P3Steel Build Log (#18) – The Hotend (Mount and Assembly)

By ChunkySteveo,

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The Hotend Mount

The hotend assembly consists of five parts in the list of printer parts from Toolson. They are as follows:

  • P3sTE_MK2_fanduct_v3_4_left_r.stl – the left hand side fan duct.
  • P3sTE_MK2_fanduct_v3_4_right_r.stl – the right hand side fan duct.
  • P3sTE_MK2_groove_mount_clamp_v1_0_r.stl – the small ‘c’ shaped part that connects the hotend to the mount within the semi-circle groove.
  • P3sTE_MK2_rework_adapter_v3_1_r.stl – the x-axis carriage mount
  • P3sTE_MK2_rework_adapter_part2_v3_1_r.stl – The small cable management clip.

Making the Bracket Stronger In Tinkercad

When printing these, I had a lot of issues with the carriage mount near to the M4 nut traps. Every time I printed it and test fitted it, the part would crack. Again, linking back to my issues with the brass bushing clamps – I think my PLA was just not up for the job, even at a high infill and three perimeters. To solve this I imported the STL into Tinkercad and added in some extra material around the bottom nut traps (which are seen below as the top ones, as the part prints upside down!). You can see the difference in the parts below.

You can download the STL part here if you need it – p3ste_mk2_rework_adapter_v3_1_r_stronger.

Even with the extra material, you can see in the test mount images below (third one) that the part still cracked. I was done at this point after several failed prints – so I opted to super glue the part together as I knew I would be re-printing it eventually in stronger PETG. In the images below you can also see the cable management clip attached at the top. To attach the hotend mount to the x-axis carriage you need four M4 nuts pressed into the nut traps in the mount part…

and four M4 bolts screwed in from the back. This makes the part rock solid to the x-axis carriage. There’s something a lot more solid about using M4 bolts compared to M3’s?! 🤔

To fasten the cable management clip to the top, you thread in two M3 bolts down and secure them with two M3 nuts which can be pressed into their nut traps in the underside of the mount. This part isn’t really required, but it does help keep things tidy and to keep all the cables and wires safe and secure.

Now you’ve seen the mount, check out the time lapse video of the stronger part being printed. Unfortunately this is the only time lapse print of the whole hotend assembly that I captured, so enjoy it.

Now that has been printed and test fitted to the x-axis carriage – you will need to take it all off to help build the hotend assembly. Now we’re getting into the hotend, heat blocks, wires, fans… ooohh! 😍

The Hotend Assembly

So the remaining parts you have printed at the two fan mounts – left and right, and the horseshoe shaped groove mount. We should also now have all our hardware too for the whole assembly. This means you should have:

  • Your hotend – an E3Dv6 or similar, or Chinese clone (more on this in a bit!), heater cartridge and thermistor.
  • Two 35mm blower fans, 12V ideally.
  • One 30mm fan (which should come with your E3D or style hotend, and the self tapping screws.
  • A couple of 2 pin JST connectors. I got a pack of multiple JST connectors, you never know when you need one – http://s.click.aliexpress.com/e/au72VJq
  • Six M3 nuts, and six M3 bolts

To get a run down of the whole assembly, watch the time lapse of the whole event below. Then follow the images after the video to give you a more in-depth breakdown of each step.

Mounting the Fans

First up are the fan ducts. They sandwich together with the two semi-circles making a full circle. You can then screw in the 30mm hotend cooling fan using the screws that it came with. If you got an E3Dv6 or similar clone, you can take the 30mm fan off the (usually) blue fan duct and use that. This will give enough support to hold the two fan ducts together.

You can then fasten the now single piece to the hotend mount by inserting two M3 nuts into their little nut traps on either side and then screwing down four in total M3 bolts through the mount and into either fan duct. You need to get the M3 bolt length spot on here as there’s not much room for excess thread. Once the whole hotend mount and fan ducts are in place, you can if you wish thread in the two remaining M3 bolts into the top of the mount piece, which will then screw into the hotend groove mount later – just leave them sticking out a little.

Next is on to the 35mm blower fans, which will become the part cooling fan(s). The two fan ducts have space for these fans, four tiny holes which allow for self tapping screws to be used, and a small cable duct which allows for neat cable management of one of the fans. Looking at the hotend assembly face on – the left hand side fan will/may (my fans had the power cable coming out the left hand side of the unit, see below) need the power wires routing behind the fan and into the small ducting channel. Once in, screw down the fan with some tiny self tapping screws.

TOP TIP: These screws need to be small, and can be hard to get in small quantities. If you’ve got some old plastic toys lying around that are broken – they will probably be assembled with just the screws you need? I managed to cobble together enough spare screws to fasten both fans down. And don’t forget to align these blower fans correctly – there should be a gap in their side housing where the air flow blows out of – that obviously need to point down and into the fan duct plastic!




