Sunday, 16 October 2011

Progress Update 6

I have made some progress, i think i have enough parts to assemble the printer to a point where it will print some plastic YAY...

Last night and yesterday i completed the heated bed and 1/3rd of the hotend for the exxtruder, i have decided that it makes sense to get the hotend made up on a CNC mill/lathe.

 Doesn't look like much at all does it? lets look whats hiding below.
At the top of this image you can see the bottom of the bed, this is what mounts onto the linear bearings. the bottom section is the underside of the top.

 this is the underside of the bottom of the bed, you can see the two straps with the holes for the linear bearings.
 here you can see the M6 Allen key bolts that i have used as adjustment screws that level the print bed. these mate with some M6 Nutserts that i have place in the 3mm heat spreading plate that the glass sits on.

here you can see where i went a little nuts on the punch in my mates workshop, this is to allow access to the terminals for the heating element. this is 240v AC, need to make sure this frame is earthed and not touching the active or neutral lines...

 here are the parts for the prototype hotend. this is only 1/3rd of the parts you need. you need 3 x all the parts you see here.. 6mm OD,5mmID  x12mm brass tube, 2x M3 x 30mm screws, Nozzle and 4r7 3watt RWM series resitstor, you can see in this shot the hole on the left has a thread cut 10mm deep for the nozzle to mount.

 here you can see the PTFE mounting block.
 first slide the resistor in to the 6mm hole that does not have thread cut in to it.
 Then press the brass tube sections into the 6mm hole, one from each end, this does two things, it makes sure that the maximum surface area is contact with metal and allows easier replacement if/when the resistor dies. the reason its in two pieces is the resistors when you get them are not uniform in their diameter, so the two pieces allow enough movement to ensure it is held tight with no adhesives. when this resitor dies, knock out the old one with your calibrated hammer and replace withe new resistor and tubes if needed...

NextI screwed in the brass nozzle, to do this i cut a slot in the top of it for a flat blade screwdriver.
here you can see the hot end assembled for testing, i have placed a thermistor inside the nozzle where the filament would normally go, this is the green and white wire.. so i applied 12volts onto the resistor and watched the results..
after a little wait (2mins) the temp reading was 200'c after another min it was @ 270'c
so i think tonight if i dont find something more interesting to play with i will mount the thermistor to the bed and wire that up an then consider mounting the hotend to the extruder and see if i can make worms of plastic.. this nozzle only has a .55mm hole as all my smaller drill bits were snapped and i am yet to have more 0.25 or 0.3mm drills arrive...

Wednesday, 12 October 2011

Progress Update 5.5

I have been working on the extruder for the last few days. i have the cold end done and the parts for the hotend ready to be drilled, will need to order some new thermistors (will make calibration easy if they are all the same), then drill the brass heater blocks and make the nozzles, i am thinking aluminum  nozzles may be the go.

i have placed the extruder onto the X carriage, no holes or bolts have been placed in yet. just wanted to make sure it will fit between the two belts.

 here is the printer, the X belts are not attached to the carriage it's just sitting there with a gravity clamp.

here you can see the cold end of the extruder sitting in my most desirable orientation, but it only measures 55mm wide so it should fit across ways onto a normal printer if it ever made it there.

 side view
 and the other side as suggested i may be required to put a guide that pulls the plastic towards the idle wheel so it doesn't scrape away when not selected.
here you can just see the three springs that push down onto the top of the levers these are directly above the camshaft and vertical.

Triple Extruder Cold End Prototype BNZII

I have completed a yet to be tested prototype of the BNZII coldend.

this is what it has turned out like it. i have taken nicely out of focus pictures of it from all sides i will try and explain whats what.
here you can see the two stepper motors the one on the left drives the filament via the hobbed axle.

here is a top down shot, you can see the hobbed axle, and the three idle wheels that run in the hobbed can't really see it here but the springs push down on the levers which then press the idle wheel against the hobbed axle.

 not much more detail here, but you can see the same drive system for the camshaft as the filament. 20:1 reduction via the worm drive and spur gear.
 here you can see the camshaft on the left the top lever is engaged to grip the filament this is done via a groove making a low spot in the camshaft this lets the tension from the spring pivot the lever or arm and presses the filament onto the axle. roughly a 1:1.3 ratio (x1.3)

 the middle lever is engaged to grip the filament, i thought it was much easy to work on a low spot to release the spring tension onto the drive axle was a better way to do it, allows the filament not to be exact 3mm.

 this is the bottom lever engaged. this extruder can be modified to take a 1.75mm filament really easy. change of bolt and idle rollers and your ready to roll..

 here all the levers are in the released state, you can turn the camshaft in this state by hand really easy as i have use 7mm OD bearings for each of the camshaft lobes to run on. costs a little and adds a little thickness to the design but i have doubts if the hotend can keep the three nozzles at three different useable temps, two plastics and a fill material may have wide temp differences! i don't know...yet

another shot from another angle, this thing was a PITA to put together in may lap on the couch so with a vice it will be much easier.. here you can really tell its a prototype you can see the hotglue that holding the bearings in place, its just keeps them from sliding out of the holes they live in when it was being handled... its not really structural when required i will epoxy in new bearings and the next one will have 6mm walls for the bearings to live in. when i next need to pull it apart i will take photo's that are in focus and that include the internals. cant wait to get onto the hotend, i cut the brass last weekend its a little over 10mm thick at the moment but i have 3/6 machined edges to go off, will need to get these CNC'd and or water cut but that should be no problem.

Saturday, 1 October 2011

The New PrintBed

I was talking with the peoples on #reprap and they brought to my attention that the PCB heaters work better than i had thought, this got me thinking do ii have to go to a HUGE mains powered heater for my new bed, this one is going to be light weight. And that has been the driving design criteria.

I was thinking that with a printbed that is 470x470mm that could be broken up into 9 squares of 156mm, looking at my local electronics shops website i see i can get 10 pieces of copper clad FR4 single sided for $6.95 a piece, and a resist pen for $9 this makes the heaters about $80 as i already have the acid and the spare time :)

there is a website that i sometimes use that will do 5 boards for that $80, so is my time worth $80 to me?? maybe but then there is the risk factor to deal with.. also there is the question is a 3x3 grid the best idea, what about a grid with 5 cells, think quarters then take a square in the center as well, this will mean bigger pcbs i might be able to make a layout that has a optional corner cut-out so i only need to order 5 boards the same and cut the corners from the 4 and leave the center one whole.

this will require me to have more analog inputs on my arduino controller, that will be 3 nozzels and 5 bed segments that's a total of 8, the mega has 16 available but they may be appropriated for other uses and may require re-routing,there are more than enough digital outputs available.

there is another pattern that i did think about using much the same as the 5 segment picture above but the square is rotated 45 degrees to make it easier for the glass cutters if i choose to go with individual tiles but that leads to wasted energy.. and thats what i was after by splitting the bed.

Update : after i made this post another suggestion was put to me for segments, I could use a similar pattern to the 5 section design but the idea was to have two hot zones ie the inside square which is where most prints get started from the middle of the printbed, and the outside square that only gets turned on for lager sized objects, this idea is interesting to me, it may reduce the number of thermistors required to monitor the bed. i am not really chasing efficiency just thinking about whats involved in removing the 240v AC heater from my printer.

BNZ's Hotend - Triple Extruder BNZII

Today I Finished my design for my new hotend this will take three power resistors and three thermistors or thermocouples, The power resistors will be fire cemented into short (15mm long) sections of thin walled brass tube, this will then be installed into the hotend, one for each nozzle. with a little heatsink paste.

the nozzles slip into place from above and will also have a interference fit, and some heatsink paste, i will be trying out a variety of nozzles so this hotend is fairly easy to remove once i complete the mounting plate for it.

Below are some screenshots from solid works showing the construction of the pieces, this section is by no means printable.

the height of the hotend is 29mm this is 4mm more than the height of SC10UU linear bearings that i have used for my X cariage. this wastes no Z axis movement.

 side view of the hotend,  the top greenish piece is peek 10mm thick as a thermal barrier and also to hold the slip in nozzles tight.

here is a cross section view from the side. you can see the nozzle section and the heater resistor cavity and on the right is the thermistor point. might not be drilled that deep in reality but meh.

 here is a bottom up view of the Hotend, the nozzles are 10mm apart and the white holes are mounting holes M3 will probably counter sink them to help clear the printed plastic. The grey holes range from 1mm to 3.5mm (except for the 5mm that power resistor's home) are to try and keep the heat from wandering between the nozzles, a probably feeble attempt but hey, this is going to be CNC machined from brass as there is no hope i could get all those holes right in a drill pres.

 here is a front view if the three nozzles the model has 0.30mm holes but we will see what works
 here is a semi exploded view of the three nozzles they have a 9mm OD flange (heheh i typed FlangE)
 here is a cross section of the exploded view

and the cross section view of the three nozzles, so far the rebuild of the extruder has saved about 10mm of wasted print height

Here is the New extruder  mounted onto the X carriage. its not fully mounted i will decide how that happen when i build the prototype,  i have to raise the axles up 3 or 4 mm more from the plate to allow for the 20toothed gears that will be used to drive the axles.

in this Design all running surfaces have been replaced with tiny 703, 7mm OD 3mm ID bearings that i get from the hoby shops at a ok rate for 2 at a time, this design will require 9 of these and 4 1608 bearings. but the wont wear too fast. this design is also missing the springs that will push down on each of the tension arms. the plate that the springs will press against is not in the drawing but will be added later.

here are the screen grabs.

this is a side view, looking along the X smooth rods.i will be able to bring the motor in a little more maybe 5mm before they will start to interfere with the filament too much. the area outside the worm drives is where the belts will run, i have to make a new idle axle and some extenders for the X axis to spread the belts to all this to mount up.

 this is a front view of the extruder mounted on the X carriage  i could have mounted it the other way but i prefer this way, i also get to shorten the X carriage length.

A 3d angle shot to help you get the picture. the two motor are not exactly in line with each other, this was done to give me a little more leverage on the camshaft.

i will be driving both the filament and the filament select camshaft with Nema17 2300g/cm stepper motors ( with a 20:1 worm drive reduction to get enough torque..)  they will be driven by a pololu stepper driver. with 1/16th the motors have 200 steps per rev and 2300g/cm so that's
64000 steps per rev, and ~46Kg/cm of torque if an can convert half of that into grip  i will be off to a good start. thats for both the feed and the camshaft which should be suffcient.

Update : The pictures here show a single piece heater block, the idea here was that there would be holes drilled between each of the three sections of the block to provide simple mounting and thermal isolation between each heater, this is too hard to manufacture for my liking, all those 0.5 and 1.0mm holes are a PITA to get right with out a decent MILL and plunge bits. so i have changed the design to use three separate pieces of brass, one for each nozzle, that will be 8mm thick this will give me 2mm of air gap  between each of the heated sections that can be packed with ceramic insulation tape if required, this does complicate the installation of the nozzles but simplifies changing of the nozzles as each one can be removed and replaced/repaired without disturbing the others, one drawback to this is that each nozzle can be installed into a slightly different position if the mounting holes are not the perfect size.