RV7Factory

RV7Factory

Chief Obfuscation Officer
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.
 
Drilling size for bolt

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.
 
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.
 
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 $.
 
Last edited:
Drill Sizing for AN3

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.
 
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.
 
Ordered!

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.
 
Another Thought

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.
 
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
 
Specifications

This one is easy... just check the specifications...

AN3 bolts

http://www.coastfab.com/pdf/an3-an20 genspecs.pdf

Diameter is 0.186 to 0.189 inches

Then check drill sizes

http://www.armstrongtools.com/reference/decimal.jsp

#13 0.185
#12 0.189
#11 0.191
#10 0.1935
and
3/16 0.1875

So an accurate, reamed #12 hole will fit all AN3 bolts.
A hand drilled #13 might fit due to poor drilling accuracy.
A hand drilled #12 certainly will fit (assumes a quality drill)
A #11 has a little slop, and a #10 is quite loose.

If it needs to be an accurate hole, I like to drill #13 and ream to #12 - you can get nice push fits (no hammers involved) this way.

Notice that there is 0.003 tolerance in the bolt size, so some bolts will be a snug fit, and other will slip in easy, into the same hole.

Good quality drills are very accurate.. probably better than your micrometer.... :)
One manufacturer has +.0000 to -.0007 as a tolerance

http://www.precisiontwistdrill.com/techhelp/help_pages/element_dimensional_tolerances.asp

All available on Google, and just use the numbers.....

Do the above calculations for AN4 bolts and you can do most RV holes with just 4 sizes of drills (#12 and #13 drills for the AN3 bolts) and two reamers...

gil in Tucson ... an engineer likes numbers...
 
just double checking ...

I'm about to order some reamers for bolts. Based on what Gil wrote, I think I need a #12, 1/4, and 5/16. For those of you who are further along than the empenage of a -10, are there any other reamers I will need? Thanks in advance! -Jim


-3 bolt (nominal 3/16" -- 0.186-0.189)
-> drill #13 (0.185) and ream #12 (0.189)

-4 bolt (nominal 1/4" -- 0.246-0.249)
-> drill #C (0.242) and ream 1/4 (0.250)

-5 bolt (nominal 5/16" -- 0.309-0.312)
-> drill #N (0.302) and ream 5/16 (0.3125)


keywords: reemer, reamer, reemers, reamers, bolt sizes, hole sizes, bolt hole, bolt holes,
 
FWIW I finally got a chance to use my 3/16" reamer to enlarge a hole for an AN3 bolt. The bolt fit the hole PERFECTLY. At first I thought the hole was small, but with VERY light pressure the bolt slid in. As usual, YMMV.
 
#12 is better...

RV7Factory said:
FWIW I finally got a chance to use my 3/16" reamer to enlarge a hole for an AN3 bolt. The bolt fit the hole PERFECTLY. At first I thought the hole was small, but with VERY light pressure the bolt slid in. As usual, YMMV.
Click to expand...

Brad... YMMV since the AN bolt you used had a tolerance of 0.186 to 0.189.
Your 3/16 reamer at 0.1875 will work for bolts in the lower half of the range. If it was a 0.001 undersize hole for your bolt, I believe it would take more than a finger push...

To cover all AN3 bolts you need the #12 reamer, or a sloppy reaming job with the 3/16.

gil in Tucson - extrapolating single data points doesn't always work.... :)
 
az_gila said:
To cover all AN3 bolts you need the #12 reamer, or a sloppy reaming job with the 3/16.
Click to expand...
So what are you saying about my reaming job??? :D :D :D

IIRC Cleveland or Avery doesn't carry #12 reamer, only 3/16", so you must go elsewhere for it (e.g. Brown Tools).
 
Last edited:
MSC

You can try www.mscdirect.com for reamers. You can get reamers in just about any size imaginable, and when you are near "standard" sizes like 3/16 or 1/4, etc., you can get reamers in .0005, or half-thousandths size. I have an .1885 reamer for AN3 bolts and a .2485 reamer for AN4 bolts. Also, you might want to pick-up a couple of tapered reamers, such as a #2 and #4, which will cover a lot of sizes.
 
az_gila said:
Brad... YMMV since the AN bolt you used had a tolerance of 0.186 to 0.189.
Your 3/16 reamer at 0.1875 will work for bolts in the lower half of the range. If it was a 0.001 undersize hole for your bolt, I believe it would take more than a finger push...

To cover all AN3 bolts you need the #12 reamer, or a sloppy reaming job with the 3/16.

gil in Tucson - extrapolating single data points doesn't always work.... :)
Click to expand...
To provide an alternative data point to Gil's precision, I've done all my AN3 holes with a .1875 reamer from Avery's. Every bolt has gone in easily with no more than a light finger push. Maybe some AN3 bolts are larger than .1875 but I haven't found one in my kit yet, and I'm pretty much all the way through the fuselage.

