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Machine Screw or Sheet Metal

behindpropellers

behindpropellers

Registered User
NE Ohio
I have been adding tabs, etc onto my fuselage the last week or so...

Whats your preference and why on either machine screws or sheet metal screws for stuff like metal belly, cockpit side panels, wing root fairings, etc. Cost is about the same, just looking for an opinion/advice.

Tim
 
Rivnuts and machine screws. Plastic washers under the machine screws. Easy to take stuff apart, which you'll do a bjillion times on an airplane you just rebuilt. The plastic washers keep the screws from backing out from Cub vibration. Plus, when you've got your hand stuffed up in the back of some compartment you won't lose skin when you hit a sheet metal screw.

If you do decide to go with sheet metal screws be sure to use the plastic washers on them.
 
Depends where they are. I hate riv-nuts. I use Tinnerman nuts, Tinnerman nut plates and regular nut plates. Riv-nuts only when absolutely necessary. They spin too easy and are a pain to remove when they do. I would use machine screws on the metal belly or cam-locks or Dzus fasteners. I found a source for #4 Tinerman nut plates and use a ton of them.
 
I am no seasoned expert but each seems to have their benefits. For metal belly, I wouldn't do anything but nut plates. The Super Cub I fly from time to time has a metal belly and the screws with tinnermans are always vibrating out. They replace screws all the time.

I used keyed Rivnuts in the Piper channel around the bird cage. They don't spin when they are keyed unless you really reef on them.
 
The aluminum threads don't have as a long a service life though. I use the steel locking nutplates in the Piper Channel. Takes a lot longer to install though.
 
Good points. Tinnermans work really well, too. I use the plastic washers on the screws to solve the vibration problem.

I haven't had a problem with the threads on the rivnuts unless I damage one during installation, which is easy to do if you get overzealous. Keyed rivnuts are preferable as they don't spin easily.

Replacing a bum rivnut is simple. I just use a larger drill and gently take the cap of the rivnut off to remove the rivnut.

Like anything there is a technique to it. The neat thing is there are several good attachment methods above and beyond the lowly sheet metal screw.

If you are using sheet metal screws you do need to replace the screw with the next size up after you've removed the screw a few times as removal enlarges the hole.
 
jrussell said:
Replacing a bum rivnut is simple. I just use a larger drill and gently take the cap of the rivnut off to remove the rivnut.
Click to expand...

Except when it spins in the hole and then you are trying to wedge a pair a flush dikes or anything else to keep it from spinning so you can drill it out. :x :lol:
 
Steve Pierce said:
jrussell said:
Replacing a bum rivnut is simple. I just use a larger drill and gently take the cap of the rivnut off to remove the rivnut.
Click to expand...

Except when it spins in the hole and then you are trying to wedge a pair a flush dikes or anything else to keep it from spinning so you can drill it out. :x :lol:
Click to expand...

:lol: Agreed! I think that's where I finally discovered the keyed ones....
 
I like the nylon washers too. They keep the screws from digging into the aluminum and eventually wearing the hole out also.
 
Steve Pierce said:
I like the nylon washers too. They keep the screws from digging into the aluminum and eventually wearing the hole out also.
Click to expand...

They also help from getting dissimilar metal corrosion from S.S. to Aluminum.
 
Tim I'm building too. I'm went Tinnermens on the side panels, be sure to test one with the tabs your welding on because tinnermens require a room to be installed correctly. You will see what I mean when installing them. so do a fit up before you are too far along. I used # 6 on the interior panels with sheet A, but B's will be needed in some applications. I installed # 10 nut plates for the belly skin located at the rear bottom of the fuse. Some places like the skin at the lower door opening, door post trim and other places will require drilling the tubing for a fastener. I also made some a handfull of L brackets that I fastened to the side of the floor boards with tinnermans to fasten the bottom side panels. The riser needs to be tall enough to install the T plates.
 
There are two types of Tinnermen nut plates. One is for sheet metal screws and the other is sized and pitched for machine screws. On side panels I used the machine screw type.

On the rest of the plane I use self locking nut plates or self locking floating nut plates.

Take care.

Crash
 
Crash said:
On the rest of the plane I use self locking nut plates or self locking floating nut plates.



Crash
Click to expand...

Crash-

For sheet metal screws?

The thing that drives me nuts is the IA who takes everything out and throws it all in a bucket. Then they try to put the sheet metal screws in the nutplates that are made for machine screws, and ruin them.

Tim
 
behindpropellers said:
Crash said:
On the rest of the plane I use self locking nut plates or self locking floating nut plates.



Crash
Click to expand...

Crash-

For sheet metal screws?

The thing that drives me nuts is the IA who takes everything out and throws it all in a bucket. Then they try to put the sheet metal screws in the nutplates that are made for machine screws, and ruin them.

Tim
Click to expand...

