Use full build volume for parts with brims and 360 overhangs

[CodyHufstetler 0]

I'm not sure if there's a solution to this, but if anyone knows, that would be great.
 

I have a part that has overhangs all the way around. they are 45 degree overhangs, so they don't require support under them, but the important thing is that the initial contact patch is smaller than the external boundaries of the part. Due to the material, a brim is absolutely necessary. 

Of course, when I add the brim in Cura, I get the grey boundary in the print area to account for the brim. The problem is, the brim is only added to the first layer of the part, which is smaller than the shadow. but the shadow is what Cura uses to determine if your print is out of bounds. so if I scoot the print right up to the edge and slice, the brim still isn't anywhere near to the actual edge of the build plate, due to the fact that it originates further into the part than the edge of the shadow. If it could check for printability post-slicing, it would be clear that I can use more build volume - but it won't even slice if it thinks something will be out of bounds.

 

Hopefully this makes sense. I'm currently trying to mass manufacture fixturing (and get 3D printing widely accepted in our manufacturing facility), so being able to pack the build volume is important. I've heard recommendations to model the brim yourself, but I would prefer not to - again, since I am trying to fit 3D printing into our engineering workflow, I want the models (and therefore the drawings) to match the final product. Besides, any kind of workaround will not help with wider adoption of 3D printing.

[gr5 2,069]

Yeah this is a bug that I've known about.  It sucks.  Another brim "bug" is that sometimes it ends up "inside" the part where I don't want it and it is extra hard to remove (I put bug in quotes because in the case I'm thinking of, "inside" is topologically still outside in my specific case because there is a purposeful crack leading to the exterior of the part).  Anyway...

 

46 minutes ago, CodyHufstetler said:

I want the models (and therefore the drawings) to match the final product.

That's a tough one.  My understanding is that other technologies such as injection molding need much more modifications to the design than FFF printing.  You even have to change the angle where the edges come together in corners (in other words corners of the mold are not at 90 degrees if you want the final part to be 90 degrees.  Crazy.  So it's wonderful that you have to change so few things in FFF printing (between desired part and model sent to Cura).

 

Also in FFF I have to make all vertical holes about 0.4mm larger than specification.

 

The difference though with injection molding is that there is a second engineer at the mold company who does all the modifications to your 3d model.  I think I prefer 3d printing where the modification is done by the primary designer.

 

Adding a brim in CAD is pretty easy.  It can be on a secondary layer that is turned off by default so most people don't notice it?  I occasionally add brim in CAD because I can only put the brim on the extremities/corners and this saves lots of time removing the brim later.

 

Sorry I'm not helping with your question.  But wondering if you might want to think differently about the overall solution to dealing with CAD models not matching final product and process flows.

 

 

[dsp 18]

Do I understand the question right? 

Your brim is not close to the edge and it still says your out of bounce right?

But if  your model is over the edge of the build plate (higher up) the print nozzle can't reach it as well.

I think that is why you get the error right? 

Once I had a model that was as big as my entire build plate but Cura thought it was to big.

So I had to manually change the build plate size in Cura to let it be sliced (but I only did this because I was 100% sure it fitted) this could be a solution.

[gr5 2,069]

As you extend the build plate size it also moves the "center" to the right and back a bit so your parts are no longer actually centered in the printable area.  So you can't extend it very much.  A few mm, yes.

 

so his part is like an upside down pyramid.  He is only putting brim around the pointy end but the code that checks if your part is printable is looking up at that base size and adding the brim to that.  So... bug.  I'm familiar with this bug.