Help, internal size of part(s) too small...

Re: Help, internal size of part(s) too small...

nophead — Mon, 21 Dec 2015 07:18:41 -0500

How are you measuring it? If it is by measuring a print some of the discrepancy will be plastic shrinkage. Perhaps your belts are inaccurate or not stretched tight enough to meet their spec. I don't know what tension belt pitch is quoted at or how much difference tension makes.

Re: Help, internal size of part(s) too small...

elgambitero — Sun, 20 Dec 2015 12:04:05 -0500

After exams, I went back to this topic. This is what happened so far:

Printed the twisted bottle. Layers were so uneven, and of course it didn't fit. Then it came to my mind that maybe perimeters were being altered during the making of the infills, so I set that from 15% to 5% (I doubt this is even necessary, Slic3r makes infills fine). This resulted in a nice finish print test, but still needs more testing.

But then i came across another issue.... I suspect that my stepspermm are a bit low, but they are the standard 80 stepspermm for T2 pulleys. It's a well-known value, and widely used. However, with belts tensioned, and no hysteresis in my axes, the value that does the trick for me is 81.42steps. It doesn't fit any other clone of this printer but mine. How can this be?

I'll keep testing until I get a nice config file. This issue needs to be tackled once and for all.

Re: Help, internal size of part(s) too small...

elgambitero — Sun, 13 Dec 2015 06:33:47 -0500

I did what @nophead said. It came down to just retensioning the belts. The results are promising:

[attachment 67573 image2.JPG]
[attachment 67574 image1.JPG]

The file is the fit.stl attached in this message, scaled to 300%. When I tried to print it at 100%, it was too smalll and there were no use trying to fit the two halves.

Right now I'm printing the classic twisted bottle, and see what happens.

Re: Help, internal size of part(s) too small...

elgambitero — Wed, 09 Dec 2015 19:32:11 -0500

The two examples i had lying around turned out not to be that bad when it comes to layer evenness. It does when it comes to hiding the seam of a perimeter start. KISSlicer priorizes vertexes with narrower angle when Slic3r takes just the nearest one. This results in a much less camouflated seam... But I won't worry about that just yet because the constant pressure approach is interesting and I haven't had the opportunity to test it...

Back to the dimensioning problem. Last saturday I was tinkering with XYCompensation and found that it shrinks the inset as much as it shrinks the outset. When your printer makes the outset fine but the inset smaller, what do you do?

I'll tackle this problem this weekend, with a previous mechanical revision of the machine. I could believe that belts may have slept and produced backlash.

Re: Help, internal size of part(s) too small...

nophead — Wed, 09 Dec 2015 14:36:16 -0500

Poor layer alignment is normally a mechanical problem. I am not sure how the slicer would affect it, other than if you only have rounded corners you don't have as much stress on the mechanics.

If you have backlash then the order and direction of the outlines can make a difference. If you always approach the start of an outline from the same direction the outline will be in the same place but if sometimes it is approached from the other side, starts in another place or goes in the opposite direction it will be displaced.

Re: Help, internal size of part(s) too small...

elgambitero — Wed, 09 Dec 2015 13:42:27 -0500

By layer eveness, I mean that every external perimeter is exactly in place, when you look at the layers from the side. For example, in a vertical wall, every perimeter is exactly on top of the previous one, and looks exactly like the previous one. The idea can be expressed with a photo but I'm not at home right now.

With Slic3r, layers look displaced from each other, while in KISSlicer the layers look like in the gcode renderer.

Fine tuning of Slic3r can decrease this effect, but I haven got it just yet. Richrap's "Slic3r is nicer" tutorials have a lot of photos of what I call "even layers"

I hope I explained. When I get home, I'll post two examples I have lying on my desktop.

Re: Help, internal size of part(s) too small...

nophead — Wed, 09 Dec 2015 11:16:09 -0500

What do you mean exactly by layer evenness?

Re: Help, internal size of part(s) too small...

elgambitero — Wed, 09 Dec 2015 11:05:55 -0500

If I could, I would include that as an option. Skeinforge included the option "Fillet corners with X radius". After all, attempting to make a sharp corner in an FFF machine is an unrealistic approach.

Like any other fabrication process, modifications must be made to the model in order to get the final product right, but I consider modifying the original geometry a bad practice, so those modifications must be made in the slicer, in my opinion.

XY Compensation parameter is wonderful for it, and the closest thing to "inset calibration" we have in the open source ecosystem, but I still don't get things to fit...

