Gas station without pumps

2019 October 18

Book progress update

Filed under: Circuits course — gasstationwithoutpumps @ 22:33
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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
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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.

2019 September 30

Thirty-ninth weight progress report

This post is yet another weight progress report, continuing the previous one, part of a long series since I started in January 2015.

My weight is almost the same as a year ago, showing a steady increase since classes ended. This does not bode well for my retirement years.

The pattern for this summer looks the same as for last summer—I’m going to have to try to drop my weight this fall, and not wait until January.

I’ve been exercising more this summer than last year, cycling up the hill to work out at the OPERS Wellness Center about three times a week. I’ve been averaging 3.77 miles/day for August and September. That exercise does not seem to have affected my weight gain, though. I like to kid myself that the exercise has increased my lean body mass while reducing the fat, but one look at my waist disabuses me of that notion.

I think that being home and having available food at all times makes a bigger difference than exercise in failing to control my weight (I say, having just eaten a chocolate-chip cookie my wife baked this afternoon). Not only are the way too many chocoloate-chip cookies in the house, but my son and I will be baking a big batch of Shakespeare shortbread cookies tomorrow, also, though we’ll be giving most of them away on the bus trip up to Ashland for the Oregon Shakespeare Festival.

2019 September 24

Fall philosophy sing-ups

Filed under: Uncategorized — gasstationwithoutpumps @ 12:05
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A couple weeks ago, I got an announcement of “Fall Philosophy Sing-Ups” through the mailing list for the umbrella school my son used to homeschool with.  Although I realized it was just a transposition typo (Sign⇒Sing), I thought the concept amusing enough to point out to my wife, who immediately thought of Monty Python’s Bruces’ Philosophers Song:

Unfortunately for the students, the description of the course did not sound like nearly as much fun.

2019 September 19

Printed 3DBenchy

Filed under: Uncategorized — gasstationwithoutpumps @ 13:32
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One of the standard test pieces for 3D printers is 3DBenchy, a design with several somewhat difficult features created by (licensed CC-4.0-By-No).  I finally got around to printing it earlier this week on my Monoprice Delta Mini using Hatchbox Gold PLA with a layer height of 0.07mm and the 0.4mm brass nozzle that came with the printer. It took 4 hours and 25 minutes to print at that resolution.

I’ve been trying to figure out how to get Cura 4.2 to dump the entire settings used to generate the Gcode, but I’ve been unable to do that—it seems to record only the differences from the standard settings. So far the best I’ve been able to do is to extract settings from the output G-code:

;Filament used: 3.85238m
;Layer height: 0.07
;Generated with Cura_SteamEngine 4.2.0

M82 ;absolute extrusion mode
G21;(metric values)
G90;(absolute positioning)
M82;(set extruder to absolute mode)
M107;(start with the fan off)
G29 P5 Z0.3 V4; (Level the bed with 5x5 array)
G1 X55 Y0 Z5 F3000;(Move to the outside of the bed.)
G92 E0;(reset extrusion distance)
G1 E5 F500;(Prime.)
G92 E0;(zero the extruded length)
G1 Z0;(Down to printing height.)
G2 X0 Y55 I-55 J0 E20 F2000;(Draw a priming arc.)
G92 E0;(zero the extruded length)

adhesion_type = none
build_volume_temperature = 0
default_material_bed_temperature = 50
layer_height = 0.07
layer_height_0 = 0.14
material_bed_temperature = 40
material_bed_temperature_layer_0 = 50

alternate_extra_perimeter = True
brim_width = 3
cool_min_layer_time = 3
fill_outline_gaps = True
infill_sparse_density = 25
line_width = 0.35
material_initial_print_temperature = 195
optimize_wall_printing_order = True
top_bottom_thickness = 0.42
xy_offset_layer_0 = -0.05
zig_zaggify_infill = True

That is enough to recreate the settings in Cura 4.2, but if the default values change in later versions of Cura, I won’t know which to reset. Some of these settings are irrelevant, also, as the brim_width doesn’t matter since I didn’t use a brim, for example.

Print speed is the default 60mm/s with walls and top/bottom at the default 30 mm/s and travel at the default 120mm/s.

I chose to print at 0.07mm (70 µm), since I read somewhere that multiples of that thickness are best for the Monoprice Delta Mini.

Bottom view shows the shiny surface from using a glass plate with hairspray as an adhesive.

The top surface looks pretty clean, but stringing can be seen from the stern and between the uprights of the wheelhouse.

The top view looks pretty good from this angle also, but some blobbing can be seen inside the bow.

The port bow shows smooth sides, but some stringing on the hawsepipes and poor bridging at the top of front window of the bridge.

The view from the stern shows bad stringing for the rear window. The 0.1mm writing on the stern is barely legible with angled lighting (not really with this flash).

The starboard view shows bad stringing between the uprights of the bridge and some blobbing on the back of the bridge, as well as some layer marks near the top of the arch.

Many of the calibration checks (measured/ideal) are hard to do with calipers, because there are not well-defined measurement points or other parts of the print interfere with placement of the calipers. I skipped some measurements entirely as impossible to measure with the calipers.
roof length 22.9mm/23mm
chimney cap diameter 6.4mm/7mm
depth of chimney hole 11mm/11mm (hard to measure accurately)
chimney inside diameter 2.4mm/3mm (hard to measure accurately)
length 60mm/60mm (hard to measure accurately)
width 29mm/30mm (hard to measure accurately)
height 48.2mm/48mm
box height 15.65mm/15.5mm
box width 11.8mm/12mm
box inside width 7.8mm/8mm
box depth 9.1mm/9mm
box length 10.75mm/10.81mm
hawsepipe diameter 3.95mm/4mm
front window width 9.95mm/10.5mm
rear window outer diameter 11.35mm/12mm (horizontally)
rear window inner diameter 8.9mm/9mm

The z-heights look about 0.5% too big and the x-y dimensions about 2% small (though I don’t trust the measurements—I’d want to use a rectangular block for re-calibrating).

I think that the biggest problem is stringing, which may be fixable by increasing the retraction, though bridging at the top of the front window is also flawed. Retraction is enabled and is the default 6.5mm @ 25mm/s.

I’ll be asking for advice on the 3D-printing subreddit, since asking for help on Benchy prints seems to be common there.

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