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Author Topic: Jin - A Kossel build  (Read 5368 times)

jinx

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Jin - A Kossel build
« on: April 21, 2016, 04:10:58 AM »
                                                                                                                                                                                         

        Brief history of the Kossel designed by Mr Johann Rocholl  also the  creator of the rostock delta, johann designed the kossel around 2013 with a goal of simplifying a delta build.  Johann and others have continued the development , although there several designs in the kossel family it's the mini that has been popularised by many makers. with it size and ease of construction coupled with its adaptability to change, it's a machine that can grow with your skills which has made it a good introduction to 3D Delta REPRAP. Several Vendors selling variation in kit form and parts easier to source nowadays.     


parts list:
   
    The parts I collected over several months ali/ebay
   

   Corners "metal"                       = £ 38.44
 20*20 Aluminium extrusion       = £ 32
 MGN12  linear rail slide               = £ 38
3x High Torque 65Ncm Nema 17 = £ 36
 geared stepper                           = £ 22
 round heat bed  "220 mm"        = £ 18
 arms                                          = £ 16
 belts & pulleys                           = £ 8
 100x M3 T-nuts                         = £ 7
 5x stepper driver "drv8825"       = £ 5
   varies bolts and nuts                = £12
                 
                                    TOTAL    = £232.44
additional items:
   RAMPS setup
   Power supply
   printed parts:
            bed supports
            effector plate
            carriages
 
     Compared to a mendel the kossel practically builds itself, I opted to use 2020 aluminium profile  just to make it a little more sturdy of its 1515 cousins. The pursuit of an all metal build drove the price up "Am building a machine that will live forever!!". Theirs plenty of guides on building a kossel mini on the WWW but one better comprehensive guide has been produced by T3P3. "link at the bottom"   
                                                                                                                                                                                                                                                                                                                                                                                                               

Metal corners came with a few dents in them, but overall they were OK found the upright slots where a little oversized for the beams " think that it's to accommodate painted beams". Once the corners where in my hands  I realised that M4 bolts are more suitable than M3x8mm but with washers you can get away with'em.
   I got the 2020 aluminium profile as part of a kit of ebay, "Sintron cut to size with nuts and bolts, the kit came short of nuts, so have a bag on standby".

   
"Off all the build guides out there on Youtube you never see them install the steppers on the corners 'just be sure to install them first fiddly bastards "

               

     I installed the steppers and and idlers on the corners first and perhaps the most fiddly and time consuming part of the construction installing those. I found the length of the steppers shaft to be about 2mm  long to be able to bolt the steppers to the corners plate. so I took a drill to them and drilled a 2 mm depression where the shaft goes. A better option would  have been some  5 mm cork pads/dampeners and a bonus they reduce the vibration from the motors.
         
   
      "A Rebel method is to make square pads from inner tubes, and just stack for desired width a Tinhead suggestion"   

   one nagging issue I have with the corners are the stepper bolts don't sit flat on the plate, I just went  around adjusting the bolts a little at a time till the stepper was bolted solid, another solution I thought about was to file  the curve till the bolt head was flat, but that's hard work with a small hand file!!!.

                         


                                                                                                                                                                                     
 
      Heat bed  A 220 mm diameter 3 mm aluminium, gives the option to either bolt straight onto the beams, having the top beam of the triangle level 'helps with having the bed level when just using bolt and nuts as spacers. Opting not to use the auto levelling in marlin I settled on a spring mount " the stl in RR model vault".
      wired up for 12V with a 10 k thermistor  wiring is no different from any other HB either square or circular what was odd though having the solder pads slapped bang in the middle of bed surrounded by the heating element, no chance of a traditional  glass mount on that surface.   Having the Heat bed flipped over and print directly on the Aluminium side with kapton tape, meant having the heating element  facing the steppers, so I made a shield using a Pin board  which turns out to have a slither of cork over corrugated card  covered with strips of double sided tape and pressed down on tin foil.
   
                 make a paper template that fills the void, then cut the pinboard with a sharpie,
               
had a moment of madness cutting that slit had visions of using industrial high voltage cabling!!! then came to my senses, and a much smaller slit will do.
       


