Deburring and dimpling the parts.
8 tedious mind-numbing monotonous hours.
Bear with us, dear reader, this is going to be a long screed.
When engaged in menial repetitive tasks, one can take some solace from knowing that throughout human existence, every epoch had jobs that were dull, boring and monotonous. Picture this: It’s the great land of Turkana, Kenya, 3.3 million years BC (Before Corona). The clink clink clink sounds of flint knapping ring out across the savannah. Hour after hour, clink clink clink, punctuated with strings of cursing from the Australopithicoid flint knappers. By evening, the sun sets over a gazelle roasting over a fire. As the meat sizzles, one of the boys pauses in his work, mops his unibrow for the umpteenth time since that afternoon, turns to his colleagues and says, “I say gentlemen, this monotony grows ever so wearisome, it makes one wish for the more speedy advent of metal tools!”
A chorus of “Here Here!” erupts amidst the flint dust covered knappers, as the gazelle patiently drips juices into the fire.
While our pithecoid ancestors of yesteryear had flintknapping, today, we have deburring Sling parts. Of course, in between the two, the Wright brothers spent hours and hours stitching the wing coverings with Daddy’s sewing machine, no doubt thinking Charles Taylor had the cooler part of the enterprise. I’m sorry, we digress.
Even though deburring is but just one of the dull jobs, it is oddly enjoyable in a tedious sort of bubble wrap popping way. It is a good thing to do when you are watching the TV, chit chatting about what to do after Covid-19, or better yet, just how nice the Sling will fly.
Let’s start with the why we torture ourselves with the endeavor. The burrs prevent a good fit between the two pieces of sheet metal and over time can lead to the pieces flying off in flight creating an unsatisfactory condition. In addition to giving you a scorching paper cut, the sharp edges are where corrosion can begin its evil.
let’s see what we are dealing with up close and personal. The Lord Slingungous, High Sub Rear Commander to the left of the Minister of Truth here at Connecticut Slingers, authorized the release of the following photos directly from the Connecticut Slingers Ministry of Truth files. Here is a burr on a straight edge and on a hole when you look at it with a microscope:
You can see all the nasty burrs on the bottom of this straight metal piece.
A really ugly burr can be seen on the upper right area of the hole, real gnarly.
All those nasty, bumpy little bits on the edge are what you feel when you rub your finger across the edge of the sheet. They are also what makes the pieces not fit flat against one another when you rivet, and those teeny tiny pointy bits are where corrosion can get a nasty foothold. This is why burrs are very bad. Very, very bad. Definitely naughty.
To get an idea of how to deburr,we visited a fellow EAA Chapter 334 member Bogdan Rotowski while he was working on his Bearcat, and Sam Watrous with is replica P-36 for some tips. We also visited several awesome online blogs and videos, such as the episode from the brilliant and inspiring series done by Evan Burnye, The Plane Lady and this one by the Dreambuildfly guys. Lots of great stuff, so let’s add ours on to the pile.
Choosing the Weapons.
We didn’t have a 6-inch ruler like what Evan used, nor his skill, so we didn’t use one of those.
Evan also had a drill bit and one of those swivel deburring tools. We had a big drill bit left over from when we built our house. And a file whose origin is lost in annals of time, and to round out our arsenal, we had a Dremel tool. Off to a good start there.
We still needed more stuff to complement our massive suite of tools:
Heavy Duty Shaviv Deburring tool Mango Ii E with telescope E holder that came with three blades – Aircraft Spruce.
Avery Speed Deburr-C Sink Tool – Aircraft Spruce.
Silicon Carbide Grinding Stone (for the dremel)-Cash’s hardware in Mystic Connecticut.
Getting started.
Just like the dunk and scrub from our last diatribe, deburring was done piece by piece. Grab piece from the Sling Parts Drying Rack, scratch scratch scrape scrape, twisty twist, set back on the SPDR. Dull, flintknapping tedious. For the most part, at least.
Here are the details.
Let’s start with the straight edges. In most cases, only one side needs deburring. This is nice, it means only half the work we thought we needed to do. For these, we used the Shaviv deburring tool. There are other tools like it which have a handle and a hook like blade that spins around in the end. This one, however, has a nice red and blue handle. You can pull the shaft out a few inches, though we didn’t, and the bits can be changed easily.
The Shaviv tool is completely and irrefutably great on the straight-aways. That said, it does need to be done carefully, or it will bind up and create more frustrating nicks which are not nice, they stress the metal out, and could lead it down a path of self-destruction.
