Friday, 13 June 2008

Support, who needs it?

I think the original Darwin design assumed it would have a support material extruder, so some of its parts require support material to be made. I.e. they have overhangs that are more than 45°. Vik Olliver and Steve DeGroof subsequently modified the parts requiring support material so that they can be made without it. That allowed Vik to replicate his Darwin without a support extruder. STL files for the modified parts can be found here.

At the time I was making the Y-motor-bracket for my Darwin, the modified file was missing, so I decided to see what would happen if I tried to make the unmodified version. I expected the result to be a mess.

Here is the original file, it has a recess in the bottom to fit the shape of the motor and stud coming out of the side at right angles: -



Here is the modified version to reduce overhangs to 45°: -



The problem with this is that it doesn't fit the motor properly. I think Vik was using a different motor.

To my surprise the original version came out fully functional. It is a bit messy, some of the outline was extruded into mid air and had to be cut off, but the infill managed to build out and recover the correct shape after a couple of layers.





It makes me think we might be able to build out into fresh air simply by going slowly and with a fan to cool the filament.

I built the modified version of the X-motor-bracket, but that has no recess as well so the motor did not fit it. To fix that I made a washer to replace the recess. This was simply a slice off the Y-motor-bracket: -



It is 1.6mm thick, which is four layers with my preferred settings. It seems to do the job. I had to use 20mm bolts rather than 15mm to mount the motor. The pulley is normally mounted 2mm from the end of the shaft so moving to 0.4mm from the end should compensate for the washer.



It should also be possible to use this washer on the other motor brackets. I uploaded it to the wiki page.
at

6 comments:

  1. Erik de Bruijn14 June 2008 at 10:40

    Good find that it may be possible to go beyond 45 degree overhangs. It's really been RepRap's golden rule which is probably wrong...

    Gravity will probably keep playing some role, so I guess we can build more than 90 degrees overhang if we intend to print 90 degrees (horizontal). If we take this into account we may be able to print 90 degrees if we set it to print at a 87' angle (just slightly upward).

    And I remain positively amazed by the print quality... every time :)

    ReplyDelete
  2. Anonymous15 June 2008 at 06:59

    Hi,

    Do you know if Darwin can produce parts of this quality, or are you benefiting from (what appears to be) a much more stable machine?

    Thanks in advance..

    ReplyDelete
  3. nophead15 June 2008 at 08:11

    I don't know for sure because I am using different mechanics, electronics, firmware and software. The only thing in common with Darwin is the extruder.

    Having said that I have seen a Darwin running and seen that it has pauses between each line segment which must be several hundred ms. That should be fixable in firmware. I think also having precise control of the filament feed rate is essential for good quality.

    When I finish my Darwin I will drive it with my electronics and firmware so we will then know what it is mechanically capable of.

    ReplyDelete
  4. vik-olliver18 June 2008 at 10:53

    Well spotted about the need for a gasket on the modified part. I used a few slices of silicone tubing on each motor mounting bolt, which also helped take the stress out of my slightly uneven coupling.

    Please do put the gasket up on the modified parts page for posterity. I should really have added the need for spacers to the modifications box.

    Vik :v)

    ReplyDelete
  5. Forrest Higgs18 June 2008 at 18:32

    This comment has been removed by the author.

    ReplyDelete
  6. Forrest Higgs18 June 2008 at 18:33

    "Having said that I have seen a Darwin running and seen that it has pauses between each line segment which must be several hundred ms."

    Don't bet the farm on that. I think the problem is intrinsic in Darwin's trying to do the calculations for drawing lines in the firmware. Should that be the case, I will, hopefully, have a workable buffering technology worked out by then that can get them past that. :-)

    ReplyDelete