Update 6-1-2017: Added instructions for how to make the silicon boot. Also added how to "season" the silicon boot after you make it.
Update 10-11-2016: After using the mold a couple of times, I found that if you do not apply enough mold release (Vaseline) to the base of the mold, it makes it near impossible to remove the silicon part in one piece, so I decided to modify the design to allow the base to be removed if necessary. I also went ahead and added some sprues/vents to the top of the mold and added a lip to help align the mold insert to the mold.
This is a silicon "boot" for your Duplicator 6 (and Zortrax M200) heater block. Its main purpose is to help stabilize the temperature of your hot-end. It has two secondary benefits. First, it helps prevent burns from touching the hot-end when clearing the nozzle or other tasks. Second, it helps keep your heater block clean as most plastic will not stick to silicon.
It is a 5 sided "boot" that slips on from front. The top part is split to allow it to cover to slide over the cold break. The boot is about 2mm thick on all sides--plenty of thickness for insulation. The back is open.
I used oogoo (high temperature silicon and corn starch mix). Here is how you make it:
As for "casting" instructions, these are the ones I followed when I made my mold:
I made a model of the hot-end in 123D design. I then made a mold from that design. It is just two parts. All you have to do is fill the mold up about a third of the way with the oogoo mixture and then push the top half flush with the bottom half. Also need to make sure all four sides are flush to make sure the mold is equal thickness all around. I use a slightly different mixture ration of 2 to 1 silicon to corn starch. Too much corn starch makes the silicon hard and it smells pretty bad until it is all cooked off.
I used PLA. 4 top and 4 bottom layers. 3 shells. The fine resolution made for less finishing as the inside of the mold was almost smooth to the touch. A small amount of sanding was required to make for a smooth sliding fit between the mold and the mold insert.
How TO make them:
I make 2 at a time and used 22grams on Hi-temp silicon to 2.5ml (1/2 Teaspoon) cornstarch all mixed up in a LDPE cup. Silicon (cured or uncured) will not stick to PE, so I use that to mix it up. You need to work the cornstarch into the silicon. At first, it will not want to mix until the silicon starts releasing the acetic acid. Then the silicon will blend with the cornstarch. Make sure that there are no pockets of cornstarch. Don't worry if you have unblended cornstarch on the sides of the cup. Just make sure that you ball of silicon is well blended with the cornstarch that it did mix with. Now, I put the cavity part of the mold on a scale and TARE it to zero. Drop in about 10.5g to 11g of silicon into the mold. Press the nozzle shape into the cavity and make sure it fully closes. You should get ooze out from the two vents on the top. Scrape the ooze and mix it back up in the cup. Now load the other mold on the scale and dump the rest in the second mold. Repeat and with any ooze out, put it back in the cup.
Now put both molds either top to top or bottom to bottom into a vice or clamp (a C-clamp or even better those squeeze trigger bar clamps) and clamp them together. You may get a little more ooze out. Scrape off the ooze and wait about 12 hours. It will take less time, but this gives it a lot of time to really form a thick "skin" so that you can remove it from the mold. It will continue to cure for a day or so. Hint, before removing the boot from the inside mold, grab a paper towel to help remove excess Vaseline off the outside of the boot. Then push down (with the split side up) and slide away to remove the boot from the mold.
Instructions for AFTER you have made them:
While these boots are silicon and they are flexible, they do not have a lot of stretch. If you pull them or squish them too much, they will crack because of the added corn starch. Once installed, they are designed to stay in place--you will more than likely destroy/tear your boot if you try to remove it.
Clean your Heater Block:
If there is plastic adhered to the heater block, I recommend cleaning the heater block before installing the boot. While it will should not hurt the boot or the heater block, it can causing tearing of the boot if there is a thick or sharp bit of plastic stuck to the heater block (the boot is a tight fit) and the trapped plastic will permanently stain the heater block.
Remove the filament from the hot-end and set the temp to 190'C with the boot on--install the boot while the heater block is cool. Let it "cook" for about 2 hours (longer is better) at this temp. You want to run the cooling fan at 100% as it will smoke and smell of burn bread for the first few minutes. This is any corn starch and Vaseline burning off. Now, the smell may turn acrid with any last bits of acetic acid that will cook off over the next hour or so. After this, there should be no more smell from the boot as they heat up.
The silicon I use is high temperature automotive type. It is good to 371'c. It will get slightly darker with heat and might even stick to the heater block after it has cooked on--mine did, making it almost impossible to remove without destroying/tearing it. It should not burn and plastic will not stick to it once cured. Obviously, the thick part of the boot with the split goes over the heat-break (top tube) while the bottom thick part goes over the nozzle. The nozzle should protrude through and, if necessary, a little bit of flashing of silicon may need to be torn away to expose the nozzle--but not much of the nozzle needs to be exposed. Do not cut or tear the thick part of the boot near the nozzle area.
I did not need to do an auto-tune of the PID. My machine was already pretty good holding a stable temperature. Your machine may be different, so up to you if you want/need to do a PID auto-tune.