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Some tips I've learned over the years. This process was taught to me by a crusty Army vet that repaired battle damaged helicopters in Vietnam.
A. Tape around the manufactured head of the rivet in case you slip off. You don't want to bugger up the surrounding surfaces. This is for beginners, when you have drilled out 20 or 30 rivets, you will stop doing this.
A. What ever drill size you decide to use, make sure it's very sharp.
B. Do not center punch the rivet head. Instead place the tip of the drill bit in the rivet head dimple and hand rotate the chuck of the drill motor at least 5 or 6 rotations to establish a cut dimple.
C. I use the same size drill bit as the rivet hole. Many will tell you to use the next size smaller. I was taught not to. The reason will be explained later.
D. Give the drill motor a short "blip" to establish the start of the drilled hole. Check for concentricity with the outer diameter of the rivet.
E. Start drilling, continuously adjusting the hole center to keep it concentric with the outer diameter of the rivet manufactured head. At first it's OK to drill a little, check, drill a little more, check, etc. After a while, you'll just drill. Concentricity is the key to success. This will only come with practice. If you can keep the drill bit parallel to the rivet shank, virtually no correction is necessary. Easier said then done.
F. If you keep the drill bit centered on the manufactured head, the head will pop off on its own. It takes a delicate touch to get the hole depth just right. It will be deeper then you think it needs to be. Again practice, practice. A drill stop or a piece of tape might help but, nah.
G. If the head refuses to pop off on its own lean the drill bit over at a slight angle to pop off the head. You can also use the shank of a drill bit the same size as the one in your drill motor, inserted into the hole to pop off the manufactured head.
H. To remove the shank and shop head, use a smaller diameter drill bit and drill into the shank. This allows the shank to collapse into itself while driving it out of the hole. For example, on a -4 rivet, use a #40 to drill out the shank. Do not drill through the shop head. To back up the structure while driving out the shank, I use a piece of end grain oak with a hole drilled in it slightly larger then the shop head and inserted over the shop head to give good support. If driving rivets out of heavy structure, this step can be omitted, but for the lightweight structure in the Bearhawk, you do not want to be hammering vigorously. Use a drift punch of approximately the same diameter as the rivet shank to drive out the remains. A second set of hands to hold the backup block is useful. This should be the only time your next door neighbor is allowed anywhere near your airplane.
I have experimented with drill sizes smaller then the rivet shanks. For example, using a common -4 rivet as a baseline, I have experimented with a 1/8th, #32 and #33. What I have found is that the head of the rivet must be "snapped off". Many times this will result in damage to the edge of the hole on the part common to the rivet head as the removal tool digs into the edge of the hole to get purchase to snap off the head. If only part of the head snaps and bends up, now you have a sticky wicket. My guess is that if you scratch build a set of Bearhawk wings, you will have to drill out a few rivets. Be prepared. Do not waste money on rivet removal tools. Instead, make up test coupons and practice. After 20 of 30 rivets, you will get pretty good at it. It's a cool skill to have and a necessary one. And best of all, much of it can be learned in a day.
Disclaimer; this is the way I was taught. It's not the only way and may not be the best way, but it works for me. Some will find all this to be balderdash. As with all postings on this site, ponder the aforementioned with a healthy dose of scepticism.
Gerry
Patrol #30
A. Tape around the manufactured head of the rivet in case you slip off. You don't want to bugger up the surrounding surfaces. This is for beginners, when you have drilled out 20 or 30 rivets, you will stop doing this.
A. What ever drill size you decide to use, make sure it's very sharp.
B. Do not center punch the rivet head. Instead place the tip of the drill bit in the rivet head dimple and hand rotate the chuck of the drill motor at least 5 or 6 rotations to establish a cut dimple.
C. I use the same size drill bit as the rivet hole. Many will tell you to use the next size smaller. I was taught not to. The reason will be explained later.
D. Give the drill motor a short "blip" to establish the start of the drilled hole. Check for concentricity with the outer diameter of the rivet.
E. Start drilling, continuously adjusting the hole center to keep it concentric with the outer diameter of the rivet manufactured head. At first it's OK to drill a little, check, drill a little more, check, etc. After a while, you'll just drill. Concentricity is the key to success. This will only come with practice. If you can keep the drill bit parallel to the rivet shank, virtually no correction is necessary. Easier said then done.
F. If you keep the drill bit centered on the manufactured head, the head will pop off on its own. It takes a delicate touch to get the hole depth just right. It will be deeper then you think it needs to be. Again practice, practice. A drill stop or a piece of tape might help but, nah.
G. If the head refuses to pop off on its own lean the drill bit over at a slight angle to pop off the head. You can also use the shank of a drill bit the same size as the one in your drill motor, inserted into the hole to pop off the manufactured head.
H. To remove the shank and shop head, use a smaller diameter drill bit and drill into the shank. This allows the shank to collapse into itself while driving it out of the hole. For example, on a -4 rivet, use a #40 to drill out the shank. Do not drill through the shop head. To back up the structure while driving out the shank, I use a piece of end grain oak with a hole drilled in it slightly larger then the shop head and inserted over the shop head to give good support. If driving rivets out of heavy structure, this step can be omitted, but for the lightweight structure in the Bearhawk, you do not want to be hammering vigorously. Use a drift punch of approximately the same diameter as the rivet shank to drive out the remains. A second set of hands to hold the backup block is useful. This should be the only time your next door neighbor is allowed anywhere near your airplane.
I have experimented with drill sizes smaller then the rivet shanks. For example, using a common -4 rivet as a baseline, I have experimented with a 1/8th, #32 and #33. What I have found is that the head of the rivet must be "snapped off". Many times this will result in damage to the edge of the hole on the part common to the rivet head as the removal tool digs into the edge of the hole to get purchase to snap off the head. If only part of the head snaps and bends up, now you have a sticky wicket. My guess is that if you scratch build a set of Bearhawk wings, you will have to drill out a few rivets. Be prepared. Do not waste money on rivet removal tools. Instead, make up test coupons and practice. After 20 of 30 rivets, you will get pretty good at it. It's a cool skill to have and a necessary one. And best of all, much of it can be learned in a day.
Disclaimer; this is the way I was taught. It's not the only way and may not be the best way, but it works for me. Some will find all this to be balderdash. As with all postings on this site, ponder the aforementioned with a healthy dose of scepticism.
Gerry
Patrol #30
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