Extrusion width compensatio .

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martinc
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Extrusion width compensatio .

Post by martinc » Sat Sep 08, 2018 10:20 pm

I am learning about 3dprinting with the intention of eventually building one. One thing I don't understand is that the 3D design or say the stl file, doesn't seem to take any account of the width of the extruded plastic. So to me this means that the resulting object is oversized in x and y by the extruded width. I also assume that if you are using a nozzle with a bore of D then the actual width of the plastic deposited is more or less than D depending one whether the speed in the XY plane is matched to the speed with which the filament id fed into the nozzle.
If this is correct then how do you compensate for this? I would have thought that cutter radius compensation would be the answer but it looks like Grbl doesn't deal with that. So how do people solve this?



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iDig3Dprinting
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Re: Extrusion width compensatio .

Post by iDig3Dprinting » Mon Sep 10, 2018 8:25 am

the slicer software that generates the g-code from the .stl file for the 3d printer takes into account the changes in width of the filament path due to different layer heights.

For more detail in the x-y plane this is why it is best to use smaller nozzle diameter (nozzle diameter is also a variable taken into account by the slicer). That way you will get less distortion in the x/y plane due to compensation of the layer height.

Your thinking about the xy width issue is correct but this is compensated for with the slicer software.

The thing that tends to have the biggest impact on the accuracy of print dimensions tends to be:

- steps/mm set for the stepper motors. i.e. if the x stepper motor is set to say 100 steps per mm, does this actually result in the gantry moving 1mm for every 100 steps.

- consistency of the diameter of the filament (always buy good quality filament)


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martinc
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Re: Extrusion width compensatio .

Post by martinc » Mon Sep 10, 2018 8:54 am

Thanks iDig3Dprinting. I don't understand this part of your answer-
"the slicer software that generates the g-code from the .stl file for the 3d printer takes into account the changes in width of the filament path due to different layer heights. "
Why does the width of the filament path change with height? And if the slicer software compensates for the extruded wdith how does it know which way the move the path? I might want the internal dimension to be correct or the outside. Does the slicer software ask about that and need to be told the nozzle bore? (I haven't used slicer software yet.)



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Re: Extrusion width compensatio .

Post by iDig3Dprinting » Mon Sep 10, 2018 1:10 pm

Yes in the printer settings for the slicer software it asks for the diameter of the nozzle used.

The width of the extrusion path changes with layer height as you still have the same volume of plastic coming out of the extruder so if its lower then it has to be wider, if it is higher it is narrower.

I cannot comment on the algorithms used, that's a bit above my pay scale. So it is somewhat of a black box, but a black box that seems to work well.

What are you looking to use a 3D printer for?


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martinc
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Re: Extrusion width compensatio .

Post by martinc » Mon Sep 10, 2018 5:10 pm

OK, I think I understand. When you said layer height I thought you meant the height of the layer from the base, but I think you mean what I would call the layer thickness or Z increment.
I haven't any real plan for what I want to make with a 3D printer. I recently had a nylon part made using SLS and I was impressed by the quality and strength, as well as the fact that the printed part was ready to use and cost about one third of the machined versions I had bought before.
I design and build computer controlled machines which have a lot of similarities with 3D printers, although my machines typically have a working area of 3 x 2.5 metres. So I just thought it would be fun to make a 3D printer.



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Re: Extrusion width compensatio .

Post by iDig3Dprinting » Mon Sep 10, 2018 7:14 pm

remember sla printers work differently from fdm. extrusion is not the issue. But I am assuming that you know that anyway.

I'd suggest having ago at building one. There are plenty of designs out there. It's good fun. We have a series of blog posts on the website about a build that we did. there is also some stuff about the software used. although I think it will be possibly elementary in nature for your self given your background.


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