                    At 400 mm the MGN railsare longer than it need to be for a mini but were cheaper than 350 counterparts

  UPRIGHTS,COLUMNS,TOWERS
        one of the few times  to get the callipers out and measure something, at this point even a ruler will do and ensure all three columns are identical, although endstop positions can be tweaked in firmware it save time tweaking.
      The recirculating MGN 12H carriage and carbon steel rails were a pleasant surprise for the price, comparable to silver ground  smooth bars. although 2 carriages glides smooth, there's some resistance when pushing on one , " so that will be replaced at some point".
        mounting them required 16 3x8 mm per rail, I set the distance of the rails on the beam rather then the endstop holders.  placed the assembled bottom triangle on a flat surface and inserted the beam, two bolts in the corners keep the upright in place. The Printed carriages  are a mod of http://www.thingiverse.com/thing:646889  basically modded it to use shorter bolts M3 x 6mm

            KNOW your nuts!!! T-nut are really straight forward  to use with extrusion profiles until you completely unscrew a nut in the middle ,then you have to slide/lift the whole rail off with traditional hex nuts. T-nuts however can save you time just align them with the gap and lift the rail off. they also allow you to add things to the frame at later stages without having to disassemble the printer!.

                                          

belts and idlers in the top corners was again sintron kit 20 teeth pulleys and 623 flanged bearing, a bit fiddly to install them. Put'em together around the same time as the steppers!!"one evening". Although suitable for the kossel first on the list to swap out, there's money to be saved sourcing the flange bearings and bolts and washes 'put the extra cash towards steel core belts.
      Once the carriages are mounted to the rails and the belts installed, I've had to loosen the top triangle and lift it slightly to get the tension in the belts. Adjusting the 25mm bolt that held in place by a couple of washer on the top of upright beams.

                     
 
                  "the use of needle nose pliers to hold the nut while fastening"

         

              With the frame near complete I only have to attach the arms and effector. the original effector for the kossel mini is to small for the sintron arms joint to move freely without coming into contact with each other. so opted for a metal one intended to be used with k800 delta  but sits happy on a mini more importantly  its better spacing for the joints" ebay auction". Used M4 20 mm rounded head bolt to attach the arms to effector plate.
         The metal arms seemed like a good idea at the start, though at 225 mm they are well longer then they need to be for a mini kossel and as a result 'reduced the printable Z height.
                                           

    although the joints don't fall apart they are loose and with vibration make a hell of rattle when homing, the solution simple enough and if you live in the UK free, Mr postman lazy git drops  elastic bands all over the streets!.   
         
  wiring:  A simple rule to follow cut nothing till you decided where the controller  going to be mounted

                   

    The endstop wiring I used multi coloured strands pairs of 1.5 meters " makes it a little easier to identify with axis" twisted. Then I tried a few methods to conceal the wiring with tape  nothing looked good  then I used 6 mm heat shrink as conduit pushed into the slots of the beams , ran the wires across the top beams then all down the Z axis beam. as it turns out the steppers came with short leads and all I had to do was add some  female headers.

           

           I've installed a RAMPS 1.4 with DRV8825 stepper drivers, Its possible to  mount a ramps with nothing more than few washers, couple of T nuts and two brass stand off 'but it's risky especially during calibrations, plugging the USB in/out, so jinx  made a plate for the ramps able to mount the electronics just about anywhere on the beams.

