Sat Dec 6 2008

Drilling rudder pedal bearing blocks

This evening I decided to work on fitting the rudder pedals. First thing to do was break out the F-6116 and F-6115 bearing blocks. You can see that the center bearing block is only 3 1/2 inches long whereas the side bearing blocks are 4 inches long.

After studying the plans for a bit I decided that I was going to make a deviation from the plans. The plans call for 3 1/4 inch center-to-center spacing for the bolts on the side blocks and 3 inch spacing on the center block. I want to have several positions available for mounting these bearing blocks and it was apparent that if I made each position half of the center-to-center distance more aft than the previous set of holes, the center bearing block hole spacing would become problematic. The only solution in my opinion is to use 3 inch spacing for all the holes. In the end I'll have adjustment positions every 1 1/2 inch. Confused? You'll see.

Even though the prints say these bearing blocks are 3/4 inch thick, there a bit shy of that.

This is important because I decided that the best way to drill these consistently was to make a drilling jig. Here's a scrap piece of .187 thick aluminum which I very accurately drilled to the dimensions shown.

Before drilling I wanted to see which bearing block was which and determine which side was up and down. The blind holes in the outer bearing blocks look like they're bored perpendicular to the surface, but they're not. The holes are bored at a very slight angle to match the taper of the sides of the fuselage in this area.

While I had this set up, I noticed that if I aligned the pedals on the left, the ones on the right aren't aligned. Hrmmm...

I clamped a piece of angle to one of the pedals...this one seems to be off by about 1/8 inch.

...and the other one is off about 1/8 inch the other way. I'll make a posting on Van's Airforce to see if this is considered normal. I might also call Van's on Monday.

Update: After getting some feedback from the folks on VAF, I'm not going to worry about this. The consensus is that once the plane is flying I'll never notice this little difference.

After marking the center of the block, I clamped my drilling jig flush to the edge of the bearing block (using another piece of scrap as a reference edge) and drilled a hole halfway through the center of this bearing block. We don't need a bolt to go here, but I'm drilling this position so that I can use it to position the drilling jig for the holes at either end.

Note that all of these holes are being drilled into the bottom surface of the bearing blocks. This is actually quite important because if I drilled through the top, the drill bit could drift by the time it broke out of the bottom surface and the holes wouldn't match up with the holes that I will be drilling in the stiffener angles.

After sticking a bolt in to hold the jig in position relative to the center hole, I drilled one end...

...then the other.

I repeated this process for the other two blocks. Because of using the drilling jig, these holes are perfectly centered and the spacing is also completely consistent.

Next it was time to drill the holes in the side stiffener angles which the bearing blocks mount to. The drawings say the forward most position allowed places the forward edge of the bearing block three inches from the firewall. Since my holes are 1/2 inch in from the edge (instead of 3/8 inch like the plans indicate) I marked the first hole location at 3 1/2 inches.

Since my drilling jig has the holes spaced .355 from the edge, but I need .375 edge spacing for this angle, I made some little spacers from a piece of .020 thick scrap.

I just wedged the spacers between the reference edge and the drilling jig so that these holes would be perfectly centered on the flange at .375 inch.

After drilling the first hole, I just used a cleco and clamps and moved the drilling jig along until I had 5 holes drilled. This gives me three pedal positions. The first is at the most forward allowable. The second and third are 1 1/2 and 3 inches aft of that, respectively.

Then I just transfer drilled these holes to the side stiffening angle from the other side.

As expected, the holes in the angles are a perfect match to the holes in the bearing blocks. The drilling jig did an excellent job. :-)