slicing of Thin Wall tube only builds 17 layers instead of 100

[degsme 1]

So I have a design that is essentailly a mounting flange for a thin bit of vacuum formed ABS  (its a model cowl of a WWI rotary engine) 

the way I made it is to take a cylinder of the ID of the cowl, set its vertical height at 10mm (1cm) and then take a second cylinder, with a bevel that is just a tad smaller and cocenter the two

so the bevel gives my a nice fade into a hole in the middle (through which runs the rubber band that drives the prop)
and I get the first few layers of the vertical flange
but the slicer only generates 17 layers (looking at the gcode)

and with the resolution at 0.12mm, this gives me a height of 1.7mm  instead of the 10mm I was looking for.

initially my walls were 0.1mm thick (ie just one layer) - they are now up to 0.4mm ie 4 layers.. and STILL Cura only gives me 17 layers

what am I doing wrong?

[tinkergnome 927]

10 hours ago, degsme said:

the way I made it is to take a cylinder of the ID of the cowl, set its vertical height at 10mm (1cm) and then take a second cylinder, with a bevel that is just a tad smaller and cocenter the two

 

I'm not sure, if i got this right...

 

10 hours ago, degsme said:

and with the resolution at 0.12mm, this gives me a height of 1.7mm  instead of the 10mm I was looking for.

initially my walls were 0.1mm thick (ie just one layer) - they are now up to 0.4mm ie 4 layers.. and STILL Cura only gives me 17 layers

 

That's a bit confusing (to say the least)... it seems you are mixing up resolution, layer thickness and wall thickness? FDM printers just can't physically print lines that are significant thinner than the nozzle diameter. That's not related to the layer height at all.

 

 

Anyway:

If you define the wall in your model, Cura "sees" two walls that have to be build - one on the outside and one on the inside of the cylinder. It will not generate any walls at all if the thickness of the wall is smaller than 1,25 times the line width (or something in that range... it may be different for newer Cura versions).

 

It sounds like you better design the model as a solid cylinder-like object. And then print it with "Wall line Count" set to 1, zero bottom and top thickness and zero infill.

This way you can control the wall thickness with the value of "Wall Line Width" (inside of reasonable boundaries - depending on the nozzle size).

 

The difference:

 

 

[agiorgitis 0]

There is a setting called "Hole Horizontal Expansion". That one should be zero.

[degsme 1]

Thanks guys!  can I ask another newbie question?

I know the nozzle diameter is 0.4mm - but the setting in Cura allows for "Super Quality" where the line width is ostensibly 0.12mm.  and in measuring the thickness of a single extruded thread, I consistently get 0.2mm with my calipers.

are you saying that even though it actually extrudes that thin, Cura wont try?  I thought that the 0.4mm nozzle could extrude as little as 0.1mm by controlling feed rate and head speed

am I wrong on this?

 

[GregValiant 1,259]

Yes...you're right in that you're wrong.  3d printing is nothing if not confusing.  Here's what I learned in 3D 101.

The line width is related to the inside diameter of the nozzle and becomes the index distance between one nozzle pass across a part, and the next pass coming back the other way.  It effects the XY movement.  Any size nozzle works best at a line width that is near it's own size so a .4mm nozzle will generally need a line width near .4mm.

The "super quality" profile provides (among other things) a LAYER HEIGHT of .12mm and that is the  distance between one layer and the next (the Z index).  You can possibly get down to .08 layer height (a human hair width) on a really finally tuned printer.

The printer always needs to have sufficient material coming out so that the nozzle smears it against whatever is below (be it the bed or a previous layer).  Feed rate IS the speed that the head moves.  It's "flow" that you're thinking of in regards to how much material comes out.

Consider an example of a .4 nozzle and a .2 layer height making an extrusion 50mm long at a print speed of 40mm/sec...

In a general sense (general because slicing software plays with the numbers) - Line Width coupled with Layer Height determine the area under the nozzle to fill with plastic (.4mm line width x .2mm layer height = .08mm²).

The length of an extrusion gives the volume required for our line (how MUCH plastic to flow) (.08mm² x 50mm long = 4mm³)

The Print Speed (mm/second) brings time into the equation and gives that amount of flow its "rate" or how FAST that volume needs to come out of the nozzle. (50mm extrusion length/ 40mm/sec = 1.25seconds) and so (4mm³/1.25sec = 3.2mm³/sec).

Any slicing software MUST assume that the printer is calibrated in the X, Y, Z, and E.  If it isn't calibrated then the prints can not be correct.  If our first layer is set in the software at .2mm and we don't level the bed right then it isn't really .2mm and there is a struggle to get a good first layer.

Mechanically - if the X, Y, and Z are not square to each other then the prints cannot be correct.  They will be skewed even though that might be really hard to measure.

 

In the real world, if it looks good it's good.  If it looks like crap, it's crap.  All cut and dry.  Getting from crap to good is what tuning is all about and that my friend is where all the confusion jumps up.

[degsme 1]

Thank you for all the help with this n00b!!

 

[degsme 1]

and Thank you TinkerGnome for the 1.25 wall diameter.  That fixed it