Drill Size for AN3 Bolt?

[RV7Factory]

Ok, I have had about enough of this... I have now seen three different references to the proper drill size for an AN3 bolt; 3/16, #12 and #11.

Which is it? I've been using #12 with mostly success, but sometimes I think a slightly larger hole would be better. Just curious.

[rv8ch]

There is probably a "right" answer somewhere in the books, but I drill the hole differently depending on what I'm doing with the hole. Will the bolt be in shear or tension? How many bolts will there be? Will it be a hassle to line up multiple holes? Will you use a nutplate or a nut on the other side? Basically I like the hole to be as small as possible when in shear.

[alpinelakespilot2000]

Brad--the smallest hole you can get away with is usually the best. #12 is best, but in some cases #11 is okay and might be needed if you are going through a lot of layers. Alternatively, I just picked up a 3/16 reamer from Avery a couple of weeks ago. It makes a "perfect" hole everytime that fit the AN3 bolts like a glove, no matter how many layers you're going through. Why I didn't spend the $6 earlier in my project I have no idea. Read up on how to use them on the bottom of the Avery catalog page on which their reamers are listed. Happy drilling.

[LettersFromFlyoverCountry]

Use a #12 and you'll be fine. The exception is those blocks of plastic (or whatever it's referred to), in which case you should use a #10.

[RV7Factory]

Steve,

Ironically, what brought this up is that I was looking at which reamer (size) to order. When I did the math, 3/16" didn't seem to add up. 3/16" being .1875" while some specs I came across on AN3 bolts indicated their diameter to be .1860-.1890", which in some cases could be larger than the 3/16" (.1875") reamer. A #12 bit (or reamer) should be .1890 and would seem to cover the range of an AN3 bolt more completely, but might seem too sloppy in some cases.

I'll probably just get both... #12 and 3/16" reamers. Why not, it's only $.

[Jim P]

Brad, while you're at it, get the reamers for the AN4 and AN5s as well. Drill holes somewhat undersized and ream for final fit. With the larger bit sizes, you'll notice that holes are not exactly round. A reamer makes the best round holes. You also hit it right in that bolt also have some variance in diameter.

[alpinelakespilot2000]

I got Avery's 3/16 and 1/4 reamers. To date I've not had a bolt that has either not gone in or felt sloppy, but I'm sure there is some variation in bolt size. I don't caliper every bolt before I use them but the reamer has been one size fits all so far.

[RV7Factory]

Thanks guys! I just called Cleveland and had them throw in the 3/16", 1/4" and 5/16" reamers into my order of earlier today (the tool orders never end).

Thinking about this, I should probably caliper my #12 bit. I've often felt the bolts go in too snug (or not at all), so I am wondering if my #12 bit is true to spec.

[ericwolf]

I always use a #12 and have had good success. On occation, upon final assembly, there is a little primer in the hole or the holes don't line up perfectly, resulting in a tight fit. If the bolt cannot be lightly tapped in, then running the bit through the hole again after the parts are together works well for me. This may not be the theoretical perfect way to do it, but it results in a bolt that is not loose and still slips in the hole. That said, I may order a reamer on my next inevitable Avery order.

[Davepar]

Here's a fun little experiment. Take a #12 drill bit and a scrap piece of Al sheet. Drill a hole through it using no backing wood block and use a lot of pressure on the drill. If you look at the resulting hole, it will probably be triangular. Or shaped like a rotary engine rotor. An AN3 bolt won't fit through the hole. Now try to round out the hole using the drill bit. For some reason, the shape of the drill bit just latches onto that triangular shape and it's tough to get rid of. A reamer will round it out quite nicely.

I guess this is why the recommended drilling procedure for Al is to use high speed, light pressure, and backing material.

Dave