By Joel Thompson
As a mechanical engineering student, I have a serious interest in firearms design, and I’ve been wanting to develop my CAD-modeling skills for a while now. So, I thought I’d kill two birds with one stone. I took one of my handguns (not my carry handgun), disassembled the slide and started measuring it with a $10 pair of Harbor Freight calipers and a basic set of fillet gauges, taking careful consideration into how the part may have been machined, and why each feature existed. I then started modeling the slide in SolidWorks, the same CAD software used by Smith & Wesson (I believe). I pecked at the model a little bit at a time until a couple days ago I created a “finished” model of the slide . . .
One way to know how accurate the model is compared to the real part is to measure its weight. SolidWorks allows you to define what material the part is made from. It then uses this information to calculate its mass properties. According to SolidWorks, my model would weigh approximately 304.5 grams in the real world.
I then took the real part and weighed it on a $10 Harbor Freight scale: 303.4 grams.
That works out to a 0.4% difference, or 99.6% the same! Now this method can really only tell you if your model is in the ballpark of being close to the real thing. I may have the right combination of features, however, if they are in the wrong place then the slide won’t work. So, how close is my model to being accurate? There’s one way to know… make it.
Yesterday, I fired up my 3D printer and let it run. Three hours and twenty-five minutes later I had a finished part.
I popped off the raft, cleaned out the supports, and attempted to assemble it. Well…it worked! Sorta… The fit was very tight, this is to be expected with 3D printers. The 3D printer is great at making parts, but it doesn’t handle tight tolerances very well.
Here’s a reminder of why gun manufacturers don’t make slides out of plastic, and why you shouldn’t either.
No, I didn’t test fire it. In order to have the 3D printer to finished in a timely fashion, I reduced the infill of the model to 2%. In other words, the plastic slide is 98% hollow inside. After playing with it for a while, the barrel slammed into the breech face hard enough to cause the devastation you see.
I also wasn’t able to clean the supports out of the striker housing or the extractor cut well enough to attempt assembling a full assembly. However, after widening a few of the spaces with my knife, I was able to insert my barrel, guide rod/spring, back plate, rack the slide, and lock it back. Everything about its function seemed to be correct, including the trigger reset.
One of the great things about being able to prototype parts with a 3D printer is that you’re able to notice minor details you didn’t notice before. For example, the slide was about forty-thousandths of an inch short (0.040-in). This was because my cheapo calipers weren’t long enough to measure overall length, and I had to rely on an old ruler. I also discovered that the barrel hole cut had an approximately 3º cant to it that I didn’t notice initially.
Without it, the barrel couldn’t move freely in the slide. A quick cut with the knife, and the barrel was in motion. All-in-all, I had somewhere around 25 hours invested in modeling the slide, most of that spent measuring, re-measuring and wondering, “how on earth am I going to model that?” Nevertheless, I successfully completed the model unaided.
While my model has yet to reach 100%, I’m satisfied with the end result. I’ve learned more about the handgun in those twenty plus hours studying it than I have in the last few years of owning it. More than that, I’m satisfied with my rapidly improving modeling skills.
This was easily the most complex model that I’ve ever created with close to 100 individual features (that number could probably come down if I had to start over again). Less than a year ago, I could barely model the simplest of parts. I’d call that a success.