Layer evenness may be a thing here, it also happens that KISSlicer gets layers to be absolutely even, and Slic3r don't, but gcodes are almost the same!!! What's happening here?

I'll make more experiments when I have more time. I think that open source 3D printing is developed enough to overcome these kind of problems.

I made a repo sharing the slic3r settings I use, to keep track of why I changed each one of the parameters: [github.com]
Tests are to be documented but right now I can't because I really really should be studying.

Re: Help, internal size of part(s) too small...

nophead — Tue, 08 Dec 2015 19:42:24 -0500

I think the inner rounding is just a progression of the outer rounding when you offset inwards by the filament width. The difference comes from the outer perimeter. KISSlicer seems to round the corners where the model has sharp corners. To some extent that makes sense because you can't actually print a sharp corner. It will have a minimum radius of half the filament width. However KISSlicer seems to round it more than that.

Objects with rounded corners always come out nicer because it lowers the acceleration which reduces ringing, etc, and also allows the filament flow to be more constant. Probably better to model that way rather than have a slicer that doesn't follow the model.

Re: Help, internal size of part(s) too small...

elgambitero — Tue, 08 Dec 2015 18:36:46 -0500

I revisited this issue, because I want to migrate from KISSlicer to Slic3r. (KISSlicer is closed, and the author tends to dissapear from time to time)

I see something that KISSlicer does with additional perimeters that Slic3r nor any other slicer does: The outer perimeter geometry is nominal, right? and the rest of the additional perimeters are just context coherent scaling of each of the features of the perimeter, but KISSlicer does more than this... KISSlicer rounds the perimeter more and more with each internal iteration, so the inner perimeters don't do much pressure upon the original geometry's features.

I'm sorry for writing this in such a heavy-reading way... It's a bit late.

For TL;DR, and clarification, I attach the output of the two, so you can see the effect:

[attachment 67295 ScreenShot2015-12-09at00.31.21.png][attachment 67296 ScreenShot2015-12-09at00.31.24.png]

This could also be part of why KISSlicer gets such an even finish! My homemade prusa i2 is a cranky old printer that shakes and breaks and de-adjusts continously, but with KISSlicer gcodes it still makes better prints that many high specs printers. With astonishing accuracy.

Re: Help, internal size of part(s) too small...

nophead — Mon, 09 Nov 2015 07:30:01 -0500

I think extrusion width and nozzle diameter also affect how much round holes shrink.

Re: Help, internal size of part(s) too small...

dmould — Mon, 09 Nov 2015 07:25:53 -0500

Quote
Mikk36
Extrusion width does affect the corner radius in XY plane, so you could say that you can get better resolution in that sense with smaller extrusion width.

Yes, true, though having a very small radius instead of a sharp corner is seldom a problem - and IME the shape of most corners are affected far more by "blobbing" and other artefacts than by extrusion radius (at least when using a Bowden extruder).

Dave

Re: Help, internal size of part(s) too small...

Mikk36 — Sun, 08 Nov 2015 03:51:20 -0500

Extrusion width does affect the corner radius in XY plane, so you could say that you can get better resolution in that sense with smaller extrusion width.

Re: Help, internal size of part(s) too small...

dmould — Fri, 06 Nov 2015 07:18:18 -0500

Quote
justcurious
well, I think you have by far too big ambitions about accuracy with 3d printers. Think about again.
You have a nozzle that can make a line that is 0,40 wide or larger, never smaller. in layer height direction you can select a layer height smaller than nozzle width and by that get better resolution, but in x,y plane, accuracy is never better than extrusion width or at least half of it.

Why do you believe that? You are completely wrong. The extrusion width affects only the smallest feature that can be printed in XY, not the dimensional resolution of the part. On the contrary, it is the Z dimension that can only be made to the accuracy of your layer height, the XY accuracy can be a lot better - it is constrained only by the motor step size and the amount of backlash in your XY axis. Neither X nor Y have to be positioned on an exact multiple of the extrusion width, only an exact multiple of the distance moved by the stepper motor micro-step. When slicing therefore, choose a layer height that will divide exactly into the Z height of the part to achieve the greatest accuracy.

