C-1212 Guide Blocks Installed

Been a while since anything meaningful has been done to the RV-12 but a handful of small tasks were accomplished in the last few days along with resolving a computer problem and rounding up a router and rounding bit … more on that later.

One of the last tasks to perform on the RV-12 prior to preparations for creating the fiberglass lay-up for the canopy fairing is to install the C-1212 guide blocks. The C-1212 guide blocks will assist the canopy to center itself when lowered so the tab on the guide plate is in alignment with the slot in the F-1254 support frame. The supplied guide blocks were measured and deemed close enough in size to not need additional cutting.

I took exception with the plans when it comes to drilling the two holes in each block. The C-1212 guide blocks are only 1/2" wide and the plans call for drilling the #19 holes 3/8" in from the edge of the block then machine countersinking the holes. If that were done, I believe the machine countersinking would bust out the edge of the block. Looking at ALL the drawings for the C-1212 blocks, it appears the two holes are dead center on the blocks. Van’s drawings have been good in the past showing exact hole placements, so I deviated from dimension in the plans and used the drawings as my guide …  the drawings show centered holes and this is where I ultimately drilled them after stewing about it for a day.

Using the drill press to drill the #18 holes in the C-1212 guide block.

Machine countersinking the C-1212 guide blocks for a #8 screw.

Completed C-1212 guide blocks … holes are drilled to #18 and machine countersink for #8 screws. There are four drawings of the C-1212 blocks on this page (three of which can be seen) and they all show the two holes in the blocks centered.

The plans instruct the builder to radius the edges of the blocks. This would involve quite a bit of sanding or filing and getting it to look remotely even would be a time consuming task. I decided to make the scary decision to use a router outfitted with a 1/4" rounding bit. I have a router at the southern outpost but didn’t want to take the time to drive all the way there and back, so asked around and Mike T. had one I could borrow. A trip to the local big box store was made to pick up a 1/4" rounding router bit.

On to the scary part … UNDER NO CIRCUMSTANCES would I recommend doing the following … but it was done as carefully as possible and yielded good results. Because the C-1212 guide blocks are so tiny I mounted them onto a scrap piece of plywood. One was a little shorter than the other so a little paper was placed under the short one so there would be no edge to catch on the deck of the router.

Both C-1212 blocks were temporarily mounted onto a piece of scrap wood end to end like this first one.

Both C-1212 blocks attached end to end onto the scrap of wood along with the paper spacer to make the height of both blocks the same. A pad was placed under the router to help keep it in place and it was clamped onto the workbench upside down using Stanley clamps. The depth of the cut was adjusted so the C-1212 blocks would only be cut by the curved portion of the router bit.

The long edges of the C-1212 blocks were run through the router bit on both sides along with the ends. The router did a great job of quickly creating tiny plastic flakes EVERYWHERE … along with nicely rounding off the edges of the blocks. The plans show the sides at the ends of the blocks also get rounded …. Unfortunately this needed to be done carefully by hand … so the blocks were removed from the piece of scrap wood and carefully run past the router bit. I was very pleased with the outcome … each block is nicely rounded.

Carefully making the rounding cuts on the ends of the C-1212 blocks. Make a pass and flip the block and make another pass. Of course, the same thing needs to be done at the opposite end of the block.

Rounding of both C-1212 guide blocks completed.

Measurements are given for the upper mounting screw holes on the roll bar so a cardboard template was marked for the hole placement at 3 3/4" up from the F-1254 support frame and 11/16" in from the outside edge of the roll bar. A block of wood was clamped onto the roll bar to make the outer edge measurement since the roll bar is rounded. Once the measurements are made for the left and right side, the upper holes are to be drilled to #30 and tapped for 8-32 threads.

Marking the positioning of the upper hole that needs to be drilled for the C-1212 guide block. Notice the wooden block established the outer edge measurement.

After center punching the hole locations, a tiny lead hole was drilled and then stepped up to #40 then to #30. A little care needs to be taken drilling the holes for the guide block. These holes need to be drilled perpendicular to the roll bar and the roll bar is at a slight angle … so a little care needs to be taken to drill into the roll bar as square as possible because these holes are going to be tapped.

Drilling the mounting hole to #40 … then onto #30.

After both upper holes for the C-1212 guide blocks are drilled to a final size of #30, the holes are to be tapped. The tap is screwed into the C-1212 guide block so the block can be used as an aid to make sure the hole is tapped squarely.

Tapping the upper mounting hole in the roll bar using the C-1212 block as a guide to keep the tap square to the hole.

After the upper mounting holes for the C-1212 guide blocks are tapped, the guide block is screwed onto the roll bar and a block of wood was again clamped onto the outside edge of the roll bar so the bottom of the guide block could be aligned with the outside edge of the roll bar. At this point, I clamped the guide block in position and ran a #19 drill bit through the bottom hole in the guide block and gave it a couple of spins to mark the center of the hole onto the roll bar.  Once the marks were made for the bottom hole placement, they were center punched and drilled to a final size of #30. Here again the tap was inserted into the guide block to help keep the tap square as the bottom hole is tapped.

Tapping the bottom mounting hole for the right C-1212 guide block for 8-32 threads.

Both C-1212 guide blocks installed.

The plans say there can be a little interference between the canopy and the bottom edge of the C-1212 guide blocks and if there is any to chamfer to bottom outside edge of the guide blocks. I have a slight amount on the left side and a little more on the right so will need to do a little chamfering of both the guide blocks during the next work session. Once the chamfering is completed it will be onto the canopy fiberglass lay-up.