To pull off a good Shaviv deburrment, Just hold the piece straight out away from you, place the Shaviv on the edge as close to the far end as possible, and pull the Shaviv toward you in a nice graceful motion, its fun to watch the little curly cue thingy of metal peel away leaving a nice smooth edge. Straight edges are as fun as peeling the plastic sheeting from the parts before the washing. Could do it for hours.
The Shaviv does a yeoman’s job with large holes as well, but we had to be careful, if we didn’t angle the shaviv right, we could nick the metal, and that is bad. the trick is to circle the large hole with your hand angled slightly outside the hole and pulling the tool around the hole. Just like the straight aways, it must be done with the right smooth moves. Got to do a video for this one.
All that said, it is all but impossible to do outside curves with the shaviv, like what you find with the inspection and access covers. Like trying to shave ear hair on a gorilla. Also, the Shaviv doesn’t do so well in the front toothy parts of the ribs. Still the flashy red and black handle fits well in the meat paw.
Let’s move on to little holes and the way to do them. For this we used 2 different implements, the drill bit, and the deburring crank thing called the Avery Speed Deburr-C Sink Tool. Both work well, and very easily. For the drill bit, place the business end into the hole, and give it a twist. Lotto ticket scratching easy.
The Avery tool is different, though same idea, except you give it just one crank instead of a twist. Any more than that and you risk removing too much, and the rivet won’t have enough metal to grip. Both work the same, but the lack of a proper handle on the drill bit may make your hand grow sore. Rather than whine about it and use it as an excuse not to do any more work, switch over to the Avery cranker for a while.
So, what about the round parts like the inspection hole covers? And the teeth on the front pieces that frame the front nose of the wings and empennage pieces? And not to forget, what about the end of the straight piece the Shaviv left behind?
All of these we did with a file. for the round pieces, so we placed the piece near the edge of the bench and file the edge lightly at an angle as you rotate the piece. The little bit left by the Shaviv on straight edges is easy with a few strokes with the file. If you can flare an airplane and reduce power while adding in cross wind correction you can do it just fine. The file also rounds the corners on the teeth parts of the nose pieces, just file back and forth lightly as you move the file around the corner. There is also another tool we used for rounding over the corners. More about that in a little bit, but first…
A scene from Wild Landings: Namibia. The wise aesthetic Mike Blyth sharing his wisdom on the building of Slings: “it is the middle parts that are difficult”
The following paragraph contains a spoiler alert. (Just thought I would let you know.)
There is one bit on the ribs that is all but impossible to get to. As the wise and astute Mike Blyth observed at 51:58 into his brilliant documentary, Wild Landings: Namibia: “It is the middle parts that are difficult.” Just as Mike demonstrated a clever out of the box solution to get to the middle parts, we had to come up with something to round the corners on the middle teeth of the ribs. Our middle parts were gaps between the teeth on the ribs where there was a curved bit which made the Avery Crank, drill bit, shaviv and file useless. The Shaviv can get into the sides of the teeth, but not the back curvy bit between the teeth. The drill bit and Avery crank would slip off the curved back end, a chainsaw file may help here, but we didn’t have one.
It is times like this we turn to another wise and great DIY philosopher, The great Red Green: “When All else fails, switch to power tools!”
Our power tool of choice: a genuine Dremel tool, fitted with a chainsaw sharpening bit. Ah Yes, 120 volts of raw power spinning at 35,000 RPM BUWAH HAH HAH HAH HAH!!
To make this work, we held the Dremel cupped in our fingers, and resting our thumbs on the edge of the piece, we could maneuver the spinning bit around the difficult parts. If you have ever peeled potatoes, you will find it easy. We haven’t really tried using the Dremel for much else yet, but it is very effective here.
We spent a good 5 hours to deburr every little hole and edge of every part. Time flies when your knapping flint.
So, after all that shaviving, cranking, bit twisting, and Dremeling This is what we get:
Nice smooth, and straight.
Nice and round
Aren’t They Lovely?
Next, We had the joy and fun of doing the dimples.
First the toys:
DRDT-2 Rivet Dimpler (Aircraft Spruce and Specialty)
Dimple Dies The small 2.8mm ones (TL-DIM-003-X-X-0 and TL-DIM-103-X-X-0) came with the kit.
Bench Grinder from Harbor fright (Yes, this beast was involved)
Before we get into it, first a word of caution.
