Drilling Tapered Holes For Landing Gear Tapered Pins

[David Paule]

After a lot of headaches, a local RV-6a owner, Rick Brennan, came to my rescue and finally got the tapered pin hole through the left main gear mount of my RV-3B. The gear leg geometry is the same as the RV-4 in its mount, FYI.

Here's what worked:

1. Secure the assembly on the mill. We used a Bridgeport mill.

2. Drill through the joint with the smallest drill that's close to the final size for the small end of the tapered pin.

3. Step drill the hole so that the drills don't exceed the taper wall sides, but going as far as possible short of that.

4. For the final reaming with a tapered reamer, put the reamer in a Tee handle.

5. Make a mandrel such that you can use the milling machine for pressure, pushing down on the reamer with the mandrel as the push-tool.

6. One person presses down on the reamer with the mill while a second person rotates the reamer by hand. Here on out, the mill is turned off. Use lots of cutting oil. There is plenty of axial force on the reamer, and plenty of necessary torque on the Tee handle. Use work gloves. Never turn the reamer backwards or pull it straight out. Keep it turning, even when you're pulling it out of the hole. It's okay to stop, provided it's turning when the mill pressure is relieved.

7. Check often. But it goes slowly enough that if you do that, you won't exceed the tolerance. When checking, don't neglect to deburr the exit of the tapered hole. That burr hinders the assessment of the progress you're making.

This worked for us.

Dave

[rocketbob]

Here's a far easier way to correct a mis-drilled or elongated landing gear bolt hole.

[David Paule]

In this case, that would not have helped.

Dave