  Using  a couple of cable ties I bunched the wires together and passed them  between the beams just behind the ramps. " keep in mind the LCD controller gets plugged in their, if the cables are short you could end up blocking it".  The first tie  holds the cables to the ramps plate and second  just ensure they don't fan out.
             "A better tidy solution is to use braided cable sleeving, I just used what was at hand"

                       M302  M119  M114
                       
          for sanity I installed a dial indicator, while I wrestled with the delta kinematics in the firmware setting, It also offers a little safety should the effector plate dives into the print surface. there's time to  hit that off switch before any real damage is done.   
   
                With the RAMPS all wired  with the exception of the hotend that can wait, I did install a thermistor to act as the HE sensor 'saves disabling it in firmware but it also keeps the firmware as  close to the final working revision.
    " With connection doubled checked leads go where they should 'there some strange voodoo mixing up the endstop"


  I have the MARLIN firmware installed on the arduino along with pronterface on the PC, .
   Am at the stage where to test the enstops and axis movement first step M119 are the endstop responding as they should. next home the axis a delta homes in this sequence XYZ, if the endstop are mixed up the carriage will crash into the endstop "so stay close to the OFF switch".
 when homed I used the M114 to report potion of the axis moved the Z down till the tip of the dial indicator touches the bed.then put the Z position into the firmware.

" There's still a hell of lot more to do in/around the firmware for configuring a delta which is a post in it self "
 
                  just enough to be dangerous!
           
                 
  "A day of testing and setting confident the effector plate is travelling parallel to the bed  I can progress to installing the extruder and hotend and remembering to adjust the  Z height!!!." 
             

    The Extruder is the modified B'struder " stl in the vault ", with an OSM geared 17 bajdi put me onto this  from ali for £22.00.
 

        Am a convert to using planetary geared stepper runs quieter,cooler and enough torque to pull your nuts through!!. I have a similar setup on YB "prusa mendel i2 " and I got no complaints  :o
 Had/having a little head scratching moment where I was mounting. frightening seeing it above the RAMPS with only a m3 bolt holding in place, but it does seem solid.
           " I'll be keeping an eye on that bolt.. the other issue so far where it is means me cutting a slit in the plex chamber wall , which I aint to fond off".  



the hotend is a copy of the V6 and is currently under review!.http://www.robotrebels.org/index.php?topic=501.0 it's a little rough round the heater block edges, it cost £6.50 of ebay. only thing missing was a push fit con for the extruder. soon as it was installed ran the PID tuning  and set the values in the firmware, "I re run that once I get to fine tuning  everything.

WARNING always check the thermistors no surer way to ruin your day than have the leads short to the heater block, least you get is temp error worst it destroy the bead.

  The cooling shroud "Dreadnought Fan System" designed by foe  on thingiverse. two cooling fans for the print and one for the hotend. http://www.thingiverse.com/thing:1291967




           

 

LINKS:

Kossel wiki:
http://reprap.org/wiki/Kossel
 

calibrations:
   http://reprap.org/wiki/Configuring_and_calibrating_a_delta_printer_using_the_dc42_fork_of_RepRapFirmware

http://reprapandme.blogspot.co.uk/ repieter calibration

       T3P3 offers an excellent calibration guide.
https://docs.google.com/document/d/1zubaHZcnuIWxRmRPNMKKIdb0FsUn6fhR_ywPZu8Y6QY/pub

delta kinemtics:  PDF worth a read
http://fab.cba.mit.edu/classes/863.15/section.CBA/people/Spielberg/Rostock_Delta_Kinematics_3.pdf


groups:

delta google group:
https://groups.google.com/forum/#!forum/deltabot

RepRap delta section :
http://forums.reprap.org/list.php?178
« Last Edit: May 16, 2016, 04:08:30 AM by jinx »
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craighissett

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Re: Jin - A Kossel build
« Reply #1 on: April 21, 2016, 10:07:27 AM »
Fantastic mate!

Smashley

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Re: Jin - A Kossel build
« Reply #2 on: April 21, 2016, 11:52:45 AM »
Great write-up! If I can ever afford to build a second printer it'll be a kossel.

 

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