Project Potpourri http://david.rysdam.org/blog Do the dumb things I gotta do. Fri, 09 Mar 2012 14:08:28 +0000 en hourly 1 http://wordpress.org/?v=3.1 The Really Real Lathe http://david.rysdam.org/blog/2012/03/09/the-really-real-lathe/ http://david.rysdam.org/blog/2012/03/09/the-really-real-lathe/#comments Fri, 09 Mar 2012 14:06:21 +0000 David http://david.rysdam.org/blog/?p=728 So about 9 months ago I still had this tiny lathe. It was so underpowered I couldn’t do much with it. I’ve also heard it described in more than one place as a “boat anchor”, which could explain why I was having so much difficulty. Another potential explanation is that I’m a n00b.

In any case, I sold that, took the money plus a bunch I’d saved up and was planning to buy a modern, bigger lathe. But just as I did, a peach fell into my lap.

Hard to tell the scale from this image, but that bench is at kitchen counter height. This is the South Bend 10k, slightly bigger brother to the famous and classic 9″ Workshop. The photo above is as I found it, after 15-20 years of storage in a garage. (It has a tailstock, I just removed it before this picture was taken on a prior dismantle-to-move trip.)

The condition seems excellent so far. Cross-feed backlash is, AFAICT, .000″ which is physically impossible but in a good way. No ridges or chips in on the ways or in the tapers. No rust on anything but the 3 way chuck. Filled with old oil, dirty grease and metal chips, obvs so I’m restoring it. Have to completely strip the entire thing, replace oil wicks and whatnot, adjust this and that and repaint. And replace the motor and switch. I’m in the middle of all that now, as can be seen from these progress photos.

]]> http://david.rysdam.org/blog/2012/03/09/the-really-real-lathe/feed/ 0 Quick Book Rec http://david.rysdam.org/blog/2011/10/31/quick-book-rec/ http://david.rysdam.org/blog/2011/10/31/quick-book-rec/#comments Mon, 31 Oct 2011 11:54:36 +0000 David http://david.rysdam.org/blog/?p=719 I’ve only finished up through Chapter 3, but that much alone justifies $20 for this book1 2

You can download the hardware simulator and build logic gates, an ALU, memory registers, etc (you are given a NAND and a flipflop). Then you write an assembler on top of that, then a compiler on top of that then an operating system out of that. Super awesome.

The book is presented as a college-level integration of other, separate college-level classes. But really, the parts I’ve read so far (only about ΒΌ of the book) could be used in high school easily. In fact, my 12 year old computer nerd son isn’t having much trouble, although he’s only up through Chapter 1. I think he’ll have more trouble writing a compiler than making an XOR gate.

  1. book site ↩
  2. Amazon ↩
]]> http://david.rysdam.org/blog/2011/10/31/quick-book-rec/feed/ 0 Or Maybe It Won’t! http://david.rysdam.org/blog/2011/06/29/or-maybe-it-wont/ http://david.rysdam.org/blog/2011/06/29/or-maybe-it-wont/#comments Thu, 30 Jun 2011 01:44:50 +0000 David http://david.rysdam.org/blog/?p=701 I said that now the serious spending could begin. And it kind of has, since I bought supplies for the countershaft, some measuring tools, a toolbox to put them in, a drill chuck, a tailstock spindle and a replacement carriage gib stock that I cleft in twain. HOWEVER.

I HAVE ALSO CREATED LIFE mwahahahahahaha!!!

In that last post, I was building the countershaft to get lower speeds. It turns out that this lathe has “back gears” which basically means “a whole nother set of speeds, lower than the regular ones so you don’t need to have a countershaft”. 1 I didn’t realize it had back gears because a) I didn’t have a manual (another thing I bought since the last post) and b) the back gears selection knob thingie was missing. But I built another forged from the molten core of the Earth itself. Observe!

indistinguishable from the drawing

It doesn't quite match the decor, but come on. It's my first project!

  1. Yes, that means all that work was for naught. ↩
]]> http://david.rysdam.org/blog/2011/06/29/or-maybe-it-wont/feed/ 1 Engine Difference Babbage’s http://david.rysdam.org/blog/2011/05/14/engine-difference-babbages/ http://david.rysdam.org/blog/2011/05/14/engine-difference-babbages/#comments Sun, 15 May 2011 01:13:45 +0000 David http://david.rysdam.org/blog/?p=608 On my old blog, I once did a post on Babbage’s Difference Engine and how to run it backwards. However, I didn’t really finish the thought there and just recently it came up again IRL. 1 So this time, I think I’ll do the whole post.

