Making better use of Flush-into object in Bambu Studio

Update after 3rd test print. 200% scale Xmas pudding tree decorations came out really well. Normal purge was 6g - so about 3 times what was predicted. There was also another 5g due to the brown filament running out and remaining on old roll having to be purged out. Prime Tower 7g.

I think that maybe 15% infill is too much for these models - and also not really sure whether the around 25g of filament saving is worth the effort for this type of print - probably more relevant for prints with more colours where having multiple copies of the same multi coloured object not really needed.

Also having less heavy off bed purges does cause a few of the ‘wisps’ to be dragged onto the prime tower - see photo.

Still running a reprint of ship model with faults corrected.

Will post both models on Makerworld/Facebook with and without ‘purge-to’ objects as next stage to see whether there is enough interest in ‘purge-free’ models to warrant further work in this area.


Purge-to table coming on - more than 1 leg now complete - think it should look quite interesting.

Tried to create a rendered version in F360 - only coloured in about a quarter of the render - but shows the general effect quite well I think.


Internal design of the purge-table done, plus found a better way of simulating likely look - using a F360 Wood appearance - with a photo of the current purge leg imported into the appearance as its texture photo.

For many of the parts it will be possible to alter the height so that top surfaces line up better with the layers with colour changes. This will also mean that the height and width of the table will be easy to alter or grow as more purge-to blocks get created.

As I am keen to print out the whole table - may have to switch around the process - and look for suitable multi colour object to print alongside these parts - in order to get a nice pattern of ‘purge-to’ lines.


Interesting to a this tweet from CNC kitchen about purge waste - thought I would try a few experiments with the model he was using ( link)

  1. Start position of part of the model he printed - waste 1kg print time 3d 23h

  2. Introducing a few purge-to objects, make the prime tower a bit small, 1h increase in print time, waste down to 64g.


Ready for another test - quite pleased with this design for the
makerworld xmas decoration competition.

At 100% scale it doesn’t use that much purge - but still think it is worth saving the waste.

Might be more interesting when I try it scaled up to 200%


Didn’t bother with purge-to objects on 200% version - but got a 75% saving on the 100% version.
On makerworld in xmas competition.

Also encountered some strangle slicer behaviours with Brims on Purge-to objects.
If the purge-to objects initial colour is different to the first layer colour on the main multi colour object then brims keep disappearing off of the purge-to objects.


Further investigation of controlled ‘purge-to’ within parts of a decorative object.

Simple version of xmas present model - purge:model ratio. 215%

Increasing copies from 1 to 14 - only 3 times the print time, purge:model ratio down to 18%

Introducing ‘purge-to’ into middle of object - print time up by another 10% - (which I don’t really understand) - but purge ratio down to 0.4%


amazing work ! looking forward to your updates and hope you will share your work in the end

Firstly - decided to change from using purge to flush in this thread from now on - to be more consistent with field names in Bambu Studio.

Next up - just tried the new Beta Bambu Studio - - and noticed a couple of nice changes.

First change - not really flush related - better handling of black objects

Current BS

Beta - blacks now shaded show you can see the detail a lot better

Next up - more relevant to this thread - glad to see that there is a new totals column in the BS Preview screen showing the prime tower usage separately - rather than including it in the model (not flush) total in previous versions.

Current version



Further updates - firstly been doing quite a lot of single colour printing - concentrating much more on print quality than I have done before - mainly creating support free spheres and balls - the reason to mention this is that this has led me to needing to do some 100% infill printing which I have never done before - and 100% infill models are really good flush-into targets - especially parts like the internal double ended screw used to hold the two parts of my spheres together.

Model on makerworld here Eight Ball

Preparing for a test of my gcode post processor to remove the prime tower - some slightly interesting results

Starting point - no flush-into objects - starting point terrible - 36g flush and 10g prime for an 8g model - so waste:model ratio 575%

Test model (black and white rectangles) with 12 flush-into cylinders - flush down by 75% - but quite high at 8g

Adding just one more cylinder though - pushes flush down to <1g

Final screenshot showing what happens if you turn off the prime tower - flush-into no longer works - and flush goes right back up to the starting point

Prime tower removed - now to run an actual test

Will probably only let it run a few layers to avoid waste - main objective is to a) Check that the printer accepts a patched gcode.3mf file ok over wifi, b) check that movements are ok and c) to see what effect it has on the quality of the flush-into objects.

