Gas station without pumps

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.

2019 September 17

Spacers for electric outlet box

Filed under: Uncategorized — gasstationwithoutpumps @ 12:34
Tags: ,

Yesterday I printed some functional (rather than decorative) parts. The problem I was addressing was one that had been bothering me in a low-key way for several years—an electrical outlet in the living room that was wobbly. The problem started when I had the front wall insulated. Because the wall is self-formed concrete, sheets of foam insulation were added on the inside of the wall, sheet rock put over the insulation, and then a skim coat of plaster added to match the original texturing of the walls. The outlet box for the electrical outlet was now rather deeply recessed in the wall, and the carpenters move the outlet forward by using longer screws.

Unfortunately the spacers they used to hold the outlet in the new position were not real spacers, but plastic wall anchors, which did not hold the outlet firmly in the right place—they were relying on the strength of the plastic wall plate to hold the outlet forward. This was never very secure, and this summer the wall plate broke while plugging in an extension cord, so I decided to print some properly sized spacers to hold the outlet securely in place.

I turned off the power and measured the spacing needed with the depth gauge of my calipers, as well as measuring the room available for the spacer. I printed two spacers that were 13mm long and replaced the outlet, only to find out that outlet was still too deep in the wall for the new cover plate to be screwed to the outlet. I tried measuring how much further out the outlet needed to be (estimated at 9mm) and printed a pair of 22mm long spacers.

These are the 13mm and 22mm spacers that ended up being extra. The ears on the spacer are not necessary—I put them on to match the outlet, to make alignment easer, as the hole was initially not centered vertically. I later changed the design so that the hole was centered, so the orientation is now irrelevant and a simple rectangular spacer would suffice. The parts are printed with 0.14mm layers in Hatchbox Gold PLA, with 25% infill.

On the first attempt to print a pair of 22mm spacers, one printed fine, but the other ended up with a long trail of tangled spaghetti after printing halfway just fine. Reprinting just one 22mm spacer failed again, this time with a blobby mess. The problem, however, was clear—the print had gotten detached from the baseplate and was moved around by the printhead. Using some hairspray on the bed increased the adhesion enough that it printed fine, without needing to add a brim.

These two prints were supposed to be 22mm spacers. The one on the right was printed at the same time as one of the successful prints, and the one on the left was an attempt to reprint just one spacer. For both, the failure was insufficient adhesion to the glass bed—I fixed the problem by using hairspray to increase the adhesion.

When I put the 22mm spacers in place, the outlet stuck out too far (my measuring skills clearly need some improvement). The outlet stuck out much more on the bottom than on the top, so I put on the cover plate and measured the clearance from the wall on both the top and the bottom. I decided that I could use the smaller 13mm spacer on top, but I would need an 18mm spacer on the bottom. After printing an 18mm spacer, I assembled the outlet once more, and everything fit perfectly, with the cover plate flush against the wall as desired.

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