updated with url experiments

README.md

@@ -2,9 +2,9 @@
 
 Rapid manufacturing of embossing tooling for permanently marking thin plastic.
 
-![101st_impression](img/emboss-today_101st.jpg)
+![101st_impression](img/url_multitest.jpg)
 
-![mfg_tool](img/mfg_tool.jpg)
+![mfg_tool](img/url_tool.jpg)
 
 ## need
 As part of our covid-19 face shield production efforts, we need to permanently mark units that end up in hospitals with a few basic identifiers: a manufacturing batch number and a shortened URL for assembly instructions. The Zund needs to spend its time cutting rather than marking, and doctors have complained about the smell of laser-engraved text.
@@ -40,4 +40,25 @@ The 101st test was performed on a scrap of 0.75 mm polycarbonate:
 
 ![101st_impression](img/emboss-today_101st.jpg)
 
-Further cycle testing should be done to test long-term durability.
+Later tests updated this process as follows:
+- 0.25 mm Cu
+- 5 mm letter height
+- no electrochemical deburr
+- sanding bottom rather than sides of letters
+- reflowing solder under letters rather than tacking sides
+
+This updated process was used to fabricate a tool with the Project Manus face shield URL, minus dots (as these were lost). Laser micromachining took 40 minutes, while manual assembly took roughly 30 minutes:
+
+![url_tool](img/url_tool.jpg)
+
+The tool was mounted with double-sided tape on a cold rolled mild steel bar, which was held to the press using NdFeB magnets (flipped sideways above for visibility). The tool produced acceptable results in 0.020" PETG:
+
+![url_multitest](img/url_multitest.jpg)
+
+Embossing was also performed on stock with both layers of protective film still in place; prior to film removal, the URL was legible:
+
+![url_protectivefilm1](img/url_protectivefilm1.jpg)
+
+However, legibility was reduced once the film was removed, suggesting film should be selectively removed from shields prior to stamping:
+
+![url_protectivefilm2](img/url_protectivefilm2.jpg)