Drilling through thin material...

[Spike]

I am currently working on the fuse drilling the main longerons to match the side skins. One area of consistent difficulty I seem to have is match drilling a non-prepunched part (especially thick ones) through a very thin material.

For instance, when working with this current task the fuse skin is 0.023" and the longeron being match drilled over an 1/8". When I start the bit will cut the sides of the hole in the skin before it bites into the thicker material. The result is that I get a fairly decent hole in the longeron but the hole in the skin gets opened up. This occurs even with a brand new bit. Its not horrible, but its more than I would like. In this case its not too bad as this skin just gets sandwiched between the longeron and the turtle deck skins, but I would really like to get this figured out.

The best way I have found to prevent this is to use an angle drill with a short bit. That seems to let me better control the bit and its movement. This I guess is probably because I can control the bit much closer to the tip. Doing it this way seems to end up with very nice holes.

But what I want to know is how are you guys doing this with a regular hand held drill?

-- Spike

[bullojm1]

Spike,

When you say "Regular Handheld Drill" are you refering to an electric/battery drill or an air drill?

I use an airdrill for everything except the countersink bits. When using it, I typically apply a little pressure and low RPM's for the drill bit to start, then decrease the applied pressure and increase the RPM's to full. Remember you don't want to push the drill bit through the material with a lot of force.

I find applying a lot of pressure with low RPM's does a great job of ensuring the drill bit will not wobble when starting through the material, thus distorting the pre-punched hole in the fuselage skin.

[Spike]

Hand held air drill. Reading that do you mean lots of force slow speed, and then moving up to low force and high speed?

Spike

[Mike Balzer]

Spike,
are you able to use a busing egg cup to keep the drill perpendicular with the skin and the spar when drilling through thick materials. Another thought would be to use a # 41 drill and open up with a reamer if possible to give a clean round hole in the Extruded longeron and not enlarge the hole in the skin.

Just My .02 worth I haven't gotten there yet,

Mike Balzer
RV-8

[bullojm1]

Hand held air drill. Reading that do you mean lots of force slow speed, and then moving up to low force and high speed?

yes, thats the gist of it. And not "lots" of force, just a little more than you would usually do. This technique also works well when your drilling holes you laid out with a sharpie marker. However, in that case, I manually spin the drill chuck with my hand one or two times to get the pilot hole started. Then work up the speed and decrease the pressure. Before you know it, it becomes automatic.

[captain_john]

Speed is life!

The longer you spend spinning the bit in the work area the more time you give it to walk.

Drill with an air drill fast and accurately.

Hold the drill perfectly perpendicular.

Shoot fast and good!

It will be fine!

CJ

[hydroguy2]

1 more drilling tidbit. If you have a hole that you absolutely have to have perfect, use an thick alignment guide or bushing to keep things from wandering. Easy to make from either round stock on a lathe or a piece of flat stock. With the flat stock version you can use clamps to position everything where you want it. I've even used a hole punched in 1/8" AL stock and double back tape to keep on track.

[TomNativeNewYorker]

When I was working on the F-14 Tomcat program, engineering implemented a hole quality program. They came up with the optimum drill and ream speeds for the different materials hand drilled with pneumatic drill motors.

800-900 rpm was the drill speeds for aluminum. If I recall correctly, ream speeds was half of the drill speed.

Slowing the speeds down made for nice clean holes, and drill bits lasted longer then when using them at 2000+ rpm.

[Bob Barrett]

If you aren't using a center punch in the to mark the center of the hole you want to drill in the longeron, try using one. I hardly ever try to drill metal without using some type of center punch. I have a sort of atomatic one that you can adjust the pressure and it just snaps when you push on it.