I use X-acto blades and the Vic metal saw


Try to find X-acto blades (or similar) to these they are about the same size as the T&T and pen, also get a fine toothed saw (the Vic metal saw works great) they will help you make groove
Also I cut a little bit of the groove then cut out the notch in the scale, with the metal saw. The metal saw is a great tool for this it is about the same width as the pen and T&T also it is slow enough that you don’t get in to trouble.
Lastly check the fit every so often and make the pen & toothpick hole a little small to keep them in but make the tweezers’s hole a little big (they stay in by the use of their spring so small opening big inside should keep them by your side)
If you would like a more detailed account of how just ask