[sbalmos]

Last night I was intending on match-drilling the parts of my F-904 central bulkhead. But trying to fit in one of the wing spar bolts proved to be near-impossible. Yes, my first attempt involved a rubber mallet no less. The "this isn't right" instinct kicked in, despite the bolts being close-tolerance.

After another half hour of yanking and twisting out with a socket wrench, the part of the bolt that managed to go into the bulkhead hole had the alodine layer peeled off. Which makes sense, given the alodine is probably a few thousandths thick.

I have read on some builder sites, notably Robert Paisley's own RV-7 blog, that some have gone ahead and scuffed off the alodine layer from all of their close-tolerance bolts. Does this seem fairly common / acceptable, before I start sending emails and pictures to the mothership?

Thanks!

 

[Dean Pichon]

It's not alodine...

On AN bolts like the one shown in your photo, the plating is cadmium. It is a few tenths of mils thick at most. I would not recommend removing the plating. The fact that you are finding so much interference is indicative of another problem than the (close tolerance) bolts being "too big". I would look to confirm alignment, and that holes are free of burrs, paint, etc.

Good luck,

 

[fixnflyguy]

Careful!

As others have said, that is cadmium plating, which is for corrosion protection. In close tolerance fit, by reason, minimal "slop" is what gives the joint the best strength. I work with this type fit in heavy jet overhaul every day, and the best description I can provide the bolts should install with a tap in by plastic or brass hammer, not "beat in". I typically apply primer to the bore of the hole, then either install quickly while primer is wet, or use a Boelube stick lubricant to assist. Removal can sometimes require rotating with a ratchet and a shot of LPS. Do not attempt to oversize the hole, or remove plating for the bolt. Also, make sure you temporarily assemble with hardware store grade bolts and then swap out one for one with the NAS bolts..it will keep the joint from spreading while you are tapping your NAS bolts in...hope this helps!

 

[sbalmos]

Ya, I'm running to Lowes Aviation at lunch here in a little bit. I've been reading in other threads this morning. Seems to be a fairly common point of heartburn for others, since it's the first time in the build that you try and fit the bolts into those center bulkhead holes. "I know it's close tolerance, but this is nuts!"

I've read about drizzling on the Boelube, freezing the bolts, heating the bulkhead holes, etc. I'll make some side notes in my manual about all that when I get to that point of fitting on the wings. In the meantime, I'll just use the Lowes Aviation bolts to align and match-drill the bulkhead plates.

 

[DaveT]

Yes, put the bolt in the freezer for a while and warm the area around the hole a bit.

 

[krw5927]

On AN bolts like the one shown in your photo, the plating is cadmium. It is a few tenths of mils thick at most. I would not recommend removing the plating.

Agreed. The bolts are plated with cadmium per SAE AMS-QQ-P-416 Type 2 Class 2, which specifies a minimum plating thickness of .0003", max .0006". By removing only the cad plating (how do you know you've removed only the plating and none of the steel?) you would gain a maximum of .0012" of additional clearance on the diameter. Probably more like .0006-.0008". And you will have completely eliminated the corrosion resistance of the bolts in the process.

Signs point to some other issue.

Also use extreme caution warming the structure. You can affect the temper of 2024 alloy at as little as 350-375F.