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Tips needed for dimpling completed firewall

D

dwranda

Well Known Member
I am trying to hang my oil cooler and would like to put nut plates in so removal will be easier in the future. Want nut plates behind everything on the firewall to ease removing from the front only. I would need to dimple the firewall where there is the angle support behind it. Obviously I can't just use the dimpler that uses the rivet puller. Is it OK to countersink these even though the firewall is so thin?
20200203-112247.jpg
 
The short answer is no - just use AN3 bolts and nuts.

But - I always use a piece of 0.063? 3/4?x3/4? angle to mount the cooler, the angle then is bolted to the firewall where, as you suggest, there is supporting structure on the cabin side of the firewall. If you still want to use nutplates, put the nut plates on the angle, the angle still bolted to the wall.

Carl
 
Ditto what Carl said

You want to be able to remove the oil cooler from the mounting angles. Put the nut plates on the 3/4" aluminum angle corresponding to the holes in the oil cooler flanges (6 total -- 3 top, 3 bottom).

I used AN525 screws to mount the ends & middle of each mounting angle to the firewall and underlying stiffeners. The AN525 has a lower profile head than the AN3A bolt so I could get the oil cooler and its fiberglass plenum right up to the apex of the mounting angle without interference.

Cheers!
 
I used a pop rivet dimpler to install platenuts. Then you can bolt it to the firewall.

Honestly, I would reinforce the #4 baffle and mount the oilcooler there, as thousands have done.
 
I don't think other posters understood your question. Because it appears the aluminum support angle is already riveted to the firewall you are asking if countersinking for a flush rivet to hold nut plate is an option. It isn't. Essentially this would remove the stainless metal layer completely. If you could still remove the aluminum support angle and install the nut plate in that alone there by causing the flush rivets sit under the firewall skin. As long as nut plate would never need to replaced this would work. I would use an AN3 bolt along with a nut and move on. You won't really need to be removing it once installed.
 
Thanks guys I was hoping there was some procedure I didn't know about but looks like I will just be using nuts and bolts. I figured the oil cooler mount wasn't something I was going to be removing very often or maybe even never but thought I'd look into it anyway.
 
Don't give up yet. Depends on how bad you want a nutplate there.

You have two flush rivet locations available already. Drill them out. Make a thin plate with holes for those two rivet locations. Put a nutplate on that plate. Rivet this new plate into position. Done.

You are essentially making a special nutplate with long ears to reach the flush holes you already have.
 
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rzbill said:
Don't give up yet. Depends on how bad you want a nutplate there.

You have two flush rivet locations available already. Drill them out. Make a thin plate with holes for those two rivet locations. Put a nutplate on that plate. Rivet this new plate into position. Done.

You are essentially making a special nutplate with long ears to reach the flush holes you already have.
Click to expand...

Duh yeah why didn't I think of that. If I decide I really want the nutplate there I will do it that way.
Thank you!!
 
for my own curiousity, would a doubler plate and riv-nuts work? Put the doubler on the inside of the firewall and then use the riv-nuts to hold it in place and mount the oil cooler with a bolt?
 
agent4573 said:
for my own curiousity, would a doubler plate and riv-nuts work? Put the doubler on the inside of the firewall and then use the riv-nuts to hold it in place and mount the oil cooler with a bolt?
Click to expand...

The question was for where there is a support angle behind the firewall and you can't dimple the hole. Other places on the firewall where there are no angles riveting in a doubler is not a problem. It is recommended to mount the cooler to those support angles.
 
You can make die holders for your dimple dies from 5/8 round steel stock. Then use your rivet gun and bucking bar to make the dimple. I also made a dimple die holder from an old 401 style air chisel bit (same configuration as your rivet gun).

Larry
 
dwranda said:
The question was for where there is a support angle behind the firewall and you can't dimple the hole. Other places on the firewall where there are no angles riveting in a doubler is not a problem. It is recommended to mount the cooler to those support angles.
Click to expand...

I totally didn't understand the angled support aspect. Makes sense now. Thanks.
 
dwranda said:
I am trying to hang my oil cooler and would like to put nut plates in so removal will be easier in the future. Want nut plates behind everything on the firewall to ease removing from the front only. I would need to dimple the firewall where there is the angle support behind it. Obviously I can't just use the dimpler that uses the rivet puller. Is it OK to countersink these even though the firewall is so thin?
20200203-112247.jpg
Click to expand...

Just run a tap through the hole, install the bolt and then install a nut on the back side. That would need you to drill the tap size first.
 
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Riv-nuts ugh

AS for riv-nuts I have installed gobs of them in another life and would never install them in an aircraft again. Junk. Once they loose their grip your screwed. Just try to drill out something that is spinning in the hole that is bigger than any other fastener will fill.
I threw my whole riv-nut kit n caboodle in the trash many years ago.
Anything than a riv-nut
Art
 
I would have no issues at all with drilling #40 holes and countersinking for the nutplate attach holes/fasteners..I have done it on mine. The firewall is more "firewall" than load carrying structure, and the fact that your countersink will knife edge the SS and lightly countersink the angle behind it is irrelevant...not something you would like to do on a skin or area transmitting loads where the rivet would start working and cause cracks.
 
Maybe you could countersink for a NAS 1097 "oops" rivet in order to minimize the amount of material removed and still have a flush rivet?
 
I decided to use rzbill's recommendation and make a plate with the platenuts on it. I drilled out a few rivets and will install the plate using those rivet holes to hold it in. Simple and didn't take too long to do. Thanks everyone !!
 
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