DIY Drilled Shank Screw

[Archer39J]

Thought I'd ask before forge ahead. When you just need that one screw. You know, you need 4 but only have 3 drilled shank AN3-7 and have a bunch of -7As sitting there, mocking your lack of procurement foresight. Can you take one of those guys, clamp 'em up in your drill press vice, and turn him into a -7. Rather... should you?

[Bcone1381]

I drill cotter pin holes in -7 's whenever I need them. The hole is used for a cotter key that secures the castle nut from backing out. I see no stress issues.

But, I don't just drill thru a bolt like you are envisioning. I am not good enough to keep the drill bit centered on that round shank. My hole would never be centered.

So I very carefully drill thru a nut using my drill press. I then position that drilled nut onto the bolt where I want the cotter pin hole to be located, and lock it in place with a second nut. Now my jig is set up for drilling the bolts using the drilled nut as my guide. This photo gives you an idea, but it does not show the second lock nut.

bolt jig.jpg

[Archer39J]

I drill cotter pin holes in -7 's whenever I need them. The hole is used for a cotter key that secures the castle nut from backing out. I see no stress issues.

But, I don't just drill thru a bolt like you are envisioning. I am not good enough to keep the drill bit centered on that round shank. My hole would never be centered.

So I very carefully drill thru a nut using my drill press. I then position that drilled nut onto the bolt where I want the cotter pin hole to be located, and lock it in place with a second nut. Now my jig is set up for drilling the bolts using the drilled nut as my guide. This photo gives you an idea, but it does not show the second lock nut.

Oh that's clever. I gave it a shot and it turned out well, though my bit was jumping some at the beginning I somehow managed, I'll use a nut as a guide in the future.

Top bolt is mine, bottom is for comparison.

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[BTAZ]

I gave up buying drilled bolts and started drilling my own(I drilled them on my mill, down to AN3) as, no matter how carefully I measured prior to ordering, I always ended up with the wrong length bolts.

Spruce(and I'm sure all the other typical vendors) sell a fixture(look for a "AERO II SAF-T-BLOK STANDARD" which, while not inexpensive, would pay back pretty quickly over buying a bunch of drilled bolts that go unused.

Instead, I kept a full set of undrilled bolts and drilled as needed.

[jaredyates]

I have a block for guiding the drill bits and it works ok, just realize that if/when you snap off a drill bit in one of the holes, the drill bit will be there forever. This happened even with the block clamped in the drill press. I like the "nut as a guide" idea, since the nut itself is semi-consumable and easier to replace. I also found that I liked to lightly debur the hole with a countersink bit, just to make it easier to guide the cotter pin in place and look more like the bolts from the store. It's definitely not a way to save money, based on the time involved, but if it is Friday afternoon and you want to fly this weekend, knowing how to drill one can be really handy.

[Bdflies]

I use a "center drill" to locate the hole. With the spot well established, switch to the drill size you want to drill through. The shank is big and stiff but the smaller drill point is very short, so it doesn't wander. They're great for spotting holes through tubing. To be clear, we're talking drill press here...

https://www.mscdirect.com/product/details/71036024

I have about a half dozen center drills, in a variety of sizes from itty bitty to about 1/2". Wouldn't be without them.

Bill

[Bcone1381]

You are the master, Bill! I don't own a center drill.....I think that might change.

[Bdflies]

Brooks, feel the force, Brooks. Let the force will be with you! 😎

Bill

[Archer39J]

Cool, thanks for the tips. I did a fair amount of searching before posting but couldn't find any discussions about it surprisingly.