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  #1  
Old 06-17-2006, 06:58 PM
Brockster's Avatar
Brockster Brockster is offline
 
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Location: Lockport, NY
Posts: 128
Default ? assembling F-904 Bulkhead

I have begun the assembly of the center section and have two questions.

1, When you attach the F-904C-L&R center sections to the F-904A fwd bulkhead and the F-904D-L&R center sections to the F-904B aft bulkhead, the instructions say to install one NAS1307 bolt in the top and bottom to align everything before drilling rivet holes to size. Using a little lubricant and slight pressure I was able to do this in the forward bulkhead but not the aft. On the aft bulkhead I can fit the shank of the bolt in the 5/8" thick bar if I feed the bolt from that side or if I feed it from the web side the shank will fit in the hole in the web but stops at the 5/8" bar. (shank of bolt being the smooth portion, not the threaded part, tried all eight holes and several bolts) It almost seems like when the aft bulkhead was riveted together that it might have been misaligned by a couple thousandths. Anyone have any similiar experiance here? My thought might be to use a little emery cloth on the hole in the web portion of the bulkhead since it can be pryed away slighty from the bar to polish the hole a little. I believe this step is important because I could see how riveting the sides on to the bulkhead you could ever so slightly have the wing bolt holes misaligned making it even more difficult to install them later. A close tolerance bolt should only take a 12 to 14 ounce hammer to "tap lightly" it in. Anything more and the fit is not right in my opinion.

2. Vans says the NAS1304-50 and the NAS1307-50 bolts are close tolerance bolts. Mine seem to be standard NAS bolts. I thought a close tolerance bolt should have a raised or recessed triangle on it. Mine don't. Also the shank should be polished with no cadmium plating and a plastic sleeve on it to protect it. Mine just have some red rubber tips covering the threads. When installing these, the cadmium plating does peel slightly and the build up could definitely cause the bolt to bind once thy are installed with the wing spars. This also could be my problem in question one.

Any thoughts would be greatly appreciated.
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  #2  
Old 06-17-2006, 11:23 PM
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Paul Eastham Paul Eastham is offline
 
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#1 There was a thread a couple of weeks ago about someone who was having trouble installing bolts as well, and at least one possible diagnosis that was discussed is the misalignment you describe. Search for 904 and 704 (can't remember if it was a -9 or a -7)

As for sanding, it sounds logical, but I would personally get Van's blessing on any modifications in such a critical area. I would also make certain you have diagnosed the problem correctly...feel around with a dental pick or similar to find the misalignment?

Those bolts do not go in easily. I'm pretty sure I used more force than described in the directions.

#2 My NAS bolts are marked with a recessed dimple and the part number. This style of marking is not shown in AC 43.13 but it is shown in my ASA "Aviation Mechanic's Handbook". Mine are cad-plated, and that seems like a good thing to me...

Good luck - Paul
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  #3  
Old 06-18-2006, 09:48 AM
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Brockster Brockster is offline
 
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Paul,
Thanks for the response. I do plan to talk to Vans before doing anything permanent, But wanted to get other peoples experiances.

I've done some more investigation and have found the following. Your suggestion to check the search menu was good. I did find where others had similiar issues and asked some of the same questions. I need to work through the problem and come up with a solution. Thats where the members of the VAF forum and Vans aircraft come in. I do not have a telescoping guage, only a vernier calipers and micrometer. Using the vernier calipers (not the best but all I had) the wing bolt holes seem to run from .436 to .437. The bolts are a different story. Using the micrometer I measured anywhere from .4365 to almost .439, the portion of the shank where the threads end being the worst. The first page of chapter 5 in my 43.13, which is pretty old,(1984) Close tolerance NAS bolts are either marked with a raised or recessed triangle. The next page has a picture. I may be wrong but even though the # NAS1370-50 is forged in the head of the bolt does not make it automatically a close tolerance bolt. Reading further on bolt fit, it is acceptable to use a standard bolt in these applications provided a light drive fit after reaming is attained. I don't believe these are close tolerance bolts that Vans provides. They are standard bolts. I am in no way saying Vans is wrong in using them but if the diameters do vary slightly there will be problems installing them. If a portion of my bolt is .4375 and the hole is .437 it isn't going in and that may be why others unknowingly had real problems installing some bolts. I will post Vans response when I get it. Thanks again.
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  #4  
Old 06-19-2006, 12:12 AM
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Paul Eastham Paul Eastham is offline
 
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Hi Paul,
Perhaps you are right, the Skybolt catalog calls these "high strength shear" bolts. Sounds like a fit given Vans' application and the rather thin head on them.

