Posts: 120
Joined: Sun Jul 19, 2015 9:05 am

sequential printing, no M190 for subsequent parts

Sun Aug 13, 2017 1:10 pm

In attached file there are two parts set up for sequential printing.

The processes are essentially the same and both have First layer bed temperatures of 102C and subsequent layers at 85C (btw the filament is ColorFabb nGen (not XT as in profile name)).

The gcode generated for the first part is of the form:

M140 S102
M190 S102 (to wait for bed temperature to be achieved).

However when it comes to the second part there is only:

M140 S102

What that means, of course, is that the printer will start the second part whilst the bed is still only at 85C and the first layer will not be printed under the intended conditions.

I think this is an oversight and in the case of the sequential printing of parts we need an M190 as well. ;-)

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Re: sequential printing, no M190 for subsequent parts

Mon Aug 14, 2017 8:03 am

Depending on the time it takes to raise the bed to the new temperature point, you could end up cooking your filament while it sits and waits. That's why bed heating is always done before filament heating.
But, a possible workaround is to print many, many skirts around the second part to give the bed time to heat and not cook the filament.
Not a great solution, as you'll have to play with how many skirts it takes to let the bed heat back up - and it depends on the size of the part as to the number of skirts.
Another option is to print a sacrificial cube between the first and second parts that takes the required time to print as for the bed to re-heat.

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Re: sequential printing, no M190 for subsequent parts

Mon Aug 14, 2017 8:08 am

M109/M190 is only typically used at the very beginning of a print. It would take forever and create all kinds of oozing issues if you used these in the middle of a print every time you were changing the temperature.

But if you really feel like you want to do this, then you can easily do it with the built-in scripting options in S3D

Just add this line to your post-processing script
{REPLACE "M140 S102" "M140 S102\nM190 S102"}

That will add the M190 command after the M140 change. Or you could probably make it even simpler and just replace every M140 with M190's (since you don't need both)
{REPLACE "M140" "M190"}

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Re: sequential printing, no M190 for subsequent parts

Mon Aug 14, 2017 2:02 pm

Thanks @brian442, that's a good idea. I'll give automatic post-processing a try.

Wouldn't replace all the M140's though because one only wants to wait for the bed to get UP to temperature for the first layer, on the second layer there's no need to wait for it to go DOWN to the temperature it will be at for the rest of the print. As you point out, that would be counter-productive with oozing and anyhows make no difference.

Figured that any ooze whilst waiting for the second part would be mopped up by something like an offset-skirt on that part. Yet you're right, that could go wrong. And setting up an ooze pillar or a return to dock with could get uber-complex in this situation. Which begs the question, what then is the best way of sequential printing with a higher first layer temperature?

Perhaps a better solution would be to allocate two processes for each item on the board. One process just for the first layer (I know someone that does that systematically in order to optimise everything to death.) Likely the first layer of ALL the parts could be allocated the same process and be printed in one go at the higher bed temperature. After that we switch to sequential printing and different processes for the remaining (L-1) layers of each part.

All parts would benefit from a higher temperature first layer. And all parts would avoid the messy start points coming from oozing during travel time....

A tiny bit of a pain to set up, but I suppose it would be difficult for an assistant to automate?

What do you think?

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Re: sequential printing, no M190 for subsequent parts

Tue Aug 15, 2017 11:22 am

@LingHunXi, sorry somehow I missed your post above.

That's an interesting idea, adding lots of skirts.

I've got quite a powerful bed heater on an aluminium bed... but it probably needs a few minutes to get from 85C to 102C.

Was printing at 40mm/s with first layer underspeed set to 30% => 13mm/s. Nice and slow!

A 70mm diameter circle would take 2 * Pi * 35mm / 13 = 17 seconds to complete.

=> approximately 4 skirts per minute

Hmmm... ;)

Sacrificial cube is definitely a winner, though.

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