Monday, 28 January 2013

Nozzle Fun and games..

Today was spent hanging out eating with the family, yay nephews and the niece running around screaming, it was a change from the drone of the printer or the mill :). After that was over with i went to my mates workshop and proceeded to make some new nozzles for the printer..

  First i took a length of 5/16ths brass rod that i had from a previous nozzle session and proceeded to center the piece in the lathe which resulted in a 7.8mm rod 30mm long, i then made a shoulder 6mm in diameter and 22.5mm long, i then cut that off at 28.5mm long.

I turned the nozzle around and pushed a 3.5mm drill bit into the piece to a depth of 25mm, i then took the nozzles to the mill and proceeded to setup to peck drill the 0.5mm hole to form the nozzle, this was a total bust I snapped two drills in the process, so i decided to attempt to drill the next one from the outside to the inside so i could see what was happening, turns out that this was not that hard a process, i placed the blank into the drill chuck and moved the bed with the vice mounted on it until the blank nozzle was touching the jaw of the vice, this took a little bit of back and forth on the handles to get it just right, using a set of feeler gauges to find the point where both corners of the V groove. i then tightened up the vice and released the chuck, then in went the 0.5mm drill, then some manual gcode to lower the head in 0.25mm steps, i noticed the amount of swarfe that was generated from a 0.25mm plunge of the drill was quite significant given the diameter of the drill i was using, i found that my previous gcode didn't clear the swarfe from the drill leading to breakages.

Using this method of drilling from the outside to the inside was actually quite easy, as long as the tip of the nozzle is formed dead flat the drill doesn't wander any noticeable distance, i had tried not to do it from this end because i was worried that i would end up with a nozzle that flared out due to the need to use a centering bit first ( on the lathe this was needed) with the bed of the mill being so nice and tight i didn't need to center drill the blank first.

One thing i noticed was that when you have a 0.5mm drill bit in the chuck of anything you gotta be very very careful, if you even think a bad move it will snap.. i broke a drill before i even started by issuing a bad gcode command, the command itself wasn't bad just the results. the spindle wasn't moving and the drill was a lot closer than i thought..

here you can see a partially completed nozzle installed and two placed in just for the photo. they still need the ptfe liner and the brass riser tubes and nozzle tips formed before they are ready to use.

The result of a half a days playing on the mill and lathe.. i have still to shape the end of the nozzle to a point, this will be done later once the riser tube and ptfe liner is installed.

 here you can see the blank nozzle with its 0.5mm hole this is in the retracted position.
here the iphone decided the flash was need, you can see the nozzle in the extended position. once i have the first channel of the extruder working nice i will duplicate the settings across to the other two channels, then it i will see if the spring loaded nozzle flaps/valves can be remade to suit the new nozzle length, i increased the length of the nozzle to see if i can get a more positive closing and opening action. the original nozzles and valves seems to work quite nice but haven't actually printed with them installed i was having a bit of trouble getting started again so i removed them to make cleaning of the nozzle area much easier, on that note i think i may run into some clogging issue of the valve area, in that if the nozzle doesn't snap shut i may end up with strings hanging and these could end up above the flaps and cause problems, with the longer nozzle length i should be able to avoid some of these problems.  they may not be a problem. one thing i did notice when i was playing with the nozzle retracting was the amount of pull the filament puts on the nozzle isn't that great, i have a plan to crowd in the end of the brass riser tube at the bottom. this sits about 5mm above the melt zone with the ptfe tube extending towards the opening of the nozzle. i am hoping this crowding of the brass tube will grip the plastic a bit more on the retract and pull the nozzle up more. with the longer nozzles i will also be able to put a bend on the leading edge of the valve as i did notice the nozzle was starting to wear due to the valve scraping the brass away and this will eventually lead the Z height issues.

once i form the nozzle tips i will have to install all three nozzles and mount a strip of emery paper to the printer bed and drag the tips of the nozzles until they are even in length when the are fully extended. this will ensure one nozzle doesn't pump out plastic at a different heights and cause layering issues.

While i was attempting to peck drill the 0.5mm hole i discovered that my mill had developed a loose Z Axis Rack gear. this is because its held in place with two countersunk screws about 5mm in diameter, they don't hold up well when you have the Z axis Quill clamp engaged and you try to crank the Z axis, the cast iron in the main post just caves to the stress. I devised a solution, i took some 19mm wide strips of steel 3mm thick, one is about 200mm long the other is about 60mm long, these were then drilled to match the other holes in the post. the top one was close enough to the top that i managed to place a nut on the back of it and some loctite to make sure it stays tight with out the fear of stripping this hole too. the bottom strip rests on a step in the rear post that out of sight, this setup ensures there is nowhere for the rack to move when too much force is put on the axis. this makes sure my backlash stays at 1.83mm in Z axis.

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