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Misshapen match-drilled holes

guidoism

guidoism

Member
While match drilling the W-707 doubler plates for the rear spar I'm accidentally causing the original holes to widen and become misshapen. I'm assuming this is because I'm not holding the drill straight, or I'm moving it around, or I'm applying pressure laterally. I'm not sure.

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Anyways, two questions:

1. Is the biggie in this pic useable or am I going to have to order a new rear spar?

2. How do I match drill without doing this? Do I need to get a drill press?
 
Dull bits sometimes wander and create odd shaped holes like that. Try a new bit.

Van's is a sane resource on quality control. My guess is they will tell you you're OK, but you should call and verify.
 
Measure the hole and compare to the mil specs on Vans web site or AC43-1b. You are allowed certain tolerances for a given hole diameter. If it is within tolerance, and you have edge distance, you are probably ok.....

Now, saying that, Vans is the only one who can approve deviations when it is a spar. However, I would rather call them with that information so they know than just sending a picture. It will also educate you.

Make sure you clear your chips on the bit. Sometimes a small chip gets stuck in the flute.
 
Pilot

This trick works for most holes and match drilling.
Credit goes to my Mentor, Dave Paule.
Go to the local hardware or hobby store. Look for brass tubing in 12" lengths. Buy one each of each size.
Cut a piece of each starting with the smallest working to largest with each a tiny bit longer.
The smallest one should fit the #41 bit with 1/2" or so of bit sticking out when chucked.
Now you can center a bit without touching the parent hole by selecting the correct tube combinations. Try to drill the pilot hole with the smallest bit you can.
Here's the Kitplanes article.
https://drive.google.com/open?id=0B7hyZ-sKQmtrN01tUXdGOWdEUlE
Lots more on my Blog (see signature)
 
By looking at the drill shavings and the hole it looks like the drill bit is no good, time for a new one, they are cheap compered to parts.
 
reamers

I try and use a #30 and #40 reamer, as appropriate for rivet size, as opposed to a drill bit. Much better hole and this shouldn't happen.
 
bret said:
By looking at the drill shavings and the hole it looks like the drill bit is no good, time for a new one, they are cheap compered to parts.
Click to expand...

+1 looks like a melted hole. I got Pan American cobalt bits (Avery - Cleaveland) and have been very happy with life.
 
Are you using a high speed air drill? I find they want to chatter as they start. No need to spin the bit fast, I prefer to use a slow turning cordless electric drill.
 
bret said:
By looking at the drill shavings and the hole it looks like the drill bit is no good, time for a new one, they are cheap compered to parts.
Click to expand...

+1 on replacing the bit. A lot of folks don?t realize that if you drop a bit on the floor (concrete) and it hits on the point, it is likely trash. I have watched people put their drill down with the bit hitting the floor. Same result. Colbolt drills fair a little better but still not good.
 
In the picture, the hole in the lower corner should first be piloted with a #40 drill. Try to get the #40 centered best you can by spinning the drill slowly and observing how centered it is. When you have manipulated the drill bit to being centered, THEN Squeeze trigger to full speed and complete #40 hole. In general, higher drill speeds is considered better than lower speeds! If hole is off center, don't worry, move on. Then go to #30 drill, the shoulder of the bit can now align itself with the walls of the top (outside) skin, and the drill will go through the bottom skin concentrically. Holes will be very accurate with little effort using this method.
 
My match drilling thoughts

1. Use sharp new high-quality bits. Change often, they get dull fast.

2. Use high-rpm (air) drill for aluminum.

3. Use very light pressure on drill. Let the bit cut its way through the hole.

Dan Miller

RV-8 N3TU, 1735 hours of fun!
Bucker Jungmann
Taylorcraft
 
One thing I haven?t seen mentioned is to be sure you are using 135 degree split tip bits for aluminum sheet. That helps.
 
cdmiller said:
1. Use sharp new high-quality bits. Change often, they get dull fast.

2. Use high-rpm (air) drill for aluminum.

3. Use very light pressure on drill. Let the bit cut its way through the hole.
Click to expand...

Thank you everyone for the advice. I've contacted Vans with the pic and the copy of the plans showing exactly what hole it is.

Also, I've done some experiments based on all of your advice. The bit was definitely done. New bit is much much better. I can't believe I didn't realize that.

And I tried the technique using the #40 first and then the #30 and these holes are absolutely perfect. I will be doing that from now on.
 
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