The DE computed polynomials and worked by simple addition. It consisted of a series of numerical columns each of which had multiple digits, each column representing different stages of the computation, as I’ll show below. Suppose you have a function like

f(x) = x^2 + 1

I can compute this using only addition by starting with a table like this:

\begin{tabular}{ r r r r } $x$ & $f(x)$ & $f'(x)$ & $f''(x)$ \\ \hline 1 & 2 & 3 & 2 \\ 2 & 5 & 5 & 2 \\ 3 & 10 & 7 \\ 4 & 17 \end{tabular}

The x and f(x) columns are pretty self-explanatory. The f' and f'' columns are the differences between successive entries in the column to the left of each. For instance, the 3 at the top of the f' column is the difference between the 2 and the 5 in the f(x) column. The 2 at the top of the f'' column is the difference between the the 3 and the 5 in the f' column. (There are exactly two difference columns because this is a 2nd degree polynomial.)

Once I have a table started, I compute the function using simple addition from the right to the left, starting with the constant in the rightmost column, like this:

\begin{tabular}{ r r r r } $x$ & $f(x)$ & $f'(x)$ & $f''(x)$ \\ \hline 1 & 2 & 3 & 2 \\ 2 & 5 & 5 & 2 \\ 3 & 10 & 7 & \rightarrow \textbf{2}\\ 4 & 17 \end{tabular}

\begin{tabular}{ r r r r } $x$ & $f(x)$ & $f'(x)$ & $f''(x)$ \\ \hline 1 & 2 & 3 & 2 \\ 2 & 5 & 5 & 2 \\ 3 & 10 & 7 & 2\\ 4 & 17 & \rightarrow \textbf{9} \\ \end{tabular}

\begin{tabular}{ r r r r } $x$ & $f(x)$ & $f'(x)$ & $f''(x)$ \\ \hline 1 & 2 & 3 & 2 \\ 2 & 5 & 5 & 2 \\ 3 & 10 & 7 & 2\\ 4 & 17 & 9 \\ 5 & \rightarrow \textbf{26} \\ \end{tabular}

So all Babbage’s Difference Engine had to do was be able to add columns and it could compute tables of values for any polynomial (of degree n for some number of columns in his machine).

Not a lot of call for computing mathematical tables today and that goes double for mechanical computers. However, this technique can be used in reverse for something that’s slightly more helpful. Say I have a function that I can compute, but I don’t have a polynomial expression for it. I’m going to choose a simple one that probably has other ways to figure out:

\displaystyle{f(x) = \sum_1^x (k+1)}

Start by just computing a few values:

\begin{tabular}{ r r } $x$ & $f(x)$ \\ \hline 1 & 2 \\ 2 & 5 \\ 3 & 9 \\ 4 & 14 \\ \end{tabular}

Then the differences of those values

\begin{tabular}{ r r r } $x$ & $f(x)$ & $f'(x)$\\ \hline 1 & 2 & 3 \\ 2 & 5 & 4 \\ 3 & 9 & 5\\ 4 & 14 \\ \end{tabular}

Then the differences of those differences

\begin{tabular}{ r r r r } $x$ & $f(x)$ & $f'(x)$ & $f''(x)$ \\ \hline 1 & 2 & 3 & 1\\ 2 & 5 & 4 & 1\\ 3 & 9 & 5 \\ 4 & 14 \\ \end{tabular}

When the last column is constant, we are done and we know the degree of the polynomial we are looking for. 2 That polynomial can be expressed as

f(x) = ax^2 + bx + c

Which means the first differences column can be expressed as:

    \begin{eqnarray*} f'(x) & = & f(x+1) - f(x) \\ & = & \left[a(x+1)^2 + b(x+1) + c\right] - \left[ax^2 + bx + c\right] \\ & = & ax^2 + 2ax + a + bx + b +c - ax^2 - bx - c \\ & = & 2ax + a + b \end{eqnarray*}


Likewise, the second differences column can be expressed as:

    \begin{eqnarray*} f''(x) & = & f'(x+1) - f'(x) \\ & = & \left[2a(x+1) + a + b\right] - \left[2ax + a + b\right]\\ & = & 2a \end{eqnarray*}


This is the function for the last column, so now we know that in the searched-for polynomial a = \frac{1}{2}. With that, let’s back up a step and solve f'(x) using the known values of a, x and f'(x).

    \begin{eqnarray*} f'(x) & = & 2ax + a + b \\ f'(1) & = & 2(\frac{1}{2})(1) + (\frac{1}{2}) + b = 3 \\ b & = & \frac{3}{2} \end{eqnarray*}


And now do the same thing to solve for c.

    \begin{eqnarray*} f(x) & = & ax^2 + bx + c \\ f(1) & = & \frac{1}{2}(1)^2 + \frac{3}{2}(1) + c = 2 \\ c & = & 0 \end{eqnarray*}


So the final polynomial is

\displaystyle{\sum_1^x}(k+1) = f(x) = \frac{1}{2}x^2 + \frac{3}{2}x

And there we have it.

