Improved Aim for a Vintage PCB Drill Press

I'm aware of the fact that there are several Instructables available already that are dealing with a PCB drill – some of them cheap, other ones very cheap, some other ones even cheaper. For some of them I fail to imagine that they are really functional. There is, however, one that features an optical aiming system. Here I show you an alternative drill press system with a different aiming system that even keeps your workbench clean.

As mentioned in an earlier Instructable (https://www.instructables.com/Modified-Laminator-for-PCB-Toner-Transfer-Revisite/), I dived again into making my own PCBs after a hiatus of many years. Back then, making a PCB was a rather messy procedure. Nowadays it has become much easier as well as cleaner, thanks to the toner transfer method and an etching system incorporating a narrow tank.

Drilling fibreglass PCBs (FR-4 – the 'FR' standing for 'flame retardant') after etching proved always to be tricky. Over the years I had tried several cheap miniature drills. The first of them even didn't have a stand but was used free-hand, which resulted in a lot of broken drill bits, some of the fragments flying around rather dangerously. I could, then, not afford carbide drill bits (perhaps I even didn't know that such a thing existed), so when drilling FR-4 material, my cheap drill bits got blunt quickly, and then rather melted the holes, instead of drilling them.

When I went to tech university about 45 years ago, we were happy to have a specialised PCB drill in our lab. It featured a large, optical focusing system that displayed a blow-up of the donut in question on a frosted-glass screen together with crosshairs, allowing a very precise aim. It was activated by a foot switch and was, of course, absolutely prohibitive for my scrawny student's wallet. In the years since, I often dreamed about having such a tool.

A little later, I invested what I considered a lot of money in a small, DC-operated drill (1st picture above) from my friendly neigbourhood DIY store. I believe it to be a Proxxon clone that is now 40+ years old. A drill stand (2nd picture above) came with it, but I learned the hard way that drilling a 0.8 mm or even 0.6 mm hole, while aiming at a solder pad ('donut') from above, is rather difficult. Now, with my eyesight not having improved over the years, it is next to impossible. The assembled drill press is shown in the 3rd picture above.

Back then, I had built a power supply (4th picture above) for this drill, instead of buying one, also for economical reasons. Today, small drill units are available with their dedicated power supply. Speed control (i.e., maintaining the speed independent of the torque currently required) isn't really a must. It's perfectly ok to drill your PCBs with the highest speed available when using the thin, carbide drill bits, so a simple solution will be sufficient.

A few days ago, I had etched my first PCBs in many years, so they of course needed drilling. I leaned back and thought for a while: What did I want to achieve, and what could I provide while profiting from already available materials – and at the same time reducing my junk heap?

Kind of a Design Phase (or Call it 'Target Specs')

1. The base of my drill stand has (as they all do) a hole which the drill bit plunges into. So how about mounting a camera below this hole and displaying the donut in question on a PC screen? First I considered installing a cheap, China-made USB microscope in parallel with the bottom of the base, and a mirror inclined by 45°. A little later I remembered a rather flat, USB webcam (Logitech C615) dwelling in my junk box, purchased for an earlier project that hadn't worked out as expected. The idea with the mirror was immediately trashed. Now I only had to find a way to lift the drill stand up by a few centimeters so that the webcam could be installed below this hole, 'looking' upwards.
2. When drilling or machining no matter what material, a mess of flakes and/or dust is created. When drilling fibreglass FR-4 PCBs, this mess chiefly consists of dust representing a health risk. So a dust collection system is strongly recommended. In order to make it not too easy, the dust needs to be vacuumed not only from the upper side of the drill-stand's base, but also from below its hole, since you don't want the webcam's lens covered in dust. A shop vacuum cleaner was already available, equipped with a cheap, China-made dimmer unit that is very useful for reducing not only its power but also its noise.
3. The drill's power supply was built many years ago, as mentioned above, and is not part of this instructable. But information about it is supplied here nevertheless.
4. Some lighting from above, shining through the FR-4 material, was required. I considered installing some white LEDs next to the drill, shining downwards and supplied by the same old power supply.
5. I have a (very) old laptop running Linux. It is rather slow but still fit enough for displaying the webcam's picture, using a website that is dedicated to this purpose.
6. The crosshairs - aiming the drill exactly without them is impossible! – had me thinking for a time, but a convenient and easy solution popped up over night.

