Dimension Issues

[Modified_Gemini 2]

Forgive me if this is in the wrong area. I recently bought a 3d printer and havnt been able to accurately search for problems im having (im probably just looking the terms up wrong). i have Monoprice Maker Select and i love it but im having a couple issues that i believe are either software or setting issues?

Inside dimension issues? Ive made some pieces with known dimensions, and i can get the outside dimensions correct, but if i make a cutaway/slot/hole they always end up smaller, a .1-.5mm width. As if youre tracing inside the line with a sharpie, on outside dimensions the width of the marker stays in, but on inside dimensions the marker tends to ride the center of the line thus printing over. Am i missing a setting somewhere?

Also, ive been searching for the ripple effect on large flat surfaces, where it looks like the line spacing is far apart. ive been seeing a lot on calibration, and i have calibrated my extruder steps. But when inside of Cura i will break down the piece on a layer view. the very first bottom layers are spaced tightly together. as well as the top layers... except, for the very last top layer, you visually see gaps in the toolpath vs the one previous tightly spaced layer. Again, i believe i may be missing a setting somewhere?

Thank you, and i appreciate any help or direction i can take

[IRobertI 520]

The reason for the holes becoming smaller is because the plastic shrinks while it's cooling down. On the outer edges of a print the rest of the model helps to push against this shrinkage. But in holes you have nothing keeping the plastic back so it collapses in on itself. It behaves a little bit like a rubber band. So you'll have to compensate in your model for this shrinkage. Something similar happens with plastic injection molding and they too have to compensate for the shrinkage.

As for the second issue, I think it would be helpful to see a screenshot, it sounds strange.

[Modified_Gemini 2]

Thank you! i couldnt find the answer is the "shrinkage"! it was pretty frustrating when trying to make pieces slide together.

Here are some pics for the second issue ive had with toolpath spacing (i could have sworn i had this issue with top layers, maybe just bottom. My extruder e steps are calibrated.

Finished print

http://i1104.photobucket.com/albums/h326/modified_gemini/IMG_20160408_005824_zpsjtipsocd.jpg

Second layer of raft, spacing of .3mm i believe

http://i1104.photobucket.com/albums/h326/modified_gemini/2_zpsj5fjwpkj.png

Top raft layer, has no spacing

http://i1104.photobucket.com/albums/h326/modified_gemini/3_zpsd4mmznuf.png

First layer of object, has clear spacing in the toolpath

http://i1104.photobucket.com/albums/h326/modified_gemini/4_zpsfom9ulry.png

Second layer of print, less spacing in the toolpath

http://i1104.photobucket.com/albums/h326/modified_gemini/5_zpskuhg2btl.png

A few layers into the print, and theres finally no spacing

http://i1104.photobucket.com/albums/h326/modified_gemini/7_zpsc3cni57a.png

Top layer of print, has no spacing

http://s1104.photobucket.com/user/modified_gemini/media/89_zpsubdu5pgu.png.html?sort=3&o=2

[IRobertI 520]

That's caused by the raft which you have enabled under "Platform adhesion type". Rafts are old school and aren't really used on UM printers these days. With a very clean glass and/or a thin layer of glue you should be able to set this to "None" instead.

Since there are so many tiny parts it's important that the first layer goes down well to make sure they stay in place. Make sure your bed is calibrated "perfectly" and consider levelling it slightly closer to the nozzle to really push the plastic down onto the glass.

[Modified_Gemini 2]

My print bed was shipped warp, but after putting on a piece of glass it over rid that issue. It also stays level pretty good, i just finished a 43hr print and the level heald.......Ah in the middle of typing this replay i started a print to work on calculating internal shrinkage, and i remembered why i use a raft. I get very little adhesion if i dont. The raft has really thick base lines about .64mm  lots of material good squishing.  If i dont use a raft it appears to under extrude, really thin and stringy about .25mm barely any squish, and the extruder head will drag it around before it pushes out enough material to sporadically adhere. In that process much hard plastic is raised above the layer, extruder head bumps into it, ripping the print off the bed.. I use aquanet as the glue, and the extruder tip is the thicknes of a paper off the glass with slight drag.

[Spilz 0]

Hi,

First of all, sorry for my bad English.

I get the same issue with internal dimension.

The explanation of iroberti is a good start, but I think it does not solve all the problem :

The plastic shrinks, it's right, but it seems that for inside part, the plastic is put on the line while for outside, the plastic is not on the line, the width of the output buse is considered. -> some people say that in other forums, I don't know if it's true or not. If it's true, the slicer as a part of responsibility on it.

For the part I draw myself, I can change the inside dimensions, but for STL parts I download in the Internet, I can't change it, and it's a problem for parts which should slide together.

I don't know how to solve it and what parameter in cura can influence it

Thanks for your help

Edited August 4, 2016 by Guest
Different topics are not agree about the slicer "responsibility"