  1. Well, sort of. It was a math puzzle. ↩
  2. Actually, we only know it for the data we have. If this were a function in the domain of the reals, it could be doing anything between the points we selected. This is sort of a least-complexity polynomial for the given data. ↩
]]> http://david.rysdam.org/blog/2011/05/14/engine-difference-babbages/feed/ 0 Just in time for the future! http://david.rysdam.org/blog/2011/04/03/just-in-time-for-the-future/ http://david.rysdam.org/blog/2011/04/03/just-in-time-for-the-future/#comments Sun, 03 Apr 2011 18:43:57 +0000 David http://david.rysdam.org/blog/?p=600 I’ve been exploiting Emacs for more than text editing recently. 1 So I was about to buy a copy of the GNU Emacs manual when I noticed that it was version 22. And $45 into the bargain. You can get version 23.3 for free but they don’t have it in hardcopy yet.

So I uploaded the PDF to Lulu to have them print and bind it for me.

It’s well worth reading. I’ve already dog-eared several pages of useful stuff I didn’t already know and I’m only on like page 30. I also just now noticed that I’m running Emacs 23.1. 2

  1. Which reminds me. notmuch is 100x better than sup. Completely awesome. ↩
  2. But it looks like Debian 6.0 has Emacs 23.2 and I’ve been meaning to upgrade from Ubuntu to Debian for a while now anyway. ↩
]]> http://david.rysdam.org/blog/2011/04/03/just-in-time-for-the-future/feed/ 0 Forensic GENIOUS http://david.rysdam.org/blog/2011/01/16/forensic-genious/ http://david.rysdam.org/blog/2011/01/16/forensic-genious/#comments Sun, 16 Jan 2011 12:53:53 +0000 David http://david.rysdam.org/blog/?p=593 I really love tomato.1 One of my favorite things is the bandwidth graphs. I just happened to glance at them last night before bed and saw they were pegged at maximum and had been for several hours.

Me: Hey, are you uploading/downloading from your photo site?
Mrs: No.
Me: Hmmmmm

I go through all my processes: Nothing is downloading that much.
I shut down computers one at a time until only my computer is left: Still downloading.
I shut mine off: Downloading ceases.
I turn my computer back on: Downloading starts again.

Uh oh, I think, I’ve been hax0red. So I start looking more closely at netstat to see what net connections I’ve got. I see my email client in there, polling the server, so I decide to shut that off to clean up my display a bit….and the bandwidth drops down to a reasonable level. What the.

Background #1: I fetch my mail with offlineimap.2 I’ve found that it has a bug or something so that periodically it will get “stuck” and have to be killed. So I set up my cronjob to kill the previous instance, if any, before running the new one.

Background #2: My brother-in-law was going to use a file-sharing site to send me a ~10MB file. I actually typed out an email to suggest he just email to me, but then thought maybe I should learn to use these sharing sites for when I really do have a biggish file. So I just told him to do “whatevs”.

As it turned out, he did in fact email it to me. And offlineimap was downloading it. But it took more than a minute (my cronjob rate), so the next time it came around my script killed the previous instance and started over. All this pegged my bandwidth usage. I temporarily modified the script to not kill the previous instance, got the file in a little over a minute and then the bandwidth finally dropped.

So that problem is solved. However, I still have the issue of offlineimap periodically hanging. I guess I’ll have to make a more sophistimacated script. Run the script every minute, but let a particular instance go for several iterations before killing it. Or maybe it would simpler to just notify myself when an instance has to be killed. My local email (i.e. from cron, etc) doesn’t go into my regular email client, but maybe it should…

  1. I also really love that googling for “tomato” finds the firmware, not the fruit. ↩
  2. It’s pretty nice, because it syncs a Maildir and an IMAP source, so you can work offline on two computers, although I don’t use it for that right now. ↩
]]> http://david.rysdam.org/blog/2011/01/16/forensic-genious/feed/ 0 Now the Serious Spending can begin http://david.rysdam.org/blog/2010/12/21/now-the-serious-spending-can-begin/ http://david.rysdam.org/blog/2010/12/21/now-the-serious-spending-can-begin/#comments Tue, 21 Dec 2010 12:37:05 +0000 David http://david.rysdam.org/blog/?p=568 I’ve wanted a metal lathe for, ooohhh, probably 8 or 9 years. I half-heartedly began building one, but after some industrial espionage (delivery trunk rolled over my furnace) I gave that up.

