Skin Dimpling and Priming

February 22, 2010

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I snuck home over lunch today to get a couple things done, one of which was work on the airplane loudly. First, I set up my c-frame and spent some time verifying, re-verifying, and trip verifying that I was going to dimple in the correct direction. These rudder skins are thin, and I didn’t want to make any mistakes here. I set the skins on the table with the exterior side up, and the c-frame with the male die above, pointing down, and then dimpled all the holes in the skin. Jack and Ginger (who were inside), clearly don’t like me dimpling with the c-frame and told me so with a pair of barks, each. We did get into a nice rhythm, though. [whack]  Bark, bark…bark, bark.  [whack] Bark, bark…bark, bark. It helped pass the time, but I hope I didn’t cause them too much stress.

My dimpling setup for the rudder skins.

After that, I flipped them over and cleaned the scuffed lines.

Skins cleaned and drying.

After drying, I shot them with some self-etching primer. I was at the end of one of the cans, and some of the stuff came out kind of splotchy, but I think it will look good after it dries. I can always lay down another coat.

The left skin after priming.

Another thing. I’ve been putting blue tape on the exterior side, then laying the skins down flat and shooting them with primer. When I do this, some primer gets into the dimple (from the underside I am priming), and kind of bounces off the sticky side of the blue tape and settles in the dimple on the finish side. Today, I made sure none of the holes were obscured; hopefully that will prevent any primer from getting on the exterior surface. I thought about taping the final rivets in the dimples, since that is the next step with the skins anyway, but I am not sure about using self-etching primer on unset rivets, then setting them. I have never seen that done before, and I don’t want to be the first guy to try. I’m sure I would have been okay, but the other way seemed to work fine.

And the right skin after priming.

After work, I put rivets in all of the dimples, taped them up, and flipped the skins over to lay the stiffeners in. One note, since I am using the tank dies, the rivet sizes must be lengthened in some places. All of the stiffener rivets were too short before setting, so I am going to substitute AN426AD3-3.5 rivets for the AN426AD3-3s called out in the plans. Except for the aft-most rivet in each row. The construction manual tells you to make sure you set this rivet fully, so I’m going to leave the shorter one in there.

See these rivets? They look okay, until you put the stiffener in

Once you get the stiffener in, you can see they aren’t the recommended 1.5 times diameter. I’m also a little concerned that the dimpled holes are a little big for the rivets. I didn’t notice this on the other components using the tank dies. Hmm. I’m going to look around and see if anyone else has encountered this.

Not long enough. (TWSS)

I was moving along merrily until I got to this hole. Doh!

Forgot to dimple this hole. I had to break out the c-frame just for this one lonely hole.

After I got all the rivets in and taped, I flipped the skin over.

These rivets will be long enough.

Then, one by one, I final trimmed the stiffeners (snipped the 90° corners off with the snips) and laid them in to see what it would look like.


A solid hour and a half. After edge prepping and priming the stiffeners, I should be ready to install the stiffeners permanently.

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Skin Dimpling, Edge Finishing, Priming, Riveting

January 30, 2010

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I worked in sections today.

There was a big storm here last night, (and all of today), but I’ve learned that cleaning off the driveway is a lot easier if you do it when it is 3″ two times instead of once after 6″ has accumulated. Here’s what I woke up to this morning.


Here’s after about an hour of shoveling. Good workout.

Coming down fast, but at least I cleared off the first 6".

Then, I got the c-frame out and finished the VS skin dimpling. I replaced the blue tape on the male die, and got almost no circles.

Simple but effective dimpling setup.

Then I countersunk all of the lower forward spar reinforcement holes from the plans. I haven’t used the countersink since I had to countersink HS-710 and HS-714 to accept a #30 dimple, so the countersink cage was already set up. All I had to do was verify in a piece of scrap. Yup. It’s perfect.

Beautiful countersinking.

Then, I cleaned and primed one interior side of the vertical skin, then the other. Here’s the first side drying.

Hurry up and wait to dry.

After finishing the second side and letting it dry, I pulled the forward section of vinyl off of the interior side of the skin. During assembly, no bucking bars will be needed in there, so there is no risk of scratching. Then I finished edge finishing the ribs, spars, and rear spar reinforcement, and primed each one. I didn’t prime them sitting perfectly horizontal, so I got some runs and some nastiness; some of them ended up getting touched up, and some got a second coat.  After they were all dry, I cleco those bad boys together in preparation for riveting.

