Public footprint libs - Is there a reason for having (some) so tiny THT pads?

[dchisholm]

@orestesmas

Of course you’re right: doing things by hands is not the way to go in the industry. Even in the hobbyist world with the popularisation of cheap PCB fabrication companies. But I still consider of pedagogical value going through the entire process of CAD a board, printing the layout, doing the toner transfer, etching the board, drilling and soldering. It’s an intermediate step between wiring a prototype circuit board by hand and sending te design to fabrication. It also helps demystifying circuit design. Moreover, sending the PCB to a fabrication company takes time and may not fit well into the course schedule.

But maybe I’m wrong and I’ll have to reconsider the course orientation in the future.

I think you are correct and have the best approach. People who design circuits, as well as people who lay out PCB’s, should have a basic understanding of the fabrication process. Sort of like the people who pack parachutes - they should be required to jump once in a while.

@Joan_Sparky

Well, one of our members here wrote some time ago that ECAD is 80% library work… which is exactly the thing you’re having a ‘problem’ with now.

I am probably that guy. Not always 80%, but it’s not unusual for library work to be 80% of the total effort on a project that’s totally new and unlike any other recently designed project.

@Joan_Sparky

So if you really want to teach your students something, get them to make a footprint each or at least modify the ones they need to get them to your liking.

I agree that learning to make footprints and symbols is an important skill for anybody who does more than a board or two per year, but I don’t think that it’ll be efficient to build a working library from a collection of classroom exercises. (Of course, I may be underestimating your students.) If you put forth the effort to make your custom library comply with KLC, please submit it to the KiCAD librarians. They may incorporate it into the KiCAD libraries, thus ensuring your immortality!

(Note on footprints for hand-drilling: Manual drilling works best when you etch away a little dimple at the center of the copper pad. This creates both a visual target and a mechanical guide for the drill bit to align with. KiCAD doesn’t have the ability to create this pad style automatically (unless it slipped into version 5 when I wasn’t looking) but it’s a feature you can incorporate into your custom footprint library. More discussion at Enable drill marks for Gerber files .)

Ordinary twist drills from the hardware store are not good choices for PCB work. The standard tip geometry does not make clean entry or exit holes, and the fiberglass PCB material dulls the drills quickly. The carbide bits mentioned by @SembazuruCDE are a better choice. You probably know that half a dozen sizes will cover about 99% of the holes you need, and you will design your custom footprints around those sizes. Their major disadvantage is that they break easily, so keep plenty of spares on hand.

@SembazuruCDE

FYI, these types of bits are made for high-speed drills (2k-3k rpm range). Standard drill presses aren’t fast enough. But a dremmel-style rotary tool with a drill-press attachment should work a treat.

To minimize broken drill bits you should also pay attention to runout (slop) and eccentricity (wobble) of the chuck holding the bit. I don’t know a particular make and model to suggest, but I DO know that Dremel-style hobby tools come in several models and grades, and bearing quality is often the major difference.

Dale