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Close tolerance bolts

sahrens

sahrens

Well Known Member
I am working on the F-704A / B bulkheads for my 7A. One of the steps is to cleco the F-704C L&R Center Sections to the forward and aft bulkheads and put a NAS1307 bolt through at least one top and bottom hole to align the parts exactly. Herein lies the problem.

I realize the bolts are "close tolerance" but I can not get the grip portion into the hole without placing some rather excessive force on the bolts. Far more force is required than I am currently willing to use. I have read through the instructions and no where do these bolt holes get modified. In fact, later the instructions say to bolt the forward and aft bulkheads together (with spacers) for a trial fit.

Has anyone else experienced this level of tight tolerance? Am I missing something here? I am having a hard time working up to driving the bolts through. Please enlighten me.

Thanks
Scott Ahrens
N418BG reserved
Empennage complete, wings 95% (waiting for parts)
 
Scott you are not missing anything the bolts should not slide easily. Lubricate them a bit and push in you have necessary force. Or tap them lightly with rubber mallet but DO NOT modify the holes. Later while attaching wings permanently there is a recommendation in the manual to freeze the bolts before driving them in. Also pay attention to alignment of the holes.
 
Just to make sure I understand you correctly Scott. Is this the process you are talking about?

forScott.jpg
 
That is it

Yes that is the process. As I look at your photo you have one of the 1370-50 bolts inserted into the upper portion of the right 704C on your forward bulkhead (on the left side of the photo.) As I zoom in it looks like the threads are in but not the grip. That seems good enough for the alignment before riveting the C to the bulkhead, but its the check for fit that is a few steps later that concerns me.
Even if I freeze the bolts I would have to drive them back out pretty quickly before they start to warm up and expand.
 
That's the only picture I have found in the archives. I completed that part early 2007 but I remember I inserted all of them. There is a website somebody explained it in detail. If I find the ref I post it.

added: I inserted may be half inch just to align the holes, didn't drive them all the way through
 
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Hello Scott

I had the exact same and was doing it also like seen in the pictures.

BUT, I was mesuring out one bolt and have seen, that the bolt at the end of the thread where the "grip" beginns is a bit larger by a few thousends! So I grinded down two bolts with emery cloth in this area.

I use these two bolts a few times, allways when those spars needs alignement and/or trial fit of the gear towers and so on.

For the final build up I will buy new one.

Clean the holes allways before you slide in the bolts and use oil or grease!

Also clamp the thin aluminum to the spar bar when you tapping the bolts out, it happend to me, that the thin web was pulled away with the bolt and the hole was a bit elongated.

The "freezing" trick does not give so much difference to the steel bolt, heating the aluminum gives double the amount of growing/shrinking (keep the limits, not overheat the aluminum!)

Good luck

Dominik
 
On mine, to get those in during pre-build, I had to take a Dremel and very very lightly open up the holes on just the thin plates that go up the side of the fuse and also the gusset that gets used for the area where the gear weldment goes if your not building an A model.

Don't touch the spar bars! The bolts will fit!

Do yourself a favor and ensure that these bolts will go in now instead of when you are standing on your head trying to fit them while installing the wings. If you use hardware store bolts or other at this pre-build stage, your almost guaranteed to have a fit getting them in later.

It takes some force to get these in when your installing the wings. If they fall in, they are too loose in my opinion. They need to be tight to do their job.

Freezing did help when I did put them in for good!
 
Thank you all for your insights. I will go back to building with the plan of purchasing new bolts for the final assembly.

Scott Ahrens
 
The fix for spar bolt installation...

Brantel said:
On mine, to get those in during pre-build, I had to take a Dremel and very very lightly open up the holes on just the thin plates that go up the side of the fuse and also the gusset that gets used for the area where the gear weldment goes if your not building an A model.

Don't touch the spar bars! The bolts will fit!

Do yourself a favor and ensure that these bolts will go in now instead of when you are standing on your head trying to fit them while installing the wings. If you use hardware store bolts or other at this pre-build stage, your almost guaranteed to have a fit getting them in later.

It takes some force to get these in when your installing the wings. If they fall in, they are too loose in my opinion. They need to be tight to do their job.

Freezing did help when I did put them in for good!
Click to expand...

Brian has made a very important point. There is usually some slight misalingment between the holes in the spar web plate and the holes in the spar bars. Because the holes are not oversized at all, a slight misalingment can prevent installation of the bolts. I am convinced that this is the source of the majority of spar bolt installation problems.

Brian's suggestion is an easy fix if you do it during initial center section fit-up. I slid a thin piece of steel shim stock in between the web and the bar, and used a Dremel tool to enlarge each hole in the web just enough to allow the bolts to be installed. The steel shim stock prevented any contact between the Dremel tool and the spar bars.
 
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