Print out of scale

I have recently purchased a Geetech I3 Pro B printer.
After playing a little with the slicer configurations, temperature etc. to get the first layer to stick to the bed, I managed printing out test parts of good quality and overall I am happy about the printer.
However I have a problem with the test pieces being printed out of scale.
The test cube I am printing is supposed to be 20mm but it turns out to be 18 on both the X and Y axis, and the z axis (which I scaled down to 10mm to speed up the test prints) seems to be scaled down proportionally to the x and Y axis, at 9mm.
Basically looks to me like the cube is being printed out of scale by 10%.
Now, I have watched some tutorials on the subject but they all advice against adjusting the stepper motors into the firmware as it has more cons than pros.
On the other hand i noticed most complaints regarding size with these printers are about it being off 0.1 mm or so, which is defenitely not my case since im talking 2mm on 20.
I guess that's nothing I can expect to fix by fine tuning the filament size and/or the multiplier as most tutorials seem to advice.

Odd behaviour I have noticed regarding objects size: all objects are loaded into my repetier host viewer at twice the intended size.
The 10mm cube is loaded as a 20mm, and the 20mm is loaded as a 40mm.
So I have to scale down any object to 50% in the repetiers software in order to achieve intended size (which ends up being printed 10% short of what it should be).
Perhaps this may indicate some other configuration issue or something I am doing wrong ?

Hi there,

So I cant help with the reperier issue, But I will try and help you get the correct print dimensions.

First step is to look into the firmware and see what the steps are currently set too.

Looking at the Geetech I3 Pro B the motors are 1.8 deg with 1/16 micro stepping, just check that all three jumpers are under the motor drivers. The count the teeth on the pulley and measure the pitch on the belt, most likely 2 but could be 2.5.

Then use this calculator to see what the steps should be for the x and y and z

Link: [www.prusaprinters.org]

If what you calculate is whats in the firmware then have a look at your acceleration and federate settings, its always better to start lower then work your way up. Also look at belt tension its hard to explain what the correct tension should be but if you pluck it you should get a sound like a low E on a guitar

Let me know how you go

Looking on the internet I have found this tutorial which seems to be as "empirical" as effective.

[reprage.com]

How about going this way instead of with the calculator ?

That is the old way to "calibrate" a reprap. In the early days of the builds when problems came up sometimes a quick solution was used, Now that the builds have gotten a lot better we don't need to do this any more but people still stick to the old solution. Same as using the 20mm calibration cube to get perfect dimensions.

Lets say you use your 20mm cube dimensions to "calibrate", its printing smaller, so you increase the steps to make it bigger, do another print and and see that its now 20mm ish. All looks good yes? Now when you go to print something bigger say 150mm that extra 2mm you added in for 20mm now makes that 150mm part 10% bigger (Give or take)

The real error could be in the belts and tension, speed and acceleration settings, extrusion width (you could be under extruding), motor current,ect

If you take the time now to setup your machine correctly you will have a lot less issues down the road. Another good read is the reprap wiki calibration guide

Link: [reprap.org]

Gumbo, for your size problem in repetier host. There is a setting for units of imported objects under config. Make sure that you have the correct units selected to match the STL file or it will change the size.

Well after printing some objects that came out perfectly scale I finally opened up the test cubes in sketchup to measure them and they turned to be smaller than what they were claimed to be.
Now, I dont have a clue why one would want to upload a test cube of 18mm claiming it to be 20, other than fooling anyone who downloads and use it for its intended use - i.e. test printing.
Stupid joke.

Yup, moral of the story:

Always analyse the STL in Repetier Host or your preferred slicer to check the dimensions, and then compare with the output.

One of the advantages of Repetier Host is that you can slice a model and then step up and down the sliced result one layer at a time and view how it is going to print. However, in Repetier, check under Config, "units of imported objects". The STL file is to an extent unitless, simply values. In repetier you need to tell the software what the actual units are so that the model is loaded at the correct size.