Gas station without pumps

2019 July 15

Shakespeare cookie cutter v3

Filed under: Uncategorized — gasstationwithoutpumps @ 20:27
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My first post on the Shakespeare cookie cutter was about versions 1 and 2 of the cutter and stamp—both of which were basically unsuccessful.  I had two ideas for fixing the problems: making the cookie stamp larger and simplifying the artwork.  For version 3, I tried both.

The face is still vaguely Shakespeare, though the mouth is not right. I increased the size to 85mm (from 50mm and 60mm for the first two versions), which is the largest size that would fit on the 100mm-diameter bed of my Monoprice Delta Mini printer.

The printing was much more successful this time, with very little stringing or blobbing.

Here is the front view of all the pieces. The knob is still the one from version 2, as I saw no need to reprint it.

The back view shows the side that was against the glass baseplate (except for the knob, which I forgot to flip over).

I was worried about installing the shaft crooked, and figured that if I just used a machinist’s square, I’d end up supergluing the tool to the stamp. So I printed out an alignment jig:

The front view shows how the alignment jig holds the shaft directly in line with shallow hole in the back of the stamp.

The top view shows how I used 5 cylinders as to fit snuggly around the stamp to hold it in a fixed position.

The hole in the alignment jig closed up a tiny bit, so I held the metal rod with vice grips, heated it, and shoved it through the hole to make the hole just big enough.

Unfortunately, the only superglue I had in the house was several years old (though in an unopened little tube) and it did not set when applied—it was still soft after 15 minutes.  I’ll have to get some more superglue (or other quick-setting strong adhesive) tomorrow to attach the shaft to the stamp.

2019 July 14

Shakespeare cookie cutter

Filed under: Uncategorized — gasstationwithoutpumps @ 14:49
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I have been trying to create a cookie cutter and stamp of Shakespeare’s head on my 3D printer.  I started by hand tracing one of the engravings of Shakespeare’s head using inkscape, to get a simplified line drawing:

The tracing looked good to me, but there may still be too much detail for a cookie cutter.

I decomposed the drawing into two parts: the outline and the internal lines (as shown by the colors).  I then used OpenSCAD to create three designs: a stamp for the embossing the lines, a cutter shell to cut the outside edge, and a knob for putting on the other end of a shaft for the stamp.  I had to install a new version of OpenSCAD, because the old one I had could not import splines.  The new one does, but gives no way to control the number of polygons created, so I often had 10-minute waits as it tried to generate the geometry.

My first attempt (to make a 5cm cookie) was a miserable failure, because the holes for the shaft closed up, being almost 1mm smaller in diameter than specified. Also the thin lines for the stamp ended up being too thin and too close together (particularly for the mouth), so the printer ended up blobbing them together.  The design might have worked with a higher-quality printer, but the almost any filament printer is going to have trouble with 0.5mm wide ridges that are 2mm tall.

My second attempt widened the lines and separated them a little, increased the cookie size to 6cm, and added some compensation for the spreading that was closing the holes.  Here are the parts:

From left to right, we have the stamp, the cutter, and the knob. The knob has been fitted with a 5cm ⅛” stainless-steel rod and a 4cm spring.

The parts looked much better this time, and the shaft fits comfortably in the holes in the knob and the stamp, though I will need to find a good glue for attaching the PLA and the 316L stainless steel.  I don’t think I want to use a 2-part epoxy (I have trouble mixing small quantities), but standard superglue may be too brittle—I’ll probably try it anyway, if I have any that has not solidified in the container.

Both the stainless-steel rod and the spring are leftovers from previous projects: Two-electrode vs. four-electrode impedance spectroscopy and Physics Lab 4: spring constants results.

I did one trick in Cura to save some printing time.  Rather than doing 100% infill for the whole stamp and knob, I used only 20% infill, but requested a thick top layer for the stamp and bottom layer for the knob—thick enough to be solid down to the end of the shaft.  I also requested thick side walls, so that the sides of the hole were solid. The reduced infill doesn’t save much on the stamp, where the hole for the shaft is rather shallow, but it made the knob substantially lighter and somewhat faster to print.

There were still some problems with stringing and blobbing around the eyes and mouth:

The eyes and the mouth still have serious problems with stringing and blobbing.

I tried trimming off the excess plastic in the details and found that the top few layers of the stamp delaminated too easily.  Things look a bit better after the cleanup, but the stamp no longer has uniform height ridges, with a variation from 1.5mm to 2.5mm high.

After cleanup, the stamp looks better, but the details still seem to be too small for cookies, and the printing is too messy.

I’m not sure what my next step is on the design is.

  • I could make a larger print (up to about 10cm), which might make an Instagrammable cookie, but would be a bit large for a really useful cookie cutter.  Even then I’ll probably have problems with stringing and blobbing on the fine details.
  • I could try to simplify the eyes and mouth further, to reduce the need for fine details.  I’m not much of an artist, so I don’t know how successful I can be at that, but I think it will be essential for a usable stamp.

I’m feeling now that I should have been less ambitious for my first cookie-stamp design (maybe even doing a simple cutter, rather than cutter and stamp).

2019 July 7

3D slug heart

Filed under: Uncategorized — gasstationwithoutpumps @ 18:34
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Earlier today I posted about adding a ring to scanlime‘s banana-slug design on Thingiverse by merging two STL files in Cura.  Today, I tried using the “include” command of OpenSCAD to get a properly merged STL file that I can post to Thingiverse.

The OpenSCAD code is quite simple:

module torus(big_radius=3, small_radius=1, big_fn=100, small_fn=30)
{   rotate_extrude($fn=big_fn)
    translate([big_radius,0,0])
    circle(r=small_radius, $fn=small_fn);
}

union()
{
    import("slug-fixup.stl",convexity=5);
    translate([-15,27,0])
        intersection()
        {   translate([0,0,1]) torus(big_radius=3.6, small_radius=2);
            translate([0,0,50]) cube(size=[100,100,100], center=true);
        }
}

I decided to go one step further and make a “slug heart” as suggested by my wife—it would be good for IEEE to sell at Valentine’s Day next year:

module torus(big_radius=3, small_radius=1, big_fn=100, small_fn=30)
{   rotate_extrude($fn=big_fn)
    translate([big_radius,0,0])
    circle(r=small_radius, $fn=small_fn);
}

module slug()
{    translate([-18,0,0]) rotate(a=[0,0,-12]) import("slug-fixup.stl",convexity=5);
}
union()
{
    slug();
    mirror([1,0,0]) slug();
    translate([0,25,0])
        intersection()
        {   translate([0,0,1]) torus(big_radius=3.6, small_radius=2);
            translate([0,0,50]) cube(size=[100,100,100], center=true);
        }
}
slug heart jewelry

View of the heart showing the ring for hanging it. This was printed at “draft” resolution (0.2mm/layer)—the jewelry will look better with 0.1mm/layer

slug heart jewelry

View of the heart showing the interior heart shape. I still only have green filament, but the slug will look much better in gold.

The slug-heart pendant weighs 13.46 grams in draft mode—I suspect it will be a similar weight for the final printing when I get the gold filament.

UPDATE 2019 July 7: I released the design as https://www.thingiverse.com/thing:3735198

3D slug printing

Filed under: Uncategorized — gasstationwithoutpumps @ 14:39
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I used my Monoprice Delta Mini 3D printer again yesterday, after a long break since the last usage.  My wife wanted a banana-slug charm to hang on her new mustard-yellow purse—she liked the color and size of the 3D-printed slug I had bought her from the UCSC IEEE chapter, but it did not have any easy way to attach it to the purse.

I found the design on Thingiverse by  scanlime, and checked the licensing (CC by 3.0), which only requires attribution, even for commercial uses.

I wanted to add a ring to the slug, so that it could be attached to a keyring.  Unfortunately, the design is only available as an STL file, and I’ve been using OpenSCAD, and I forgot that OpenSCAD has an import option for importing STL files, so I did a crude hack instead:  I made a ring in OpenSCAD, exported it as STL, then placed it in Cura overlapping the slug STL file.  When I sliced the models, the two files were merged producing a single gcode file, that printed as a single object. I think I want to see if I can also use the “include” command and get a properly merged STL file that I can post to Thingiverse.

I printed the model with 0.1mm resolution (finer than the resolution used for the IEEE printing, but I was not trying to produce slugs in sufficient quantity to sell them, so a slower printing to get a smoother surface was fine for me).

The gold slug is the one I bought from the IEEE student chapter, and the green one is the one I printed with the added ring.

The green color is obviously not suitable for banana slugs, but I’ve ordered some gold filament to print the slug properly.

One interesting side effect of slicing two overlapping models is that the exterior wall of each model was preserved, so that there were interior lines in the finished slicing corresponding to the original exterior walls.  This is an interesting, if somewhat awkward, way to get Cura to create specific interior structure, in addition to the generic interior fill patterns that it uses.