I use stainless steel machine screws everywhere I can backed by a nut plate. Not a big fan of sheet metal screws. They're too easy to strip out then the only thing you can do is drill out and go to the next larger size. My old Cub had size 6, 8 and 10 screws holding the wing root panels on. It was a pain re-installing them and trying to remember which size screw went where with a hand full of different size screws.

Use a Univair butt rib (only Univair rib I'd use) and install floating nut plates to attach the wing root fairing with.

Crash
 
Would anyone know of a source for self locking nut plates or self locking floating nut plates #4-40. Seem to be hard to find item.

I'm no fan of sheet metal screws for the reasons previously described.

# 4 mach. scr. would fit many uses in the SC IMHO.
Vidir
 
Love how his picture shows a pile and he's selling EIGHT ! lol But for 99cents you can't go wrong I guess.

I have around 3000 x AN366-F440 440 THREAD NYTROL/STEEL, and I have mine listed at $2.75 each (and compared to aircraft spruce or other..that's a steal) I also have about 70,000 of other sizes.

http://www.irishfield.on.ca/inventory/index.htm

Tell me you're from SC.org and there'll be no handling charge (that is really for the 5 mile drive to town to mail stuff).
 
Steve Pierce and others,
I'm close to covering a new set of Dakota Cub J3 wings. Unfortunately, the butt ribs may require drilling to accept only sheet metal screws to hold the fairings. I guess with some work one could replace the new butt ribs with Univair butt ribs and then use nut plates or rivnuts.
But, is there a way one could use nut plates or rivnuts on the Dakota Cub butt ribs that would not entail much work?
Thanks,
Jim
 
The Dakota ribs accept sheet metal screws very well. I drill with a #44 drill bit and pre-tap the holes with a tool I made that has a #4 PK screw in the end of it that chucks up in a cordless drill set on a real slow speed. I don't know of a way to use nut plates unless you rivet tabs on the ribs.
 
Thanks Steve for the tip. I'll try as you suggest. It does look like the rib caps are thicker and maybe a harder metal than the Piper ribs.
 
OldCuby said:
Steve Pierce and others,
I'm close to covering a new set of Dakota Cub J3 wings. Unfortunately, the butt ribs may require drilling to accept only sheet metal screws to hold the fairings. I guess with some work one could replace the new butt ribs with Univair butt ribs and then use nut plates or rivnuts.
But, is there a way one could use nut plates or rivnuts on the Dakota Cub butt ribs that would not entail much work?
Thanks,
Jim
Click to expand...

On Dakota ribs, a strip of aluminum riveted to the capstrips of the ribs, and then with nutplates installed into the strip works very well. It also gives some extra strength to the rib, which is great in places like the fuel tank bay and also the butt/root rib.

I would never rivnuts in a rib capstrip, but I'm a rivnut hater! Those things always seem to get loose and require a very difficult removal process...plus, when installed, the little head protrudes above the surface they're installed in, so whatever is getting screwed down doesn't lay flat!!!!!*(@#)&%@!#&%

DAVE
 
Machine Screws at Butt Rib - Smith Cub

It appears that there may be problems using nut plates in some root ribs to hold the tank skin and top wing fairing. Does anyone know if there is a problem using # 6 anchor nuts on a Smith Cub root rib? Is the concern taking too much material out of the rib cap strip? Looks like I need them in about 5 places if I match the fuselage tabs.
 
SMith uses the 'mini' non-floating machine screw nutplates in their rib caps for their auxiliary fuel tank cover screws.

I've installed the 'mini' non-floating nutplates in Smith rib caps for fiberglass wingtips, wing root fairings, and fuel tank cover screws.

It seems to work very well.
 
I hate sheet metal screws. On my Colt restoration I found a way to avoid them altogether and very simply. On the Piper channel very carefully drill necessary holes in center of channel. Then enlarge to #6 screw size and use 3/8 inch long #6 SS screws screwed into plain non-floating #6 nutplates that you drop into channel. (This is done with sheet metal removed). With all these screws tightened-holding the nutplates into their proper position-fill the piper channel with fiber-fil two part epoxy/fiberglass and remove excess leaving the channel slightly overfilled. After 24 hours sand the excess flush with channel sides and remove the #6 screws. The nutplates are now held in place with no rivets required. Not only are the nutplates held in position the piper channel is filled and sealed and won't later fill-up with water, dirt, stray hardware, etc. It worked great for me.

Jim Miller
 
Great idea Jim. In the gingerbread channels I have riveted the mini non float nutplates and it can take some effort, custom rivet squeezer dies, etc.

I'll check out your method next time. D
 
What about using SS pop rivets to install the mini nut plates in the channel? Seems like that would work just fine. Thoughts on this?

Marty57
 
Marty
That would work but extra effort and extra holes in channel.
The Superfil method fills and seals the channel and leaves a
smooth surface with no rivet heads. It worked great on my Colt
project. The non-floating nutplates just barely drop into channel
so they can't turn anyway and just need something to hold them in
position.

Jim Miller
 
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