1 (edited by lawsy 2012-11-18 04:47:13)

Topic: Replacement hot end guide

This guide shows how to change the hot end for a setup which should be more reliable, more durable and above all, much easier to take apart.

The setup is also designed to use as many of the original parts as possible, making it a simple and cheap upgrade.

The Problem

The factory hot end is a maker gear model, which requires the forming and curing of a ceramic material around a nichochrome wire. To unscrew this heating element, force must be applied to the outside of the ceramic, and in my case trying to disassemble to clear a blockage destroyed the heater. The brass barrel also sheared when trying to get everythng apart:

http://img690.imageshack.us/img690/9744/01oldhotend.jpg

The default thermistor is also placed delicately and simply taped to the outside of the nozzle. Temperature readings for this are questionable. Pulling apart the whole thing to change or clear the nozzle is a big pain.

One considerable advantage of the hot end, however, is how slimline it is.

Step 1: Parts & Tools

The minimum needed are these parts or equivalents:

Tools required:

  • Soldering iron

  • Heat shrink

  • Thread tape

  • A hacksaw and file

  • A drill and ~6mm or countersink drill bit

  • Replacement wiring plugs and a crimping tool (optional)

Step 2: Prepare Metal Parts

The aluminium heater block needs to be shortened to stop it from touching and melting the plastic extruder motor carriage. It may be possible to shop around and buy an aluminium block that is smaller and does not require this.

Cut approximately 6mm off the rear of the block with a hacksaw as shown. Quickly file the freshly cut surface to remove any burrs.

The brass barrel also needs shortening. If may be possible to reuse the original brass barrel or buy one which is the right length to begin with.

Cut down the new barrel until it matches the old one. File the end clean, taking care not to damage the thread. Now drill slightly into the freshly cut end to give it a filament friendly conical opening.

http://img443.imageshack.us/img443/2267/02cutandfile.jpg

Step 3: Wire Up Heating Resistor

The new hot end does away with nichochrome wire is favor of a heating resistor (like the bed uses). Simply snip the old wires just past the nichochrome wire, and solder them to the ends of the resistor. Clearly you will need to thread the resistor through the aluminium block and have heat shrink ready before you do this.

It is important to insulate the wires coming out of the resistor well. Don't let them short on the aluminium block.

Use the thermal paste from the kit to either coat the resistor or fill the hole the resistor will sit in. This helps the heating performance.

Please note that in my image I chose to rewire the plug for the heater to be more reliable. This is an optional step.

http://img835.imageshack.us/img835/9071/03resistorwired.jpg

Step 4: Mount Thermistor

The thermistor reads the temperature of the heater. Although the hot end kit comes with a new one, the original one is better to use so firmware changes can be avoided. As a bonus it also fits snugly in the small hole. Push it in with some thermal grease and use 6mm kapton tape to wrap it in place.

Please note that in my image I chose to rewire the plug for the thermistor to be more reliable. This is an optional step.

http://img442.imageshack.us/img442/5055/04thermistortaped.jpg

Step 5: Assemble Barrel and Nozzle

While you have it handy, use the 6mm kapton tape to wrap the aluminium block a few times sideways. This hold the resistor wires in place and stops the first section of tape coming undone.

Now Place some thread tape on one end of the brass barrel. This should NOT be the end you drilled the conical shape into.

http://img607.imageshack.us/img607/51/05threadtape.jpg

Screw on the nozzle as tight as you can with your fingers, and then screw on the aluminium block from the other end against it. The beauty of this system is that you can place the block in a vice and then use a spanner to screw the nozzle aganst it.

http://img689.imageshack.us/img689/7787/06hotendassembled.jpg

Step 6: Prepare PEEK and Complete Assembly

Take a file to the sides of the PEEK barrel so that they become flat and a spanner can be reliably placed. This is a simple step that makes assembly and disassembly much easier in the future.

You can now use a spanner on this and the nozzle to screw the hot end assembly into the PEEK barrel tighly. When pulling everything apart in the future, just reverse these steps starting with this. It is immensely easier than pulling apart the old system.

http://img9.imageshack.us/img9/2372/07assembly.jpg

The completed assembly is pictured below. Note that the PEEK barrel spins freely in the acrylic extuder, so take advantage of this to get the wires coming out the right way.

Step 7: Minimal Software and Firmware Tweaks

Firstly, if your nozzle is anything other than 0.35mm, set the new value in your slicing software. Mine was 0.34mm.

Secondly, the heating performance of the new unit will be terrible because the PID settings in the firmware are optimised for the old heater. Fortunately this is an easy fix, and requires no firmware flashing thanks to the Sanguinololu's on board EEPROM. This stores some configuration variables, regardless of power outages or firmware upgrades. Using the screen below is the best way to make calibration changes.

Send the manual command in Pronterface or Repetier-Host:

M303 S200 

The firmware will now test the heater by cycling it to the temperature you specified, and then give you the best PID settings.

Look for the message pictured and write down the values. You may need to reset the machine at this point. For me I receive errors afterwards.

Navigate to 'Config > Firmware EEPROM configuration' in Repetier-Host. The dialogue box below will appear. Enter your PID values and click 'Save to EEPROM'. A confirmation message will appear in the log.

