Hot End MKII-b

Please note that I have made myself another hot end since the MKII-b from all metal. It may be the worlds smallest hot-end. It is the size of a AAA-battery and uses a fan to cool. I have printed both PLA and ABS with it but I am not ready to release it yet. I am extremely busy at the moment and need to do some more testing. But it just shows that you can make hot-ends without a lathe and they work fine.

This is my current hotend. (Used only on my own designed printer)

14/11/2012

Ok, I have built my second printer and it is way faster than my first good old “wolfie”. The hot end has performed flawlessly and I am absolutely wrapped about it. It proves that this design works. It does not leak and it has never failed me. I have stripped the filament due to trying to print too fast, but never had any leakage happen.

I have made one change, instead of the copper pipes making up the heatsink for cooling I use an aluminium heatsink made for an LED downlight. $3 on ebay. Drilled a tight fitting hole for the center pipe to fit through. I use a small 40mm fan powered from the 12V rail to cool it. It is needed on hot days! If I print on days when the temp is 30 or more, I need to cool the upper part. (cold end) I tried with 5V, but that does not cool enough of hot days.

Anyway, easy to make DIY hotend that works a treat.

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It is the same design as my previous MK-II with a slight modification. Both have been working reliably on my Wolfstrap based design and I have done hundred+  of printing hours (started using this 8/4/2012) without any issues.

I made this modification after I realized that my printer being a slow printer, will never build up the same pressure inside the nozzle as a more normal fast printer will do.

I was very excited about my “new” hotend and totally forgot about the speed difference. My problem at the moment is that I can’t print at high speeds as I do not have a fast printer.

The way I have tested this design is like this:

• I heat it up to operating temperature of 230C. I then manually extrude at speeds starting from 25mm/min in pronterface. I have increased the speed up to 75mm/min and did not find any problems. Since I can’t print at these speeds by far, this is only an indication of what this design may be capable of. During printing the pressure builds up, releases and builds up again endless times and is a different scenario compared to just doing a manual extruding.
• I have crashed the nozzle while printing into cold plastic by accident. I have hit the end of my table, I have used a pair of pliers (with reasonable force) to see if it comes loose (brass and PTFE), but it is still going.

This test is not conclusive at the higher speeds as more testing needs to be done, but I feel that this modified way of mounting the PTFE and the brass nozzle inside a copper tube is working. I am currently printing, and when I have made another printer that can do normal speed printing I will most certainly do high-speed print tests.

The Modified MK-II is now MK-IIb:

The overall length is around 55-60mm.

Body and heat sink is made from half-inch copper pipe.

PTFE rod inside body is 10mm diameter with a 3.5mm hole down the centre.

The nozzle is made from a brass rod 3/8″ or 8mm threaded.

Making it:

Cut the middle copper pipe approx. 30mm long. Clamp carefully in a vice taking care not to squash it out of shape.

Cut small grooves about 2mm deep as shown in photo and clean off any burrs/sharp bits using a drill or knife/file.

Cut 2mm deep grooves in a pattern like on this photo, using a hacksaw.

Now make the nozzle from a approx 43mm long brass rod (3/8″ or 8mm threaded rod). Shape it using drill-press, hacksaw and file, as explained in more details here but use measurements from this page. 3.5mm hole down the middle and 0.35mm nozzle hole or what ever size you are after.

The principal of holding the nozzle inside the copper tube is the same as before, but the grooves have changed a bit. See photo below:

Brass nozzle with “new” grooves.

Grooves in my new nozzle

The large grooves are 4mm wide and I put a chamfer on the end to make it easier to press fit into the PTFE after. I also took the sharp edge off the top of each groove as well. The diameter of the end with the grooves is 7mm.

Approximate dimensions of the nozzle.

My sketch when making this hotend

The thinking behind the groove change is this: The smaller grooves are like fingers. The PTFE is pressed into the groves for grip. When the pressure builds up these fingers holds on to the nozzle. But it only has to move 1mm and all grip is lost. By making the grooves larger (4mm wide) they go from fingers to hands, For any movement to occur there is much more PTFE to shift. Only testing on a fast printer will tell if my thinking is right I guess. I do not allow for any movement at all as to me that will be a failure.

Cut the PTFE approx 35mm long and drill a 3.5mm hole down the centre. I find that it is easier to clamp the PTFE and also to hold it straight if you do this: Place 2 small pieces of wood (10 x 10 x 50mm) together and clamp in vice. Drill a hole right in the middle of the joint which is approx 10mm dia. You should now have  two pieces of wood with a half hole in each. Use this to clamp the PTFE with in the vice. If you drilled it accurately, this way the PTFE is straight to the drill s well 🙂

Now drill a 5mm (yes 5 not 6 as before) hole in one end of the PTFE and 20mm deep. Must be deep enough for the groove end of the nozzle to go all the way in.

The next step is to press the PTFE onto the nozzle 7mm end. That’s correct, we are going to press a 7mm brass end into a 5mm hole in the PTFE. Trust me, it will be fine. Just need some careful handling. I use a small copper pipe to support the PTFE. Approx half the length of the PTFE. Just make sure this pipe is there for support only, and does not get pressed onto the PTFE.

It should look something like this after it has been pressed together:

PTFE tube after it has been pressed onto the nozzle

Time to make the heat sink or body for the nozzle. Cut 6 pieces of 1/2″ pipe at length of 15 to 20mm. I have used both 15mm and 20mm and have not noticed any difference. But this is yet to be tested later when I have a higher speed printer. Use a wire in a loop to hold the pipes together and then solder them. See photos.

Use wire to hold pipes together. (I reused some pipes for this one. Hence the extra solder mess 🙂

Note the position of the middle pipe. The one with the slots cut into it.

After you have soldered this together using a large soldering iron, or a cheap blow torch from the hardware store (any clean flame will do, no, not a candle light), you press the whole body onto the PTFE making sure the slots in middle section goes past the end of the PTFE.

Next you will carefully bend the little flaps slightly over the end of the PTFE. See photo:

Pressing the body onto the PTFE. Use an extra piece of pipe to push it all the way, as the pipe is much shorter than the PTFE.

Very carefully press the flaps over the end of the PTFE. MAKE sure they DO NOT touch the brass. If they do the heat transfer to the copper will be too big and the hotend WILL fail for sure.

After this the hot end needs to have a mounting. I have used some brackets. One each side and one at the front. I drilled and tapped a 4mm hole in the pipes and mounted it with the PTFE sticking into the extruder.

This is a good time to clean off any burrs and sharp edges if you wish.

I also made a chamfer in the PTFE to make it easier for the filament to enter. See photo:

Chamfer the PTFE to make it easier for the filament to enter.

Ready to have holes for brackets drilled and then fitted to my extruder.

I have used this hot-end on my machine with great success. If you look at photos of my machine, I also have tried this hot-end with lots of holes drilled in the surrounding copper pipes. This is to increase the airflow and hopefully the cooling of the hotend. Both work fine on mine, and I can’t tell if it makes a difference. You can also mount a small  fan but I don’t like that as it complicates the build and adds another element to the machine.

I guess when I have my next printer up and running I will be more on the same playing field as the rest of you who have a “normal” printer, and I will then be able to do some more testing on a faster printer.

Please note, I am not planning on buying a hotend yet. 🙂

Cheers