I try to use GIMP to make pencil sketch and here is the result.

Step of doing this:
Go download gimp_scripts-2.8 and extract it.
All the .scm file go to scripts floder under gimp.
All the gimpressionist gradients and patterns transfer to respective folder.
Open GIMP and you see a new tag call script-fu

Then look for sketch then quick sketch.

This is how my final project look like. I can draw in in both software.

However, Inkscape not easy to trim a line. CorelDraw can trim any line that intercept.
CorelDraw have a good function call transformations > Position. It allow you to duplicate and align objects

Both Inkscape and CorelDraw can trace image to line. Inkscape have a wonderful function call extensions. You can download software that you need and put inside. I get a extensions call Tabbed box marker. It can generate a tabbed box very easily.

Step of doing this:

Download boxmaker0.85
Extract to inkscape share > extensions folder
Open inkscape under extensions> laser tools. You should see tabbed box marker.

Converting Bitmap to Vector Image

I use Inventor to draw my final project. This is not easy to learn how to draw as I don't have any cad drawing background. For tinkercad, I first selected Helping Tools > Ruler as a guide for my drawing, then draw a box and key in the size. I then drew another box, 6mm smaller than the first, and choose hole, to cut the shape out of the first box. After that I grouped them together so that only the outline is appeared. For the hole I choose circle and turn in 90degree and choose hole and group. Then I make a thin box to be layer and move the z axis to make it floot. lastly I do the top circle.

This is how I draw in tinkercad. Tinkercad is easy to pick up as a beginner and this is web-based drawing. You can go anywhere to draw as long as you have internet access. However this software has a lot of limitations, for example, you can't draw complicated design such as spring.