I’ve written recently about machining my own custom pen because, much like lamps, they are a “form over function” project where the end result can be gorgeous as well as useful. Aesthetically pleasing to everyone, not just techie people. And they don’t take up a lot of space!

 

Initially, my design for the first pen was sketched out in notebooks, and then modelled in CAD, then back to the notebooks when I was in the shop. This helped me get a general feel for what I wanted, but many style, material, and mechanical considerations had to be redesigned on the fly as I found techniques that didn’t work, and others that did.

A lot of the dimensions of final product came down to how they felt in my hands, as I was building. That’s fine for a one-off, but I’d kinda like to parameterize basic measurements so that I have some guidelines on what works for future pens.

 

So here’s a pretty generic pen, modeled in Solidworks.

 

Here are a few pens I had within arm’s reach.

 

 

Starting at the top, I named these 1-4, and made some basic measurements based on the generic model:

 

Now I’ve got a good baseline for what makes a comfortable writing utensil, a recommendation for critical dimensions to stay within, and some language (or at least letters) to be able to intelligently discuss the anatomy of a pen.

This is a pretty rare combo: using a premium PCB package with the budget board house.

 

Kinda funny.

 

Generally these small run PCB houses provide DRU and CAM files for EAGLE design rule checking and Gerber outputs, respectively. Because I’m using Altium, I had to make it up as I went along.

 

 

It gets much easier when you understand what Gerber files are. While we’re all used to standard, unified output formats that contain all of the data we need, Gerbers are very much still a holdover from manufacturing in the 80s.

 

When you export these, a whole bunch of files get generated. This is intimidating, but don’t panic! They all have different extensions like GBO, GTL, etc. These are all the same type of file.

As I’ve said, while you’re used to unique file extensions being different formats, these are a holdover from 80s manufacturing and the PCB industry still hasn’t caught up. That means that by changing file extensions, you can play around with different layers doing different things.

 

 

So here’s how you generate the appropriate Gerbers. I used a mostly the default rules for this, I’m not pushing the limits. Maybe next time I’ll generate the proper rule sets.

Read and understand these directions before you start. They require some forethought.

 

Start out with your finished PCB.

 

Do the thing.

 

The resolution options matter here. There’s no way Dirty PCBs can handle the higher res, so turn it down a notch.

 

In the next tab, this is where you’ll have to do some thinking. Every project is slightly different. So for this one, I want the top overlay (silkscreen), top solder (gaps in solder mask for your pads), and top layer (copper). Same thing for bottom.

You also need a board outline. Older versions of Altium don’t have a dedicated “outline” layer, although I believe newer ones do.

So what I did was change the board outlines to Mechanical 1, and now I’m exporting that.

A couple more notes:

If I wanted to create a solder paste stencil, I would also export the Paste layers.

If you want through-hole slots, you will need an additional layer. This includes slots that allow you to panelize. Export them on another mechanical layer, and I’ll talk about it a little later. I’ve done this before, DirtyPCBs does a great job of this.

All of the other tabs in this dialog are kept at default values. Don’t mirror the bottom layers as shown. I did that and it was Wrong.

I lied a little bit above. Of the exported files, there is one that is not like the others. The drill file (.TXT in this case) requires it’s own export.

Do the resolution thing again, and everything else is default.

Okay! Now we’ve got all the files we need, let’s make sure they’re in the order they need. Here’s the key on the DirtyPCBs website.

As you can see, it’s super similar to what we have. The top 6 are exactly what we exported, and the drill TXT, too. The outline is the only thing that’s not quite right.

We exported it this time as mechanical layer 1. Easy fix, just rename the GM1 file to GKO. If you’re doing internal slots or self panelizing, you’ll also have exported another mechanical layer. Say, GM2 or GM15 or anything you like. Rename this to GML and include it with the others.

And there you go! Zip up all of these files, and they should turn out alright. GD1 is the Gerber drill file that this board house doesn’t use, just ignore it.

An important step: Check your files.

CircuitPeople is an excellent and simple online Gerber viewer. Look at all your layers and make sure nothing is terrible.

 

And you’re done! Send it off and enjoy your boards.

