Bed drops quickly after print finishes

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Bed drops quickly after print finishes

Postby bryankerr » Thu Apr 10, 2014 5:07 am

Got our first test prints out today and noticed that when a print finishes, the bed drops rather dramatically to the bottom. It seems to fall less quickly with taller prints when the bed is already closer to the bottom. Is this the correct behavior? Seems it might throw the bed out of level more easily.

[edit]
I should add that this happened when printing the bracelet from the SD card using Simplify3D
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Re: Bed drops quickly after print finishes

Postby Toby » Thu Apr 10, 2014 5:36 am

Yes, that's normal. And yes, it does seem like it throws off the bed leveling. If you're using Simplify3D you can put in some end g-code (in the scripts part of the process dialog) to drop the bed almost to the bottom under power. Then it only has a couple of millimeters to free fall. Here's what my end g-code has:

M104 S0 ; turn off extruder
M140 S0 ; turn off bed
G90 ; absolute mode
G1 Z198 ; get lower before cutting power
G4 S10 ; pause 10 seconds
M84 ; disable motors

It's the G1 Z198 command that does it, but you need to have the G90 command before it. 198 is cutting it close. I think most people use 195. I pause for 10 seconds afterwards to give myself a chance to grab the handle even to prevent the 2 mm freefall, but that's probably overkill.

BTW, congrats on your first print :)
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Re: Bed drops quickly after print finishes

Postby bryankerr » Thu Apr 10, 2014 5:49 am

Brilliant Toby. Thanks!

We'll definitely have some unattended prints and won't be there to catch it every time, especially with big overnighters.

I'm thinking about rigging up a raspberry pi and a motion sensor to send out an email when the print finishes. I'll probably use the camera as a webcam so our school can monitor our prints.
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Re: Bed drops quickly after print finishes

Postby Toby » Thu Apr 10, 2014 7:33 am

Actually I got the idea from Jin.

BTW, there's a flaw in my end Gcode I forgot about until now. I don't move the extruder away from the print, so if you're not there it's liable to ooze on your print. If I remember right the command is G28 X0 to get it to the home position in the X-axis.

Others have also devised more elaborate end sequences to do different things like retract the filament and move the bed fan around to cool the print a bit. But fitting out a motion detector to send an email is a good one I hadn't heard of yet.
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Re: Bed drops quickly after print finishes

Postby Dale Reed » Fri Apr 11, 2014 9:51 pm

bryankerr wrote:Brilliant Toby. Thanks!
We'll definitely have some unattended prints and won't be there to catch it every time, especially with big overnighters.
I'm thinking about rigging up a raspberry pi and a motion sensor to send out an email when the print finishes. I'll probably use the camera as a webcam so our school can monitor our prints.

Bryan,

I'm not at my printing PC right now, but I'll try to remember to post my ending G-code if you need it. It backs out the filament, turns off the heaters, drops the bed about a centimeter, cranks up the fans, and moves the extruder assembly slowly back and forth with the fans at full and the heat off to cool the bed and the part -- for about a minute or two. Then it does the controlled Z to 195 (like Toby mentioned), moves Y to about 230 to move the bed forward to "present" the part, then shuts down motors and fans (all, including extruder and electronics fan if not hard-controlled by firmware) to conserve energy. Just what you need for unattended printing.

Dale
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Re: Bed drops quickly after print finishes

Postby Dale Reed » Sat Apr 12, 2014 4:10 am

Toby wrote:Actually I got the idea from Jin.
Others have also devised more elaborate end sequences to do different things like retract the filament and move the bed fan around to cool the print a bit. But fitting out a motion detector to send an email is a good one I hadn't heard of yet.


On the printing PC now. Here's my ending G-code -- everything after the semicolon (;) on each line is comment text:

Code: Select all
G91 ; relative mode
G1 Z20 ; lift 2 cm
G90 ; absolute mode
G1 F6000 ; medium fast
G1 X200 ; off to right
G92 E100 ; extruder relative pos
G1 F300 ; set speed
G1 E0 ; retract remove filament
G92 E0 ; extruder relative pos
M104 S0 ; turn off extruder
M140 S0 ; turn off bed
M106 S255 ; cooling fan high
G1 F6000 ; medium speed
G1 Y80 ; reasonable Y
G1 F600 ; slow speed
G1 X180 ; move slow right
G1 X20 ; move slow left
G1 X180 ; move slow right
G1 X20 ; move slow left
G1 X180 ; move slow right
G1 X20 ; move slow left
G1 X180 ; move slow right
G1 X20 ; move slow left
G1 X180 ; move slow right
G1 X0 ; move slow left to home
M106 S0 ; fan off
G1 Z195 F2500 ; run platform down to near bottom
G1 F6000 ; medium speed
G1 Y240 ; present part
M84 ; disable motors
M106 S0 ; stop bed fan
M108 S0 ; stop extruder and electronics fans


Note the little trick of establishing an extruder relative position at 100 mm (with G92 E100), then running the extruder position to zero (with G1 E0) -- backwards -- thus retracting 100 mm --- more than enough to clear the gear for a few seconds. You could probably make this 50 to 60 and still get complete retraction --- you'll get to the turning off the heat and cranking up the fans a tad sooner.

I hope that gives you some useful parts to copy out and paste into your own. There's a general G-code reference posted at http://reprap.org/wiki/G-code --- take note of the little boxes there for which firmwares support which codes --- look for a 'yes' in the Marlin box before you go typing it into your scripts or sending it to your printer!!!

Dale
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Re: Bed drops quickly after print finishes

Postby bryankerr » Sat Apr 12, 2014 6:24 am

Awesome Dale. Thanks heaps!
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Re: Bed drops quickly after print finishes

Postby Dale Reed » Sun Apr 13, 2014 1:10 am

bryankerr wrote:Awesome Dale. Thanks heaps!

You're quite welcome. Feel free to delete the redundant M106 S0 near the end! Oopsie! Guess I wanted that fan off-dammit.
(New word for the weekend.)
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Re: Bed drops quickly after print finishes

Postby jsc » Sun Apr 13, 2014 5:04 am

I've linked Dale's end gcode sample into the tips thread.
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Re: Purely mechanical fix

Postby problemchild » Mon Apr 14, 2014 3:42 am

If you are willing to sacrifice a little height, and don't want to fiddle with G code, just slit a short length (~3/4") of tubing (e.g. tygon) in a spiral fashion and put it around the Z lead screw to buffer the drop. If the tubing comes off, wrap it with a loose loop of wire. The tubing should fit very loosely and not create any resistance for the lead screw.

Drops also occur when the motors time out. This method solves this issue, but I'm not sure if G code does. Any spongy material will probably work pretty well, too.
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