Read the plans, study the build drawings, research, ask questions and make sure you think about how the pieces will go together!
I wasted about three evenings worth of work that I didn't have to because I didn't clearly understand the order in which I should have been riveting the lower rudder skeleton parts together. It's fixable as most things in the build are, the only cost is time and money, in this case about a week and $60. Lesson learned. That's part of it, it's not if you will screw up, it's when and how much time and money will it cost.
I was advised to start on the rudder first because it was complex enough to make you think and really learn the build and plans yet simple enough parts wise to be able to recover fairly quickly and inexpensively from a error like this one.
So what did I do? Unfortunately I started to rivet the lower rudder skeleton with the whole assembly put together. This put the rudder horn brace on and made it nearly impossible to rivet the large rudder spar doubler, nut plate, etc, set of rivets because I was trying to get a bucking bar inside the lightening hole that is part of the rudder horn brace, R710. That little voice in my head kept saying 'no way are guys doing this...' I should have listened to that little voice earlier.
So BE CAREFUL in this space, DO NOT DO what I did which was to try to rivet the whole thing as assembled. Instead what you should do is to rivet the lower rudder skeleton structure together in this order:
Cleco everything together EXCEPT the R710 rudder horn brace. That part should be riveted to the structure LAST!!!!
So here's a suggested order:
Rivet R606 to R802PP including R717 (the shim) through the rudder horn R405PD and through the lower rudder rib, R704.
THEN when that is finished, you need to decide whether you will use pop rivets for the 4 skin rivets on each side of the rudder horn brace R710. You need to make this decision BEFORE you start the final riveting of the rudder horn brace to the rest of the lower rudder skeleton structure. The plans do not make this clear. Reference the plan drawings, they allow you to sub CS4-4 blind rivets for these four holes on each side because it is difficult to get the skin riveted to these holes due to the R710 brace structure getting in the way! If you do that, you will need to drill those holes to a #30 and re-dimple for that size. Again the plans don't explicitly spell this out. The good news is that if you followed the instructions, they told you to drill these holes to #40 and dimple already. So this can be enlarged and re-dimpled pretty easily.
So with all that riveted together, insert the R710 rudder horn brace and rivet it into the structure with the three vertical rivets that join it to the rudder horn and bottom rudder rib.
That's how it should be done. Lesson learned. Fortunately I was able to save the rudder spar, doubler plate, shim and even the lower rib tip by drilling out the rivets. That means I only need to remake the rudder horn brace and rudder horn. Easy enough and not that costly. Just a little time to prep and paint those parts.