Skeleton and rear spar taking shape.

I started with the skeleton, middle rib. Here’s my first VS rivet.

First VS rivet.

Then, I moved to the tip. See the upper rivet? The skins are sitting flush, this will have to be drilled out.

Ahhh! I suck at riveting.

And the lower rivet there started to bend over. I’ll have to drill out both rivets.

Two rivets to be drilled out.

Back to the middle rib, two more perfect rivets.

There are pretty good. I need to make sure that bottom one is driven enough.

See the fourth rivet from the right? Started to bend over, so I’m going to drill it out. Also, I’m going to put the shop heads on the thicker material here, also, they’ll be easier to inspect.

Uh oh. See the third rivet from the right? I was supposed to wait and rivet this with the skeleton. Slow down and follow the directions!

Two more rivets to be drilled out.

But I was feeling good about squeezing, so I kept going. Until these 4 rivets. Terrible…they all started to bend over. I think my rivet squeezer sucks. I have to squeeze really hard and it it tough to keep everything aligned. I think after I drill these out I am going to shoot and buck these.

4 bad rivets to be drilled out.

At this point, I had to walk away, I was tired, frustrated, and not making any progress. Ugh.

So far, 3.5 hours. I set some rivets today, but I’m not going to count any of them until I drill them out. I’ll update the rivet count later.

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VS skin Deburring and Dimpling

January 29, 2010

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Today, I didn’t make it outside until late, so I didn’t get a lot of work done. Here’s me starting on deburring the skin. Yes, I am using the Van’s recommended “spin a drill bit in your fingers” method. It works for me.

Action shot of me deburring.

An example of a deburred hole. The hole on the right is deburred. There is a very small chamfer on it from the oversized drill bit. It’s easier to see because it’s catching the light from above.

Deburred hole there on the right.

After deburring, I scuffed up the interior of the skin with a maroon scotchbrite pad.

Scuffed, ready to dimple.

Because it was so late, I didn’t want to break out the c-frame. I grabbed the hand squeezer and finished what I could reach.

These are regular (not "tank") dimples. No circles when you use the blue tape trick.

And here’s the vertical stabilizer skin, deburred and dimpled around the perimeter. When sound level permits, I’ll get the c-frame out and dimple the remaining holes.

Almost done with the skin.

I counted 104 holes per side for deburring. That’s 208 holes, 416 deburring operations needed. I usually spin the bit 4 times, which makes 1664 spins of the drill bit. Oww…

1.0 hour closer to being done.

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More Right HS Riveting

January 17, 2010

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After a nice day off (had to work), I got back in the garage this morning for some good progress.

I started off by assessing the damage from the other day’s skin denting fiasco. I contemplated removing HS-707 entirely (from the top skin, too) so I could really get in there and smooth this sucker out. I even got everything mocked up in the c-frame again to look at the feasibility of getting rid of this dent. Then I decided I would have probably caused more harm than good, and that it looked a lot better today than it did the other day. After re-clecoing HS-708 into the skin with HS-707 and re-riveting the bottom skin to HS-707, I took this picture. The dented area is between the bottom two rivets in the picture. It’s really not that bad.

The denting between the bottom two rivets is really not that bad. And, it's on the bottom of the right HS. No one will look there. Unless you are reading this, and come to see my airplane, and want to see the dent on the bottom of the right HS. Damn you.

Anyway, with that done and behind me, I clecoed in the front spar assembly from Friday.

Upside-down HS assembly after starting to cleco the front spar (already riveted to the left HS skin) into the right HS skin.

CRAP! I forgot to remove the blue vinyl from the inboard bay before clecoing everything together. Okay, let’s un-cleco, remove, the vinyl, and recleco. Great. After inspecting (admiring, really) the assembly, I noticed a loose rivet (as opposed to a prude rivet. Hehe.). It was one of the two forward HS-707 rivets (by the denting). Grrr. Okay, should I un-cleco everything, and risk scratching everything in the process, or drill out two small rivets in the HS-404 to get my arm in there. I decided to go with drilling, since apparently I am really good at drilling rivets out. Without any issue, I got HS-404 removed and reached in to replace the offending rivet (second from the right in the picture).

HS-404 removed so I could reach in to replace the loose rivet.

Then, I reinstalled HS-404. (But took this picture before I actually riveted it to HS-702 (front spar) and HS-405 (aft root rib) behind the spar. Just pretend there are perfectly driven rivets there.