In the paragraphs above, my task is split up in several smaller steps – which, at least for me, is very helpful when tackling a larger project.

There is a Kind of Disclaimer as Well:

Please let me emphasise that this quick-and-dirty project didn't include careful planning or design phases, so the result might be somewhat hurting your eye. In addition, I admit that it isn't designed with ergonomics in mind - but hey, you won't be using it for days at a time anyway, so you might as well sacrifice some comfort for simplicity, practicality and economics. And I never intended having it exhibited in the MoMA anyway.

First of all, a support was required to lift the drill stand upwards from the workbench level, to make some room for the webcam below the drill stand. I used four pieces of scrap wood, glued and screwed together. The drill stand is inserted into this support from above with some momentum and is jammed there well enough. The exact dimensions were determined by the dimensions of the drill stand and the available scrap pieces. For your project they depend on the dimensions of your own drill stand that will be different for sure.

The pictures above show the support, with the webcam and the two hoses for dust collection already in place. I didn't want to remove them for the pictures after a successful first test. As you can see (or rather not), some attachments were removed from the webcam. It was installed using two more parts made from scrap wood and some hot glue (3rd picture above). At the rear of the drill stand support, two large holes are provided, one of them for inserting the lower (webcam) dust collection hose, the second for feeding through the webcam's USB cable. As shown in the picture, the webcam was positioned inside this support and, after carefully aiming it using the laptop and a drill bit inserted into the drill, fixed with some hot glue.

For dust collection I used some plastic hose that was lying around in my junk box, together with an upholstery nozzle that connects to my workshop vacuum cleaner. I cut the nozzle shorter and I inserted the two hoses into the remaining stump, fixing them with hot glue (visible in the 2nd picture above).

One of the hoses was fed through one of the holes at the rear of the drill stand support and fixed there with a generous amount of hot glue, in such a way that it pointed to the webcam's lens, but without obstructing its upwards view. The second hose proved to be a bit too short, a bit too fat and not flexible enough for placing it near the drill bit, so it was extended by a piece of narrower hose that came from the junk box, too. I fixed it with two U-shaped brackets and matching screws to the drill stand support, as shown in the picture.

At the time of purchase of my drill there was a commercial unit available, but I considered it to be too expensive for my tight budget - the best reason for building it myself. I followed an article that was published in the German 'Funkschau' magazine, issue 26/1983. I OCRd the article and translated it with a little help from DeepL into English; both versions are attached here. The circuit uses standard components around a TL494 switch-mode PSU controller that is somewhat abused in this application – and still available today. It seems that I could not, then, locate a TL494. I used a TL495 instead that is almost compatible. It comes in an 18-pin dual-inline package (the TL494 has 16 pins), and I simply ignored the functions provided by the two additional pins.

The article even suggests a PCB layout artwork that accomodates everything except the mains transformer. The artwork and the component layout drawings needed some heavy editing since my 'original', 40-years old article was a less-than-optimum photocopy. The PDF file will be printed in the right size on a DIN A4 sheet when selecting 'Page scaling: None' in the printer dialogue.

My own matrix board layout does not include rectifier, smoothing capacitor and power transistor, and it is therefor quite smaller than the suggested PCB, while the component layout remained similar. I admit that – for financial reasons, too – I had to use a mains transformer specified for only 1 A at 12 V, whereas, according to my drill's type label, it should be able to deliver a current of at least 5 A at maximum load. But since the drill is mostly used with very slim drill bits it works well enough with the rather feeblish transformer.

If you don't want to build it yourself, or if you cannot afford a commercial unit, let me tell you that you don't really need to control or reduce the drill's speed. The small holes in your PCBs are drilled comfortably enough using the highest speed of your drill anyway. So you might just use a mains transformer with the correct secondary voltage plus a bridge rectifier with the required power rating, or perhaps an adjustable power supply if you've got one – or, hey, why not, even a recycled PC (or laptop) power supply out of your junk box could be used, if your drill is specified for 12 (or 18) Volts DC.

