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Author Topic: Toolmarks on 3D printed pistol frame  (Read 1830 times)

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Offline kgarrison

  • Posts: 36
  • Gender: Male
    • San Bernardino County Sheriff's Department - SID website
Toolmarks on 3D printed pistol frame
« on: June 21, 2022, 03:44:04 PM »
Inspired by the recent 2022 AFTE presentation: Identification of Toolmarks Present on Additive Manufactured Components
By Corey Scott

I looked for some of these markings on a 3D printed pistol frame I received in casework. This photo is from two casts I took of the bottom of the trigger guard. I phased on a start/stop mark on the far side of the casts, then shifted the left cast over a few layers to see if the marks repeated with the photo'd results. Toward the left of the frame you can see the semi-circular marks which I'm assuming is from the nozzle as it starts to extrude the layers of the curved trigger guard.

Also attached is a photo of the trigger guard area. You can see several of the donut shaped start/stop areas from the nozzle in this photo.
« Last Edit: June 22, 2022, 10:15:50 AM by Wendy Gibson »
Kirk Garrison
Firearms and Toolmarks
San Bernardino County Sheriff's Dept.
Scientific Investigations Division
kgarrison@sbcsd.org

Offline Steven Pavlovich

  • AFTE Friend
  • Posts: 8
Re: Toolmarks on 3D printed pistol frame
« Reply #1 on: September 28, 2022, 01:26:39 AM »
Hi Kirk,

A very interesting article. Do you have a copy of the 2022 AFTE presentation by Corey Scott?

Best regards

Steve Pavlovich
PhD candidate (Mechanical Engineering)
+61 452161957    steven.pavlovich@research.uwa.edu.au
The University of Western Australia   
CRICOS Provider Code: 00126G

Offline kgarrison

  • Posts: 36
  • Gender: Male
    • San Bernardino County Sheriff's Department - SID website
Re: Toolmarks on 3D printed pistol frame
« Reply #2 on: September 30, 2022, 02:15:28 PM »
I only took notes, so no actual presentation from me. Here are the notes I took however. It also has the presenter's email.


Identification of Toolmarks Present on Additive Manufactured Components
[/color]Corey Scott[/i]
[/color]Additive Manufacturing
  [/color]CAD to STL file to Physical ObjectOr OBJ fileSTL file slices CAD into series of layersBuilds from base up7 main typesMaterial extrusion - most popular currentlyVat Photopolymerization - might be next trend  Material Extrusion[/font]
  [/color]Hobby grade 3D printer  Toolpath[/font]
  [/color]FDM tool path parameters1 infill, 2. Infill angle, 3. Infill width, 4. Perimeter, 5. Air gapImperfections on cylindrical surfacesHard to do true circle, has evidence of many small flat surfaces along circleEvidence of layer depositionCan be smoothed with sanding or other methodsstart/stop points for filamentstart/stop has layer stops, plate moves, starts next layer   Byproducts of Extruded Material[/font]
  [/color]Project for fingerprint model showed signs of repeatable striated marksSeems its when nozzle contacts printed partNozzles are cast, turned, and finishedDuplicated across 10 exemplarsChanged nozzleDifferent nozzle caused different, repeatable striated marksDiameter of layers should correlate to diameter of nozzle0.4 is most common, but other diameters existSeems like striated defects on parts could potentially be related back to nozzleAlso, tool to scrape off print from print bed, could transfer marks onto bottom of printed partscscott1@fbi.gov[/font][/email][/color]PLA and some of the other products react poorly to acetone, per FBI latent print processingDont use acetone-based products 
Kirk Garrison
Firearms and Toolmarks
San Bernardino County Sheriff's Dept.
Scientific Investigations Division
kgarrison@sbcsd.org

Offline Steven Pavlovich

  • AFTE Friend
  • Posts: 8
Re: Toolmarks on 3D printed pistol frame
« Reply #3 on: October 01, 2022, 12:17:50 AM »
Hi Kirk,


Thank you for your response. Your notes are very helpful.


Best regards
Steve



Steve Pavlovich
PhD candidate (Mechanical Engineering)
+61 452161957    steven.pavlovich@research.uwa.edu.au
The University of Western Australia   
CRICOS Provider Code: 00126G

 

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