There are a few factors that affect the accuracy of printed circles, but probably the biggest is the fact that the inside circumference of a circle is smaller than the outside circumference. Most slicers will position the extruder to a position that is half the extrusion width away from the outside or inside perimeter, assuming that the centre of the nozzle will run along the centre of the extruded line. So (for example) if it "draws" a rectangle that the design file shows as being exactly 10mm in X using an extrusion width of 0.4mm, the extruder will move (in X) a distance of 9.6mm (from relative positions 0.2mm to 9.8mm) With straight lines and the correct extrusion factor that will give pretty good accuracy - 0.05mm or better IME. If however the extruder is describing a circular path, there is more plastic deposited in the inside of the circle than the outside, because it has a shorter circumference. This has the effect of displacing the centre of the extrusion toward the inside of the circle.

Dave

Re: Help, internal size of part(s) too small...

nicksears — Thu, 05 Nov 2015 12:59:15 -0500

@mikh3x4 have you figured out the answer? This is an old post, but I've carefully read all 6 pages and while there are lots of great improvements and insight, I feel like there's no comprehensive solution.

To sum up what we've learned: Slic3r incorrectly approximated the profile for EW<=nozzle diameter, but I personally think this was not far off enough to cause issues on the order of what most people see. Slic3r details many of the issues (http://manual.slic3r.org/troubleshooting/dimension-errors) including XYZ calibration, shrinkage, polygon approximation for circular holes, filament cutting corners, z wobble, inconsistent filament diameter, backlash, and dragging filament towards the center of a circle (there may be others).

I've made (thing:1113412) to test some of these issues and I'll post if I find a reasonable solution. I've set out to test the effect of a single perimeter, external perimeters first, number of perimeters, perimeter speed, and nozzle diameter.

@nophead, I agree with you that the nozzle diameter should have nothing to do with flow calculations (if extrusion width is constant) and I've found just that. With a constant EW of 0.5 and a nozzle of 0.25, 0.4, or 0.8, I get different filament usage!
@sound is this right? I thought it had something to do with the filament cross-section slic3r uses with a little more info here (http://forums.reprap.org/read.php?263,134103,137818#msg-137818)

Any one figure out an end-all be-all solution? I don't think XY compensation is it...

edit1: formatting
edit2: thing#

Re: Help, internal size of part(s) too small...

CraigRK — Tue, 29 Jul 2014 14:19:35 -0400

Quote
Sound
Okay, I confirm I have now extended the usage of the rectangle model with semicircles even in those cases that were previously handled by very similar yet different formulas. The main reason I did this hypothetical "fix" is to stop discussing on a secondary factor that has very limited impact on dimensional issues, but was still attracting too much attention giving users the feeling that flow math was the main thing to blame. Release 1.2.0 will include this minor change (and will also include the XY Size Compensation option which is way more important for handling dimensions).

Thanks for doing this. I am sure you are right, but often the easiest way to stop the debate on a point is to prove it by doing what people say and proving your point.

Quote
Sound
CraigRK, I bought parts from nophead as well in 2010 or 2011, and I confirm they were quite good. (Oh, my prints from these days are very good and precise as well, do you want to check? I can mail you one :-)). Saying that their quality was only caused by flow math is unfair, since nophead as a knowledgeable person has always been able to build very good machines, tune them, use good quality filament etc. Even in 2014, the average user can't do all of those. Nophead even invented the polyhole OpenSCAD function that addresses one of the main factors for hole errors lying at the CAD stage. I'm not sure all Slic3r users are aware of polyhole.

I've just re-read my post in case I got the tone wrong, I don't think I did. I didn't say you were not producing equally good stuff, or that their quality was only caused by flow math. I worked very hard to make sure I worded things evenly as I didn't want to offend either of you. This is why I said:

Quote
CraigRK
I value the contributions both you and Nophead make to the community.

As I said, the issues are probably caused by multiple factors, and eliminating as many of them as possible will help

Quote
Sound

The "outside perimeters first" option was introduced in Slic3r about two years ago or something.

I keep saying that even with this hypothetical -0.05mm compensation, the OP issues are not fixed at all given the numbers he reported. So, my best effort for helping OP is this answer: [manual.slic3r.org]

Thanks again for all you are doing for the community.

Craig

Re: Help, internal size of part(s) too small...

Sound — Sun, 27 Jul 2014 14:38:03 -0400

Okay, I confirm I have now extended the usage of the rectangle model with semicircles even in those cases that were previously handled by very similar yet different formulas. The main reason I did this hypothetical "fix" is to stop discussing on a secondary factor that has very limited impact on dimensional issues, but was still attracting too much attention giving users the feeling that flow math was the main thing to blame. Release 1.2.0 will include this minor change (and will also include the XY Size Compensation option which is way more important for handling dimensions).