HS-404 reinstalled and the rest of the skin clecoed together.

Time to skin rivet. I like this part. Here is my technique. I stick the appropriate sized rivet in the hole, cover with blue tape, then reach in with the bucking bar, and shoot with my flush set, which is also covered in blue tape. Then, I remove the rest of the clecos, put rivets in again, and move all this little pieces of blue tape over one. (Then I figured out that on the second round, I could remove all the blue pieces of tape and run a whole line of tape along the line. I just had to make sure verify which rivets I had the bucking bar behind by pushing up on it a little. you can then see the rivet pushing up behind the tape. Bucking bar in place, I can set the gun down on the rivet and shoot.)

If you were counting, you noticed there are now two pieces of blue tape between the flush set and the rivet (and my fragile HS skin). This worked well for me, prevented further damage, and gave me some friction to help keep the set in place.

Rivets ready to set, covered with blue tape.

So, I knocked out all of the rivets needing to be bucked (I think it was 42 per side) before inspecting all my work for any issues. I think I found 5 skin rivets I wanted to replace. Here is a good example. The shop heads of all of these look great, but I want those rivets perfectly flush. I didn’t take an after picture (sorry), but I assure you, the one on the right now looks like the one on the left.

Bad rivet on the right. Replace.

After bucking all of those, I moved the now very big HS assembly to the floor while I cleaned off my workbench. Nice and clean again.

Clean workbench!

Then, I brought the HS back up on the table to squeeze the rivets that could be squeezed on the HS-601PP (skin) to HS-404 (inboard tip rib), HS-405 (inboard aft rib), and HS-706 (tip rib). The instructions have you leave 5 holes open on the inboard lines for the empennage fairing attach holes on the top only, but I decided to leave the same holes empty on the bottom for now, just to have clecos there on both sides to hold the HS off the table.  I also left some clecos in both sides of the tip ribs (although I left less on the right than I had on the left the other day, so I squeezed a few more on the left. ) Anyway, the HS is upside-down here. Left side is in the foreground.

Oooh, pretty.

Another shot. Still need to get that rear spar done. Look in upper right side of the picture. The dented area (I really shouldn’t call it dented anymore) is in the middle of the leading edge there. (I know the picture is from a distance, but the point is it’s not that noticeable.)

More pretty!

And after I flipped the HS right side up.

Shiny and clean.

After a hard day’s work, I stood back and admired the almost finished product.

I need a bigger workbench.

Good 3.5 hour day today. 146 rivets set, 14 drilled out.

Next up:

1) Remove rest of blue vinyl from inside of HS.
2) Rear spar work.
3) Finish riveting holes in HS.
4) Figure out what is going to “fly” when I finish the HS.
5) Hang HS for storage

I also decided that I am going to keep a separate page for tips. I keep learning these little tricks along the way. I should write them down.

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Right HS – Primed skeleton, Dimpled skin

January 14, 2010


Today, I used my lunch hour to swing by NAPA to pick up some more self-etching primer and then get a few minutes of work done before playing with the puppies. Jack and Ginger love it when they get to go outside and play during the middle of the day.

Anyway, I finished edge-prepping, cleaning, and drying the right HS ribs and front spar before priming them.

Then, I broke out the c-frame and finished dimpling the right HS skin. This time, I put a piece of blue painter’s tape (sticky side toward the male (exterior side of the skin) dimple die) between the dies and squeezed them together. I figured this layer of tape would help prevent some of the circles I am getting during dimpling.

3/32" Dimple Dies covered in blue tape.

The resulting dimples don’t have as much of a circle around them, and the dimples are just as deep. I wish I had known that the first time around. I’m not very happy that my right HS is going to end up looking a lot nicer than the left.

It was a little short of an hour today, but I ran a little long yesterday, so I’ll log an hour.

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LH skin dimpling, some HS riveting

January 9, 2010

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This morning, I snuck out into the garage and starting dimpling the left hand HS skin with my new (borrowed) c-frame.

After thinking about the setup and trying a few things, I quickly realized I wanted the female dimple die underneath and the male dimple die on top.

I set up the skin on 3 2x4s (I haven’t built a dimpling table yet because I wanted to see how I liked doing it) which was less than a 1/4″ above the female dimple die. Then I basically moved the c-frame around until the male dimple die was lined up (this way I don’t scratch the skin with a male dimple die while trying to locate the hole from underneath, like some builders do). Then I held the male dimple die down into the hole and…WHACK! Perfect dimple. I am far happier with these dimples than the pop-rivet dies. Keep in mind here, I am dimpling with the standard spring-back dies here, not the tank (deeper) dies.

