Finally I got my v3 extruder nozzle and thermal isolator redesigned, fabricated and installed. This time I used the smooth transition from conical sides to flat tip and it makes a smoother finish on the plastic parts.
My pocket microscope shows the .41mm hole well too. My old tip was using a sharp step to transition from the flat tip to the conical sides and that was recommended by some builders. This hot end is my 3rd revision derivative from a wildseyed simple hot end with a retaining nut and seals instead. https://www.youtube.com/watch?v=EsRoYJ2CWNk&feature=endscreen
MIG welding tip nozzle manufacture method
- put M6x1.0 nut on copper weld tip (.6mm/.025in Lincoln Electric KH710), screw till flush with thread end when sitting on flat surface. Hold tip standing tip up against surface.
- Use a relatively flat and smooth head hammer and strike straight down on the weld tip end lightly. About 4-6 blows should form the .6mm hole down to almost closed. No need to overdo this as it only needs to be less than what you plan to drill it out to (.35 to .50mm) down to a depth of 1mm anyway. Too much will cause the .250 O.D. of the tip to deform as well and that will cause issues later.
- Leave the nut on and drill the threaded end of the weld tip up about to 3.5mm or .140in to a depth of about 1mm from the opposite tip end. It will be helpful to use a drill stop or mark the drill bit with tape to know where to stop. A drill press and vice are pretty much necessary.
- Shape the tip by chamfering the edge at about a 45 deg angle. Down to leaving about 1.8mm or .070in of the tip flat at the center. The exact size of flat is not critical, nor is its exact centricity. Chamfering now is easier before fine hole is drilled and damage to the hole may occur. I used a flat file and the drill press.
- Drill fine hole .35mm to .50mm using mini drill bit at center of weld tip. I used a piece of paper card stock to steady the drill bit from wobbling since it is so fine until it touches the weld tip. Go slow as it is very easy to break these fine drill bits. I broke 2 bits and ruined 2 weld tips before I got the hang of it.
- Use fine abrasive paper about 600 grit or finer on a flat surface by hand to produce a flat surface on the nozzle tip with a good transition edge from the fine hole in the center. Check your progress with magnification. I used a 25x pocket microscope to see enough detail.
- Ensure to clean the nozzle out with water or alcohol to rinse away all abrasive and fine chips to prevent plugging up the tip when you go to use it.
- Protect the nozzle tip from now on until the extruder is installed as the copper is very soft and easily scratched. I used a rubber cap over the tip.
- Remove the M6x1.0 nuts hex with a file and round it down to a cylindrical shape to fit inside the air fitting inner hole about .380in.
Air coupler processing
- Take an industrial compressed air quick disconnect coupler 3/8in NPT female pipe thread and modify it by mounting it in the drill press vice- align it using a matching drill bit in the existing small hole and clamping it up. Replace the drill bit with a .250in bit and drill the fitting through.
- I reduced its length by cutting off the straight part up to the coupler’s retaining ridge.
- I also trimmed the coupler’s retaining ridge to make a flat to fit to my heater block’s anti-rotation feature (a screw with one side of its head filed flat).
PTFE thermal isolator processing
- The thermal isolator is PTFE rod .625in diameter. http://www.mcmaster.com/#catalog/119/3598/=mwauck
- I trim it down and turn it on a drill press or lathe to accommodate threading by turning it into the air coupler. Use a vice to hold the coupler and pliers with pipe teeth to turn the isolator (it will mar the isolator external surface). Do not strip out threads by over-turning once the isolator bottoms out.
- The other end is shaped to accept an o-ring where it presses against the nozzle threaded end and nut. Silicone O-Ring, AS568A Dash Number 008 http://www.mcmaster.com/#catalog/119/3470/=mwavdi
- The shorter the thermal isolator the more a cooling fan may be helpful to prevent jams. The heat will travel up the filament if the hot end is left heated and not extruding. At 1.50 inches long, mine takes about 25 min to jam, so I limit the hot time without extruding at least 10mm to 15min since I don’t yet have a cooling fan for the thermal isolator.
Assembly of hot end
- Place o-ring on nozzle neck adjacent to threads. Screw nut down toward o-ring 1/4 turn past when it touches the o-ring.
- Put nozzle in coupler ensuring the o-ring rests on chamfer inside coupler. Scribe nozzle side with a needle around the perimeter of the interface with the coupler.
- Place second o-ring on PTFE isolator neck.
- Orient PTFE end with o-ring up and screw coupler down onto it to help keep the o-ring in place. Screw coupler down until the nozzle scribe mark moves about .050in indicating that the o-rings are properly compressed.
- Install a hot end retaining bracket which will be screwed to the extruder base to keep the PTFE isolator from creeping under tension and heat. I did use non-metal washers and a necked PTFE bushing for thermal isolation from hot-end to the screws.
- Assemble hot end to heater block which clamps onto the .250 O.D. nozzle and has a grip of no more than .375in. Use as small a block as possible and insulate it to reduce radiated heat to printed part. (shown without bracket-oops, I had to take it back apart to put it back on)