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  #1  
Old 04-30-2016, 07:38 PM
StuBob StuBob is offline
 
Join Date: Oct 2015
Location: Indianapolis, IN
Posts: 258
Default Drilling the Spar --- Eek!

Just double-checking before I do something stupid. I'm on the first step of SB RV8 wings. The manual says to rivet the tank skin platenuts to the spar after countersinking. But the holes in the spar aren't up to size. I assume I'm supposed to drill them to #40 and debur the bottoms of the holes? (The tops will be countersunk.

I only ask because the plans go on at length about countersinking but don't say anything about drilling to size. I'm pretty sure I already know the answer, but the spar is so perfect I hate to take a drill to it.

Here's what I'm talking about:

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  #2  
Old 04-30-2016, 08:03 PM
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Mark Dickens Mark Dickens is offline
 
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Yes you need to run a #40 drill through the holes and debur. All of the pre punched holes are slightly undersized and are intended to be opened up to the final size. Even those pretty anodized spars
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  #3  
Old 04-30-2016, 08:18 PM
StuBob StuBob is offline
 
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Thanks. I figured as much, but I've been out of the shop for 2 months awaiting wings, and it's affected my confidence!
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  #4  
Old 04-30-2016, 09:15 PM
Robin8er Robin8er is offline
 
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VERY IMPORTANT:


When you counter sink the spar, make sure you have a piece of steel with a pilot hole for the counter sink.

Take a piece of .25x1x3 inch piece of steel and drill a #40 hole in it. Clamp the steel onto the inside of the spar in such a way that the hole in the steel lines up with the hole in the spar that you are about to countersink. This make it so that the counter sink cant wonder. If you dont do this, you will get very ugly chatter marks from your countersink.

If this doesnt make sense let me know and I can try to explain it better.
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  #5  
Old 04-30-2016, 09:46 PM
StuBob StuBob is offline
 
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Location: Indianapolis, IN
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Quote:
Originally Posted by Robin8er View Post
VERY IMPORTANT:


When you counter sink the spar, make sure you have a piece of steel with a pilot hole for the counter sink.

Take a piece of .25x1x3 inch piece of steel and drill a #40 hole in it. Clamp the steel onto the inside of the spar in such a way that the hole in the steel lines up with the hole in the spar that you are about to countersink. This make it so that the counter sink cant wonder. If you dont do this, you will get very ugly chatter marks from your countersink.

If this doesnt make sense let me know and I can try to explain it better.
Got it. Thanks.
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  #6  
Old 04-30-2016, 10:19 PM
terrye terrye is offline
 
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Default Drilling Spar

The way I did it was to get a length of aluminum angle (1" x 1" x .063 from memory) the same length as the tank skins and clamp it to the underside of the spar. Then drill through the rivet holes with #40, cleco them and then drill through the screw holes with the same pilot diameter as your screw countersink. Now you have a hole that will keep your pilot centered as the flutes cut the countersink.

A piece of aluminum flat bar would work just as well
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  #7  
Old 05-01-2016, 07:52 AM
sblack sblack is offline
 
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Ya I can 2nd that. Learned that lesson the hard way like so many others.
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  #8  
Old 05-02-2016, 12:19 PM
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longranger longranger is offline
 
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I didn't care for the thought of running a countersink pilot in the nutplate threads as recommended in the instructions, so I made a jig (Photo 1) with a # 30 hole for the countersink bit pilot, and two holes for rivets to be used as locator pins. The rivets can't protrude above the spar flange, as they would interfere with the foot of the countersink cage, so I used 0.125 stock to make the jig and 3-3 rivets (3/16" long). I taped the rivets in place, and used cleco clamps to hold the jig in place for countersinking (photo2). I had to add a different set of holes on the edge of the jig to allow room for it to be clamped to the #6 access cover nutplate holes (photo 3).

Also, cutting those big countersinks can generate enough chips that it's hard to tell when you're done with the countersink. It helps to have someone hold a vacuum cleaner to suck up the chips as you work.






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  #9  
Old 05-02-2016, 06:48 PM
StuBob StuBob is offline
 
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Good stuff, Miles!
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  #10  
Old 05-02-2016, 10:57 PM
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longranger longranger is offline
 
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Thank you, Stuart. If you received your wing kit April 28, you sure aren't wasting any time!
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RV-7 TU 904KM (reserved)
Wings Fitted and Finish Kit on site

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1955 Cessna 170B flying since 1982

'To get something you never had, you have to do something you never did.' -Unk.
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