CraigRK, I bought parts from nophead as well in 2010 or 2011, and I confirm they were quite good. (Oh, my prints from these days are very good and precise as well, do you want to check? I can mail you one :-)). Saying that their quality was only caused by flow math is unfair, since nophead as a knowledgeable person has always been able to build very good machines, tune them, use good quality filament etc. Even in 2014, the average user can't do all of those. Nophead even invented the polyhole OpenSCAD function that addresses one of the main factors for hole errors lying at the CAD stage. I'm not sure all Slic3r users are aware of polyhole.

The "outside perimeters first" option was introduced in Slic3r about two years ago or something.

I keep saying that even with this hypothetical -0.05mm compensation, the OP issues are not fixed at all given the numbers he reported. So, my best effort for helping OP is this answer: [manual.slic3r.org]

Re: Help, internal size of part(s) too small...

CraigRK — Tue, 17 Jun 2014 23:00:50 -0400

Quote
Sound
I'm open to testing the change in the upcoming experimental release.

Great, thanks. I've been quietly following this thread and was going to suggest this.
I value the contributions both you and Nophead make to the community.

Quote
Sound
So, luckily this change won't raise too many complaints since it will change very little. But unluckily, it's not the definitive solution for getting exact dimensions… and probably not the main cause to blame either.

As a software developer, I understand this problem, often things are affected by multiple elements, but this still means it is worth fixing everything we can.

As a person who has bought plastic printed parts from Nophead (both for my original Sells Mendel back in about 2008 or so and last year for a friend's M90 (I printed my own, but he was in a hurry and my printer was broken), I can attest to the fact that nophead's parts have good dimensional accuracy. With the Sells parts I could see some evidence of cleanup/reaming of holes. With the latest M90 parts they look like they're straight off the printer, and they're perfect.

I guess a secondary element to this is the point made about slicing with the "outside perimeters first" setting when wanting dimensional accuracy. IIRC this is what Nophead also does. Could this combined with the above account or some of the OP's original issues? (Sorry on an iphone, so not rereading the entire thread although I have previously read every word and gone and re-read the relevant posts on nophead's blog and your manual and GitHub tickets/comments)

Re: Help, internal size of part(s) too small...

Sound — Tue, 17 Jun 2014 17:20:06 -0400

Okay nophead, you have a point. You're talking about the shape that extrudate gets after nozzle has moved on. Viscosity of plastic rounds the sides until they become semicircles, even if they weren't such while each section was being extruded. That makes sense.

I'm open to testing the change in the upcoming experimental release. Both luckily and unluckily, I think that things won't change much anyway since the change is going to affect a limited set of situations (those where target width is smaller than nozzle diameter + layer height). Also, using a spreadsheet I calculated how thinner would extrusion width be in those cases, i.e. how much would the error be reduced by.
To do this, I calculated the cross-sectional area with current formula, and then divided using the new formula solving by width.

For a 0.35mm nozzle and 0.1mm layer height, the actual width (according to the new formula) will be -0.02mm over the current one. And -0.06mm for a 0.4mm layer height.

For the OP issue raised by Qsilver who started this thread, the difference according to his settings would be -0.05mm, which is way less than the errors he measured so not very useful for fixing his issues. (It's even less than the difference in error he measured between X and Y, 0.1mm, that he thinks might be caused by mechanical issues.)

So, luckily this change won't raise too many complaints since it will change very little. But unluckily, it's not the definitive solution for getting exact dimensions… and probably not the main cause to blame either.

Re: Help, internal size of part(s) too small...

mikh3x4 — Fri, 13 Jun 2014 13:42:35 -0400

Ignore this post. I missed all 5 pages. Stupid me

Re: Help, internal size of part(s) too small...

ketil — Thu, 12 Jun 2014 18:19:24 -0400

Quote
nophead

Quote

Concluded from the above thread, from the start, i think that it has been verified that Slic3R selects correct path as expected and for W/T>1 it is probably selecting proper flow as well. question is would flow be better for W/T=1 and W/T<1 if the same formula was used? I do not know. i do not even know if the formula used at present version is failing!

No Sli3r only uses the correct formula when W - T > nozzle.

