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countersinking spar for tank screws

A

alpinelakespilot2000

Well Known Member
I've seen a couple methods for tank screw (size 8) dimpling on the spar.

1. Van's method is to attach the nutplate first and then use a #30 cutter and go deep enough for the #8 screw. Here the nutplate serves to guide the #30 countersink pilot, though I've seen other people report that this is not the best way to go because the punched spar holes are already bigger than #30 allowing the bit to wander a little bit before the platenut can engage the cutter's pilot.

2. The other method is to drill a hole big enough for the appropriate countersink in a piece of scrap, clamp that behind the hole to be countersunk, then countersink the spar using the scrap as the guide for the countersink's pilot. People who have used this report the best results. (Dan C. method and others).
** Question on method 2: If I use method 2, will I need to first enlarge the holes in the spar to #19 (to accept the #19 countersink)? #19 is the proper countersink/clearance hole size for a #8 screw, correct? (I got #19 off Cleaveland's pull out chart). OR, should I be using some other size pilot hole drill or countersink cutter.

Votes for method 1 or method 2?
If method 2, do I need to go ahead and predrill all the tank screw holes in the spar to #19 before I begin countersinking with a #19 cutter?

(As you can tell, I'm terrified of messing up the beautiful--and VERY expensive--wing spar. All of the emp. parts that I messed up on were chump change in comparison!)

Thanks,

Steve
 
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I used method one and it worked out fine. In the latest issue of the RVaitor they talked about using an electric drill rather than the air drill. I used my air drill at a slow speed and the countersinks came out great. If you have a portable electric drill use the high torque setting and just go slow. In my experience the nutplate worked fine. Hope this helps. If I can figure out how to do it I could post some close up picts of mine, or just email me and I will send them to you.
Ryan
 
I used method #1 with my rechargeable drill on the "torque" setting. I also used a 1/2" dia. 3-flute c'sink cutter I bought from Brown Tool. A piece of aluminum drilled and dimpled for the #8? screw was the depth gage per Van's instructions.
Steve
 
Spar countersink

I used the Van's method. It does seem daunting, but just dig in, it's not difficult! I started with a DeWalt cordless but ended up using my air drill with better results. I think it depends on the type of countersink bit you have that will determine the speed that makes the best countersink. For me the slower speed seemed to chatter and slightly misshape the hole. Of course do some practice and depth calibration tries on some scrap. First start on the bottom of the spar. That way if you are a little off at least it won't be on top of the wing right by the door where you see it every time you get into your airplane. I just went slowly and carefully on the first couple of countersinks on the spars. Also don't start on the first hole and move two or three holes away on your second countersink, so that if you need to fine tune your adjustment your first two countersinks will not be on a more critical edge screw or side by side.
Steve RV-10 #40212
 
Thanks

Thanks to everyone above for the suggestions.

If I go with Van's method, do I wait to drill out the screw hole in the spar to #19 until after I've countersunk it, or do I drill it out right away before starting the countersink process? The advantage of the former is that I've got a smaller hole in the spar to help guide the countersink before it engages the platenut. On the other hand, it may be kind of difficult to drill it out later to #19 without running into, and messing up, the threads on the platenut.

Thanks again,
Steve
 
Install the platenuts first. That 3 flute cutter I used was better at self-centering than 2 flute until the c'sink pilot got deep enough into the threaded part of the platenut.
Steve
 
alpinelakespilot2000 said:
I've seen a couple methods for tank screw (size 8) dimpling on the spar.

1. Van's method is to attach the nutplate first and then use a #30 cutter and go deep enough for the #8 screw. Here the nutplate serves to guide the #30 countersink pilot, though I've seen other people report that this is not the best way to go because the punched spar holes are already bigger than #30 allowing the bit to wander a little bit before the platenut can engage the cutter's pilot.

2. The other method is to drill a hole big enough for the appropriate countersink in a piece of scrap, clamp that behind the hole to be countersunk, then countersink the spar using the scrap as the guide for the countersink's pilot. People who have used this report the best results. (Dan C. method and others).
** Question on method 2: If I use method 2, will I need to first enlarge the holes in the spar to #19 (to accept the #19 countersink)? #19 is the proper countersink/clearance hole size for a #8 screw, correct? (I got #19 off Cleaveland's pull out chart). OR, should I be using some other size pilot hole drill or countersink cutter.

Votes for method 1 or method 2?
If method 2, do I need to go ahead and predrill all the tank screw holes in the spar to #19 before I begin countersinking with a #19 cutter?

(As you can tell, I'm terrified of messing up the beautiful--and VERY expensive--wing spar. All of the emp. parts that I messed up on were chump change in comparison!)

Thanks,

Steve
Click to expand...
I used Van's method and it worked out fine. Actually when you countersink to the depth required to nest the #8 dimple in an .032" skin, you will probably lose the pilot support of the #19 cutter as well, so you may as well use the platenuts as a pilot guide for the #30.
Unless you want to build a pilot support block specific to either the #30 or #19 to insure "perfect" countersinks, the platenuts work just fine.
The geometry for either cutter is identical once you exceed the #19 diameter on the exit side of the countersink.


-Mike
 
Steve,


Don't sweat the #19 hole...once you countersink deep enough to accept the screw, the hole will have been expanded by the countersink just enough to accept the #8 screw. That is why I used the #30 countersink and the back plate a-la checkoway. This allows perfect holes using just the #30 c-sink which I already had on hand....it was already said, but the angle is the same on the #30 as the #19 once you get past the diameter of the guide.

As a side note, I tried one hole Van's way with a platenute and one without anything before this method...both holes wallowed quite a bit which is why I went with the back plate.
 
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