This proved to be the easiest of all these steps. In the beginning, I thought that providing some light for the donut in question from the top side, i.e., from above, shining through the PCB, is necessary. But I realised that the light in my workshop is bright enough for sufficient contrast when drilling FR-4 material – point solved without doing anything! I like that :-)

As I said above, a retired laptop running a Linux OS is sufficient for the simple task of displaying the USB webcam's picture. I found a website (https://webcamtests.com/) that displays the webcam's output on the computer screen in your browser and so is independent of your OS. It allows swapping the picture left/right and up/down on request. This is very convenient because you don't want the on-screen picture shifting to the left when you slide your PCB to the right (or up/down), and vice versa.

The only thing to consider is that you need internet access at the location where you drill your PCBs, unless you find a different offline application.

Crosshairs are an absolute must for aiming exactly. To be honest, I had not the faintest notion how they might be superimposed over my webcam's picture. Fortunately, one night, Ockham's razor found me and gave me the idea of a (kind of) hardware solution: A piece of transparency film on which a crosshairs is drawn with a bright-coloured permanent marker pen, fixed in the correct position on the laptop's screen with painter's tape. Dark colours, such as black or blue, are hardly visible when laid over the dark donut, but the gold-coloured marker I had in my desk since last Christmas came in very handy for the purpose; a white-coloured marker might be even better visible.

You don't have to use a ruler to draw the crosshairs – the important part is the intersection of the (more or less) vertical and the (more or less) horizontal lines only, so you might even draw them freehand.

Most of the required calibration was already done during installation of the webcam and checking its output on the screen of the connected computer afterwards, so there is, in fact, not much to be done.

For the initial calibration during the setup of the system, as well as for a re-calibration after lifting the drill in order to change the drill bit, I suggest the following procedure:

1. Fire up your computer, connect the webcam to it, start your browser and open the 'Webcam Test' application (https://webcamtests.com/) – or, if setting up the system for the first time, carefully aim the webcam and fix it temporarily
2. Select 'Webcam Mirror' and click on 'Turn on the mirror'
3. Use the two 'Flip webcam...' buttons so that the image moves up and right when you move your target PCB up and right, and vice versa
4. Click on the 'Fullscreen' button for maximum display size
5. Connect the hose of your dust collection vacuum cleaner to the dust collecting adapter fixed to the drill stand support and turn it on
6. Prepare a piece of non-transparent material at the right position and fix it temporarily with adhesive tape, so that it cannot move away during and after drilling
7. Drill a hole of the desired diameter into this piece
8. Let the drill go back up to its rest position so that the freshly drilled hole is open now and becomes visible on the computer screen
9. Place the transparent sheet with the crosshairs over the computer screen, exactly over the center of the hole, and fix it with some painter's tape
10. Make sure that the copper (solder) side of your PCB points downwards – this is the only way to get a well-defined picture of the solder pads on your screen
11. Drill some solder pads on a scrap PCB while checking the pad's positions on the computer screen, then check whether the holes are precisely centered – they should be.
12. Once everything is as you desire, you can fix the webcam permanently. I did this the cheapo way by just adding some more hot glue to it.

From now on, all the holes you drill with this contraption should be centered well enough in the solder pads of your freshly etched PCB. However, be aware of the fact that this is not an expensive, high-precision, industrial tool, but adequate for home-brew PCB designs nevertheless – and better by far as when you aim your drill from the top side with the naked eye only. Once you change the drill bit (for which you need to lift up the drill), a re-calibration is required, as described above.

When using a rather cheap and/or old drill stand with a bit of slack, the precision will not be perfect. But by lightly pushing the drill stand's lever arm always in the same sideways direction while pressing it downwards, some of the slack can be compensated for.

One last hint: When changing the drill bit, both your hands are busy. In order to prevent the bit from dropping down through the hole in the drill stand's base and scratching the webcam's lens, a third hand would be required but isn't available. Instead, you can either cover the hole in the drill stand's base with a piece of cardboard or whatever, or protect the webcam's lens with any convenient cover – that also prevents it from collecting dust while not in use –, or simply lift up the drill and rotate it away sideways before releasing the drill chuck, so that the drill bit will drop down somewhere else.