View Full Version : Airframe drilling sequence
01-18-2005, 07:14 PM
Hi everyone. I'm sorry about beating a dead horse with regards to airframe drilling, but damn It the process needs tolernancing.
I'm told that the "optimal method" is to punch, then center-drill, then thru-drill a few thousandths shy of the finished diameter, then use a reamer to get the hole the exact diameter. I'm also told to use a vise to maintain concentricity. That's the published accepted method, but no drill sizes are mentioned even though there's usually only two.
Problem is, there's not enough clearance between the chuck and the material to change bits.
Thus I must ask you all, how many of you were able to drill your airframes in that sequence?
For those that could, please share how you managed to change bits without moving the material to put a new bit in place.
01-19-2005, 03:11 AM
Brian, that is why I like the center drills so much, The long ones, you don't have to change from a pilot bit to a regular bit. The center drill, drills a "rounder" hole than a twist drill, then you can use a reamer in a hand drill, or drill press, as needed.
01-19-2005, 04:31 AM
The only problem with doing that is that the body of those long center drills is the same as the cutting diameter and will get very hot very quickly if used for drilling through holes. They are also very limited in sizes so you'll have great trouble finding one properly sized for finishing up with a reamer, as he wanted to do. I'm not a big supporter of using reamers for holes such as these though. Reamers would be more appropriate for dowels than capscrews (IMHO).
01-19-2005, 04:49 AM
True, you shouldn't have to use a reamer on every hole, use oil on the center drills.
A sharp 1/4" drill bit is plenty adequate, if you have a pilot hole.
The only time I have had a problem is with NAS bolts, they seem to be a tighter tolerance than a standard AN bolt.
01-19-2005, 06:35 AM
To keep things in perspective; I believe that Bensen originally designed the gyrocopter so it could be built by the common man with hand drills, etc. ;)
There's certainly nothing wrong with trying to do a perfect job, but try not to loose too much sleep. :o
01-19-2005, 06:58 AM
To keep things in perspective; I believe that Bensen originally designed the gyrocopter so it could be built by the common man with hand drills, etc. ;)..............We do need to keep in mind that Dr. Bensen was in the business to sell Gyrocopters. Consequently he wasn't going to put up any impediments to building one by saying that tools, other than what was commonly in the garage, needed to be purchased.
This isn't to suggest that his method of construction doesn't work because a bunch of people built perfectly adequate flying machines from his plans and construction manual. However, given a choice, I will use the best methods available and what is good enough for Boeing is good enough for me. In the ole days they would drill and ream by starting with gang drilled pilot holes but then these holes are mostly for rivets. I don't have a means or need for gang drilling but I can setup and drill close tolerance holes otherwise.
To each his own!
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