So by now you should have a lot of fans bolted and screwed on. You will need to manually route their power cables neatly back and up through the “back top” of the whole assembly mount. Try to keep it neat and not block any fan ports or blades with any cabling.



Wire Up The Fans

There are three fans in use on this assembly, but in reality there are only two – as we are going to combine the two side blower fans into one single fan (that the RAMPS board and firmware can see). The other fan is obviously the rear 30mm hotend cooling fan.

To combine the two side cooling fans we need to connect them IN PARALLEL, not series. This means that the red of one fan connects to the red of the other, and black to black. We wouldn’t connect them in series (red to other black) as this would mean the first fan would get the 12V it needs, and the second one would barely spin, if at all. Wiring them in parallel allows them both to get the 12V they need. Follow my guide on the RAMPS Cooling Fan build log to give you an idea how to do this – to give yourself a single red and black power cable.

You should now have two power cables that need to get to their power, via the RAMPS board. Both will be controlled by the RAMPS board, or even simpler – they could both be hard wired to a 12V supply and be on – all the time. But to get to the power we need to route these wires from the moving hotend assembly and x-carriage up and down to the power and RAMPS board.

This is where you should start thinking ahead… You may want to experiment with different hotends, new fans, whole x-carriage assemblies. You may damage a fan or need to replace one that starts to make horrible grinding noises when it starts up (!!!!!). The plan is to make the whole hotend assembly a single unit which will screw into the x-axis with four simple M4 bolts. It makes sense to allow the cabling to be connected in such a quick way too – this is where connectors come into play. Instead of hard wiring the two fans, heater cartridge and thermistor with a metre or so of cable, introduce a break in all connections so you can quickly and efficiently detach all cables when you physically detach the assembly from the printer – much like a re-usable umbilical cord!? 👶

To do this – for the fans at least – you need a couple of 2 pin JST connectors or similar. A connector that will take the red and black wire, allow you to easily unplug it, and also be capable of taking the power (Amps) needed. For these fans, they will only be drawing several hundred milliamps of current – so some JST connectors would work great. Crimp away! If you missed my affiliate link to some packs of JST’s that I used – http://s.click.aliexpress.com/e/au72VJq – take your pick!


As you can see in the image below, I have cut the cables to a suitable length that  I will be able to cable tie them to the cable management clip (that you can just see poking up in the image!). I can worry about the length of the other part later when I know what to measure up. I have connected one end of the JST to each fan power cable, and then added in some black heat shrink to keep it all neat.


More observant of you would notice that I connected the female part of the JST connector to the hotend assembly. This means I will have the male end on the live 12V supply which could be shorted by a lazy screwdriver or a stray piece of metal. Following my advice when wiring up the PSU and the XT60 connectors (here) I would not follow the image below, but crimp and connect the MALE part of the JST connector to the removable hotend assembly. Then the (possible) live 12V line will be tucked away inside the female “bits”.


The fans should now all be wired up. It might be wise to mark which JST connector is the parts cooling fan, and which is the hotend cooling fan. I didn’t do this, and had to visually track the cables several times when connecting everything up. It became is a pain!

Mount the Hotend to The Mount

Now we are going to mount the hotend into the hotend assembly. The whole unit is designed for E3Dv6 hotends, or similar clones from China. There is little room between the two fan ducts, so it’s going to get tight very soon – breath out and suck your gut in!

E3Dv6 Hotends, or a Chinese Clone?

The following images and the time lapse video above shows me installing a Chinese clone E3Dv6 style hotend. They are almost identical in design, only suffering in the quality of the build and consistency of finish. I had intended to use a Chinese clone for my build, but if you skip ahead to when I got to my testing and calibration stage (i’m not writing this in real time, people!!) I had major issues just getting the printer to extrude more than a few centimetres of filament before it blocked. I had to disassemble and unblock the whole hotend several times. In hindsight – I didn’t truly know what i was doing with these aluminium hotends and I can now clearly tell I wasn’t securing the nozzle into the heat block and the heat break into the heat sink. Follow E3D’s guide to properly setting these up, even if they are the clones.

To cut the sorry story short – I was getting stressed just trying to get my pride and joy to print more than a maggot, so ordered a genuine E3Dv6 from Ooznest (here in the UK, check them out, they are great!) as they had a sale on at the time – fate right?! I now know a heck of a lot more about these hotends now, and have ordered smooth heat breaks and other “cloned” parts for me to experiment. With the ability to remove the whole hotend, fans and all within seconds – I wanted to create a couple of hotend replacements to print harder materials, more exotic experiments, and just to play. I want to use my genuine E3Dv6 as the work horse, printing day and night without issue. I want to play with the Chinese clones like an irritable teenager – problematic, prone to failure, but potentially a hidden genius of rainbows dust and glitter!

