Taper pin help

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Kurt Ayres

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Oct 12, 2019
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Could someone please help educate me about taper pins? The Mini Coupe I'm building uses them to attach the outer wing panels to the center section, but I can't find any of the size the plans call for -- AN386-5-12a. The ones commonly available seem to be sizes 2 and 3. Are there any suitable alternatives, etc.?
 

TFF

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The days of cheap surplus or just having some on the shelf is long gone. People who still use these buy the batch.

There is this long surplus one AN386-5-18A Pin

You also might call these people, they have odd stuff. Homepage

A good machine shop should be able to make some too. You just have to specify exactly what it’s made out of and quality of finish.
 

TiPi

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The taper pin is only one part, you will also need a matching reamer for the holes.
As an alternative, Morse taper #1 is a 9-12mm taper, reamers are available and lots of Morse #1 drill bits etc. Just check material specs against requirement.
ww.mcmaster.com/morse-taper-reamers/
 

karmarepair

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The Teenie Two used a standard industrial taper pin, with a slower, self-locking taper, I don't remember the size, but I found suitable pins at a well stocked Ace Hardware and the reamer at McMaster Carr. Drill a hole in the small end for a cotter, knock them in, pull the pin to knock them out. They are loaded in pure shear. Rumor has it Bjorn Anderson, the Swedish aeronautical engineer, designed the Teenie Two when he and Calvin Parker worked at Convair.
 

Bill-Higdon

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The Teenie Two used a standard industrial taper pin, with a slower, self-locking taper, I don't remember the size, but I found suitable pins at a well stocked Ace Hardware and the reamer at McMaster Carr. Drill a hole in the small end for a cotter, knock them in, pull the pin to knock them out. They are loaded in pure shear. Rumor has it Bjorn Anderson, the Swedish aeronautical engineer, designed the Teenie Two when he and Calvin Parker worked at Convair.
Bjorn had a lot of input on both the Teenie 2 and the Tinwind
 

Aviacs

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IIUC, AN taper pins are the same as Browne & Sharpe tapers. The reamers are at least still reasonable.


Figure out what the intended shear strength was for the size pin the designer specified (cross section). If none was available commercially, I would then use 4140 prehard to grind a set . increasing the diameter as necessary/if necessary over AN to attain the intended overall shear strength.

smt
 

JimCrawford

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The Teenie Two used a standard industrial taper pin, with a slower, self-locking taper, I don't remember the size, but I found suitable pins at a well stocked Ace Hardware and the reamer at McMaster Carr. Drill a hole in the small end for a cotter, knock them in, pull the pin to knock them out. They are loaded in pure shear. Rumor has it Bjorn Anderson, the Swedish aeronautical engineer, designed the Teenie Two when he and Calvin Parker worked at Convair.
Please don't "knock them out".
I shudder to recall the number of times I've seen people derig a K13 glider (very substantial taper pins at the main spar join) by knocking them out, usually by strong blows from a heavy hammer. I've pointed out numerous times that, until the pin frees up, the hammer blows are transmitted from the pin to the fittings and then to the spar itself. The pins come with an internal thread at the head end to attach a puller to draw them out without the unnecessary violence. Most times the offender wanders off to find the puller, can't find it, and belts the pins out anyway when I've gone.
Please scheme a way to draw the pins without striking them.

Jim
 

TFF

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The plans of the T2 have a spring to keep them from backing out, but they are not supposed to be driven home. All the small pins I end up replacing if I remove them. Once you seat one, they are there. **** if you do; **** if you don’t. When they hold my wings on, I want to make sure they are in there. You end up damaging them if you bottom them. Catch 22.
 

Kurt Ayres

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I also have a set of H5 plans, which is an airplane of identical gross weight and similar performance. It uses AN6 bolts for wing attachment (with a note on the plans that reads, "Use tapered pins here if removing wings often," which I won't be). Is there any reason that I couldn't do the same?
 

karmarepair

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Please don't "knock them out".
I'll strongly concur with this; I was being a little too flippant. I never finished this project, but I had in mind a "pusher", sort of a clamp that looped over the joint and pressed on the small end of the taper pin to remove them without violence.

Sonerai also used taper pins for wing attach and this page reproduces from the Sonerai newsletter one builders experience in actually folding and unfolding the wings on his airplane, including dealing with the taper pins Towbar
Notice that the nut welded onto the fat end is just to break the friction fit of the pin in the tapered hole. Once you wiggle it a little, the pin should slide right out.

The advantage of taper pins over AN bolts for this type of joint is the tight fit you can easily get. The diametric tolerance on normal AN bolts is a little loose, and it's slightly underize from standard reamers. Close Tolerance bolts are hard to find and expensive. And if you don't have the joints on the spars completely lined up before you insert the bolts, the threads on the bolt will broach the holes oversize in the soft aluminum of the spars, and you'll NEVER get the joint tight. The Brown and Sharpe pins and reamers used on the Teenie and Sonerai are cheap, and it's pretty easy to achieve a slop-free joint.
 
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