What I really want is something like the awesome old South Bend 9″, but I haven’t saved up the $ for that yet. In the meantime, I thought I’d get my toes chopped offwet with a smaller, crappier and cheaper Craftsman 109. Mine isn’t in quite as nice a shape as that one (yet!) but that’s actually kind of by design. Fixing it up and training on a junker are all part of the plan.

Here it is more or less as I bought it:

craftsman 109 20630

And here I’m in the process of adding a countershaft for more granular speed control, including a much slower lowest speed. Was about 900 RPM(!), now hopefully about 100 RPM (actually, closer to 300 RPM but that’s OK for now).

new countershaft

In between those photos I’ve already learned a ton by fixing/adjusting the tailstock, lead screw, cross slide and all the gibs.

]]> http://david.rysdam.org/blog/2010/12/21/now-the-serious-spending-can-begin/feed/ 1 One of my favorite egg-based robots http://david.rysdam.org/blog/2010/10/16/one-of-my-favorite-egg-based-robots/ http://david.rysdam.org/blog/2010/10/16/one-of-my-favorite-egg-based-robots/#comments Sat, 16 Oct 2010 23:43:00 +0000 David http://david.rysdam.org/blog/?p=538 I bought an Egg-bot. It’s pretty hilarious and awesome. Here it is in action (sped up 4x…or 8x? I don’t even remember now):

I’m working on a mathematical recasting, but it seriously took me 2 days to figure out how to post this video right, so now I think I need a bit of a lie-down.

]]> http://david.rysdam.org/blog/2010/10/16/one-of-my-favorite-egg-based-robots/feed/ 2 Putting the “ow” in “browser” http://david.rysdam.org/blog/2010/10/04/putting-the-ow-in-browser/ http://david.rysdam.org/blog/2010/10/04/putting-the-ow-in-browser/#comments Mon, 04 Oct 2010 15:34:16 +0000 David http://david.rysdam.org/blog/?p=532 So I upgraded, as they put it, from Ubuntu to Debian (don’t ask why). I was using Firefox on the old system and I had no real problems with it. I wanted to use it on the new system. I also want to let my package manager do as much download; make; make install; asking-if-that-was-so-hard; for me as possible because I have a lot of important web browsing I have to do.

Problem the First! Firefox, per se, is not in Debian. Debian prefers to separate “upgrades for new features” from “fixing major bugs and security holes”, so they take future fixes and apply them to old releases so you can have software that works the same as it used to, just with added stability/security. OK, that makes sense. But I guess Mozilla doesn’t like that and made them rebrand it. It’s actually “IceWeasel” in Debian.

Problem the Second! The proxy at work blocks Firefoxen below version X.Y because of security problems. My IceWeasel is nominally below X.Y and therefore blocked, even though I probably have those security problems fixed (see Problem the First). No, I can’t just change the useragent string. For one think, that’s probably in violation of the DMCA. For another, it isn’t in the easily-changed portion of the string (I think it’s actually the Gecko revision string that it’s looking at). So I guess I’ll use Epiphany, which is based on WebKit instead of Gecko.

Problem the Third! Epiphany sucks! Slow, unconfigurable and the tabs Just Don’t Work Right (why would I want tabs to become invisible and be linearly-accessed?). So let’s download a recent version of Firefox.

Problem the Fourth! Only 32 bit versions are available and I have the 64 bit Flash plugin.

So I think I have 3 alternatives now:

Alternative the First! Forget about Flash. I wish.

Alternative the Second! Install the 32 bit Flash. Probably outside of Debian’s package management which means a treadmill for me.

Alternative the Third! Compile Firefox myself. Very unattractive prospect, but possibly the least unattractive.

I ♥ Computers

]]> http://david.rysdam.org/blog/2010/10/04/putting-the-ow-in-browser/feed/ 3 Overheard at a Tea Party http://david.rysdam.org/blog/2010/09/27/overheard-at-a-tea-party/ http://david.rysdam.org/blog/2010/09/27/overheard-at-a-tea-party/#comments Mon, 27 Sep 2010 12:14:11 +0000 David http://david.rysdam.org/blog/?p=528 Due to a malfunctioning audiobook device, I was forced to listen to a little NPR this morning. They had on a woman who was protesting the “socialism” of the American government. Pressed for details, she complained about “giving handouts to bankers and corporations and doing nothing about regular working class people”.

where do i begin i don’t even

]]> http://david.rysdam.org/blog/2010/09/27/overheard-at-a-tea-party/feed/ 0