North90's hot-end

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Easy to build Hot End by North90ty

Release status: Working

North90 hot-end overview.jpg
Description Easy to build Hot End by North90ty
License GPL
Author North90ty
Contributors
Based-on Sui Generis
Categories Extruders, Hot End
CAD Models none
External Link none


Contents


This Hot End is designed to be build with simple tools and without the need for great engineering skills. This design is now superseded by Version 2!!

North90 hot-end overview.jpg


About the design

WHY another design? The complexity of most Hot End designs (lathe needed) and the use of hard to obtain and expensive materials (Peek) make it hard for the average person to build their own Hot End . This design is great for everyone who wants to build a Hot End but who doesn't have access to a lathe, cnc-machine and drill-press.


Thermal design

Each Hot End consists out of three main parts:

  • hot end where the plastic is melting (usually brass tube + nozzle)
  • insulator which keeps the heat away from the extruder (usually PTFE(=Teflon) rod)
  • cold end the cool part of the Hot End which mounts to the extruder (can be any kind of material)

This Hot End uses stainless steel as an insulator. Stainless steel conducts heat less easily than normal steel, brass or aluminium, but much better than PTFE. Here a table with thermal conductivities of commonly used materials in Hot Ends.

MATERIAL THERMAL CONDUCTIVITY W/(M*K) NOTES
PTFE 0.25 will deform when hot: can't be used as structural part
PEEK ~0.25 expensive+hard to obtain
normal steel 45
stainless steel 18
brass 120
aluminium 220
dry wood 0.05-0.12

from http://en.wikipedia.org/wiki/List_of_thermal_conductivities

The thermal conductivity of stainless steel is about a 100 times larger than that of PEEK or PTFE. To have a similar insulation value as a PTFE insulator the cross-section of the stainless steel insulator has to be a 100 times smaller.

A normal 16mm PTFE insulator (with a 3mm hole) has a cross-sectional surface area of 194mm2. The heat transfer for a PTFE insulator that is 25mm long at a temperature difference of 200C is 0.38W.

The stainless steel insulator of this Hot End has an 1/4" (=6.35mm) outside and an 5.7mm inside diameter. It has a cross-sectional area of 6.14mm2. The heat transfer for this insulator (25mm long and 200C) is about 1.1W. This is almost 3 times as high as a PTFE insulator of the same length.

The extra heat transferred through the stainless steel insulator has to be dissipated with a heat sink.


Tools and supplies

  • Drill + drill bits
  • Vice
  • Tap and die set: M3 tap, M6 tap and die
  • Tube-cutter (or fine metal saw)
  • File(s)
  • Cutting oil (olive oil works great)


  • Stainless steel tube with an outside diameter of 1/4" (6.35mm), inner diameter is not important
  • PTFE tube 1/8"(3.18mm)(3.5mm is fine too) inner diameter and 1/4" (6.35mm) outer diameter
  • M6 brass bolt (25mm long) or welding nozzle (0.6mm)
  • Piece of aluminium sheet 5-6mm thick

North90 hot-end parts.jpg

How to build the stainless steel insulator

Cut a piece of stainless steel tube of about 40-45mm long. An easy and very clean way to cut the tube is to use a tube-cutter. Stainless steel is very hard so it will take a while to cut through. Use (olive) oil to ease the cutting Personally i put the tube in the drill and let the drill do the hard work.

North90 hot-end tubecutter.jpg

Next step is to drill the inside of the stainless steel to have an inner diameter of 5-5.2mm.

  • Put the stainless steel tube in the drill and the drill-bit in a vice.
  • Drill the tube out in small steps, maximum 0.5mm at a time.
  • Use loads of oil (olive oil works great) to save your drill bits and make cleaner cuts.
  • Go slow, try to get long pieces of metal coming out of the drill instead of small pieces. If you start smelling the oil: stop, cool and add more oil.

North90 hot-end tube drilling.jpg

When the tube is drilled out to 5-5.2mm inner diameter, at least one end is threaded with m6 thread to be able to attach the hot end. Put the tube in the vice and use a M6 tap to tap thread in the drilled out end of the insulator. Use plenty of oil and go half a turn in, quarter turn out, half a turn in, quarter turn out. etc. Tap the tube as far as you can (when you tap it further the inner diameter of the tube is reduced over a longer length making it a better insulator). At least 10mm deep threads on both ends will work, but preferably try to get threads over the whole length of the tube.

North90 hot-end tube m6-thread.jpg

The stainless steel tube will be lined on the inside with a PTFE tube to reduce friction. The 1/4" (6.35mm) outer diameter PTFE won't fit in the 5-5.2mm inside diameter insulator. To make this fit the PTFE tube will be reduced in diameter with a M6 die. Put a +/-65mm long piece of PTFE tube 1/4" od (=6.35mm) in the drill, you might want to put a piece of metal in the PTFE tube to clamp it tight in the drill chuck. Slowly drill the PTFE through the die. Thread about 40 mm of the PTFE. Turn the welding tip in one end of the tube and turn the PTFE in the stainless steel tube all the way down until it is stopped by the welding tip.

North90 hot-end ptfe-thread.jpg

North90 hot-end insulator-parts.jpg

Clean the inside of the insulator by manually drilling it out with a 1/8" or 3.2mm drill.

North90 hot-end insulator-cleaning.jpg

How to make the hot end nozzle

Here it is shown how to make a heating tube with nozzle out of a welding tip with a inner diameter of 0.6mm. Alternatively you can make a tip out of a m6 brass bolt. The welding tips I found in Canada have a m6 thread on one end and has a smooth part of 1/4" (6.35mm) on the other end.