For the sake of argument, couldn't you fudge slic3r's configuration and set a really small nozzle to get slic3r to use correct math? For example, let's assume you set the nozzle size to 0.1mm (regardless of your actual nozzle size), set layer height (T) to 0.4mm and set all extrusion widths (W) to 0.6mm. Then you'd have W/T = 1.5, and you're tricking slic3r into using your ideal formula, right? Does that give you correct sizes? If people start doing this and get correct sizes as a result, while getting wrong sizes when using slic3r normally, that'd make a strong argument for changing slic3r's formulas.

If you try this, slic3r will give you some error messages because extruding at layer heights way greater than the nozzle diameter probably wouldn't work all that great, but for the experiment you could comment out lines 254 through 257 in lib/Slic3r/Config.pm to trick it into accepting these anyway:

#    die "--layer-height can't be greater than --nozzle-diameter\n"
#        if grep $self->layer_height > $_, @{$self->nozzle_diameter};
#    die "First layer height can't be greater than --nozzle-diameter\n"
#        if grep $self->get_value('first_layer_height') > $_, @{$self->nozzle_diameter};

Regards, Ketil

Re: Help, internal size of part(s) too small...

justcurious — Wed, 11 Jun 2014 09:24:19 -0400

@nophead
I would be surprised if @sound is introducing scaling as a solution to above problems, i would rather believe it is some sort of inset feature, but I have not seen any description yet.

The extra parameter offered is just another variable I believe for experimenting. You already had settings for perimeter extrusion width, now you get an extra for specific setting of external perimeter (if I understand it correctly)

Re: Help, internal size of part(s) too small...

nophead — Wed, 11 Jun 2014 09:04:23 -0400

Quote
justcurious
you did not answer my question whether you think Slic3r would be performing more correct for W/T<1 if the same algorhitm was used, but if you always select extrusion width greater than nozzlewidth it of course is nothing but a theorethical question with no practical value, is that correct?

W/T can't be less than 1, i.e. you cannot extrude a filament taller than it is wide. W = T means the filament is not squashed at all and makes a cylinder. It is only relevant when bridging. Slic3r's documentation is self contradictory as it shows a cylinder in the bridge section but also shows a square in the flow section.

Quote
justcurious
We somehow were untracked here so let us get back to the original issue of object sizes and the new possibilities that Slic3R is offering with latest version despite the above discussion on performance of algorhitms:
1. XY size compensation, i wonder how that is going to be used for solving problems mentioned above or is it not needed, now we know that more carefull selection of params eliminate problems ;-).

Well you always need an overall X Y scale factor to compensate for shrinkage. It can't compensate for flow rate calculation errors as they create an offset in dimension, not a multiplier. There would be no flow rate to width errors if the right formula was used throughout to relate the two. Then it could either reduce the flow rate to give the desired width or use the same flow rate and offset by the predicted width. That would fix all error not due to shrinkage.

Quote
justcurious
2. variabel external perimeter extrusion width, which may have influence on dimensional print accuracy.

Don't know exactly what is meant by this.

Re: Help, internal size of part(s) too small...

dzach — Wed, 11 Jun 2014 08:58:10 -0400

Quote
dzach
a ratio at which the formulas I used start to fit closely the shape of the plastic.

That was a wrong statement, indeed. At lower ratios the filament continues to be pressed by the nozzle, which still gives it the rounded rectangle shape. Things change when W /T < 1, or when W > flat bottom of nozzle. Which, I think, puts the limits of the practical extrudate Width sizes to "nozzle orifice diameter" <= W <= "nozzle flat bottom diameter".

EDIT:
... a fact that is indicated in the same dynamic graphic, but not shown in the above animation (it been so long ago I had forgotten about it)

[attachment 34736 wt9.png]

Re: Help, internal size of part(s) too small...

justcurious — Wed, 11 Jun 2014 08:43:04 -0400

Thankyou for clarifying Nophead, you are an endless source of information :-).
However it frustrates me that I see different rules for different setups and for some selections you are left in grey areas.

you did not answer my question whether you think Slic3r would be performing more correct for W/T<1 if the same algorhitm was used, but if you always select extrusion width greater than nozzlewidth it of course is nothing but a theorethical question with no practical value, is that correct?

We somehow were untracked here so let us get back to the original issue of object sizes and the new possibilities that Slic3R is offering with latest version despite the above discussion on performance of algorhitms:
1. XY size compensation, i wonder how that is going to be used for solving problems mentioned above or is it not needed, now we know that more carefull selection of params eliminate problems ;-).
2. variabel external perimeter extrusion width, which may have influence on dimensional print accuracy.