If something screws up in the order, I’d like to hear about it, but I take no credit. These steps have always worked for me, but this particular company probably won’t tell you if anything is wrong with the files. They’ll just manufacture it and send it on.

 

Side note: A summary of something I’ve been using for many hardware hacks in the past while.

A lot of commercial machines use gears for transferring forces. Well, duh. It’s often necessary to change gearing around, though, and it’s nigh-impossible to find commercial solutions with appropriate ratios, tooth profiles, and mounting options. So usually I laser cut my own.

The easiest way to generate a gear that meshes with an unknown is to use Inkscape’s Gear extension. It needs circular pitch, which you find by:

1. Measuring the gear’s outer diameter, OD
2. Counting the teeth, N
3. Getting diametral pitch: (N+ 2) / OD
4. Calculating circular pitch: Pi / Diametral pitch

For the pressure angle, it’s a little more complicated. You need the base pitch:

1. Use your digital calipers to measure right down in the gaps of two teeth
2. Measure three teeth
3. Subtract the two-teeth measure from the three-teeth one to get a single tooth
4. Do the same for 5 and 4 teeth
5. Take an average result of those to get an approximate base pitch measurement
6. Base Pitch * Diametral Pitch = Pi * Cos(Pressure Angle)

Of course, that looks difficult and error-prone but generally you’ll only run into pressure angles of 14.5 or 20 degrees, so only do rough measurements pick the closest one.

 

For mounting holes, you’ll need to know how far apart to space them. Pitch diameter is what you need: Teeth / Diametral pitch

 

This is a quick summary of everything you need to know. There are a lot of dimensions associated with spur gears, and it’s good to know what’s what, but these are the only ones you actually need to make your own. All of these formulas are unitless, so pick and choose, as long as you match the same unit in Inkscape. I uses inches for these, but I tend to switch back and forth to metric with impunity for everything else.

Like many (many many) engineering types, I have a goal of easy workbench PCB fabrication. I think I’ve done more research than most, however, and in this case, sharing the wealth means everybody wins.

I’ve posted this up here in its original form, but an updated version will live at the VHS wiki so that everyone can join in. So, without further ado, here are avenues I have approached, intend to approach, or discounted.

Objectives

To design a machine, method, or process to generate one-off printed circuit boards with the following conditions:

1. Time from finished PCB layout to physical board must be less than 3 hours excluding setup.
2. Traces for TSSOP packages must be possible (0.19-0.3mm traces, 0.65mm pitch).
3. Two layers must be supported and properly aligned with minimal frustration.
4. Board quality must be consistent and dependable.
5. Minimal tool changes or chemicals.

Methods

Traditional

Toner Transfer

Works. Not well.

The traces are laser-printed in reverse onto some sort of glossy paper (e.g. magazine or photo paper), then transferred to a copper-clad board using a hot clothing iron or t-shirt press. The traces transfer to the board and act as an etch-resist.

Issues:

• A dedicated clothing iron is required
• Inconsistent transfer (i.e. gaps in solid areas)
• Multiple layers are difficult to align

UV Exposure

Works. Not well.

The traces are laser-printed onto clear acetate, then overlayed on a copper-clad board and exposed evenly to UV light. The board is then washed in developer solution that either washes away the exposed portions of UV-sensitive chemical, or wash away then unexposed portion, depending on chemical process used. The traces that remain on the board act as an etch-resist.

Issues:

• UV chemicals are required to coat the board OR
• Presensitized boards must be used, which are:
• More expensive
• Inconsistent from different manufacturers both in exposure time and development time
• Require handling in a darkroom
• Require rushing the process so as not to allow ambient light to ruin process.

Laser Cutter

Spray Paint

Has potential.

The board is evenly sprayed with a single coat of paint. After drying, the laser cutter vaporizes the paint along where the traces should go. Remaining paint is left as an etch resist.

Issues:

• Laser power/speed must be fine-tuned to vaporize paint layer with excess copper heating (cut paths widen when copper acts as a heat-sink).
• Paint layer is undesirably thick. May not be an issue?
• Paint layer is difficult to apply evenly.
• Vaporized paint leaves a residue that interferes with etching. Clean it with hydrogen peroxide or very very mild acetone bath?

