#4 spar screws. What size drill bit?

[Dave Calkins]

Okay, I'm wondering what the consensus is on the drill size for the #4 truss head screws for aluminum spars.

I use a #40 (3/32") and it seems like the screws get scary tight before the sheet-metal or rib brackets are pulled up tight to the spar.

I was at Reeve's today buying some angle drill bits and was recommended to buy a #44 !?! That cain't be right :evil:

So...............lemme have it.


....and Thanks! DAVE

 

[Dave Calkins]

PS. I've run this by a few other professionals and #40 is all I've gotten for answers.

Anyone got feedback. Let me know>

 

[JP]

3/32 number 40. And those are truss head B's (the blunt ones). And they do get scary tight in that last little bit....

 

[Alaska_Rallyer]

I use a # 40 when installing them in any thick material(spars). Yes they do get very tight. Installing leading edge the screw will sometimes strip out before you can get it as tight as you would like. The key is new screw tips. When attaching trailing edge to ribs, leading edge to nose ribs or other such thin material a #40 is too BIG. That is when i use a 44.

 

[mike mcs repair]

#40 is what I use too.......

but life has been so nice since I got a FULL set of drill bits (115 piece) now i always have the right size... bought a cheep costco set first, then a real set, so nice to always have the right size for whatever variations!....

 

[Steve Pierce]

I have always used a #40. The stainless steel screws that Univair sells sometimes break. I have been getting the screws from Dakota Cub. They fit my screw driver nice and haven't had any problems with the new holes. I also use a long screw driver so I can get straighter on the screw when installing ribs and you can push on it and I think the flex gives a little better torque. New tips are a must. Glad nap On started coming by every week again.

 

[Dave Calkins]

Thanks guys. I thought I was crazy there when they said, "...don't you want a #44..." or something like that.

I'll believe using #44 for the the non-spar stuff, as AKRallyer said.

 

[WWhunter]

I am currently constructing a wing for a Murphy Rebel and ran out of clecos. Being in Hawaii it takes forever to get anything shipped. So I asked around to borrow some and a guy told me to use #4 screws in place of clecos. Has anyone done this before? The holes will be drilled out to 30 later. I am installing the leading edge.
Keith

 

[Dave Calkins]

Yes, especially if they will be upped to a #30 later, it's not a problem. Sometimes I use cheapo hardware store machine screw adn nuts when I need more draw clecos than I own or than I can borrow. That works very well. I use a 1/4"drive impact wrench, set very low, to tighten and loosen them, and it's plenty fast and no pain at all.

I just got a PM with a tip to use some grease to lube the #4 PK where it goes into the spar. An idea I had been considering, and it seems this guy has put it to good use.

Also, unrelated, but: the SMith wings I'm working on have some lube (Dow DC4?) between the ribs and the LE skins. I'm not sure if its' for corrosion protection, or maybe it's so the skins will slip up on the ribs for easier leading edge wrapping/tensioning. Anyone???

 

[Steve's Aircraft (Brian)]

Well lets see, DC #4 is an electrical insulating compound. Usually used in the aircraft world for oil filter seals. I also use it on rubber fuel lines to make them slip on easier over metal barbed lines. Probably be useful for making it a little easier for leading edge wrapping, but I would have to try it out before making any conclusions. I would assume that it would help a little with corrosion protection due to DC #4 being a dielectric compound designed for the corrosion protection of aluminum electrical connectors.

As for the original thread question, I use a #40 bit for the spar drills, and usually a smaller (44 to 46) bit for rib screws. At the moment I am building up a set of wings using Dakota ribs and I am using a #40 on them due to the rib cap-strip being a solid extrusion.

Brian.

 

[gdafoe]

Don't tell anybody, but it is plain old vaseline so that she can get the skins pulled up really tight. I replaced a damaged section :roll: and could not get it as nice and tight as she got it using straps. Leave it to a Lady eh? Aren't those wings a work of art? A person should put clear covering on them like they do on some RC Model airplane so you can see the workmanship.

 

[Steve Pierce]

I was at Legend and they were using tape on the nose ribs for the same reason.