Internal dimension

Vertex 3D Printer Vertex - Issues while printing
1

Hi
I have problems with internal dimnensions.
Printed thingiverse.com/thing:5745/#comments and measured
external should be 20mm was 19.94 really good
internal should be 10mm was 9.54 not very good
Since the external dimensions are good (have tested other prints to) I am guessing stepper values are ok.
Was printing in velleman ABS @ 240*c 75% flow 1.4 mm shell 1mm top bottom
3mm retraction @ 150mm/s
Quality is good, but every internal dimension is too small.
I am trying to build the openrc truggy, but no bearing or wheel hex nut will fit.

2

This margin can be corrected in the design. This is just how 3D printing and slicing works.
In the picture below is exaggerated version of what happens

3

Hi
Since it’s a square interal opening, there should not be a problem right?
Is there settings youc an do in the software?

Regards Klas

4

you cant with repetier but you can compensate it in the design file

5

Can it be some “over extrusion” and temperature shrinkage
During extrusion are the PLA extruded little outside the ideal dimensions. I.e. the outer dimensions are some bigger and the inner dimensions some smaller.
Outside: D= 20 + 2DT
Inside: d= 10 - 2DT

With DT=0.12 we get D = 20.24 and d = 9.76

And above this with 1.5% temperature shrinkage
D=20.240.985= 19.94
d=9.760.985= 9.61

I.e. the outside dimensions will be good but all inside will be too small

A good adjustment of the model would be (if this theory is true)
1/ substract 0.12 from all outside surfaces in X and Y directions
2/ add 0.12 to all inside surfaces in X and Y directions
3/ scale model in X and Y with 1.015

just a theoretical approach trying to explain the dimension diff…

6

He largab,

I have the same problem. I have a rectangle W: 128,3 L: 10,8. After printing i measure it, W: 127,3 L: 10,4. The Wide of the rectangle differs 1 mm and the length 0,4 mm.
It looks like how longer your object how more difference you measure after the print job.

Velleman,

You say that I can compesate it in my design file. But i don’t have a constant difference.

Best wishes,
Jim

7

It’s a factor…

If you want to compensate it:

  1. Print different times the same rectangle or cube.
  2. Measure the differences and take the average of the differences.
  3. Now calculate the percentage:

(average difference / dimension) * 100

  1. Now slice again the rectangle or cube but now you scale the rectangle or cube by the percentage given in step 3.
  2. Print it and check the difference, if it not OK repeat the steps…

Cheers,
Dylan

8

That looks like standard shrinkage rates of around 0.5% to me. Just scale your model up by that amount.

Unfortunately shrinkage is never absolutely even, it’s affected by the model geometry and which parts cool first. Getting really precise prints generally takes a few attempts.