For those who are trying to decide what tools to get, I don't think you need to get any other than the 3/16, 1/4, and perhaps the 5/16 reamers. I hate to see new builders think they have to buy every tool out there to the point that they can't afford their project any more--your tool budget is already going to bust sooner than you think. Start from what Van's recommends and then add what makes your work easier. (Again, of course, I'm just another single data point :), YMMV.)
 
Last edited:
Why not just buy the correct sie?

alpinelakespilot2000 said:
To provide an alternative data point to Gil's precision, I've done all my AN3 holes with a .1875 reamer from Avery's. Every bolt has gone in easily with no more than a light finger push. Maybe some AN3 bolts are larger than .1875 but I haven't found one in my kit yet, and I'm pretty much all the way through the fuselage.

For those who are trying to decide what tools to get, I don't think you need to get any other than the 3/16, 1/4, and perhaps the 5/16 reamers. I hate to see new builders think they have to buy every tool out there to the point that they can't afford their project any more--your tool budget is already going to bust sooner than you think. Start from what Van's recommends and then add what makes your work easier. (Again, of course, I'm just another single data point :), YMMV.)
Click to expand...

Maybe... but this is one of the problems... Van does not recommend any reamers.
A hand held 3/16 drilled hole (the size Vans recommends) will probably meet the 0.189 number... :)

If you are going to spend $8, why not just buy the correct size?

http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=02318129

No extra $$ - or "he who has the most tools" bragging rights involved... :)

gil in Tucson
 
3/16" drill used for AN3 Bolts

It took me 8 years to complete my QB RV-6A as I worked toward retirement with a 4 hour commute each day. If I had tried to ream all of the holes to close tolerance fits at all the AN bolt locations (Wing spar attachment excepted) I would still be building (and working at JPL - that may not have been so bad actually). I used 3/16" drills for AN3, 1/4" for AN4, 5/16" for AN5, etc. and deburred the holes.

Bob Axsom
 
No big deal...

Bob Axsom said:
It took me 8 years to complete my QB RV-6A as I worked toward retirement with a 4 hour commute each day. If I had tried to ream all of the holes to close tolerance fits at all the AN bolt locations (Wing spar attachment excepted) I would still be building (and working at JPL - that may not have been so bad actually). I used 3/16" drills for AN3, 1/4" for AN4, 5/16" for AN5, etc. and deburred the holes.

Bob Axsom
Click to expand...

Bob... it's not that big a deal.

It's one extra step, Drill one size down with the drill bit in your air drill, and keep the straight reamer in your slower speed cordless drill. Takes 30 seconds extra maximum.... The reamer works better at the slower speeds.

I don't know how the AN3 holes come in the QB, but if they are at the slightly undersize already, then it's no extra steps, just open up the hole with the straight reamer.....

Try it both ways and look at the inside of the hole with a magnifying glass, and then decide which one you would prefer to have in your plane...

But luckily, you are the builder, so you get to choose... :)
 
jlfernan said:
What to do if you used a 10 when you should have used a 12?
Click to expand...
An AN3 bolt is going to fit very sloppy in a .1935 hole. I am not sure that oversize bolts are even available, if they are, are probably expensive. I'd call Van and get his opinion. He might say to let it slide, then again he might not. We cannot presume to know what the calculated design load happens to be at the area in question. Generally speaking, I would say that if you can maintain at least 1.5 D edge distance around the parts, your best bet is to ream the hole to .2495 -.2500 and install a AN4 bolt. Minimum edge distance can vary but in my production experience, engineers almost always accepted 1.5 D. and occasionally even less when installing a 1/4" bolt. Again, call Van and see what he says.
 
I know this is a silly question, but I plan on using a 3/16 reamer when I drill the bolt holes for my gear weldments. Any problem going thru steel, anything else I should look out for?
 
jlfernan said:
What to do if you used a 10 when you should have used a 12?
Click to expand...

Jorge,

Did you ever get an answer to your question? I wonder if you can use shim stock to take up the extra space around the bolt?
 
jlfernan said:
What to do if you used a 10 when you should have used a 12?
Click to expand...

Jorge,

Did you ever get an answer to this question? I wonder if you can use shim stock to take up the extra space around the bolt?
 
If you want close tolerance

There has been really good advice concerning AN3 bolts on this thread.
Great for those with less experience. I love this forum, this is how we learn without having to make all the mistakes ourselves.

If actually have the application requiring it, and you want close tolerance

Don't use AN3 bolts, they are not close tolerance by any means.

The AN173 is the close tolerance version, but....

They are getting less available as time goes on and the industry is using NAS bolts such as the NAS1103, NAS1303, NAS6203, or the one that would be the most likely close tolerance sub for the AN3, the NAS6603.

If you are not looking for the structural shear strength, go with the AN bolt and any of the 3 size drills all the others have recommended, 10,11, or 12.
They should be perfectly fine for almost everywhere on an RV.

If you're installing for an actual structural application, use an NAS bolt as above or similar, in this example AN173-??.