I have ordered two different gold filaments: Hatchbox Gold, which is what the IEEE slug was printed with, and CC3D Silk Gold, which should be shinier.  I’ve also ordered some hardware for attaching the slug to the purse (split rings and lobster hook).  I’ll have enough filament to do hundreds of slugs, since it only weighs 6.51g (not that I plan to make more than a handful—one in each color for my wife, and maybe another one for my backpack). The extra shiny gold filament can be used to make costume jewelry for WEST Performing Arts perhaps.  The filament costs a little over 1¢/gram, so the only real cost is the design and printing time.

Incidentally, the photographs were taken using another recent acquisition: a large Shibusa Photo Studio in a Bag, which I got from American Science and Surplus.  I think that the reason they were marked down is that the sides are so warped that they unsnap under the weight of the top.  I managed to make the thing work by using binder clips to insert some MDF pieces to stiffen the sides.  I think that I want to cut a couple of permanent MDF pieces that are exactly the right size and shape to support the top cleanly.  It would probably be best to use a laser cutter, but I’ll probably just use my scroll saw.

UPDATE 2019 July 7: I released the model as https://www.thingiverse.com/thing:3735186

2018 August 29

3D printed names

Filed under: Uncategorized — gasstationwithoutpumps @ 11:57
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To explore OpenSCAD and 3D printing further, I have made two more objects: a key holder for my home and office keys and a nametag.  I’m not planning to put these items on Thingiverse, since they have my name on them and would need to be customized.

The key holder was printed as two plates with holes 65mm apart. One hole had a round surround to accept a socket-head M3 screw, while the other hole had a hexagonal surround to accept an M3 nut.

The basic idea of the key holder is simple: two identical plates held together with M3 stainless-steel screws, with the keys capable of rotating on the screws. The hexagonal socket for the nut was just a little tight, so I had to hammer the nuts into the plate, which turned out to be a good thing, as the nuts are then held firmly by the plate.

I printed a textured surface by designing in shallow V-shaped grooves, and removing my name somewhat deeper. My first attempt printed the lettering and grooves on the top of the print, which resulted in a rather rough surface, due to all the retractions made between printing the separate islands. My second attempt printed face down, to get a smooth surface as seen here.

The keys fold out like a utility knife and provide a more convenient handle for turning the key than the usual small tab. I’ve deliberately erased the information-bearing part in the picture of the key.

Because the name did not stand out well, I tried painting the recessed areas with acrylic paint (no primer). The paint does not stick all that well to the bare PLA, and I got some paint stuck in the little crevices on the surface outside the letters. It looks ok from a distance, but closer up it is rather messy, as can be seen in the photo above.

The key holder holds 6 keys—3 at each end. The keys were not of equal thickness, so I added some 3D-printed washers with the thinner stack of keys. I printed several washers in different thicknesses (1mm to 3mm in 0.5mm steps), and tried different combinations until I got a pair that provided the right spacing. Putting the spacers outside the keys seems to work better than putting them between the keys.

I’m still not sure about the wisdom of having my name on my key holder—it makes it easy for someone to return my keys if I accidentally leave them somewhere, but it also makes it easier for a thief who finds the keys to figure out where they are keys for! I haven’t lost my keys or had them stolen in my 32 years of living in Santa Cruz, so I’m not too concerned about either outcome.

One problem I have noticed with the key holder is that the stainless-steel screws can work loose, particularly from repeated use of the bike key, which has high friction to the screw passing through it. I may want to get a little threadlock to reduce the chance of the key holder coming apart accidentally.

The nametag is thinner than the plates of the key holder (2mm instead of 4mm), and printed with finer layers, but its diagonal size (103.8mm) is almost the largest that can be printed on the Monoprice Delta Mini (which has a 110mm limit).  It took about 2 hours to print.

I printed this only 2mm thick with the lettering recessed 1mm. Once again it was printed face down and I tried painting the recessed areas with acrylic paint.  I had a little less paint in the crevices around each letter, but still enough to look a bit messy.

The nametag was slightly too large for the holder I had designed it for (probably due to a combination of spreading of the first layer and my not allowing for the 2mm thickness), but it works ok in this somewhat oversized holder.

The nametag “worked” but does not look very good—I think that a maker would be better off with a PC board or laser-etched nametag, either of which could provide much better quality.

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