JetFlex Revisited – Ammonia = Better Cleanup

After doing the final preparations for primer this morning, the parts prepared over the last few days were primed with Akzo primer. After doing a disassembly of the HVLP gun followed by a good cleanup, the gun was reassembled for a round of JetFlex.

Another batch of JetFlex was prepared using the same 15% thinning with distilled water as last time. The parts that will show inside the cockpit were then sprayed. This time two light coats were sprayed waiting 15 minutes between coats. The results look OK but I feel there is room for improvement. Think the 1.4 mm spray tip on the HVLP gun is barely big enough for this paint. Unfortunately, the next size larger tip available for the HVLP gun is 1.8 mm which may be too big … but tempted to order one just to see if it makes for a silky smooth finish.

Frequent readers of the DOG Aviation Blog may remember the first time JetFlex was used, distilled water was run through the HVLP gun but basically did little to clean the inside of the gun ... so the equipment cleanup was a bear. After spending a lot of time cleaning, it was discovered the JetFlex application data sheet suggests using a water and ammonia solution for cleanup.

This time, things were done differently. A 50/50 mixture of distilled water and ammonia was prepared prior to painting. The measuring ladle was not left in the air for 5 minutes like last time and was immediately placed in the ammonia solution to soak. It was immediately apparent the cleaning solution actually cuts through the paint. Frankly, I was a bit shocked at how well it worked compared to the plain water used last time.

For this spray session the HVLP gun was not run dry and when the last piece was finally sprayed with JetFlex, the ammonia cleaning solution was immediately run into the gun. This time the gun cleanup was no more difficult than when using solvent based paint … in fact, it may have been easier. The ammonia solution did a splendid job of cleaning the inside of the gun! I also feel not running the spray gun dry also plays a big part in easy cleanup … because JetFlex forms a film almost instantly so if the inside of the gun is kept wet, there is really no film buildup inside the gun to speak of.  That said, the ammonia solution will still cut through the film with just a little elbow grease.

Now that the cleanup issue has been resolved, I’m very pleased with JetFlex but feel there is room for improvement in my spraying skills and/or using a larger spray tip. Think it is time for the DOG Aviation procurement department to acquire a larger tip for the HVLP gun to see if that improves the final product.

More Parts Dimpled – Ready to Prime

After a little more smoothing of edges on the twelve W-1275 corner skins, all of the rivet holes in the skins were dimpled for the flush rivets being used on the RV-12 project. Because the skins have a curve, the small diameter female dimple die was used so the skin would be distorted as little as possible. The W-1274-L&R corner skins also required dimpling for flush rivets and were dimpled next.

Using the pneumatic squeezer outfitted with #30 120 degree dimple dies to dimple one of the twelve W-1275 corner skins.

Dimpling one of the W-1274 corner skins for flush rivets.

 

Looking forward in the plans, there were only two other components that required attention before all the major components in Sections 20 & 21 would be processed. Decided to move forward and finish up the two pieces so all the components will be ready to go. The W-1236 step attach angle came predrilled on one side but required being separated into four pieces. After the four parts were separated, they were deburred and marked for additional cutting.  The plans call for cutting off an edge of the un-drilled side of the angle. The pieces were marked at 1” per the plans, run through the band saw and deburred on the Scotch-Brite wheel.

 

Using the band saw to separate the four W-1236 step attach angles.

 

The last piece prepared to comple all the components for section 21 was the F-1251-L&R nutplate brackets. Here again, the brackets came as one piece and required separation on the band saw followed by a smoothing on the Scotch-Brite wheel. The plans also called for machine countersinking the #40 rivet holes for the nutplates.

 

                                    Using the countersink cage outfitted with a #40-100 degree bit to countersink

                                    the nutplate rivet holes in the W-1251-L&R nutplate bracket.

 

The F-1251-L&R nutplate brackets and the F-1236 step attach angles complete the parts preparation for section 21.

 

The last batch of parts worked on the last few days will be cleaned with Acetone, scuffed up with Scotch-Brite pads and primed. The weather forecast is for a perfect painting day tomorrow so will try to make the most of it and get things primed early and perhaps also spray a little more Jet-Flex if all goes well.

 

Parts prepared the last few days now ready for the DOG Aviation paint department to cleaning and primer.

RV-12 Fuselage Bottom Skin Receives Dimples

The RV-12’s F-1276 bottom skin was fished out of the shipping box so it could be prepared for primer. Once the bottom skin was out of the box, decided to first use it to mark where it will be overlapping the F-1274 corner skins that were deburred yesterday. The plan is to prime those areas that will be overlapped to provide added protection from the elements.

Marking the area where the W-1276 fuselage bottom skin overlaps one of the W-1274 side skins.