Test result - success -

went up into infill layers - and printer seemed ok with not having prime tower. Lines went down ok into flush-into objects and colour changes worked ok. Bottom layers of flush-into object put down far more plastic than is needed to flush out the old colour - number of objects determined really by size of infill layers.

Next step - try it on next proper multi colour print.
NB/ This method of removing the prime tower is only relevant when there is sufficient wasted flush to warrant the use of flush-into objects - whose quality probably isn’t as important as the main multi colour object - so can be used from priming as well as flushing.


This is about the best use of purge-to I have seen. I NEED this table model! Is this going to be available anywhere for either pay or free?

Thanks - Yes - will release it - once I have refined it a bit and have at least a small version printed - progress has slowed a bit because I am not doing a lot of multi coloured printing at the moment.

I am hoping it works out that once you have created the basic parts and produced a fairly small table (or potentially other shapes) you can then just expand the dimensions as more flush-into parts became available as a byproduct of other prints.

Think I will have a go at doing a smaller scale single test print tomorrow - using low value filament in order to try and make a bit more progress on this initiative.

Update. 28/11. - print now ready to go with most of the essential parts to create a corner of the purge-table - one 1g of flush.

Also trying it with prime tower removed by post processing GCODE
10046 G0 and G1 commands commented out
2.5 M prime saved


Update - purge-table starting to take shape - all individual parts now tested.
Just need to build up a few more top parts and legs - big incentive to get on with some nice big multi colour prints


Not strictly related to the subject of purge reduction - but I have just seen this interesting post on Facebook about problems with prime towers in ‘multi material’ support interface prints - Redirecting...

Interesting issue. My thoughts are

  1. Priming is probably even more essential than normal for multi material support interface layer prints - as you need a really clean flow of both of the materials when they are overlapping each other - so turning off the prime tower is probably not a good idea.

  2. In the prime tower the initial inconsistent flow in combination with poor inter layer adhesion between different materials does mean that it is more likely to fail than a single material prime tower.

The solution I think has to involve separate prime towers per material. This then leads to the issue of creating masses of extra material swaps to in this case keep the PETG tower the correct height.

The solution to this issue I think is introducing a variation of the ‘no sparse layer’ prime tower logic in Prusa slicer - which allows the prime tower to have less layers in it than the actual print.

This method though would suffer from the same height restrictions as you get when ‘printing by object’.

I think however that you could work around this issue by keeping the PETG prime tower not too far behind the PLA tower by adding just the occasional extra PETG colour change - which is used to add a few layers to the PETG prime tower - so that it doesn’t get too far behind.

Whilst ideally this should all be done in the slicer - I think it would be possible to write a gcode post processor to

A) split out the materials into separate prime towers

B ). Add ‘no sparse layer’ type functionality

C) enhance ‘no sparse layer’ to stop towers from getting too far behind the main level

Any extra colour changes required for this would have to be created by manually adding them into the model at the correct heights.

Sounds like an interesting technical challenge - for waste reduction purposes I was already considering having a go at creating a GCODE post processor to
a) alter the shape of the prime tower to make it into a more useful shape (such as a section of ‘purge-table’) rather than waste
b) adding in a ‘no sparse layer’ capability -
so might have a look at the splitting the tower into materials too at some point.


Your discoveries are impressive.
This started as a forum thread but feels like a complete research paper when I read it.

In the past few days I began to do the same as you, only I was using the Hive model as purge into object.
I had satisfactory results but I was interpreting the numbers in the BL final table quite bad. Your thread makes it clear.

My question is: do you keep in BL flush volumes auto-calculated with fixed multiplier?

I had good results with my colors that I mostly use with multiplier 0.6 even with prime tower only and poop out the chute.
Increasing the number of sacrificial objects that does not matter the color composition will decrease the wasted plastic with flush.

I am no near able to automate a script to remove prime tower but I am interested in that if you want to share.

