Please note that I have designed a newer version MK-II which I am now using with great success. The methods of making the parts are still here on this page. But dimensions have changed.
I have tried a few designs and to my surprise my first ever hot end and nozzle, worked quite well. But I soon realised that I was going to have some trouble keeping the temperature at 230 degrees. The trick is to avoid the heat travelling up the hot end during printing. If it does, then the filament goes soft and you lose pressure and jamming is unavoidable. The temperature in the nozzle drops as well as the heater is struggling to keep up with the heat loss travelling up the hot end.
I have now made a hot end and nozzle which seems to work very well. I have printed many parts and can’t say I have come across any problems yet. It is rock solid. When it heats up and the pressure from the extruder builds up, I have not noticed any movement at all in the Z-axis.
I use a brass rod with 8mm thread for nozzle. 10mm round PTFE as barrier and a half inch (10.5mm internal diameter) copper pipe to support the PTFE. I cut the pipe approx 80mm long. Clean off any burrs inside.
PTFE is cut to a lenght of approx 90mm and I drill a 3.5mm hole through. I found it easier to drill from both ends and meet in the middle. This way it is centered at both ends. Open up one end to 6mm and to a depth of 30mm. Clean out any bits of plastic very well.
Put the brass rod in the drill press and flatten both sides using a file.
Using a file make one end pointy, just leaving a small flat in the center.
Using a good file this is quite easy to do.
Drill a 3.5mm hole almost through leaving approx 1 to 2mm left for the small 0.35 hole at the end.
Place the pointy end in the drill press and lower it down into a vice which is fastened to the drill press. Clamp the brass rod with the vice and release the chuck.
When you now insert the fine 0.35 drill bit it should be very much in center of the brass rod. Using extreme care, and keep adding cooling (WD40) onto the drill bit, you drill the fine hole. Bit by bit, up and down very gently to avoid breaking bits.
You can polish the tip by using fine paper and drag it under the tip while it is turning in the drill press.
Place pointy end in drill press and file other end down to approx 7mm diameter and 30mm wide. Put a small bevel on the end.
Then use a hacksaw to cut grooves, 5,6 or 7. Not critical but they are very important. Be careful not to cut too deep as there is a 3.5mm hole in the middle of the rod. 🙂
Using a vice or equivalent, press the end of the brass rod you just cut grooves in, into the PTFE end having the 6mm hole. Make sure it goes all the way in. Now you take the copper pipe and press that onto the PTFE rod all the way down towards the nozzle so it covers the PTFE fully. This will secure a very tight fit around the PTFE which again is pressed hard around the brass nozzle to avoid any leakage. See my pictures.
This hot end has been running for hours with no problems. I normally don’t retract the filament after a print anymore as I used to. I just let the nozzle cool down with the filament in. When I start up again I let the hot end heat up to correct temperature and off we go. No problems.
To finish it off I attach the hot end to the back of a heatsink with an aluminium bracket. The copper draws heat off the PTFE rod very well and it is dissipated through the heat sink. I also have a small fan blowing air through the heat sink. Under the heat sink I put a shield to stop any air beeing blown onto the nozzle and heater. No problems holding the temp steady at 230 and above, but don’t heat your nozzle up too high as it can cause problems.
This may not be the most fancy hot end, but it works for me and has shown to be very reliable. And it can be made quite easily at home without a lathe.
It is very important that the diffence between the size if the brass-end and the hole in the PTFE is 1mm or more, and not less. 7mm brass and 6mm hole. If not, you will not get enough expansion of the PTFE to fit tight inside the copper pipe. This is crucial for the operation of the hot-end.
I have also made this in a shorter version (aprox 70mm), works very well. I don’t think size is too critical, so it can possibly be made much smaller if necessary, but you do need a heat sink and the heat sink will in most cases determine the length. Depending on your extruder design, the top of the hot end probably needs to be customized to suit your individual needs. I use brackets attached to the heat sink to mount it to the extruder.
This hot end can probably be improved in many ways and especially the cooling of the PTFE and copper pipe. At the moment the copper pipe is only touching the heat sink with a very small area. If the contact surface was to be increased the efficiency of the cooling would most likely be dramatically improved. Using a copper heat sink you could solder the pipe to it, but then it can’t be dismantled. Maybe solder some copper fins to the pipe instead of using a heat sink may work. Solder a flat copper plate to the pipe and then screw the plate to the heat sink or drill a large hole in a heat sink for the pipe to fit through.
You could also replace the tip with something like an acorn nut. This way you could change the hole size by just replacing the tip. I have made a nozzle wich is similar but find it quite hard to make it seal properly over long printing times. PTFE tape (plumbers tape) or similar is a must, but I find it quite fiddly to work with.
New MK-II hot-end is under development: MK-II
If you find that you extruded plastic curls up and attaches to the nozzle (very annoying), you have most likely got a hole which is not perfectly round and finished off flat with the tip. It is a bit hard to explain, but if there are any dents or marks on the edge of the hole it will flow towards these marks. It has got to do with the force applied to the filament coming out of the hole. If there is anything slowing down the flow the flow will be directed by this. Ok, imagine you have a polished hole that the plastic comes out of. If the friction is even all around the hole and the hole is finished off perfect all the way around the exit the flow should be even and go straight down. If there are any marks in one side of the hole (on the inside) the flow will be slowed down here. What this means is that more plastic will come out on the opposite side of the hole where there are no marks and push the output towards the side where the damage is. So if you have a minor damage to the hole opening, it will control or direct the flow. Make sense? Hmm, I will try to take some photos later on and post here for clarification. Another example that may make it easier to understand and see what is happening is to turn on your water tap. Now put your finger near the opening on one side. Gently touch the water coming out and it will flow towards the side where your finger is. A minor mark on the orifice of the nozzle will have similar effect.
If your nozzle is blocked I have found that the easiest way to unblock it is to:
- Remove the hot end from your machine.
- Heat it up to extruding/operating temperature (ABS 230 degrees).
- Carefully push a wire with a small eyelet on the end down the hot end until it is all the way down to the nozzle end. It should now be well embedded in the plastic.
- Cool your hot end down to approx 130 degrees or maybe a little bit less. Try.
- Now try to pull out the wire gently and all the plastic will follow. Like opening a champagne bottle. 😉
- Any rubbish that had found its way down the hot end should now have been removed