There is a bit of fun with this, and if you are not paying attention, you can get carried away with making dimples that you forget where to stop. Indeed, it happened when we were having way too much fun with it and went a bit too far. We ended up dimpling the inboard ribs of the elevator, and this lead to a febrile fit of worry.
We made the first of many panic calls to The Airplane Factory. The brilliant and genteel Jean D’Assonville enlightened us on the subject. He assured us there is no harm in doing too many, it’s only a bit of wasted effort. In fact, the dimpled rivets might add strength to the joint since the dimpling provides a little more surface for the rivet to grip. That part was reassuring, but the wasted effort didn’t sit right, we certainly don’t want to do that. Even if it was fun.
So my dear reader, learn from those intrepid dimplers who dimple before you. Guard your dimpling zeal. Steal yourself. When referring to the instructions, don’t just count the circled holes to be dimpled. Check a few times, and then mark where to stop dimpling on the part. Then check a few more times to be sure.
Let’s move on. As far as tools go, we decided to go with the DRDT-2 for our dimpling campaign. The mechanism looked like it would be a lot more consistent with dimple quality, and the gray color complimented the gray tool rack we had in our garage, arguably the most important factor in the decision.
mark the place where to stop and start dimpling in the row, don’t get carried away.
The DRDT-2 came with assembly required; However, it wasn’t too hard put together. We found that after it is assembled, it needs to be bolted down to the work bench as when you start to dimple, it will lean forward as you apply pressure with the handle, and possibly the 44lb DRDT-2 will fall off and hit your foot, or worse, bend the part being dimpled.
The next thing is setting it up with the dimple die. for the empennage parts we used the smaller set of dies provided. We installed the male die in the ram (the part that moves up and down with the handle), and the female die in the die receiver (The part that doesn’t). If this confuses you, the male die has the little teeny tiny knob that looks like a teeny tiny VOR ground station. Having the dies installed this way will allow you to dimple in the same direction that the rivet would be installed, which helps you not dimple in the wrong direction. Plus, when dimpling ribs, the bulk of the rib will hang downward, away from the mechanism.
2This is the female die in the reciever of the DRDT-2.
With the dies in place, we had to get the ram set just right. If it wasn’t, we could scratch the work piece, or make the dimple to shallow where the rivet would stick out when it was installed. This was easier to accomplish than we thought. We found Katie, an RV-3 builder who made a nice treatise on the subject: Katies blog.
To adjust the ram, we lowered the handle down until it stops. The loosened the big nut on the ram. Next, we unscrewed the ram downward until the two dies touch together. Then, we lifted the handle up, and unscrewed the ram ¾ turn. Finally, while holding the ram so it doesn’t turn, we tightened the nut, used a wrench for that. Then came the moment of truth. We tried a few test holes.
Since the male die will fit through the hole snugly, we had to be careful not to miss, but to line it up right. We found it may be easier to fit the part onto the die rather than try to lower the die into the hole, your choice. After the facile step of getting the die into the hole we simply lowered the handle until it came to a stop, then raised the handle, and admired the dimple. It was easy to do, and Repeat. We checked a few of the dimples. They didn’t fit.
We consulted the directions, which we read once already and kept for just such an occasion. We also called TAF and confirmed with Monsessier D’Asonville that we are supposed to drill the holes using the 3.3mm bit. (1/8”, here in People’s Republic of Connecticut). Success! We found the rivet fit snugly, and the top of the rivet was flush with the piece!
With the process mastered, We started with the frame pieces. The spars were easy enough, However, we had to mark where to stop to keep from getting carried away and going too far. The ribs were challenging. Some of the ribs did not have enough space between the hole and the web (The part that is vertical) for the die to fit. After a commensurate amount of hand wringing, we followed the experience of other builders and ground down a side of the dies using the Harbor Fright bench grinder. We wish they sent two or three sets of dies. Still, the ground down dies continued to work well, and we dimpled on.
3The Harbor Fright grinder proves itself useful. For once.
The large Rudder and Horizontal skin pieces took a person and a child to do to keep the ungainly sheets from flopping all over the place and curving over the dimple receiver. The skins were also clamshelled, which added to the challenge. Never the less, We got them dimpled with tender loving care.
The DRDT-2 is the only system we used for dimpling. We can unequivocally and safely say, without any reservation whatsoever, that it was the best system we used. It was fast, simple and easy to use, the dimples were accurate, and precise. And it was flint knapping fun.
Next: Alchemy