Layout Gauge: Too warm to work on the plane

By trade I work with binary files, electronics, and disassemblers however I have a fair amount of hobby experience with metal to include mills, lathes, and welders of all kinds. If I have to lay something out I am quite comfortable with layout fluid but as we know (or so I am told) blue Dykeem, calipers, and an awl don't mix well with the thin aluminum alclad skins of the airplane that I am building in my garage.

It is August in Virginia, and it is over 100 degrees outside so tonight was a good time for a basement shop project on the mill. A layout gauge capable of holding a xtra-fine tip sharpie was tonight's project. I started with a 1/2" by 3/4" by 6" long bar of 6160 aluminum.

I faced off the end and then marked out the bars mid-point as well as .30" in from the clean face. I put a .100" hole all the way through the bar. From there I put a #1 counter bore down the hole and stopped the shoulder roughly .10" from the bottom of the bar. I realize that I have not cleaned up the rest of the faces yet, but I am fine with that for now.  

From there I followed up the hole with a 'U' bit. The sharpie has a taper on it, so I fine tuned the depth of this hole by going back and forth between taking a couple tens of thousands off and then fitting the sharpie. I was looking for the sharpie to just barely clear the base of the bar because I still intended to face off the bottom of the bar at some point.

With the sharpie fitting well it was time for the next step of the project, a ruler built into the bar. The ruler will need to be accurately located after I make the slider bar, but for now I needed to mill a channel to bring the ruler flush with the bar.

With the ruler inset into the bar, the next step was to build a sliding block that will be used as the gauge. I intended this to work like a carpenters scratch awl, but used with sharpie instead of a roller wheel or nail. I took a piece of Delrin and milled a channel into it that fit the faced off bar.

The way I laid out the slider was 2 pieces. In doing this, I was able to easily make square corners in the channel, I also wanted to put screws into the face plate of the slider that would allow me to adjust the tension of the slider (and even lock it down). In my head when I started milling I was going to put a thumb screw onto the slider (like a caliper) however at this point I like the idea of using the face screws to adjust the tension/friction.

I made a face plate to fit the slider and drilled some #43 holes in the main slider and some #33 holes in the face plate. I then counter bored the face plate holes and tapped the main slider to accept 4-40 socket head cap screws.

That was it. A fun night in a cool basement. I still have to calibrate the location of the ruler at which point I will epoxy it in place. I also have to break the edges but for now this came out just as I wanted!