Monday, August 22, 2016

A free band saw

Thanks to my wife's keen eye on our neighborhood message board, I just scored a FREE band saw.  It seems that someone was cleaning out their garage and just wanted to get it out of their ASAP.  It's a Craftsman 12" band saw from the 80s.

Check out the pictures below.  It needs one new tire and a new table insert (which I might be able to make myself).  It seems like the bearings are in good shape, the tensioner works, and the motor runs.  So after some cleaning, lubricating, adjusting, and $30-40 in parts it should be in good shape again.

This is after I brushed off the loose dirt and cobwebs

It's dirty, a little rusty, and several generations of
wasps have lived in there, but the bones looks
pretty good.

The motor pulley and belt need to be re-attached.  No biggie.

This is probably the biggest issue (which still isn't bad).  The
top wheel needs a new tire since a section of it is missing.

Monday, August 15, 2016

Sharpening old tools

If you thought, based on the title of this post, that I'd be discussing refreshing some previously learned skills, you may be disappointed.  Instead I'll actually be showing off how I sharpened some vintage woodworking tools.

I've recently been re-discovering my woodworking hobby, while learning to use hand tools in place of the power tools I've previously used.  There are many reasons I've decided to use less electricity to make wooden objects, but I'll save all of that for another post.  I'll just focus on sharpening for now.

Rough Grinding
Usually you start sharpening by rough grinding the bevel angle on the blade.  This step is only required if you are setting a new bevel angle or if the blade is otherwise damaged.  You can do the rough grinding by hand but I opted to use a power grinder with a 40 grit grinding wheel.  So I lose some hand tool merit points for using electricity here.  All of the blades I sharpened were to 25 degrees, which is pretty standard.

Honing Methods
There are tons of ways to sharpen metal blades: oil stones, water stones, diamond plates, etc.  I'll be using a lesser-known method: sand paper.  I learned about using sand paper from the Naked Woodworker, but there are many people that prefer this method, often known by the name Scary Sharp.

The basic requirements are three or four grits of sand paper going from around 150 grit up to 800 or 1000.  Spray adhesive (or similar) is used to attach the sand paper to a flat surface like plate glass.  When I went to the Home Depot to get supplies they only had very thin window glass, and I wanted something thicker.  I was impatient so rather than waiting to go to a glass shop, I looked around in the tile section and found a large floor tile that was dead flat (I checked it with a straight edge).  I haven't heard of anyone using floor tiles before but I can't think of a reason it shouldn't work.

With any of these methods it's common to use a honing guide to keep the angle, though some people like to freehand the bevel angle once it's been rough ground.  I used two different honing guides, an Eclipse and a Veritas.

The Block Plane
The first thing I tried to sharpen was an old Craftsman block plane (circa 1920). It was the first time I've use a grinder and I had a little trouble getting the tool rest set to the right angle.  The end result is that the blade has two bevel angles as you can see in the photo below.  Functionally it works fine, even if it's a little ugly, and after honing I can shave with it.

I tested the plane out by cutting some end grain bevels (something a block plane is ideal for).  It seemed to perform pretty well even while taking a pretty aggressive cut.

The Smoothing Plane and Chisels
Next up was a nice Millers Falls Smoothing Plane.  This one was straight-forward except that whoever had previously sharpened it had kind of messed it up and put quite a bit of skew on the blade (maybe it was intentional).  I ground off the skew and made it straight across again.  I also knocked down the corners of the blade a little to reduce tear out.  After honing I was able to take paper-thin shavings which is what you need in a smoothing plane.

I also sharpened some chisels, but they were brand new and factory ground to 25 degrees to they just required a quick honing.  I didn't even get any pictures of the chisels.

The Jack Plane
I left the most difficult one for last.  A jack plane is usually used for taking off lots of wood quickly.  To optimize for this the blade geometry needs a little curve, which is called camber.  Although the curvature is slight this allows the plane to scoop the wood out and take off much larger chips.  This is really useful if the wood is twisted or cupped and you need to take off an eighth of inch or so.

I wanted to take about a sixteenth of an inch off of each corner, and beyond that I just planned on free-handing it on the grinder. I got a tip from watching some YouTube videos that it easiest to take the corners off by putting the blade into the wheel at 90 degrees and then once the curve is ground the same 25 degrees bevel is established all the way across.  It took a while but I eventually got the camber you can see below.

Honing a cambered blade was a little trickier than a straight blade, since you need to sort of lean the blade back and forth as you hone.  For this I used the eclipse guide since it has a small wheel that lets you lean the guide much easier than the Veritas guide.

To test I took a fairly conservative cut, and although it may be hard to see in the photo below, it took some quite thick chips.  It was interesting that I could feel the camber of the blade in the chips, in that they were quick thick in the middle but got paper thin at the edges.

