Pinewood Derby Axle Polishing

As you’ve probably read elsewhere, most of the speed comes from the reduction of friction, which is all where the wheels rub against the axles.  Do reduce this, you want to spend lots of time polishing them.  Here’s what I found can be done to get a mirror-like finish.

Ideally use a drill press (like shown in my previous post) to hold your axle nail.  If you don’t have a drill press, a corded or cordless drill in a mount or vise of some sort will also work (make sure it’s secure though).

Optionally mill away the middle section where the wheel would touch, leaving only the inner- and outermost areas.  This reduces the surface area the wheel will touch the axle.  I did this with a file mounted in a vise on my drill press.

Use a file and grind away any burrs that are around the nail head.  Also bevel the inside of the nail head if allowed.  For grinding I use a set of jewelry files.

Start with a coarse sand paper and work your way down to finer grits.  I used 400, 800, and 1200-grit.  Cut strips of sandpaper about 1/4″ x 3″.  While the axle is rotating at medium-high speed, pull the sand paper back and forth over the axle.  Do this over the areas where the wheel will touch the axle, including the inside of the nail head.  It might help to have a small piece of wood to push the sandpaper against the nail head.

Compressed graphite sticks used for axle polishing.

1200-grit produces a pretty reasonable result, but you won’t quite achieve a final mirror finish yet.  To get to the final finish, I decided to use compressed graphite sticks.  Again while the nail is spinning, press hard (but not too hard to bend the nail) with the graphite stick to polish and lubricate.  Parts of the graphite stick will break off, and this is OK.  After a few minutes of this you should have a very shiny and pre-lubricated surface for your wheel to run on.

Standard BSA axle before polishing.
Axle after milling, sanding, and polishing.

As you can see, there are still some minor scratches on the polished part.  Next time I might add an additional higher-grit polish before the graphite.

Of course you will want to add additional graphite powder to your assembled wheel, but with a polished axle you will have greatly reduced the friction produced.

Build your own axle lathe

I have quite a few tools, but I don’t yet have a lathe.  In this case, I needed to mill grooves in the axles for my son’s Cub Scouts Pinewood Derby car.

There are plenty of pages out there that talk about using a hand drill to hold the axle and then polish it up, but to reduce friction even more ideally the wheel only makes contact at a few small points on the axle.  Plus if you mill a groove, technically you have somewhere to store more graphite, which could possibly help improve lubrication over many runs (assuming it doesn’t just all fall out).

In my case, I was going for essentially one small point on the inner and outer edge of the wheel.  This way the wheel shouldn’t wobble any more than when the entire axle is present.

Obviously a drill press would work better than a hand drill, since it is more stationary.  For the cutting tools I had a set of jeweler’s files that work well for fine grinding like this.  As for holding the tool I initially started by resting my hands on the drill press table and tried manually grinding down the area I wanted.  I couldn’t get a very consistent result though, given occasionally the tool would get pulled more, causing it to graze the area where the wheel would make contact, ruining the smoothness of this area.

I then decided to make a tool holder of sorts by using a vise and a few blocks of wood (in this case oak) to hold the file in place.  Then I could simply raise and lower the table to the correct height, then slide the vise along the table to grind the axle at the location I wanted without worrying about it running away from me.

Grinding an axle with a file mounted in a vise.

It takes a bit of patience to adjust the table to the correct height, but with some practice I was able to finish the last axle in less than 10 minutes.

The head is also ground back with a triangle file to add a groove at the head as well as an angle to reduce the surface area touching the wheel.  This I could do reliably enough by hand that I didn’t make another fixture for it.

Milling breakout PCBs

Components continue to come in smaller sizes, which makes it harder and harder to prototype with unless you also buy the vendor’s evaluation module or breakout board.  With the right tools, a bit of patience, and a few tips you can build your own basic breakout boards.

The primary tool I use is a 3040T CNC mill. I purchased it on eBay for around $650.  I’ve upgraded it with a better spindle and stepper controllers, but I could get the same results with the original setup for these projects.

I use the free version of Eagle PCB tools to design my breakout boards.  There’s a free CAM tool for taking your designs and outputting machine code.  Here’s where things get interesting though.

When the tool generates the cuts, it wants to place the center of the tool at the edge of the trace, assuming the tool diameter is 0.000″ For a perfect tool, this would be great, but unfortunately you won’t be able to find a tool like this.  You will find tools that have relatively fine tips, but anything below about 0.010″ is going to be unreliable.


Milling with a 15-degree engraving bit.

When creating your PCB, with fine-pitch part you will want the tool to run in the areas between the traces, and not necessarily mill out each trace individually.  I’ve managed to do this by lying about the size of the trace in Eagle.

