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Archive for August 19th, 2013

Storm Door Latch: Repair Parts

The discussion following that post on getting feature coordinates from an existing part reminded me of an old project that I’d written up for Digital Machinist: making repair parts for the half-century old storm doors on our house. Here’s the whole latch, with a replacement drawbar and cam:

Latch Assembly

Latch Assembly

The other side of the drawbar and cam:

Door Latch Parts

Door Latch Parts

An early version of the drawbar that engages the latch strike and gets pulled by cam:

New and Old latch pulls

New and Old latch pulls

Three iterations on a cam; the messed-up one in the center, IIRC, helped track down an EMC2 bug:

Latch Cams

Latch Cams

Now that I look at it again, there’s nowhere near enough meat around that square hole for a 3D printed plastic part… so the notion of printing the complex part of the cam and adding wear bars along those ears just isn’t going to work.

I made a fixture for the Sherline CNC mill to hold the drawbar for inside milling:

Latch pull - Inside milling

Latch pull – Inside milling

Then a block screwed down in the middle clamps the drawbar in the same place for outside milling:

Latch pull - Outside milling

Latch pull – Outside milling

The square post in the left rear corner holds the cam:

Latch Cam - First Attempt

Latch Cam – First Attempt

Note that I had to file the square hole before milling the cam shape, which meant that if the CNC process screwed up, all that handwork went into the show-n-tell bin… which I’m not going to show you.

I used an early version of the grid-overlay technique to map out the drawbar coordinates; this was an illustration for the column:

Latch Pull Dimensions

Latch Pull Dimensions

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