Saturday, August 13, 2016

LabVIEW for BBB and RPi Internals: Yocto, chroot, and other strange words

I recently helped create a toolkit to allow running LabVIEW VIs on a BeagleBone Black (BBB) or Raspberry Pi 2 (RPi2).  In this post I'd like to get into some of the technical challenges we encountered along the way.

SamK, the author of the LINX toolkit, took over creating the LabVIEW I/O library.  LINX was originally written to allow LabVIEW to easily access the I/O on Arduinos and similar devices, so he naturally chose to use the same LabVIEW API to access I/O on BBB and RPi2.  The underlying implementation on the BBB/RPi2 is fundamentally different than the normal LINX toolkit.  Details on the architecture is available here.  The source code for the library is available here.

Issues encountered
I worked on making the LabVIEW run-time engine work on the BBB/RPi2.  The LV run-time had previously been ported to the ARMv7a CPU architecture and the Linux operating system in order to enable the latest generation of NI's CompactRIO industrial controllers.  This made things way easier but there were still some issues that had to be overcome:
  1. The run-time was already built around the fact that it was running on the an armv7a architecture.  This is fine for the CPU on the BeagleBone Black and the Raspberry Pi 2 and 3.  But the Raspberry Pi 0 and 1 use an older CPU that only supports the armv6 instruction set, so for this reason we decided not to support the older Raspberry Pis.
  2. The LV run-time usually runs on Linux in NI's own embedded Linux distribution, but for the BBB and RPi we wanted to make LabVIEW run on the recommended Linux distro for each of these targets which happens to be debian based.
  3. The ARM Linux versions of the LabVIEW run-time and the rest of the NI software stack are compiled with the softfp gcc flag, while most ARM Linux distros use the hardfp flag.  Binaries built with one flag are incompatible with binaries built with the other.  These means that the LabVIEW run-time cannot use the hardfp libc that is present on Raspbian.  That's a problem.
Solutions found
The first issue is kind of a limitation of the CPU in the Raspberry 1 and since most people are using the
newer Raspberry Pi 2 or 3, we decided that the easiest way to resolve the issue was to not support the RPi 1.  I know it kind of sucks for people that want to use the RPi1 they have lying in a drawer somewhere but considering how cheap RPi's are in general, it doesn't seem like such a big deal.

To solve the rest of the issues, I decided to use a Linux chroot.  At it's core, a chroot, or root jail, runs a process with a different root directory.  That's really all there is to it, but the implications are pretty far reaching.  When a process runs it loads its libraries from the /lib directory among others, so if we provide a softfp set of libraries in a different directory and chroot the LabVIEW process to that directory then we can solve issue 3.  And if, also in that same chroot directory, we provide a simple Linux distro that is custom-tailored to LabVIEW, then we can solve issue 2.

Building chroots in Yocto
To make this little chroot Linux distro, I used the Yocto project, which I was already familiar with because I use it at work on a daily basis.  I created a Yocto layer that has everything needed to create chroot.  The image recipe includes the LabVIEW run-time engine and the VISA and LINX I/O libraries.

Installing the chroot
With the chroot image created, I needed some way to install it on a target.  Since both the BBB and RPi use Debian-based Linux distros I create a deb package installer.  The install includes the chroot image created using Yocto, a systemd unit file to start the chroot and LabVIEW run-time at boot, a dependency to the schroot utility, and a small daemon that I'll discuss below.

Emulating the NI System Web Server
On traditional NI Linux RT targets, there is a system web server which provides various system configuration services like changing the network settings.  We don't support most of these system configuration services, but we do need to support restarting the LabVIEW run-time.  This is needed because when deploying a LabVIEW startup app to the target, the run-time needs to be restarted.

Since we only needed this service, rather than skimming though the significant codebase of the System Web Server, I instead took the tact of reverse-engineering the reboot web service using Wireshark.  Basically, I ran a Wireshark capture while remotely restarting a traditional LabVIEW Real-Time target.  This worked far better than I would have guessed, and soon I had a small script which implements a small subset of the NI System Web Server's functionality.  I created another systemd unit file to start the script at boot time and put it all into the debian installer.

On important note is that the NI System Web Server does lots of work to ensure that all of it's operations are handled securely, but for my quick-and-dirty python script I did not implement any of these security features.  The LabVIEW run-time is also run as the root user so that it has access to the I/O resources that it needs.  On other LabVIEW Real-Time targets, and on Linux systems in general, daemons like the LabVIEW run-time do not run as root due to security concerns.

The implications of these choices is that anyone with access to your local network can restart the LabVIEW daemon remotely, and can run VIs on the BBB/RPi2.  This probably isn't a big deal if your network is private and has a firewall between it and the rest of the Internet, but it's still something to be aware of.