If you can afford one, get a genuine E3Dv6 hotend, they rock, and just work – one less thing to pull your hair out for! On with the build – imagine the images below are a genuine v6 hotend, or not.


I’m assuming you have an assembled hotend with heat sink, heat break, heater block with a cartridge, thermistor and nozzle screwed in? The don’t need to be all fitted for final use, but screw everything in and finger tight it all ready for assembly. The groove mount part slips into the top slot of the heat sink. It’s a tight fit, so sand it down until it slides in tight. Don’t let it be loose, or it will rattle about and ruin your print quality. Keep testing the fit until it slides in tight. Then you can slide the whole hotend into the space in the hotend assembly. It should slide in with the heater block facing in or out, not sideways – as it won’t fit. See the image below as to how it slides in.


Told you there isn’t much room in there! It may not fit. You may have to bend the heater cartridge wires to 90° to get it to fit. Just wiggle the cables about and it should fit without any of the heater block or cartridge touching the plastic fan ducts. You can see the cables coming out to the back of the assembly in the image below. I have also cut them to a similar length of the fan cables. We’re going to do a similar treatment to them too so we can swap out whole hotends with one easy swoop.


At this point you can also test fasten the hotend down. You can screw down the two top M3 bolts down into the groove mount into two M3 nuts that you should have put in the plastic part. Did you miss that part? Take the hotend out and the nut traps on the c-shaped groove mount should be facing down. Add in two m3 nuts and then try again. The groove mount allows you to securely and tightly fasten the hotend to the mount assembly. It should be rock solid. Now lets take care of those wires!

Wiring up the Heater Cartridge and Thermistor

In similar style to the fans – I want to be able to quickly and efficiently remove the hotend from the assembly with repeat ability – to swap out nozzle ends, clean it, fit blockages etc. Another connector comes to the rescue. Now, you may just be thinking – lets use a couple more JST connectors, one for the thermistor and one for the heat cartridge. Unfortunately the JST connectors are only designed to take small loads – i.e. the amount of Amps going through the pin connections. The more amps you drive through a connection interface, the hotter it gets. The hotter it gets the more likely it is to melt or short out and fail.

We could use a JST connection for the thermistor – this connection uses little to no actual power as it is acting as a resistor. The small amount of power used would work fine with a JST connection. The heater cartridge however is all about turning power into heat – A standard heater cartridge for a 12V system is 40W, so that’s about 3-4 Amps used to heat it up. This is too much power for a JST connection, we need something else.

Using MPX Connectors For the Hotend

Toolson gave a solution for a suitable high power connection, which is the MPX connection. This connection is used in RC setups and is designed for high power lines, up to 40A in fact. This connection is a little overkill in terms of power rating, but it is small, easy to connect/disconnect and also has several individual lines in one package. This allows us to use a single MPX connector to route the heat cartridge and thermistor in one package. I was able to get a pack of these, which allows me to wire up and prepare several hotends for replacement and/or testing:

MPX Connector’s plug 24K Goldplated pin 40Amp

Similar to how we have connected the XT60 connectors we now solder together the four wires (two heater cartridge cables and two for the thermistor) to the MALE part of the connector. There are six connections to use, and you can use which you like. I chose to keep the heater cartridge cables apart from each other so they can’t overheat one part of the connector – this should help any heat build up dissipate. Don’t forget some heat shrink over the solder joints to eliminate any short risk, and to make it neater. You should end up with a connection that looks like the images below:



The hotend is now fully wired up. You can wire up the other end of the MPX connector using the remaining lengths of heater cartridge cable and thermisor wire. Don’t forget to match up the connections before soldering! Once soldered – add in some heat shrink wrap to the individual wires to protect them, and then add a single larger heat shrink to the whole bundle. With the hotend assembly going bath and forth all day, you want to keep all your wires together for added strength and stiffness.





You can even see more cracking issues I had with the hotend mount. The sooner I get this printed in PETG the better! 😩



Cable Management of the Hotend Assembly

We can now secure all the wiring to the hotend assembly to keep it all neat and make it a single unit when disconnecting and removing. The whole assembled unit is a solid package and a really great design – Toolson has done a lot of work designing this, and it shows!



  Comments: 13

  1. Nice thorough presentation. Quick question: why are you using PLA instead of ABS. The heat from the hot end may melt the PLA near it. And ABS isn’t as brittle so you probably wouldn’t have the cracking issues.