will1384's Ord Bot Hadron

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Re: will1384's Ord Bot Hadron

Postby OliverK » Fri Apr 11, 2014 12:45 am

There are two separate issues at play here:
- The initial jerk/lurch/over-travel that happens during rapid change of direction. That results in the single/first post-change-of-direction bulge.
- The subsequent jitter/vibration which results in the additional waves.

The stiffer the whole assembly and drivetrain, the smaller the initial lurch. The steppers change direction, but everything else wants to continue to travel along it’s original path thanks to inertia. The answer there is to make everything as rigid as possible to remove slop in the system, and everything that moves as light as possible to reduce inertia.

The subsequent jitter is due to vibration. Vibrations are related to the setup’s resonant frequency (rigidity, mass, density, etc.) Adding dampers reduces the resonant frequency (making a dull thud when hit), while increasing rigidity makes it higher (earlier observation about it sounding like a bell).

We want precision in our prints (which is why we like OrdBots) so we don’t really want to add too many dampers as they reduce accuracy. This means we have to make everything more rigid. Resonant frequency can also be tuned with mass, which is why I really like the idea of filling the extrusion/frame (non moving) with something heavy. Oh, and the speed at which everything travels has a big impact as well: slowing things down (print speed and acceleration settings) naturally reduces inertia, remembering the speed of change of direction is where this all started. That’s why I’m so impressed by the TinyG controller. And just to be clear, I’m not saying “no” to damping, I just want to have as little as possible and in as controlled-a-fashion as possible.

The complex interaction between speed, rigidity, and mass means it’s usually possible to tune the printer for a specific setup, only to find problems re-appearing as soon as one variables changes (this includes the geometry of part that’s being built).

General design goals are: reduce mass of moving parts and increase rigidity of everything else to allow fastest possible movement. Expanding those parameters means there is more room to play with other settings to improve overall build quality.

The attraction of the moving the extruder drive off the moving parts (Bowden) is great for all the above reasons, but it does bring with it a new set of printing problems, mainly to do with hysteresis, i.e. you’re losing control over the end of the filament - feed, retraction, blobbing, stringing, etc. There are software settings that can help mitigate these, but I’ve not had the chance to experiment with them. When designing a Bowden system, it would pay to keep the filament feeder as short as possible, i.e. mounting it on the X-gantry, not the frame… the extra mass on the gantry acting as mass-damper as long as Z steppers are up to it.


PS: The above parts are ABS printed at 235degC - authentic (grossly overpriced) MakerBot True Grey… but am willing to pay for the less glossy finish and excellent extrusion characteristics. The little bubbly bits are moisture because it’s an old reel.
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Re: will1384's Ord Bot Hadron

Postby will1384 » Fri Apr 11, 2014 5:00 am

For the Bowden extruder I used the block and lever from:

http://www.thingiverse.com/thing:153592

and cut the "UMHW Filament Drive Block" that came with the MBE Extruder to fit, then drilled a hole for the push in connector.

Image

I also used part of this, the "coldmount3.stl" part:

http://www.thingiverse.com/thing:193433

Image

I could not figure out how to mount the Bowden extruder so I used a zip tie to attach it to the spool holder, LOL, I did a test print and it does work, also the Ord Bot seems to move more "gracefully" now, but the print looked no better than the last print, I want to do a larger test print tomorrow

Here are the parts I ordered:

Push in Connectors

http://www.amazon.com/dp/B00CJCWWU8

PTFE Tubing

http://www.amazon.com/dp/B00ID7E5VM
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Re: will1384's Ord Bot Hadron

Postby orcinus » Fri Apr 11, 2014 11:30 pm

Forgot to mention two more factors that make vibration artifacts more/less visible (on top of material, temperature and color/finish): layer thickness and extrusion width. Basically, the smaller the volume of the extrusion "trace", the easier it is to deform it, plus, the faster it cools. So what happens is, high frequency vibrations that would normally get absorbed by the filament, after which it'd spring back into the shortest path, instead get preserved.
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Re: will1384's Ord Bot Hadron

Postby will1384 » Sun Apr 13, 2014 4:01 am

I had a problem with the "coldmount3.stl" part from:

http://www.thingiverse.com/thing:193433

the fan blows down onto the hotend, and then the hotend cools down two much, so I cut a small piece of sheet metal and placed it under the heatsink to block the air.

