[jlfernan]

Putting a Cherrymax rivet in a tough spot. The mandrel seemed to break early. The madrel extends too far out the back and is not flush on the head side. What would be the cause of this? Too long too short a rivet? Or, operator error? I managed to drill it out. Sorry about the photo qualty, but you can see how far out the mandrel sticks out. The spot is where the subpanel attaches to the bulkhead. Using a Cherrymax guage it indicates a -2 but you can see how the rivet reacted.

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[jlfernan]

Also, I know on solid rivets a certain amount of the rivet extends out through the hole. With a Cherrymax rivet, how much should it extend out?

 

[Geoff]

Putting a Cherrymax rivet in a tough spot. The mandrel seemed to break early. The madrel extends too far out the back and is not flush on the head side. What would be the cause of this? Too long too short a rivet? Or, operator error? I managed to drill it out. Sorry about the photo qualty, but you can see how far out the mandrel sticks out. The spot is where the subpanel attaches to the bulkhead. Using a Cherrymax guage it indicates a -2 but you can see how the rivet reacted.

Try this link for everything you ever wanted to know about Cherry rivets. Instructions, animations, specifications, troubleshooting, etc.

http://www.cherryaerospace.com/html/product/blindrivets.html

 

[WilburD2]

Broken early

Jorge, every time I've ever used Cherry's, the reason the shaft wouldn't go flush is the rivet being too long. Since the shank is wrinkled all the way up that seems to be the case here. Also, the cheerymax shank will break off if too much a side load is on the shank when your pulling it. Finally, a properly pulled cherry on the back side will be nicely rounded. The base of the shank will form a perfect little cap over the opening the shank caused

 

[jlfernan]

Jorge, every time I've ever used Cherry's, the reason the shaft wouldn't go flush is the rivet being too long. Since the shank is wrinkled all the way up that seems to be the case here. Also, the cheerymax shank will break off if too much a side load is on the shank when your pulling it. Finally, a properly pulled cherry on the back side will be nicely rounded. The base of the shank will form a perfect little cap over the opening the shank caused

Hey Bill,
It worked! I made sure this time there was no side load on the rivet and it came out perfect. Thanks for your help.

P.S. Can you give me some advice on how to drill the holes for the HS attach brackets prefectly perpendicular...

 

[RV7Factory]

Try this link for everything you ever wanted to know about Cherry rivets. Instructions, animations, specifications, troubleshooting, etc.

http://www.cherryaerospace.com/html/product/blindrivets.html

Page 17 of the Process Manual was interesting. It says that if you want to install a CherryMax in dimpled sheet, you should ream the hole smooth (a diagram is included). My question is, how do you do this? Not how do you ream, but how do you drill, dimple then ream (e.g. what sizes) to eventually end up with a dimple with smooth walled holes? If you drill and dimple #30, the hole will stretch and you can't then ream it with #30. Maybe the answer is that for us (RV builders) it isn't critical, but I am curious.

 

[GAHco]

Oversize Rivets

Page 17 of the Process Manual was interesting. It says that if you want to install a CherryMax in dimpled sheet, you should ream the hole smooth (a diagram is included). My question is, how do you do this? Not how do you ream, but how do you drill, dimple then ream (e.g. what sizes) to eventually end up with a dimple with smooth walled holes? If you drill and dimple #30, the hole will stretch and you can't then ream it with #30. Maybe the answer is that for us (RV builders) it isn't critical, but I am curious.

CR3242-4 is oversize for the CR3212-4

The 3242 uses a #27, which will clean up a dimpled#30 hole real nice.

Have Fun!

 

[WilburD2]

Straight holes

Most every one will agree with me, if you have the room with the brackets, a drill press with the piece gently clamped to the table to keep it from moving and squared to the drill bit..

 

[RV7Factory]

Thanks Tom - Great info! I had a suspicion the answer involved the oversized versions, but I glad to hear it from an expert .

 

[GAHco]

Your certainly welcome!

Thanks Tom - Great info! I had a suspicion the answer involved the over-sized versions, but I glad to hear it from an expert .

Your certainly welcome!

The subject brings to mind another kind of oversize application.

this would be even more likely in the RV realm.

I have had to put a cherry-max where a -3 countersunk rivet was.

In these cases I have used a smaller head countersunk CR3214-4-2 (shortest they come) and drilled out the hole normally dimpled for an MS20426AD3 rivet with a # 30 drill. Then taken the 100 degree countersink and knocked out about 5-10 thousandths from the inside of the countersunk dimple, installed the said cherry-max and gotten a decent replacement rivet, installed in a difficult to otherwise do spot.

 

[az_gila]

Careful...

.......

In these cases I have used a smaller head countersunk CR3214-4-2 (shortest they come) and drilled out the hole normally dimpled for an MS20426AD3 rivet with a # 30 drill. Then taken the 100 degree countersink and knocked out about 5-10 thousandths from the inside of the countersunk dimple, installed the said cherry-max and gotten a decent replacement rivet, installed in a difficult to otherwise do spot.

Tom, and anyone who copies this... you need to do this with extreme care.

If you remove even 0.010 from inside a dimple in a 0.025 skin you have reduced the strength by 40%... and measuring that 0.010 is extremely difficult..... a little more action with the countersink cutter, and it's easy to lower the strength of the rivet joint by over half....

gil A

 

[GAHco]

Good Advice

Tom, and anyone who copies this... you need to do this with extreme care.

If you remove even 0.010 from inside a dimple in a 0.025 skin you have reduced the strength by 40%... and measuring that 0.010 is extremely difficult..... a little more action with the countersink cutter, and it's easy to lower the strength of the rivet joint by over half....

gil A

Good advice, I should have given a little more info.

This would be a non issue on the .032 inboard wing skins.

I would not advise any form of cut countersinking on .016 material.

The .020 and .025, proceed with caution commensurate to the application, or let the rivet head stick up oh-so slightly. test a peice it might be acceptable to you.

As far as raw strengths go, an 1/8 rivet has about 43% more cross section than a 3/32 rivet and therefore that much more shear strength.

The AD rivets have a shear strength of 30 ksi.

The Cherry max rivet has a rated shear strength of 55ksi.

Gil is right, the real issue would be machine countersinking in thin skins, not because of rivet strength limitations.