Please note that even when upgrading the firmware, values stored on the EEPROM are prioritised. The 'Restore factory settings' button will wipe the EEPROM values and then read from the firmware values.

http://img703.imageshack.us/img703/6710/09pidcalibration.jpg

Step 8: Print!

Don't forget to recheck your z-height with the new nozzle. Avoid any silly mistakes where the nozzle crashes into the bed. Apart from that, the new hot end should work exactly as the old one did.

I've found that the temperature needs to be set higher for good printing with the new hot end. I put this down to the thermstor no longer reading so far under. This means that the actual temperature is probably similar, but the reported temperature is now more accurate.

I used to print at 200 but now 210 is required.

Since the new hot end is compatible with the old PPEK barrel, the acrylic extruder can be changed to another design without complication:

http://img839.imageshack.us/img839/1595/01originaldesign.jpg

2

Re: Replacement hot end guide

Thanks for the guide! I'm looking forward to getting my parts from BilbyCNC.

Two questions for you - how quickly does this heat up in comparison to the old nozzle?
Have you had to insulate the hot end to minimise any damage to the carriage or any other component?

3

Re: Replacement hot end guide

Before the PID change was made, it was bloody slow. After, it seems to have the same performance.

I think insulation would be a good idea just to help it heat faster and then use less power to maintain that heat. The surrounding components at this stage seem fine. IR thermometer on the peek barrel has it at ~135 degrees C.

One thing I think is happening is more accurate temp readings. The old setup had the thermistor on the outside of the nozzle, where as now its inside the block in between the nozzle and the heater. I'm printing at 205 or 210 instead of the previous 200 and this is getting good results.

4

Re: Replacement hot end guide

I guess you are bailing on the cooling fan?  I wonder if the block could be machined to a small cylinder and still work effectively. As soon as school ends in a few weeks, I will be trying the Bowden set up and would like to move to different extruders and cooling fan setup. This one seems promising.

5

Re: Replacement hot end guide

I'm too reliant on the fan to ditch it. Upcoming will be a new fan shroud to fit over the new hot end. Might change the style though, getting one to fit nicely will it very bulky.

The other one was too bulky for my liking, but credit to Ian's original design because I couldn't really find anywhere to make it smaller or more efficient.

6

Re: Replacement hot end guide

Try the left side.  I think there would be room there, and it wouldn't bump the door.

7

Re: Replacement hot end guide

Currently for reasons unknown I'm unable to move the print head the entire way to the left. In the last 10mm something fould but I can't work out what. I though it was the plugs for the hot end but holding them out of the way does nothing. I've also taped the loom so it comes out the back and this didn't fix it either.

8

Re: Replacement hot end guide

Can you move it manually all the way by just pushing it back and forth when the motors are off?

9

Re: Replacement hot end guide

Good question. Will check later today when big print is finished. Just having to restart it as two hours in the filament spool was stuck and causes the y stepper to skip a few mm. Not happy at all.

10

Re: Replacement hot end guide

Just like to point out my edit in the original post for those thinking of doing the mod:

I've found that the temperature needs to be set higher for good printing with the new hot end. I put this down to the thermstor no longer reading so far under. This means that the actual temperature is probably similar, but the reported temperature is now more accurate.

I used to print at 200 but now 210 is required.

At 205 or lower I was getting filament strips on the faster extruding sections. I haven't really cranked up the pace yet but even higher might be needed for faster printing.

11

Re: Replacement hot end guide

I notice you use PTFE tape on the threads. what about using hi temp anti sieze on the threads  instead of the tape.


Thanks
Dubbsd

Ultimaker S3.

12

Re: Replacement hot end guide

All I had lying around was ordinary plumber's thread tape. The first time I put it together, molten plastic oozed up the thread and out above the nozzle, which seems to be gone now. In the first pic you can see that my original hot end had plastic in the threads too.

Perhaps thread tape or your solution should be in place for any hot end.

13

Re: Replacement hot end guide

You don't mention where you bought or what size Resistor you used as there isn't one on the OEM hot end. Also no mention
if you have it of a source for a new thermistor? My reason for both these is I though I might want to build up a couple of new hot ends so I could have one ready to go in if one went down on me. Just two days after starting up my SD2 I believe I have a clogged nozzel. I need better production than that. [chuckle]

Thanks.

14

Re: Replacement hot end guide

Roughly a 6ohm resistor would be OEM replacement.

15 (edited by lawsy 2012-12-10 20:09:27)

Re: Replacement hot end guide

Irish wrote:

You don't mention where you bought or what size Resistor you used as there isn't one on the OEM hot end. Also no mention if you have it of a source for a new thermistor?

Please read carefully.

I bought the resistor and thermistor as a kit with the aluminium block which is described and linked to in step 1.

I also explain in step 4 that I used the original thermistor instead of that from the kit.

16

Re: Replacement hot end guide

Lawsy,

I went ahead and added an entry to the 'Modifications' page of the wiki that just links to this post.  I see that there is a partially created wiki page on this topic already where this information could be mirrored.