Perhaps (I'm guessing now) they are also sized for a drive fit, which might be defined differently from "close tolerance". They certainly don't go in as easily as comparable AN4 or AN7 bolts in the same size hole.

Paul
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  #5  
Old 06-19-2006, 07:24 AM
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Brockster Brockster is offline
 
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Van's not open yet since I'm in eastern time zone and found some more info in EA-AC 65-9A A&P Mechanics General Handbook under "Installation of Nuts and Bolts".

1." Light Drive fit for bolts (specified on the repair drawings as .0015-inch maximum clearance between bolt and hole) are required in places where bolts are used in repair, or where they are placed in the original structure."

2. "The fit of holes and bolts cannot be defined in terms of shaft and hole diameters; it is defined in terms of the friction between bolt and hole when sliding the bolt into place. A tight-drive fit, for example, is one in which a sharp blow of a 12- or 14 ounce hammer is required to move the bolt. A bolt that requires a hard blow and sounds tight is considered to fit too tightly. A light drive fit is one in which a bolt will move when a hammer handle is held against its head and pressed by the weight of the body."

Using four of the bolts I believe I have a light drive fit in my forward bulkhead and spars. Two of the remaining four I think will end up being tight drive fit, and the last two have diameters along them that are .001 to .0015 larger than the hole and would be an interferance fit and will not use them. My rear bulkhead I won't be sure until I can borrow a telescoping gage from work and measure the diameters along the length of the hole. My suspicion is when the assembly was reamed at the factory they started through the fwd bulkhead, then the spars, and lastly the rear bulkhead. Possibly the reamer was slightly worn at the tip and the bottom of the hole might be a little tight. I can't get any of the four bolts that have a light drive fit to go completely through the 5/8 bar in the aft bulkhead and it it too early to start hammering. My questions to Vans will be as follows:

1. Are these true close tolerance bolts you provide in the kit and if not and a standard bolt is acceptable, why is called out in the parts list? (dimple in center of head just means it is an NAS bolt)

2. What fit is required here, tight or light?

3. What are the specs for the hole and bolt diameters so at least a starting point can be determined on the type of fit we can expect?
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Last edited by Brockster : 06-19-2006 at 07:31 AM.
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  #6  
Old 06-19-2006, 09:21 AM
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Brockster Brockster is offline
 
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Just got off the phone with Bruce at Vans tech support. Here is what he said.

1.The plans do call for close tolerance bolts but as far as the question of whether the bolts supplied are actual close tolerance bolts or a raised or recessed triangle must be present to be close tolerance bolts he would have to refer to engineering.

2. As far as bolt and hole diameters he could not specifically say except that tolerance for AN bolt diameters is plus .000, minus .003 and for NAS plus .000, minus .001.

3. Could not specify tight or light drive fit but bolt diameter cannot exceed hole diameter.

4. There is history of some webs when riveted to the 5/8" bars of some slight misalignment and that it is OK to slightly shave or srape material from the hole in the web to provide clearance, but don't touch holes in the 5/8" bars.

5. It would be acceptable to polish the shank of the bolt at the point where it meets the threads, to reduce the diameter, if it has swelled from the process of rolling the threads.

I will probably follow up with an e-mail to Vans engineering. Still not warm and fuzzy yet. I know it is not a huge deal now because I'm just attaching the sides to the bulkheads but I think it will pay off down the road. IMHO those bolt diameters should be perfect the whole length of the shank if they are real close tolerance.
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  #7  
Old 06-19-2006, 10:25 AM
ninerhawk ninerhawk is offline
 
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Default F904 and bolt clearances

My initial fit on these bolts was the same as yours. From my experience, I know that sometimes coatings can build up around sharp edges, i.e. the edge of a hole. In my case, merely swiping the anodized coating on the edges of the affected parts with the deburr tool, as if to deburr them, yielded sufficient clearance.

YMMV.

Howard
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