Sharpen the point of the welding tip, if you don't do this the plastic will stick to the flat side of the nozzle making ugly prints. Put the welding tip in the drill and sharpen it using a file.

North90 hot-end nozzle-sharp.jpg

Reduce the diameter of the smooth part to about 6mm so it can be threaded with M6 to attach a heater block or wire. (this step (and threading) is not needed when you make a clamping heater block)

North90 hot-end nozzle-reduce diameter.jpg

Now put m6 thread on the smooth part of the welding tip with a M6 die. I found it easy to clamp the drill chuck in the vice and thread it. (so leave the welding tip in the drill and clamp the drill chuck in the vice) otherwise the soft welding tip will likely get damaged in the vice.

North90 hot-end nozzle-thread.jpg

(i did a shitty job here, I started off on an angle. No problem though, this works fine)


Put some m6 nuts on the m6 thread and tighten them to each other. Put the nuts in the drill chuck and put a 1/8" (=3.2mm) drill in the vice. (update: a slightly bigger hole works better, drill to 3.5-4mm) Drill a hole in the welding tip to about 1-2mm from the nozzle. Use plenty of oil, go slow, make long chips. The drill will follow the 0.6mm hole in the welding tip making centring easy!

North90 hot-end nozzle-drill.jpg

North90 hot-end nozzle-drill2.jpg

North90 hot-end nozzle-drill3.jpg

When done clean out the nozzle, make certain no dirt is left in it!

The finished insulator and heater with nozzle. (you can easily do a better job the i did ;)

North90 hot-end insulator with nozzle.jpg


How to make the heat sink and mounting plate

Cut a piece of aluminium (5-6mm thickness) of about 16 by 75mm. You can put the aluminium sheet in the vice and let the blade slide over the vice. It helps to go straight ;) Probably not so good for the saw blade.

North90 hot-end heatsink cutting.jpg

Drill a hole of 1/4" (6.35mm) where you want the Hot End. Use a centring punch to make accurate drilling easier. Go slow and use oil. You can also drill holes for mounting now.

Put the mounting plate in the vice and drill a 2.3mm hole (3/32") sideways through the aluminium into the 6.35mm hole for the insulator. Now tap m3 thread in this hole, be careful a m3 tap is not that strong! (you are free to use a different type of thread here, m4 might work easier in thicker aluminium)

North90 hot-end heatsink retainer thread.jpg

Stick the insulator in the mounting plate and drill a 2.3 mm hole (3/32") through the other side of the aluminium and through the stainless steel AND PTFE tube. Tap m3 thread in this hole too.

North90 hot-end heatsink retainer thread2.jpg

Now put a m3 bolt in the last host, make certain the bolt goes into the insulator and PTFE, but doesn't stick out inside the hole in the PTFE. Check this by feeling with a 1/8" (3.2mm) drill. Add the right amount of washers and tighten.

North90 hot-end heatsink retainer bolts.jpg

The insulator is kept in place with the two m3 bolt, one makes certain the insulator doesn't slide out of the heatsink/mounting plate. The other prevents the insulator from wobbling.


How to get the Hot End to print

  • Clean out all parts. You do not want pieces of metal to jam in the nozzle.
  • The connection between the stainless steel insulator and the nozzle might leek a bit, seal the threads with heat resistant silicone to prevent this.
  • Add the heater and temperature sensor of your liking.
  • Mount to your extruder.
  • Print.

I used a thermistor and nichrome heating wire wrapped in kapton tape:

North90 hot-end in-action.jpg

(this print is made with a heater tube with 0.4mm nozzle made out of a m6 brass bolt.

Upgrades/improvements

  • A nozzle of 0.6mm is a bit large. Make a nozzle out of a m6 brass bolt and drill a 0.3-0.5mm hole.
  • A nozzle of 0.6mm is a bit large. Hammer the 0.6mm hole so it closes down (cooper is pretty soft), then drill it with 0.3 or 0.5mm. The more you hammer, the thickest the close will be!
  • The mounting system is a bit tricky. Using a 1w led heatsink (search on ebay) might make a great mounting system.
  • Widen up the entry to the steel tube a bit, so it can't flush through the hole in the aluminium plate, even without the fixing screw. --Traumflug 09:34, 14 November 2011 (UTC)
  • Use a heater block. They're easier to make than winding nichrome wire. --Traumflug 09:34, 14 November 2011 (UTC)
  • Figure out ways to utilize other dispenser needles sizes than 22GA. (ebay) Heck, maybe even all the way down to 25-27GA, where I heard its all rainbows, unicorns and such. --Danielpublic 14:43, 17 November 2011 (UTC)
  • PLEASE ADD MORE IDEAS HERE

Needle insert into the welding tip

Welding tips are a great easy way to make a heater barrel with a nozzle, but the downside is that the 0.6mm hole is a bit too large for nice prints. An easy way to reduce the size of the hole is to insert an dispensing or injection needle of the right size. Here I used a 0.7mm od and estimated 0.37mm id injection needle. I cut off the needle at the not-sharp end, drilled it manually through the welding tip, pulled it all the way down, and cut it of about 1.5mm from the end of the welding tip.

North90 hot-end needle-insert parts.jpg

North90 hot-end needle-insert.jpg

First results are great!

North90 hot-end needle-insert printing-400px.jpg

Version 2

There is a newer version of this hot-end which doesn't require tapping: see http://www.reprap.org/wiki/North90%27s_hot-end_V2

North9o he v2 finished.jpg