For example, a 0.008″ trace might need to be 0.020″.  This seems crazy, right?  But in the end, this causes the tool to run in between each trace, rather than cutting away a majority of what you wanted to be that 0.008″ trace.

Breakout board and module that will be connected to it.

The best bits I have found are Kyocera 2-flute 15-degree engraving bits.  Search eBay for the seller “drillman1“.  Their store happens to be a few miles from me, but either way they seem to have the best prices.  You’ll spend $8-15 on a bit which seems a lot compared to the Chinese equivalent you’ll also find online, but every time I’ve tried using one of those the tip literally breaks off within 30 seconds of starting to mill copper due to their brittle carbide composition.  Do yourself a favor and buy a good tool that will last awhile, you’ll save yourself a lot of frustration.

Fine pitch at 30x magnification

Another variable is cutting depth.  Unfortunately boards are not perfectly flat, which means you’ll end up cutting to different depths across the board.  The photo below shows the case where the top was higher than the bottom, so the tops were cut through, while the bottom still has a small amount of copper where it was engraved.  Once the copper gets that thin, it generally will tear off at the engraved spots though, so cleanup is pretty easy.

Boards are never perfectly flat, resulting in undercut areas

There are fancier tools that will account for this, but with what I have I try to find a zero point near the center, so I don’t cut too deep, which would result in cutting traces too thin, but do end up with some edges not cut completely though.  It’s better to err on the side of cutting shallow rather than deep, since you can always take more away, but it’s harder to add something back.

Mach3 Milling Software

X and Y movement rate also matters a lot.  If your CNC machine has some backlash or slosh, you will want to run the cuts slowly in order to allow the bit to keep up with the commanded position. If you run too quickly, you’ll end up with traces not very straight, and worst case accidentally cutting some portions of a trace too thin.

Assembled breakout board for a GPS module. You can see the first attempt below the assembled circuit.

Finally, it still comes down to trial and error.  I usually end up milling a portion of a design and then making some adjustments and starting again.  The most common changes are to the trace width and cutting depth.

With a bit of patience you can mill your own breakout boards.  Others have built fixtures for mounting their PCBs, which allows them to create 2-layer PCBs as well.


Build your own wooden open-frame rack

My “networking” closet was a mess, so I decided it was time to build a rack of sorts to better organize everything.  I could buy a rack, but I decided to build one out of some scrap wood I had laying around instead.  This way I can size it for exactly what I need, plus customizing it just involves screwing stuff into the wood where ever I wanted.

Wood isn’t perfectly straight, so you need to leave some room for warping.  I used to cheap grade 2×4’s for the rear posts and higher grade 2×4’s for the front (I only had 2 laying around).  For the sides and top/bottom I used some 1×6.  The frame opening is 17.5″ wide, and I decided a 20″ depth worked well for the equipment and space I had available.  For putting it all together I used 2″ drywall screws.

My main piece of equipment is a Cisco Catalyst 4503-E chassis with a GBIC fiber card and POE gigabit card. Air flows right to left through this chassis, so having the sides open is nice.  I plan on adding more venting to this as I have time.  Also the fans are pretty loud, so adding vents should help muffle the noise too.

Rackmount ears would probably hold in wood, but I decided to build a makeshift shelf by adding two more 2×4’s along the sides where I wanted to mount the chassis.  This way the chassis just sits on these 2×4’s at each end.

Wire routing involved using some open frame panels with keystone jacks, plus some wire conduits of various types I found recycled at work.  The photo shows what I currently have complete.

Wire routing in open wooden frame rack.

There is a vent loosely attached to the intake side that runs to the ground. This helps somewhat with circulating air from bottom to top of the closet.  Eventually I’m going to add more permanent vents.

There’s also a few other pieces of equipment that will be added once ventilation is improved.

Does the Chelsio 110-1040-20 Support 10GbE Ethernet?

I’ve been playing with FreeNAS, as well as upgrading to 10Gb Ethernet in a few areas where it makes sense in the home (including on the server that houses this website).  I’ve read that FreeNAS has the best support for Chelsio cards.  It wasn’t clear whether this particular card was simply a Fiber Channel only card, or if it was also capable of supporting Ethernet.  Since it was only $23 on eBay (including the optics for both ports) I decided it was worth a shot.  Here’s a shot of the part number on the board.

I plugged it in and at first got some red lights on both ports, plus my switch port didn’t light up.  It wasn’t promising at first.  Once FreeNAS started booting and detected the card, it displayed a message saying that it was downloading firmware to the card.  A few seconds later the lights lit up green and I had network activity!

The card shows up as cxbg0 and cxgb1.  I haven’t tested throughput yet, but it does obtain an IP and I can communicate with the FreeNAS control panel through it.

Showing that the device shows up.

So it looks to be like a success for this very inexpensive dual-port card.