now have aligment between the axis of the drill press and the axis of the bolt.