Prep the hole by first drilling the hole just big enough to allow the pilot of the reamer to go in the pilot hole. Ream the hole using a reamer that will make a clean hole with an interference of .0005 to .0015. The best reamers will produce a hole that will require a light to medium drive fit using a small (4 to 6 oz) hammer struck several times per inch. The fastener should not be able to be pushed in by hand. Possibly if you pushed it in with a hammer handle and about 10 pounds of force it should go in the hole, but a tight fit is not an easy fit.

A loose hole and fastener combination in a sing shear situation, stressed to the point of structural shift will normally stretch the fastener or pop the head off.

Pop the head off, but it was in shear???? The structure shift allowed by the lose holes allows the fastener to rock in the hole changing the load on the fastener to a combination load of both shear and tension. The tension part comes from the edge of the head being relieved on one side and pressured on the other, while the same thing is happening to the nut end also.

That is why so many thing in aircraft are designed in double shear, thing may get strained, but the strength is greater and the fasteners are not as easily subject to combination loads.

You will notice that the spar splice plates ar all in at least double shear, and they call for close tolerance fasteners and close tolerance holes.

If as time goes on and you do your inspections, you find bolts loose on your plane that used to be tight, something has moved. :eek: Just tightening them may not be the best solution.
 
Tom,

What's the difference between an AN-173, NAS1103, NAS1303, NAS6203, or NAS6603?

If structural shear strength is important, which one of the above would be best to replace an AN-3-10A bolt in a #10 hole that should have been drilled to #12?

Thank you,
 
Gus from Vans said I should not worry about it. He said I could install a doubler with a #12 hole, but that it would be overkill. I went the overkill route and used some .041 with flush Cherrymax rivets on the forward side of the bulkhead. I would rather overengineer and have peace of mind. Seems just fine. I'll let you know more after first thousand hours.
 
To add my $.02:

I work for Cessna, and was an experimental A & P on the Citation Mustang.
We used the splined type reamers daily for close tolerance holes. Unless I have forgotten something, you will notice that the reamer size is 'slightly' larger than the bolt that goes in the hole. By slightly, I mean mere thousandths of an inch. We used certified "go-no go" gauges, to ensure that the holes were not oversized. Those gauges, while not cheap, are available in a similar form commercially, and are worth the peace of mind.

I hope I am not sounding too 'elementary' but I have had numerous folks ask me why use reamers. As mentioned, a drill bit doesn't make a round hole. A drill bit 'eats' the material in a circular manner, but those reamers do a very good shaving job, to clean up the hole. Bolts fit perfect almost every time. (If they don't, change bolts. Bet you find one that will fit perfect.

Gregg
 
To further what RV4Gregg said:

Reamers are actually made oversize, in the 3/16 size range they are .0001 to .0006" over the nominal size. Correspondingly, drills are actually undersize simply because they make oversize holes. You're picking over thousandsth's on an inch when in reality if you are doing it by hand you're still a thousandth or two over with out using a reamer bushing in some sort of guide. I spec out and design these types of tools for the F-22 as well as do the day to day liason to production. Our designs almost always use a piloted reamer with the pilot size set up about .015" (1/64) under the desired hole size. For the NAS6204 (the Ti version of the 6203 about .1885-.1895 in diameter) series we actually go with a .190-.193 spec with the reamer set to .1905. Everbody uses a drill block and reamer bushing. This sort of thing is still the norm on the C-130 and C-5 programs. The most important thing is to be straight in the hole (hence the need for a pilot/bushing and try to stay with 2 degrees of normal) and use a consistent feed rate.
 
Structural Shear Joints

Sorry I didn't get back you you last night, I logged off after my previous post and did not see yours after that.

In order to structurally fill the #10 hole, You could not use the AN173, because its max dia is .1894 an the #10 drill bit will make a hole no smaller than its dia of .1935.

The other bolts have an allowance for a first or second oversize, the first oversize is (X) .0156 additional diameter, the second(Y) is .0312

So we will just talk about the first (X) oversize for illustration.

The NAS6603-(??)X has a diameter of .2016 to .2026, which is funny because the print states that the 1st oversize is .0156 larger than the nominal, but when you read the min max on the print its .0121 to .0141 larger than the min maxes on the standard diameter. But thats just trivia.

The reamers that will give you the proper fit for the 3/16ths 1st oversize using NAS bolts or Hi-Lok pins will be .201 in diameter. Preferable with a solid pilot of 3/16" in diameter.

In most cases you won't need this, but if you do, its just a little more knowledge. Hope it helps.
 
FWIW, here's what AC43.13 says:

"Generally it is permissible to use the first-lettered drill size larger than the nominal bolt diameter..."

Lettered sizes? They appear to also mean numbered size. Letter sizes are used for bits larger than .2280. So, as others have said, for a 3/16 hole (.1875), use a #12 (.1890), according to the FAA.

Dick Scott
RV-9A Wings
 
You must log in or register to reply here.