Cura overhang support questions

[mastory 44]

First I need to say I'm not on the latest realease.  I think 3.0.2.  Not sure, I'm at work atm, and machine is at home.

 

I print some rectangular parts often that have large horizontal overhangs.  I have been splitting my models when possible and fabricating after print.  I'd like to print as one piece with support and save fabrication time at the cost of print time.

 

I'd like to be able to define the support interface to be severly underextruded, but with a dense line spacing to give a nice bottom surface, but easily break away.  Is there a way to do this?   Is the support interface underextruded by default?  If so, by what degree?  Can I define it?  I havent tried the support interface yet.

 

I'd like the support to extend laterally a couple mm from the model so the bottom outside model perimeter is fully supported.  Is there a setting for this?  Couldn't find one.

 

I see in the version I have, the tool tips are missing recommendations that used to be there, with much more generic and in my opinion lacking decriptions of the various slicing functions.  I hope there are plans to renew the old tips that were helpful.

 

Thanks

[gr5 2,210]

The easiest answer first:  "support horizontal expansion".  Set that to say 3mm and it will expand the support 3mm out horizontally from default.

 

If you are really printing lots of these parts and if you have a single extruder printer like the UM2 then I recommend you design your own support structure.  I typically make thin walls that touch the outer edge of overhangs but every print is different.

 

Some of your questions are confusing (because I don't know what your model looks like) and I may have answered both questions wrong so please post a photo of your model if my answers aren't enough.

[mastory 44]

Thanks as always @GR5,  I did find the horizontal expansion setting.  Also I've upgraded to 3.2.1.  I'm setting up to use my single extruder UMO. 

 

Below is an example of the sort of parts I am often asked to print.  It s prototype part nest for automation.  It needs to be accurate when finished.  At first glance, you might think the best would be to split the model and glue.  I have done that often on past parts.  I would like to print as one piece instead of splitting and fabricating, so I can reduce hand finishing time, and remove the painstaking glue operation and chance for error.  A longer print time is in my opinion cheaper than my manual labor.

 

This part is 45x65x105mm.

 

I'm considering a custom support model such as the red item below.  I would like to figure out how I can print these two parts with different parameters defined for each body.  I would like to separately control the red body to be printed at a high line density, but under-extruded and only a few layers thick on top of a support roof.  Sparse auto generated support would be used beneath the red item.

 

 

I went thru all the support options in 3.2.1, and have sort of achieved the above with a support roof, tapered support, etc.  I think I'm pretty happy with it overall, but I like to be able to under-extrude the support roof, or at least the very top of it.  This could be termed as separately controlling the roof line width.  I have not printed yet, just parsed all the slice settings and sliced.  I'll start the print tonight.  It looks like about a 5 hour print.

 

 

Edited March 2, 2018 by mastory

[gr5 2,210]

You could print the support first and remove it from the bed.  Then print the "real part" and pause it at the level where it needs support.  Then insert your support part (with some oil or some kind of mold release) and continue the print.

 

Or you could print the support first with "break away" filament.  Then again pause the print just before it does the overhang layer.  then when the print is done break it away and re-use it.

 

Personally I would make walls under the overhang and just have the walls touch in tiny spots (0.4mm square) every 5mm or so along the outer edges of this part.  Then rely on bridging to span the gap (which isn't perfect but usually close enough for what I do).

 

Of course if you rotate the part 90 degrees you only need support on that one "arm" overhang.

[peggyb 171]

what also works very well is to have the support with a sparse infill, with a support interface and then, like gr5 said, pause the printer at the top of the support interface. Use blue tape on top of the support interface, the next layer will adhere better then with oil I guess. The separation is easy..

[mastory 44]

Thanks for the tips.  Have considered printing roof, stopping at Z and applying tape, but never tried it.  I did find there is a setting for "support interface line width', which is meant to be above a roof I think.  This is essentially what I was getting at before.  I gave it a try.  There are some errors on the code relevent to that line width and its association with interface and roof; which options enable it and what it controls.  The intent is there, but I think with some tangled associations in the code.  I think it could be very powerful if sorted out.  I'll do a bit more testing and post another thread on the specifics.

 

I ended up splitting the part horizontally and placing the glue joints against the build surface.

 

Matt