drill for #8 screws?
 

The first thing to do on the wing spar is attach all those nutplates. Question: should I drill out the holes in the flange where the #8 screws pass through to the nutplates? If so, what drill bit?

At one point someone gave me a nice little table summarizing the drill bit sizes to use for common rivets and screws, but I've lost it. Anybody know where I can find a similar quick reference chart?

oh... one more thing... should i prime inside the holes that I drill out in the spar, before putting the rivets in? Or is that overkill?

Hey Phil


Try number #29. Hve a look at this link:

http://bobmay.astronomy.net/misc/drillchart.htm

Cheers

A #21 drill bit will work, a 8-32 screw is approximately 5/32" , #21 is what we use for #5 rivets. it will give a slightly loose fit to allow for minor misalignments. Priming rivet holes is not required

A #19 works best. However, once you follow the instruction to countersink the flange, you will discover that the hole becomes enlarged anyway. Pick a size you have a counersink pilot for around 5/32 and make sure to back the hole up when you countersink it. -- Les

Bad holes?
 

Gregory... if #21 works for you, your holes are not very accurate.... :)

A good (MS type) #8 screw is 0.0161 to 0.0164 diameter on it's shank.

A #21 drill is 0.159 ... this would be an interference fit if your hole was accurate.

A #20 at 0.164 would be the close fit, and a #19 at 0.166 is more usual for a nice slip fit.

Screw (and other hardware) data is here

http://www.gen-aircraft-hardware.com/

with the specific #8 data here...

http://www.gen-aircraft-hardware.com...Structural.pdf

"approximately 5/32" isn't very accurate if you want correct holes.... :)

gil in Tucson

Doh! Stupid keyboard. 19 was what I meant, not 29.

Ignore me :o

If you are using a nutplate jig to drill the rivet holes for the nutplates, then make sure you use the size drill required for that jig.
For example, I usually use a #6 jig for all nutplates and the first hole should be drilled to #28 to use the jig correctly. Then drill out the hole to the appropriate size for the screw, after drilling the two rivet holes.
When using nutplates, I prefer to drill a slightly larger hole for the screw to fit through, since the nutplate is really doing the holding, not the skin. If you have a row of several nutplates, this wiggle room can make it much easier to get all of the screws in, without them being so tight.

gil
I stand corrected, A # 19 is the correct size for a slip fit hole. I worked on big airplanes too long , I used a #21 for an interference fit of #5 hi-loks ,
I will try to do better the next time I anwser a post.