1.75mm Reprap Home Made Hot End Design V2

Parts:

• 1/2 inch teflon rod
• ID 1.8mm, OD 2.3mm teflon tube
• ID 2.0mm, OD 4.0mm teflon tube
• 5/8 square aluminum block
• 5/16 inch, 18 threads per inch, brass rod
• 5/16 inch, 18 threads per inch, brass acorn/cap nut
• 2.5 x 1.15 x 3/4 inch wood block

Tools:

• Size #77 drill bit (for nozzle tip)
• 3/32 drill  bit (for thermistors)
• 5/16 bottoming tap bit
• F drill bit (or 1/4″, for 5/16 tap)
• #6-32 tap bit
• #36 drill bit (or 7/64″,  for #6-32 tap)
• 5/ 32 drill bit (for 4mm teflon hole)

Teflon Rod

The rod acts as a heat buffer between the hot aluminum block and the extruder body.   Use the 5/32 drill bit core out a hole down the center.   Drill half way through one end.  Flip the rod and drill the other half from the other end of the rod.    You do this because getting a hole straight through can be tricky without a lathe.    This hole needs to be just big enough to thread the bendy 4mm Teflon tube through it.

Aluminum Block

Start with a stock 5/8 x 5/8 bar of aluminum and cut to length.  Drill a 5/32 hole all the way through the middle.   Then follow that hole with a F (or 1/4″) drill bit just half way through.    Tap the hole with 5/16-18 threads.   Drill two #36 holes for mounting screws.   Drill two 1/4 holes for the power resistors.   Drill two 3/32 holes for the thermistors.

The bottoming tap bit, vs a taper, will give you more threads in the hole and get them closer to the bottom.

To cut a length from the bar, use a circular saw with metal cutting blade (small teeth).   Put some oil on the blade and aluminum to help the chips come free.    Or you can also use a hack saw by hand if you are doing just one.   If you don’t have a blade for cutting metal, you can use one for wood, but go really slowly so the bar doesn’t get jammed in there.

Brass Rod

Drill 5/32 hole through the rod, halfway from each side to minimize stray from the drill bit wandering.    This piece should screw into the aluminum block and should allow Teflon tube to go all the way from the Teflon rod to the tip.   Since the tapped threads in the block will be tapered a bit, you can also taper the brass rod a little to let you screw it in more.   Any gap in between the brass rod and the 5/32 hole in the block will let the teflon tube expand when under pressure and could pop a leak.   So it’s best to taper enough so the end of the brass actually touches the block.  Also taper the other end so the nut cap can fit on more.

Brass Nut

Drill #79 hole from the inside out if possible.   The drill bit will self center if the nut cap has a divot on the inside.    Otherwise, you can put the nut in a vice and come at it from the outside.      Spin the nut in a drill press to remove some of the material around the hole to reduce drag and heat transfer with plastic already deposited.