Image

I had two problems with the bowden extruder I cobbled together, one was it overheated, the other was slipping, so I tried this

http://airtripper.com/1764/airtrippers-direct-drive-bowden-extruder-v3-bsp-edition/

http://www.thingiverse.com/thing:126778

I had printed this up before changing my extruder to a bowden type.

Image

Image

Image

I mounted the heatsink to the stepper motor by removing two of the M3 screws that hold the stepper motor together, and substituting them for slightly longer M3 screws, then using those same two M3 screws to attach the heatsink, I also used some heatsink compound.

I had to recalibrate the extruder, and it looks like I need to figure out temperature and retraction.

http://www.thingiverse.com/thing:259676

Image
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Re: will1384's Ord Bot Hadron

Postby will1384 » Mon Apr 14, 2014 5:13 am

I searched and found the Ultimaker uses a bowden setup, so I changed my print speed and retraction settings to be similar, I changed my print speed to 150, the retraction speed to 35, and the retraction distance to 4.5, I kept my temperature to 230.

Image

I will have to keep playing with the settings.
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Re: will1384's Ord Bot Hadron

Postby madmike8 » Mon Apr 14, 2014 4:32 pm

It's looking good. I've been following your progress as I work on getting mine together. Right now I'm trying to get the binding out of the Z axis.
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Re: will1384's Ord Bot Hadron

Postby will1384 » Mon Apr 14, 2014 6:02 pm

madmike8 wrote:It's looking good. I've been following your progress as I work on getting mine together. Right now I'm trying to get the binding out of the Z axis.


Thanks.

I had some squeaking on my Z-Axis threaded rod so I used a very small amount of Vaseline, another thing I do is to put the Ord Bot on a perfectly flat table and use a small ruler to make sure both the left and right gantry carriage brackets are both at the same height.

Sometimes you can feel how tight the V Wheels are against the Makerslide to tell what side is misadjusted.
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Re: will1384's Ord Bot Hadron

Postby will1384 » Thu Apr 17, 2014 2:07 am

I have had a lot of trouble with the hotend getting plugged, and I think that the MBE extruder mount plate was acting like a heatsink and helping to keep the PLA from swelling up and plugging the filament Barrel, so I may have to change the way I have it setup, also the settings are much more fussy for the bowden extruder.

I have tried a 0.5mm nozzle, thinking less restriction might help, and also tried a SD88825 stepper driver, thinking more power might help, I also tried Canola oil for filament lube, but nothing has helped.

I have a E3D hotend on order.
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Re: will1384's Ord Bot Hadron

Postby will1384 » Sun Apr 20, 2014 4:16 am

I printed this up a long time ago:

http://www.thingiverse.com/thing:59855

Seems to work well with the E3D hotend, I just opened the filament hole enough to screw in a push in connector.

Image

One thing I did not like is how the thermistor is mounted on the E3D hotend, there is a small hole that you press the thermistor into then use Kapton tape to hold in place, the Kapton tape I tried heats up then loosens, and when that happens thermistor falls out of the hole, I have this on order:

"Permatex 81878 Ultra Copper Maximum Temperature RTV Silicone Gasket Maker"

http://www.amazon.com/dp/B0002UEOPA

I found out about it over in the E3D forums, right now I have mess of Kapton tape holding the thermistor on the best I can, another thing I disliked was the printed fan shroud that came with the E3D, it was printed with less quality than my own prints, and my prints are not all that good, and it was cracked, thankfully I did not need it.

I printed the test object again and it looks OK, but still a little rough.

Image

But on larger prints, it seems like I am getting some under extrusion but only in certain areas, the extruder is calibrated so I wonder if its speed or my retraction settings.

Image
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Re: will1384's Ord Bot Hadron

Postby will1384 » Mon Apr 21, 2014 3:51 am

I made two tabs out of sheet metal to let me lower the fan so I could better cool the E3D hotend.

Image

I tried a lot of different settings but it does seem like its the retraction settings that are causing under extrusion, and I still can not get the overhangs to print very well, I may have to print with support, other than that the parts look decent to me.
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