Tuesday, August 5, 2025

Doh! A Delicious Dish of Dumb Dumb!

Alright.  I'm only posting this because of the blatant error in my own reverse engineering.  I had a Coleman pop-up canopy, with fancy "push button" locks and unlocks.  It's really not bad - it's survived for 10 years with only minimal issues.  (Two years ago, one of the locking mechanisms on one leg wouldn't release.)  Here it is in all it's glory (still in it's bag).
 

This year, that same locking mechanism released (perhaps a better term is it fell apart).  Since I had silver filament and these were gray, I thought, what could I lose?  I'll see if I can draft and model up a replacement part, and print it.

I started out by taking the few remaining parts off to see what was broken.  This is a pretty ingenious device.  I'm impressed with the design (but not so much the implementation).

The broken part is circled in red above.  A few more photos, just to make sure :


It is time to create the model.  I whipped this up in FreeCAD :


About 50% done (I'm doing 100% in fill so it is solid), I picked up one of the parts, and realized - I didn't look deep enough.  There are two locking tabs on each end (I got both of those), and... recesses in the mating part where there were supposed to be four more locking tabs on the sides.

Really?  I play the part of an idiot VERY well, sometimes.  I'm missing the ones in green here.  Notice, I had them listed as an alignment pin.  Looking closer to the original, and these locking tabs had broken off (three of the four were down to the plate, one was half height, and I built all four off of that one).

So, back to the drawing board. I simply copied one of the two tabs and positioned the four new instances.

Okay, we can try printing this once more. Here we go.  8 hours and 38 minutes.

Alright.  The overall length should be 2.904", but the final print came out at 2.890.  In Cura, it shows 73.6, which is about 2.898", so we're losing about 0.008" in the print, and Cura is also not getting sizes from the STL file with much accuracy from FreeCAD.  That should be just fine, really, as long as I remember to adjust the size by 100.48% before slicing.

It looks good, the clean up was good (the aborted print gave me an idea of how this was going to be cleaned up), and with some fine adjustments (hobby knife and a Dremel for some inside work), it works exactly as I'd hoped.

I went to install it, and definitely had to trim a few things up (e.g. more clean up) in order to get it to install, but hoo-yah!  Canopy is back up!

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