 

Once the overlapping areas were marked, the blue protective film was removed from the edges of the W-1274-L&R skins by using a soldering iron to melt the plastic film. While the soldering iron was still hot, it was used to melt the outlines of the doubler plates that were drawn onto the bottom skin weeks ago. The reason for this is because the doubler plates were too thick to dimple and were machine countersunk for flush rivets ... therefore all rivet holes in the W-1276 fuselage bottom skin associated with the W-1268 doubler plates will not be dimpled for the flush rivets being used to build the RV-12.

Using a PVC pipe to aid in the removal of the blue plastic film from the W-1276 fuselage bottom skin.

Remaining blue film shows the areas where the rivet holes in the W-1276 are associated with the W-1268 doubler plates. No dimples will be created in these areas because the W-1268 doublers have been machine countersunk for flush rivets.

 

After removing the blue film from the W-1276 bottom skin, the dust was blown off Pete’s C-frame (which has not been used since last fall) along with the mallet. The C-frame was outfitted with #30-120 degree dimple dies for the flush rivets being used on the project. After donning eye and hearing protection, the pool noodles were placed under the W-1276 bottom skin to elevate it to the level of the dimple dies and the W-1276 skin was beat into submission … leaving perfectly formed welts at every rivet hole.

Whacking the C-frame plunger (outfitted with 120 degree dimple dies) with a mallet to create dimples in the W-1276 fuselage bottom skin for flush rivets.

Creating the last 120 degree dimple in the RV-12’s W-1276 fuselage bottom skin for flush rivets.

Countersinking W-1268 Bottom Skin Doublers

Today consisted of several short work sessions working on the six F-1204Z L&R bottom stiffeners and the W-1268A-E bottom skin doublers. The six F-1204Z bottom stiffeners come all attached to one another and required being run through the band saw to separate the pieces. Once separated the pieces were deburred and are now ready for priming.

The ten W-1268A-E bottom skin doublers were separated and deburred a few weeks ago when it was necessary to determine which rivet holes reside above the doublers. At that time, all the rivet holes on the bottom flange of the ribs were dimpled except for those holes that are directly above the W-1268 doublers.  The reason for this is because the doublers are too thick to dimple so all of the holes in them will be machine countersunk for the flush rivets being used for the DOG Aviation RV-12 … as such, the rivet holes in the ribs above the doublers will not receive dimples.

The only thing that was left to do to the W-1268 doublers prior to priming was to machine countersink the doublers to accept flush rivets.  A small board was clamped onto the workbench and used as a backstop to secure the doublers onto during the machine countersinking.

                                       Using the countersink cage outfitted with #30-120 degree bit to machine
                                        countersink one of the W-1268 bottom skin doublers for flush rivets.

The six W-1204Z bottom stiffeners and ten W-1268 bottom skin doublers ready for the primer department.

Preparing Fuselage Corner Skins

Having successfully primed the last batch of fuselage components, decided to take advantage of the upcoming good weather and forge on with the preparation of more fuselage components. When the time comes to assemble the lower fuselage, it should take shape rapidly because almost all the parts have been deburred, dimpled or countersunk as necessary and primed.

The only lower fuselage components remaining to prime are the fuselage corner skins, some doubler plates, a few stiffeners and the bottom skin.  Each side of the fuselage receives six W-1275 corner skins labeled A through F. For each of the six types of corner skins, there is a left and right version ... so the skins must be separated. These skins are overlapped and become the transition between the fuselage bottom skin of the fuselage's side skins.

The six W-1275-A through F corner skins require separating on a band saw to obtain the left and right skins.

                                Using the band saw to separate the W-1275A corner skins into left and right skins.

After all the skins were separated, all twelve corner skins were dressed up on the Scotch-Brite wheel to smooth up the edges. Because of the way the W-1275 skins overlap one another decided to remove the blue protective film with a soldering iron so the area of overlap can be primed as well.

                Using a soldering iron to melt the protective film along the edges of the overlapping W-1275 corner skins.

                                    Protective film removed from overlapping edges of W-1275 corner skins for primer.

The W-1275 corner skins will also require having all holes dimpled for the flush rivets being used on the RV-12 project but that will be in a future work session.

The 30 Mile Dimples

There are six F-1212 step ribs, three left and three right. The six F-1212 ribs required deburring and some dimpling. Per the plans, the two F-1212 ribs that will become the centermost two ribs receive 120 degree dimples along the entire top flange of both ribs … because they will become a portion the tunnel and a removable cover plate will sit on top of them. The bottom most rivet hole in the forward flanges of the outer most rib on each side also received a 120 degree dimple. In addition, all of the F-1212 L&R ribs received 120 degree dimples in all the rivet holes of the bottom flange to accommodate the flush rivets being used on the RV-12 project.

                Using the Scotch-Brite wheel to remove burrs and smooth edges on one of the six F-1212 step ribs.

                                                 Dimpling one of the F-1212 ribs with the pneumatic squeezer.

