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Wednesday, August 27, 2014

Brake/Rudder pedals - part 4

Bracket testing (6.0 hrs)

No soon had we finished machining the first short bracket, than Wade and I started beating the crap out of it with a rubber mallet! 

Though silly, the abuse might well represent the one inflicted by boots stepping on it over the years, and highlighted the fact that the top rails and webbing needed to be made thicker. Actually, they should have been thicker already, but I had made a drawing mistake while reducing its dimensions in CAD from 12” (30 cm) to 9.5” (24 cm), and didn’t catch it until we had already machined the bracket.


Because this had been Wade’s first foray into CNC, I decided I let him keep the bracket as a souvenir of his hard work. In turn, he promised to send me picture of the mangled bracket next to the unit he had purchased. 

Short bracket after being struck with a rubber mallet multiple times, next to Wade's (any similarity between brackets is mere happenstance). Photo courtesy of Wade.

Meanwhile, I decided to do some load testing on the 12” bracket I still had in the EZ shop, and depending on the outcome, make additional changes.

Overload testing of the 12" bracket

Satisfied and encouraged by the latest testing results, I moved on to machining the first one incorporating a few improvements (mostly increased webbing thickness, and edge distances)

This beauty will end up in the nose of my plane shortly.

The chamfering came out just perfect

3 bolts will hold it down, and its position will be adjustable to plus or minus 1" (2.5 cm)

It will attach to nuts, secured to an aviation-grade plywood, itself floxed and glassed to the nose floor.

A common misconception about CNC is that you can just press the start button, then walk away from the machine, but that's not even remotely true, at least not at my level. 

Not including the weeks spent designing it, and testing its geometry on the computer, this bracket took over 6 hours to produce (2 hours per side x 3).

What made the process so slow were the 6 repositioning moves necessary due to its size (compared to my mill) and shape, and the countless tool changes. Actual milling time added up to "only" 3 hours! 

Time lapse bracket machining

Master cylinder attach point

Sadly, once installed it might never be seen again.

Here is the 9.5" bracket next to the 12" one (aka "the original").

"Shorty" right below "the original"

Note the thicker webbing. No part of it is now any thinner than 0.200" (5 mm).

Sturdier and even lighter new design

Looks and strength, what else can a bracket hope for?

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