object dimension inaccuracy

hello everyone,

essentially the issue ive been having is that all my parts dimensions are wrong by some margin generally in all directions. the parts im modelling are in solidworks (not sure if this has any effect but i doubt it should do), ive mainly been slicing with slicer as it seems to give stronger structural parts compared to my personally preferred kisslicer, and ive been printing with abs.

im almost certain that the e steps etc are calibrated as spot on as my equipment allows, the inaccuracy in the z axis i believe might be an issue with z home point which i will re calibrate and test.

the inaccuracy's in the other directions i cannot work out.

i can upload images if requested but its essentially on all parts i design.

any ideas as to what i can do to make my prints more accurate will be welcomed.

thanks

The only way I get objects the correct size is to use Skeinforge and set the Perimeter Flow rate Multiplier to 1 + (pi/4 -1) / (W/H) whenever I change the Edge Width over Height ratio.

I think all the other slicers require you to mess about printing thin wall boxes and adjust the overall flow rate to get the correct wall thickness.

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[www.hydraraptor.blogspot.com]

I agree with nophead. If you want dimensionally accurate parts (and holes) then SF is the only way to go. I printed replacement extruder gears for my machine last week using SF, Slic3r and Cura. SF was the only one to produce usable parts. (My machine is set up perfectly for E Steps and the slicers are all set with correct Extrusion Multipliers or equivalents.)

IMHO:
Slic3r works well if you do the set up they suggest; [github.com]. You can get wall thickness and external dimensions accurate to around 10u. However, I found it impossible to get other things to work really well like infill neatly overlapping perimeters and holes were badly undersized. Infill around holes was awful.

Cura prints much nicer than slic3r (infill and shells are really excellent) but, maddeningly, the external dimensions and hole sizes are unusably undersized for machine parts and you have no control of layer width (which it appears to assume is 0.4mm). You therefore have to design your model to suit this restriction. I investigated this shortcoming and discovered that the perimeter extrusion rate is just plain wrong and it's not easily fixable as the Cura engine is not open source now.

SF did the job in the end after large amounts of time, trial and error. It's such a shame that it's so slow, user-hostile and lacks features the newer slicers have though.

well i guess for my project work its back to skeinforge then thanks for the input, ill try it out and see how things go hopefully i can get my head back around it again.

thanks guys

> Cura engine is not open source now
Let me correct this for posterity: Cura engine is open source and is at [github.com]

When sliced with software other than SF is this problem of inaccurately sized parts common to all RepRap printers, and if so, is there any hope these other slicers will improve their accuracy in the future?

Garry Bartsch Wrote:
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> When sliced with software other than SF is this
> problem of inaccurately sized parts common to all
> RepRap printers, and if so, is there any hope
> these other slicers will improve their accuracy in
> the future?

No. For my printers I get the correct outer and inner dimensions all the time with Kisslicer and Cura as well as when I used Slic3r a long time ago (0.7.2b). But I also never print over 0.2mm and rarely over 0.15mm layers. I also use a lot of cooling and PLA. The issue does not seem to be with the slicer but rather the printing style used and SF is the only one that allows you to compensate for the problems printing thick layers causes.

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Sublime Wrote:
-------------------------------------------------------
> No. For my printers I get the correct outer and
> inner dimensions all the time with Kisslicer and
> Cura as well as when I used Slic3r a long time ago
> (0.7.2b). But I also never print over 0.2mm and
> rarely over 0.15mm layers. I also use a lot of
> cooling and PLA. The issue does not seem to be
> with the slicer but rather the printing style used
> and SF is the only one that allows you to
> compensate for the problems printing thick layers
> causes.

Thank you. I'm eager to try all the slicers with the Mendel90 my daughter and I are building. I expect to do most printing at 0.2mm and lower. I will be disappointed if they won't allow the Mendel90 to print accurately sized parts. I am assuming the issue is NOT particular to the Menel90 in any way.

I would say out of all Mendel variant printers M90 should be one of the most rigid and sturdy so I can see no reason why it should not be able to print the same way. But with that said you will not be able to follow the same instructions to print with other software as you would to print with SF the way Nophead promotes. My printing style and Nopheads are different and result in very different results. To use the settings I use you can use the link in my signature to my Calculator which will give you the numbers that I use to get my results.

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Sublime Wrote:
-------------------------------------------------------
> My printing
> style and Nopheads are different and result in
> very different results. To use the settings I use
> you can use the link in my signature to my
> Calculator which will give you the numbers that I
> use to get my results.

Thank you, I am going to try as many methods of printing as possible. Sounds like there is a fair amount of variation in the way to print. An 'artistic' or 'individual' element?

