Print starts be heated TAZ 4

Just got a new TAZ 4 and I am working out a few minor kinks.

Using Slic3r to slice then loading into Repetier host the printer will try to print right away without waiting for the nozzle or heated bed to get to temperature. I can do it manually but want to know the proper code to put into slicer to generate a wait to heat.

In my start G Code, I have the following:

M140 S[first_layer_bed_temperature]
M104 S[first_layer_temperature]
M190 S[first_layer_bed_temperature]
M109 S[first_layer_temperature]

The first two set the temperatures of the two heaters, but does not wait.

The third line waits for the bed to reach temperature

Line 4 is put there just in case. Usually by the time the bed heats up, the hot end has been at temperature for a while. This line just makes certain of that. There's almost never any actual waiting here.

Note how the lines are parameterized. This same stanza can be used for PLA and ABS.

That makes perfect sense.

The only thing that bothers me is that if you want to change the temp for one print I would change it under Filament Settings but I assume these would override whatever I put there. Seems pointless to have temperatures set in 2 places (under filament and start gcode)doesn’t it?

you only have the temps in one place - under filament. That's the whole point of using the parameters. At slice time, the temperatures you have for the chosen filament will be substituted into the above G Code. There is no actual temperature in the G Code What I showed you before is literally what you put into the start code - brackets and all.

OK, I did not realize that.

I thought I had to put a number where the S is like S230 but you are saying the [first_layer_bed_temperature] gets the variable from the filament setting. Perfect!.

Tried this exactly as posted but did not work.

The reason is that while I set the bed to 85c (per Lulzbot instructions) the bed only got to 84.9c (I assume pid controller figured that was close enough). So I took out the M190 command. I have not tried it yet from dead cold but hopefully the bed will be hot enough by the time the hotend is ready.

It sounds like the behaviour you've described is correct - if you need a higher first layer bed temp then set it in the filament tab. What problems are you having at 84.9C that you don't see at 85C?

Extruders usually heat up much quicker than beds, so if you take out the M190 command then you will almost definitely notice that the bed is below temperature when the print starts - unless your extruder is particularly slow at heating up!

The software (repertoire host & slimplify 3d) don't think it's up to temperature and won't start printing. They wait to see the actual temperature it's set to, so if iet it to 85c and it only gets to 84c then they never start printing.

Hmmm. Interesting. I know the temperature fluctuates around the target temperature value but the M190 command should never be blocked by the bed never hitting its target! I'm sure you've checked already but is the bed getting enough power? Does M190 *ever* return control back to the host - is there a temperature below which the bed comfortably reaches its target and the print job starts?

I was going to suggest an improvement on the above code to avoid having the hotend sitting at extrusion temperature for long periods (which would encourage oxidisation) which involves first using M190 to set the bed to a lower starting temperature like 70C (and wait until that temperature is reached), then firing up the extruder using M104 before coming back and pushing the bed to the first layer bed temperature. This would still give the extruder plenty of time to heat up and stabilise without having it sit there at 200C+ whilst you wait for the bed to hit its target from cold. If your M190 command doesn't work however then this approach wouldn't work.

The bed never reaches 85c and that is why M190 never releases control. Now I can trick it by preheating the bed to say 87c then it will reach 86c and if I hit print then it works as it sees it got up to (and past) 85c

It's a new TAZ 4 and for some reason the bed seems to heat up to 1 degree cooler than it is set. Not sure what the cause of that is.

Turns out Lulzbot has seen this before and they are sending me a modified firmware to fix it.