Gas station without pumps

2019 October 18

Book progress update

Filed under: Circuits course — gasstationwithoutpumps @ 22:33
Tags: , , , , ,

At the beginning of the summer, I set myself the goal to clear the 161 to-do notes from the draft of my book by the first of December, which meant doing about 1 a day.  I kept up for quite a while, but I am now a little behind schedule, with 48 to-do notes left, which would have me finishing on December 5, if I maintained one a day. The book is now 637 pages, with 315 images in 256 figures (many have subfigures).  I think I may be done adding figures, but the remaining to-do notes include adding a few pages of text (which may or may not increase the page count for the overall book, depending of how much white space there is at the end of the relevant chapters).

I was keeping pretty well to schedule over the summer, but I fell behind during the Santa Cruz Shakespeare trip to the Oregon Shakespeare Festival in Ashland. The trip was worth the time—I saw six plays: two very good (La Comedia of Errors and All’s Well That Ends Well), one well-acted but with a bit of a thin script (Mother Road), one well-acted but with awkward sets and strange direction that did not really work (Macbeth), one interesting but deliberately uncomfortable play (Between Two Knees), and one awful production (As You Like It) that failed in almost every way.  The original script for As You Like It is good, but the director managed to mangle it by rearranging speeches, assigning them to the wrong characters, cutting excessively, and generally making a hash of it. Gender roles were randomly reassigned, the wrestling match was played for laughs (like a video game), Touchstone was played very stiffly, and Jaques was changed from a melancholy character into a giddy one.  The costuming was also poor—I felt very sorry for the actors having to put up with such a poor interpretation of the play.

I’m on leave this quarter, so I don’t have to teach, go to meetings, or hold office hours, but I’m taking a physics course (PHYS 102, which is an introduction to quantum mechanics).  The homework for the physics class has been taking quite a bit of time, and I have been prioritizing it over the book writing. I brought my laptop with me on the Ashland trip, but I didn’t do any writing for the book—I finished the first homework for the physics class instead, as it was due the day after we came back.  Today I finished homework 3 for the physics class (due Monday), so I should work on the book this weekend.  Maybe I can get back on schedule? (Or maybe I’ll try mowing more of the back lawn—I’ve cleared about a quarter of it.  Creative Procrastination!)

I’ve also been wasting a lot of time reading news, humor, and a few subreddits on the internet—the physics class is only taking about 15 hours a week, so I can’t really blame the class for my being behind schedule on the book.

2019 October 15

Extruded clamp

Filed under: Uncategorized — gasstationwithoutpumps @ 16:51
Tags: , ,

A few years ago, I found a little (6.5cm long) aluminum clamp on the street, probably fallen out of someone’s truck. I liked the design of the clamp(though the original rubber band has died):

Although the “Taylor” brand name is clearly stamped on the extrusion, I have been unable to find clamps by Taylor for sale online.

Extrusions are particularly easy to copy with a 3D printer, and so I decided to make my own clamps. I took off the rubber band, put the extruded aluminum pieces on my flatbed scanner and scanned them at 600dpi. I then used Inkscape to manually draw a Bézier-curve outline of each piece. I used the circle tool in Inkscape behind the curve to tweak the hinge contacts to be very close to circular.

I imported the SVG files into OpenSCAD and extruded the pieces to 12.5mm (the thickness of the original clamp). The first printing was not entirely successful:

The first few layers warped on the end of the handle—apparently the thin end of the handle did not adhere well to glass plate and warped up.

I fixed the problem in two ways: I made the handle a little beefier (it seemed a little thin on the original anyway) and I printed with a brim. While I was at it, I increased the extrusion from 12.5mm to 15mm to make a slightly fatter clamp. The resulting clamp was successful:

Here are the two pieces of the clamp separately.

The clamp assembled. By using three wraps of the rubber band, twists in the rubber band can be avoided.

The difference in the handles between the first print (on the left) and the second print (on the right) is clear in this image.

Removing the brim was a bit of a hassle—I need to think about applying a brim only to the handle part. I don’t think that the Cura slicer makes that easy, so I’d probably have to design it into the model (union with a 0.14mm thick plate around each handle).

Now that I have the basic model working, I can play around with different jaw shapes and different sizes of clamps.  With the jaw all the way open the clamping force seems to be about 15N, though that obviously depends on the rubber band used.

Update 2019 Oct 21:  I have released the design as  I was reluctant to release the design, as it was reverse-engineered and not my original work.  I contacted the company whose logo was on the clamp for permission, and they responded:

I have looked through our old brochures and have not seen a clamp like that.
We have not built anything like that in my 41 years here.
Good luck with your project.

I took that as permission to release the model on Thingiverse.

Update 2019 Oct 28: After some image searches for the logo, it looked to me like the logo might be Taylor Guitars, so I wrote to them and asked them about the clamp.  They said

Thanks for writing!
That is a clamp we made, it’s called a kerfing clamp. We use them in our factory and there was a time, many years ago, that we sold these clamps to guitar builders. We no longer sell them but we did give this guitar supply store, Stewart MacDonald, permission to copy the design.

I wrote back asking for permission to put the design on Thingiverse, and if it is denied, I’ll take down the Thingiverse post.

%d bloggers like this: