Are you using the stock firmware of your printer? Sounds like to me that you have 16 tooth pulleys and your firmware is set to 20 tooth i.e. 80 steps per mm

The calculation behind the steps per mm is $\frac{\text{Steps per Revolution} \times Microsteps}{Teeth \times Pitch}$. The reason for this is that one revolution of the pulley will move the belt the number of teeth times the pitch of the belt. Now take the total number of steps, Steps per Revolution times microsteps, and divide by the distance moved giving the steps per mm.

In $\underline{most}$ hobby 3D printers you have:

- 1.8 degrees steppers which equals $\frac{360}{1.8}=200$ steps per revolution , Less common is 0.9 degrees steppers $\frac{360}{0.9}=400$
- GT2 is the most common belts now which have a pitch of 2mm
- The two most common pulleys are 16 tooth and 20 tooth,
- Depending on what stepper drivers and or configuration you have
- A4988 $\to$ 16 microsteps
- DRV8825 $\to$ 32 microsteps
- Trinamic $\to$ 16-256 mircosteps

In your situation I believe you have a 1.8 degree stepper with 16 microsteps, a gt2 belt, and a 16 tooth pulley. Which means your XY steps per mm should be $\frac{200 \times 16}{16 \times 2} = 100$. While your firmware is expecting 20 tooth pulleys, yielding $\frac{200 \times 16}{20 \times 2} = 80$. This would result in your prints being $\frac{100-80}{100} = 20\%$ smaller, which explains your results with the circles.

Generalizing, the steppers, microsteps, and pitch don't matter. To go between 16 tooth pulleys to 20 tooth, multiply by $0.8=\frac{16}{20}$. From 20 tooth to 16 tooth, multiply by $1.25=\frac{20}{16}$.

2in reprinting: did you use the same gcode? did you resclice it? What does the Sicer tell you is the size of the disk? – Trish – 2019-06-20T11:25:25.193

I used simplify, just generate the file with the g-code, copy to the pendrive, insert that in the print, and lets go. – Pedro Miguel Pimienta Morales – 2019-06-20T11:48:54.843

Good question, i Will try today with Slicer, but simplify show me the same measures than i put yo the model un the software – Pedro Miguel Pimienta Morales – 2019-06-20T11:51:10.920

Is it true that the first picture shows a 70mm output for a 90mm model, and that the second picture shows a 110mm output for a 110mm model? If so, something other than scaling (or wrong steps per inch) is happening. Also, what is causing the cross-hatching? That seems to be scale invariant. – cmm – 2019-06-21T18:09:28.953

110 mm model 90 cm output – Pedro Miguel Pimienta Morales – 2019-06-21T18:12:07.943