Here's my setup for now. I like this because you move the c-frame, not the skin.

After finishing each row, I put a line of blue painters tape on the outside of the skin. I learned on the practice kit to protect whatever I didn’t want to scratch. The tape will come off just before riveting.

Blue tape on the outside of the skins. Hooray protection!

After I finished both sides, I scuffed up the internal lines, cleaned, then primed the inside of the left HS skin.

Here's the inside of the left skin, all suffed up, ready to prime.

While I waited for skins to dry, I riveted together HS-705, HS-702, and HS-704, but only the middle two holes. The rivets didn’t bend over, per se, but set a little crooked. (My fault for not keeping the squeezer steady.) I drilled them out perfectly, and then decided shooting them might be a better idea. After practicing with a piece of scrap for a minute, I actually ended up shooting these rivets. They look really good.

Shop head picture. Rivets 7 and 8.

Machined head picture. This just looks good.

This is not the order the directions has you rivet, but I was getting antsy to get some primed pieces together. Notice I didn’t slide in the HS-710 and HS-714 yet (still need to finish those), as you can set HS-404 to HS-702 to HS-405 without them. Then, it is off to run some errands.

When we got home from running some errands, my latest Avery tool order had arrived. Finally, a scotchbrite wheel! 6″x1″x1/2″ CP-7AM “Cut and Polish” Medium wheel. Also, I’ve heard some good things about the Permagrit line of products, so I picked myself up one of the 12″(?) ones. Fine on one side, coarse on the other, flat (I heard not to get the curved (convex) one.. Much better for making a straight edge than my regular file.

More tools!

First thing after mounting the scotchbrite wheel, I finished the edges of HS-710 and HS-714 with the wheel. So easy. I should have ordered the wheel at the beginning. (Serves me right for trying to piece together a toolkit instead of buy one all at once. I thought the scotchbrite wheel was a luxury. It is not.) Then I countersunk the holes in HS-710 and HS-714. I had done this before, but sized the countersinks perfectly for a AN426AD4- rivet. When you cleco the dimpled HS-702 front spar to either piece, the spar doesn’t sit flush, so you have to enlarge the countersinks.)

Enlarge countersinks. Check.

Then I finished surface prep, cleaned, and primed those two.

While waiting for the primer to dry, I clecoed HS-707 (leading edge “middle” rib) and HS-706 (tip rib) to the left skin to get in the mood for riveting. The girlfriend and puppies are taking a nap, so I’ll have to come back to this later, but I’m getting excited to start skin riveting.

HS-707 and HS-706 all clecoed to the left skin and such.

Anyway, I put in a few minutes of right HS skin deburring, scuffing, and dimpling before coming in for the day. (Notice I decided to scuff the interior of the right skin before dimpling? It’s easier to scuff the skin without all of the dimples getting in the way. It’s these little things that will save me time the second time around.)

Let’s see. 9am to 11am, 2pm to 4pm. 4 hours today.

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Primed Front LH Spar, Devinyled RH Skin

January 6, 2010

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After getting home late from work and running back out for some takeout, I got in about an hour before heading to bed.

First, I finished cleaning up (scotchbrite, dawn detergent, and lacquer thinner) the left HS front spar in preparation for priming. I don’t love doing these one piece at a time, but the spray can makes it easy, and I can complete a few parts in an evening. I did the front spar so I can maybe start riveting stuff together this weekend. I still have some work to do on cleaning up the rear spars and rear spar reinforcement bars, but I could start with the skins and ribs, then finish the rear spar stuff once I have to plug it into the back of the completed HS.

Left front spar (HS-702) sitting next to the left ribs I finished the other day.

Then I devinyled the right HS skin, which went much faster than the left skin.

Right HS skin. Doesn't that look nice?

Here's the inside...

Also, a fellow RV (-8A) builder at work was kind enough to lend me his Avery C-frame. Maybe I’ll get a chance to do a little skin dimpling this weekend.

Borrowed c-frame. Wuhoo saving money!

Next up:

1) Finish dimpling left HS skin
2) Deburr right HS skin
3) Dimple right HS skin
4) Prep and prime inside of both skins
5) Finish prep for right HS ribs and front spar
6) Prime right HS Ribs and front spar
7) Prep and Prime rear spar components
8) Rivet HS together

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