Ok after a discussion in the Slic3r RepRap forum I decided to write a post processing script for Kisslicer that will allow you to change the flow rates of each extrusion type independently. It just looks for the comments stating when each extrusion type starts (perimeter, loops, solid infill, sparse infill, support, support interface) and injects a M221 S code which changes the flow rate in Marlin in percentages. The script is written in lua so you will need lua installed or an executable copy in the same folder as the script and the slicer. You will also need to add this

lua "Flow_rate.lua" " < FILE > " 
without the spaces around the word FILE (the forum removes the < FILE and > if the spaces are not there

to the post-process field in the firmware tab of Kisslicer. Then at the top of the script file you will see where the variables are set to adjust the flow rate of each extrusion type, default 100%.

This should allow you to seamlessly use other slicers like Nophead uses Skeinforge by reducing the flow rate of the perimeter and then the polyhole test should work the same.

Note: The script creates a second gcode file marked processed.

It should work with Slic3r and Cura as well if anyone would like to make the changes.

EDIT: I just updated the script to use Nopheads equation from above to automatically calculate the correct extrusion rate for the perimeters. Now you enter the extrusion height and width and it calculates the perimeter flow rate instead of entering a percentage.

Edited 4 time(s). Last edit at 12/06/2013 11:03PM by Sublime.

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i tried your post process sublime, i like the idea but the processed file changed the actual g code and failed to print. any ideas?

OK first, do you have a working profile for an M90 for Kisslicer already? If not that is where to start. This script only changes the flow rate of paths.

This is what Kisslicer would normally produce

; 'Wipe (and De-string)', 0.0 [feed mm/s], 25.0 [head mm/s]
G1 E-4 F30000
G1 X54.83 Y59.68 E0 F1500
; fan on
M106
;
; 'Perimeter', 0.3 [feed mm/s], 25.0 [head mm/s]
G1 X63.46 Y63.23 E0 F9000

And this is after the post processing

; 'Wipe (and De-string)', 0.0 [feed mm/s], 25.0 [head mm/s]
G1 E-4 F30000
G1 X54.83 Y59.68 E0 F1500
; fan on
M106
;
; Set perimeter flow rate.   <--- This comment is new
M221 S100                        <--- This M code is new

; 'Perimeter', 0.3 [feed mm/s], 25.0 [head mm/s]
G1 X63.46 Y63.23 E0 F9000

It should not change anything else.

If you have the correct profile for M90 and it still does not work then post your ini files and I will give it a try and try and find the issue.

Edited 1 time(s). Last edit at 12/06/2013 10:29PM by Sublime.

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Also be sure to have comments enabled since it uses them to find the correct spots to inject the code.

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Ok I just had an Idea to add the equation that Nophead mentioned above to the script. Now you enter your layer height and extrusion width and it calculates the correct percentage setting for the perimeters. The rest you can still enter manually if you would like.

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I created a github repo for it and added parsing for Cura gcode as well. [github.com]

Sic3r parsing will be harder since it adds the comments to the end of every single line of code.

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i have a working profile, i even went back and printed the non processed file and it printed perfectly, the processed code missed out entire sections for some reason, mainly when doing solid infill layer. i only changed the perimeter flow parameters ill try your new one if its available and see if it was just a fluke.

I wonder if this is an issue with the carriage return symbols and windows. I use Linux and it excepts \r and \n as the same thing but windows does not and it requires both (Mac should be like Linux). I have both in the code but when it carries over the original comment code it may be skipping one of them on Windows. If is still has issues post a small gcode file that exhibits the issue (maybe a 20mm cube if it happens on it) and I will try and see what is happening.

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I just updated the script file itself to use Windows style line ending just in case the issue was with Windows reading the script itself and not the processed gcode output.

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ive just recently been able to get back into printing and i just remembered your post process, it works really well its brilliant.

i was wondering if you ever got it working with slicer?

Quote
qwert75
ive just recently been able to get back into printing and i just remembered your post process, it works really well its brilliant.

i was wondering if you ever got it working with slicer?

I have never actually tried. I never use Slic3r so I concentrate on Kisslicer and Cura. If you think it is a must for Slic3r I would consider trying to implement it if you can provide a small sample gcode file from a current build of Slic3r that includes all the possible extrusion types (Perimeters, infill, bridges, support, brim/skirt and any others it produces.

Also I have a special build of Cura that has a perimeter inset that accomplishes this in a another way. [forums.reprap.org] there are Binary builds for Debian (Ubuntu) and for Windows in one of the posts.

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