Sharpie

Has potential.

Copper-clad is covered in Sharpie (permanent marker ink). Laser appears to “burn in” sharpie layer and make it resistant to acetone. After acetone bath, burnt in layer is left as etch-resist.

Issues:

• Layer evenness is very difficult to achieve. Ink bath and rubber rollers will be attempted.
• Acetone bath dilution must be tweaked.

Sugar

Laser printer toner is effectively sugar as a binding agent and carbon as a colourant. Because colour is unnecessary, sugar alone was attempted to be used as an etch mask.

Doesn’t work.

• Laser cutter has “air assist”, airstream designed to push slag through the workpiece as it is cutting. It blows the sugar off the copper instantly.
• Using water to form a paste, still difficult to consistently achieve thin traces.

Toner

Doesn’t work. Bad idea. Not dumb enough to try this.

Issues:

• See above for air assist issues.
• Nigh-impossible to work with cleanly.
• Biohazard.

May be do-able on custom laser-diode CNC platform.

Acrylic Trench

Works. Not well.

Laser etch traces into acrylic medium. Fill etched area with conductive paint.

Issues:

• Thick traces.
• High trace resistance.
• Can’t be soldered onto.

Printers

Inkjet

Works. Not well.

Modify printer to print traces directly onto copper-clad. Use as etch resist.

Issues:

• Typical inkjet ink is a dye as opposed to a pigment and is water-soluble. Ink cartridge must be filled with special MISPRO pigment:
• Expensive.
• Messy to refill.
• Runny/blurry edges.
• Double sided boards have alignment issues.

Laser

Works. Not well.

Laser printer can be modified to print directly onto copper-clad. Use as etch resist.

Issues:

• Larger printed areas have inconsistent fill/gaps.
• Alignment issues for 2-layer boards and multiple passes to fill in gaps.

Wax Inkjet

Works. Current status unknown.

Jeff Gough had some success with this. A piezo inkjet head (as opposed to a thermal inkjet head) used by Epson printers can be modified with a heated reservoir to print directly with wax.

Issues:

• Print heads eventually had clogging issues.

Dye-Sublimation

Has potential.

Dye-sub is now available for the consumer market with Canon’s Selphy line of printers. It works through a thermal print head sublimating wax or resin into a gas, then allowing to to solidify onto the print medium. It should work as an etch resist.

Potential issues:

• Sublimation results in soft edges, may lead to improperly etched traces if print resolution is too low.
• May rely on special coatings on print medium for ink to bind properly.
• Water insolubility may rely on final clearcoat layer that is printed.

Thermal Transfer

Has potential.

Similar to dye-sub.

Issues:

• Printers are expensive, niche, and difficult to find in appropriate sizes.

Thermal Wax Transfer

Has potential.

Similar to dye-sub. Replace ink transfer cartridges with wax paper or similar. Thermal print heads should transfer etch resist wax to copper-clad.

Issues:

• Very likely.

Wax Printer

Has potential.

Some Xerox Phaser printers use a solid wax block as ink. Would work as an etch resist.

Issues:

• Only available on business lines.
• Expensive.
• Huge.
• May be difficult to modify to accept copper-clad.

3D Printer

Has potential.

Single layer of plastic laid down as etch resist.

Issues:

• Accuracy?

Mechanical

CNC Milling

Works. Not well.

Issues:

• Messy.
• Requires babysitting.
• Limitations on trace sizes.
• Endmill bits are expensive.

Vinyl Plotter

Works. Not well.

Issues:

• Terrible accuracy.
• Results in the strangest looking PCBs imaginable.

Electrical Discharge Machining

Has potential.

Electrical arc from brass wire to workpiece removes material in a very controlled and accurate manner to isolate traces. Reaction happens in a dielectric such as mineral oil or distilled water.

Issues:

• Difficult to design machine for precision.
• Expensive.
• Terrifying.

Electro-Chemical Machining

Doesn’t work.

Workpiece is set up as an anode while electrode is used as a cathode. Reaction takes place in a conductive electrolyte, such as salt water.

Issues:

• Extremely inaccurate.