Re: Help, internal size of part(s) too small...

dzach — Wed, 11 Jun 2014 08:23:23 -0400

Quote
QuackingPlums
For printing purposes I think we are more interested in the cross-section as it leaves the trailing edge of the nozzle (nozzle aperture removed to illustrate that this is the trailing edge):

At this point, the plastic is securely adhered to the plate/object below and the movement of the nozzle/bed has dragged the plastic into the squashed cylinder that Chris describes.

Yes, that was the intention. So, different coloring of the extruder internals may make it clearer:

Re: Help, internal size of part(s) too small...

nophead — Wed, 11 Jun 2014 08:18:51 -0400

Quote

Concluded from the above thread, from the start, i think that it has been verified that Slic3R selects correct path as expected and for W/T>1 it is probably selecting proper flow as well. question is would flow be better for W/T=1 and W/T<1 if the same formula was used? I do not know. i do not even know if the formula used at present version is failing!

No Sli3r only uses the correct formula when W - T > nozzle.

Quote

if i should always select W/T=1.5 i would certainly get in troubles. my nozzle is 0.35 and I mostly print at 0.2mm that would say that if W/T should be 1,5, I should select extrusion width of 0.3mm, but what if i select layerheight of 0.1mm? that would give me extrusion width of 0.15mm, that does not make sense, does it? and it does probably not care which formula is used anyway.
Could anybody clarify my frustrations?

No W/T = 1.5 is only appropriate for high layer heights. In fact it the smallest value that works and together with the dies swell diameter determines the maximum layer height that you can use.

W should always be >= nozzle, so with a 0.1mm layer and 0.35mm nozzle it should be close to 0.35mm. To get the correct math in slic3r W would have to be > 0.35mm + 0.1mm, i.e. 0.45mm. W/T = 4.5.

Re: Help, internal size of part(s) too small...

justcurious — Wed, 11 Jun 2014 08:02:46 -0400

I think it would be nice for any programmer if one formula could do the job and from the above discussion i may believe that this would work as good as any other as many other factors probably have greater influence.
In my opinion many users generally have no clue on how to adjust W/T and certainly not why, that is the impression I get from forums. That is why it is good to have the program select autoadjustment, and for other users to take responsibility of selecting own values, but i am not sure programs generally is good to set limits to choice of params for best results.Trial and error is what get results mostly.

Concluded from the above thread, from the start, i think that it has been verified that Slic3R selects correct path as expected and for W/T>1 it is probably selecting proper flow as well. question is would flow be better for W/T=1 and W/T<1 if the same formula was used? I do not know. i do not even know if the formula used at present version is failing!

if i should always select W/T=1.5 i would certainly get in troubles. my nozzle is 0.35 and I mostly print at 0.2mm that would say that if W/T should be 1,5, I should select extrusion width of 0.3mm, but what if i select layerheight of 0.1mm? that would give me extrusion width of 0.15mm, that does not make sense, does it? and it does probably not care which formula is used anyway.
Could anybody clarify my frustrations?

Re: Help, internal size of part(s) too small...

dzach — Wed, 11 Jun 2014 08:00:19 -0400

Here is my concern:

In doing the calculation of the cross section of the area of the filament outside the nozzle, I'll have to correct the graphic and make it detach earlier from the bed, assuming speed doesn't change. That is, I'll have to reduce the size of the circle to compensate for the area missing in the connection of the vertical (cylinder) rectangle with the (horizontal cylinder) circle. I guess I made a compromise when drawing the graphic (EDIT) and concentrated to the filament shape as it is laid on the bed instead of its picture as it leaves the nozzle. Actually, the extruder and nozzle are there just to show the height (Thickness) setting and do not take part in any calculation.

Re: Help, internal size of part(s) too small...

nophead — Wed, 11 Jun 2014 07:35:23 -0400

> It is exactly for that reason that I use W/T > 1.5, a ratio at which the formulas I used start to fit closely the shape of the plastic.

The general formula works all the way down to W = T because the rectangular part shrinks to zero and the two semicircular ends then form a circle. As I keep saying there is only one formula needed for calculating the relationship between flow rate and outline width. Does anybody have any experimental evidence that contradicts this formula? There may be some second order effects like gravity causing the bottom flat to be a bit longer than the top, etc, but it is accurate enough for FFF printing and more accurate than assuming the semicircular ends degenerate into rectangular ones as the width reduces. They definitely don't do that. In fact the opposite happens. The wider the filament is compared to its height the less significant the semicircles are.