Monday, February 18, 2008

Finished Shoulder Discs

I had originally planned to work on the front vent harness assembly today, but I remembered that I really can't fit it into the frame until the frame is glued up, because I need to figure out how far forward the vents must rest so that they will emerge through the skins by about 1/4".

Instead, I decided to finish up work on the shoulder discs. The steps taken here follow those in my downloadable wooden leg tutorial, and are copied from Mike Senna's approach.

I started by marking up the discs. First, I drew lines at 60 degree intervals.

Next, I scribed concentric circles with a compass. The inner two circles outline the gas pipe holder (to help center it during later drilling), the outer circle is drawn to accommodate enough space from the outer edge for washers to go where six more holes will be drilled.

I took the discs and gas pipe holders to the drill press. With the gas pipe holder centered as indicated by the drawn circles, I drilled through the 1/4" holes in the gas pipe holder, and through the disc underneath. Four holes are drilled for each gas pipe holder on each disc. As each hole was drilled, I dropped a 1/4" x 2" bolt through it, to keep the gas pipe holder from moving.

After that, I used the gas pipe holder as a template for drilling the backing plate that is used to distribute the stress of the bolted-on gas pipe holder (and eventually, the gas pipe).

The last step was to drill six 5/16" holes along the outer circle I drew, at 60 degree intervals. These holes allow for the six bolts that will hold the assembly onto the leg, once the legs are built and ready to go. The bolts are 5/16" x 2". Placement of these holes is not ultra-critical, but it's good to get them as close to the mark as possible.

Both shoulder discs are done. I had cut down the bolts ahead of time during my build of droid #1, but I may have to cut down the bolts even further to allow the shoulder hubs to fit in the legs, we'll see. Either way, the discs are going to have to wait quite a while until I have wooden legs to attach them to.


Anonymous said...

How do you find the center? I know you started with the center but my round disks came with no exact center in the first place.

Victor Franco said...

Oops, I didn't see this comment until today (2/26/08). In my case, the center was defined by me when I drilled the hole and spun the disc with a nail through the center on the router table.

If one starts of with a predefined circle where the center isn't marked, a geometric construction can be used to find the center.

See, for example:

or Google "finding the center of a circle"