I’ll keep a close eye on your thread
Thanks in advance


Thanks, yes I use auto calculate and usually 0.5 multiplier. Using flush-to objects mostly slightly increases the effective flush a tiny bit. Removing the prime tower reduces it a little bit - so I guess it may end up resulting in having to push the multiplier up a little.

Will share the post processor once I have tested it out a few more times, plus worked out the best way of sharing python3 code in such a way that it is easy for others to install.

I have tried out some of the flush checking methods like the AMT_MW test models - bit I think it is probably going to be too complicated for to keep track of all of the different flush volumes for different colour combinations - so will probably just stick with auto calculate for now - because as long as you are flushing into useful objects an extra little bit of flushing isn’t necessarily a bad thing.


This is amazing. Just got the AMS added to my P1S and coloured my first print (turned Barry Bear into a panda) and I was disappointed to see my 90g print was going to make 180g of waste. I figured someone must have found a way to reduce that. I knew about flush-to-object so I had a couple of functional pieces I had waited to print for this reason but they only reduced the waste by 20 g or because they were either too thin or too short. Your experiment (which is how this read like Cmaneaonline said) was extremely helpful and got my waste down to 23g and 330g of functional. So although my filament usage increased to 22% my waste was reduced by 89%. And this was without using your table pieces or your python code (since I felt too inexperience to try it). I hope your research here becomes part of the Bambu Wiki as I think everyone could benefit from it.

Decided to have a go at individual colour swap purge lengths based on the AMT_MW models on maker world. Initial results showed definite benefits over auto calculate for some colour combinations - without a clear pattern.

As am currently away from printers - have used the time to create some automations on top of Bambu Studio using the Mac only ‘Keyboard Maestro’ app.

  1. First macro is an easy one to automate the setting of all flush lengths to 50.

  2. Next set of macros can then be used to store any newly calculated optimal lengths against the associated filament types and colours - so that they can then be easily re-applied whenever required.

It should also be possible to enhance these macros to do more generic enhancements to the build in auto calculate.

Initial ‘set lengths to 50’ macro shared below - if there is any interest in the others let me know.


Brief update -

I’ve got quite a few ideas for ‘flush into as colour doesn’t matter’ objects - such as

  1. Large multi part functional items - designed with ‘flush-into’ specifically in mind, that can be built up over time - such as:
    A flexible size table - made out of multi colour flush - that I am calling the ‘purge-table’.
    Plus other big multi part things like shelving etc.
  2. Xmas decorations - such as multi coloured balls etc -
  3. Printer add ons - like AMS risers / AMS helpers / Scrapers etc
  4. Storage - like Gridfinity etc.
  5. Decorative things like Vases and 3DPB string art etc that are actually enhanced by the ‘random’ multi colouring
  6. Big strong functional things - like the parts for the MPCNC for example
  7. Custom packaging for fragile designs
  8. Internal components of decorative items

Additionally I have a couple more ideas

Have made a start on a collection here to try and illustrate the sort of thing I am talking about. Flush-into colour doesn’t matter | Collection - MakerWorld

Finally got round to doing another multi colour print too tomorrow - this time of a BS hand coloured (my first using BS) Star Wars Corvette (from Thingiverse AirTeuteu Star Wars CR-90 Tantive IV split by AirTeuteu - Thingiverse) - flush will go down from 34g (30%) to about 1.25% (1%) using the ‘prime-table’ parts. It does push print time up by about 45 mins though.

Update 19/12 - First attempt at print failed - due to not spotting that top rows of engines needed support added - pretty happy with reprint though - and fairly small amount of flush waste.

Support removal quite tricky

But came out ok I think

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Bit controversial I know - but I was wondering if I could be a bit more creative with the ‘purge-table’ legs as I am not doing enough multi colour prints at the moment to make much progress - so I was thinking about maybe incorporating some other ‘waste’ material in them in addition to the multi colour flush.

So printed with first ever Bambu Lab built in Benchy - have tried and failed a couple of times before - but it seemed to work very well on the cool plate on an X1C with the latest firmware ok. Quite noisy though I guess due to the high speed.

Not exactly sure how the structure the part - to make best use of the pretty strong structure of a benchy into the table structure - my first attempt is going to be something like this…

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