My PCB milling work flow is working well for single sided boards with through hole components. I am still working on support for surface mount devices and double side boards but the capability I have now is enough to speed up the progress on my queue of projects. This post is a general update on what I have been doing with that capability.

Milling Bit Holder

I saw this tip on a blog post mentioned on Google+ but unfortunately I can't find the original link. Essentially you take a block of wood, drill some largish holes partially through it and use it to keep the tool bits you need for the particular task you are working on. This makes it a lot easier to get at the bits you need for the next phase of the operation.

In my case I gave it a coat of paint with the first color I found - the horrible purple actually works well, the holder is easily noticable on my normally cluttered bench.

Isolation Cuts

In order to mill boards suitable for surface mount components I am going to have to get the isolation cuts as small as I can. The photo above was taken with my phone camera and uses a standard ruler for reference. I've bought myself a small USB microscope with a micrometer reference card to do future comparisons.

These particular cuts were made with a 0.2mm, 30 degree tip and came out with what looks like about 0.25mm width. I'm hoping to get the cuts to below 0.2mm to allow for SOIC footprint parts.

Milling Tips

As well as the 0.2mm tips I have some 0.1mm/10 degree tips as well (shown to the left in the image above). I haven't had much success with these unfortunately - the tips keep snapping part way through the process. I can't really increase the spindle speed on my machine (it's running at maximum already) but I can play with the feed rate and try tips with a wider angle. Luckily these tips are readily available on eBay at reasonable prices so I'm waiting on some 30 degree tips to experiment with.

Benchtool

Although using surface mount parts is still a work in progress that hasn't stopped my milling boards for friends and catching up on some of my projects in waiting. The board above is an implementation of my multidrop serial design.

The goal is to have a range of sensors measuring voltage, current, frequency or whatever is needed for the circuit under test and sample them over a single serial connection for logging and display. Think of it as a multimeter with multiple input channels. The resolution and sample rate are not going to be great - I'm using the 10 bit ADC channels on the ATtiny and support up to four channels per unit; this gives at best 30 samples per second if all six slots are occupied. It's not an oscilloscope but it should be enough to help debug basic timing and power management issues.

All in all the workshop is set up nicely now - the combination of the 3D printer and the CNC machine gives me the ability to create just about anything I need for one-off or low volume projects without depending on external services.