Start sequence explained

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bam
Posts: 117
Joined: Thu Sep 19, 2013 11:37 pm

Start sequence explained

Post by bam » Thu Jan 29, 2015 7:15 pm

Hey all

The mini's start sequence is critical to it's ability to print, it's what tells the printer how to heat up, clean the nozzle and find the plane of the bed before the print. It's written in g-code, which is a set of movement commands ("G") and modifier commands ("M), which change things like acceleration and temperature. Here's an explanation of what the start gcode actually does in case you want to modify it for new filaments, or are just wondering what it's actually doing between when you click print and when it starts.

*First, it starts heating the bed and nozzle to the temperatures that you've set in the print configuration. It also sends the printer to the top front left so it knows what position it's in.

"G92 E0 ; set extruder position to 0
M140 S{print_bed_temperature}; get bed heating up
G28 ; home all"


*Once it reaches the lowest temperature that the filament can be removed at, it retracts the filament out of the heated part of the nozzle so it doesn't start to drip during the bed probing. If you're printing with a new material, you can find this temperature by slowly heating up the nozzle with the filament cooled in the hotend, and chose the lowest temperature where you can easily pull the filament out.

"M109 S160 ; set to cleaning temp and wait
G1 Z150 E-30 F75 ; suck up XXmm of filament"


*Next, it heats the nozzle to a temperature where the plastic can be wiped off, but won't flow out of the nozzle. The printer moves down and wipes the nozzle on the pad behind the bed, you can change the movement commands in this section if you find a material that needs a different kind of wipe sequence.

M109 S170 ; heat up rest of way
G1 X45 Y174 F11520 ; move behind scraper
G1 Z0 F1200 ; CRITICAL: set Z to height of top of scraper
G1 X45 Y174 Z-.5 F4000 ; wiping ; plunge into wipe pad
G1 X55 Y172 Z-.5 F4000 ; wiping
G1 X45 Y174 Z0 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X45 Y174 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X45 Y174 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X80 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X80 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X90 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X115 Y172 Z-0.5 F1000 ; wipe slower and bury noz in cleanish area
G1 Z10 ; raise z
G28 X0 Y0 ; home x and y
M109 S170 ; set to probing temp
M204 S300 ; Set probing acceleration
G29 ; Probe
M204 S2000 ; Restore standard acceleration
G1 X5 Y15 Z10 F5000 ; get out the way
G4 S1 ; pause
M400 ; clear buffer
M109 S{print_temperature} ; set extruder temp and wait
G4 S15 ; wait for bed to temp up
G1 Z2 E0 F75 ; extrude filament back into nozzle
M140 S{print_bed_temperature}; get bed temping up during first layer

Hope that helps someone :)
-bam

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GunZ McGraw
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Re: Start sequence explained

Post by GunZ McGraw » Fri Feb 13, 2015 9:39 am

It does. Hope it helps with the problem I'm having now. Thanks for posting.

Rickta59
Posts: 19
Joined: Thu Feb 05, 2015 7:13 pm

Re: Start sequence explained

Post by Rickta59 » Sun Feb 15, 2015 4:14 pm

I'm using lulzbot orange PLA from Village Plastics. Sometimes I still get a bogus probe reading on X0, Y0 the first time ( often as much as .79mm too low ). If I add a couple more G29 commands, the last 2 readings are the different than the first reading but consistent with each other. I've seen -1.93 then -1.14 and -1.14 for the second and third probe of the same point. It seems to me that the last 2 readings are more representative of the actual bed height.

What do you think? Is there any harm of adding extra G29 commands in start.gcode other than the time it takes to complete the probe?

-rick

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Orias
Aleph Objects | LulzBot
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Re: Start sequence explained

Post by Orias » Tue Feb 17, 2015 9:32 am

You'll want to have your start/end gcode updated with a better cleaning temperature if you're not using our pre-tested filament from LulzBot. The cleaning temperature needs to be high enough to allow the filament to be wiped off the nozzle, but not hot enough to cause the filament to drip out of the extruder nozzle.

Rickta59
Posts: 19
Joined: Thu Feb 05, 2015 7:13 pm

Re: Start sequence explained

Post by Rickta59 » Tue Feb 17, 2015 10:08 am

Orias wrote:You'll want to have your start/end gcode updated with a better cleaning temperature if you're not using our pre-tested filament from LulzBot. ...
I'm using lulzbot PLA ordered from lulzbot .. the more expensive PLA from Village Plastics.

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Orias
Aleph Objects | LulzBot
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Re: Start sequence explained

Post by Orias » Tue Feb 17, 2015 6:33 pm

you may want to clean your nozzle shortly after each print, or before it begins the homing process. If the bed visibly moves during the probing process the nozzle isn't clean enough.

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