                    Bottom flange of all F-1212-L&R ribs were dimpled for flush rivets being used on the RV-12 project.

And now for the 30 mile dimples … overall the DOG Aviation procurement department has done a great job amassing the necessary tools and specialty items required to bring the RV-12 to fruition. One tool which was overlooked was a set of #40 dimple dies for 3/32” rivets that are the type with the holes in them used with a hand rivet puller … or the type that has the dimple dies welded onto the end of a vice grip. The shop is outfitted nicely with various dimple die sets for #30 rivets but only has one set for making #40 dimples using a typical rivet squeezer with a yoke.

As luck would have it, the W-1226-L&R floor pans required quite a few dimples … however, there were two dimples on the front edge for a nutplate that the tools in the shop just could not reach. The edge on this piece of metal is bent way more than 90 degrees so there is not enough clearance for the squeezer yoke to get low enough to allow the dimple die to align with the hole.

This photo shows how the tight bend interferes with the squeezer yoke preventing the dimple die from getting low enough.

Tom to the rescue …. I contacted a fellow RV builder who is building a Van’s RV-10 (a beautiful four place aircraft). Tom lives around 15 miles away and had two types of #40 dimple dies that would do the job … so the two F-1226 floors were packed up and carted over to Tom’s house and dimpled there. The tool that was used to make the dimples resembles a vice grip which has a set of dimple dies welded onto the end of the jaws. Fortunately, there was just enough room for the tool to fit and the rivet holes for the nutplate on both floors were successfully dimpled. Sadly, I forgot to take my camera to Tom’s so don’t have photos of the tool used to form the dimples or of his project to share. Thanks Tom!!!.

                              Dimples in the F-1226-L&R floors made at Tom’s house are circled in red.

The last item to be worked on before the next primer session is the W-1202F bulkhead. The edges were deburred and Smoothed on a Scotch-Brite wheel then the nutplate rivet holes on the top flange were dimpled. In addition, the bottom flange and the side flanges were dimpled for the 120 degree flush rivets being used on the RV-12 project.

                               Making 120 degree dimples in the bottom flange of the F-1202F bulkhead for flush rivets.

                                  Pile of parts ready for cleaning, scuffing with a Scotch-Brite pad and priming.

F-1203A Bulkhead Prepared

The pile of parts that were prepared over the weekend were cleaned, scuffed up with a Scotch-Brite pad, wiped down with Acetone and primed Monday … it was a productive day and all hanging locations in the shop had painted pieces hanging from them.

To make the most of more upcoming good spray painting weather, decided to continue preparing parts for primer and top coating as necessary. Next up was the F-1203A Bulkhead which required quite a bit of attention. There are three side by side holes at the center bottom of the bulkhead that require being enlarged to 7/16” and two adjacent holes that required being enlarged to 3/4". Step drills are a great choice in this situation, so the drill press was outfitted accordingly and the drilling commenced.

Using the drill press outfitted with a step drill to enlarge one of the holes in the F-1203A bulkhead to 3/4".

The plans call for lots of machine countersinking on the forward side of the F-1203A bulkhead … a total of 46 rivet holes for AN426AD3 rivets to secure nutplates and 6 #30 holes along the top edge for 120 degree flush pop rivets.  In the photo bellow, the areas that require work are outlined in red … the 46 #40 rivet holes are circled in red and the 6 #30 holes requiring 120 degree machine countersinking are marked in green.

Holes in the F-1203A bulkhead requiring machine countersinking marked & ready to meet the machine countersink cage.

                              Machine countersinking one of the fifty two holes in the F-1203A bulkhead per the plans.

The F-1203A bulkhead is made from .040 aluminum … this is near the upper suggested limit for dimpling. Thicker materials are usually machine countersunk but the decision has been made to dimple the bottom of the bulkhead for the flush rivets that are being used on the RV-12 project. The bottom flange of the bulkhead is not quite 90 degrees so knowing thicker material tends to flatten out a little when dimpled, an angle gage was used to measure the angle before dimpling so that angle can be reset after dimpling.

Dimpling the bottom flange of the F-1203A bulkhead for the 120 degree flush rivets being used on the RV-12 project.

The dimpling process relaxed the bend of the flange only a few degrees so it was tapped back into place with a soft hammer. Next the flange angle was checked to verify it is now at the same angle as it was prior to dimpling.

Checking the angle of the F-1203A bulkhead flange after dimpling and subsequent adjustment to verify the angle is the same as prior to dimpling.

Even though the autopilot will not be installed until much later, the RV-12 forum consensus is to install the autopilot mounting brackets now while building the fuselage as opposed to installing the brackets afterwards. The autopilot bag was opened and the brackets were removed, deburred and prepped for primer.

            Almost done smoothing the edges of one of the autopilot servo mounting brackets … four down one to go.