Double vs Single Flare

[RVG8tor]

I am at the point that I have to learn to flare aluminum tubes. I have searched this site for info and it seems single flare is what most builders use. I have also googled the subject and Kitfox has a bulletin for fuel lines and it does not mention double flares.

The only reference to double flares is in the Hydraulic section of 43-13, which due to the low pressure should not apply to pitot and fuel lines. I am curious what you A&Ps or IAs where taught and or what you use in practice. The double flare tools are expensive for the 37 degree variety. I wonder if you could use a 45 degree tool to turn in the tube end for a double flare then us use the 37 degree tool to make the actual flare. Any help and clarification would be helpful. I have bought the Rolo 37 degree tool from Avery and have been practicing, I made a nice flare on 3/16 tube that is used in the Dynon Pitot.

Cheer

[cytoxin]

i was taught in A&P school to do the double flare up to 3/8 IIRC but the tooling for this is quite expensive to do properly..that said many here will tell you they have had single flares and for many many hours...single is the way ive gone on the RV based on the testimonies of a certain few here that i feel confidant in listening to.

dont forget to debur the end of the tube prior to flaring. i do it before and after.

[dhammer]

Although I had to make them in A&P school, in 40 plus years of working on aircraft from Cubs to Boeings, the only time I can ever remember seeing a double flare was on steel car brake lines. In other words, don't bother. If you get a flare that won't seal well, get yourself some conical seals and put one on the flare. See - http://www.toolsforaircraft.com/conicalsealmain.html

Don

[tomcostanza]

For some reason, I thought the 3003 tubing was supposed to be double flared, but the 5052 tubing could use a single flare. The 3003 is much softer, and several builders have remarked that it is easy to over-torque and mash the flare (single flare I assume) until it's paper thin...and then it cracks.

[az_gila]

Originally Posted by tomcostanza

For some reason, I thought the 3003 tubing was supposed to be double flared, but the 5052 tubing could use a single flare. The 3003 is much softer, and several builders have remarked that it is easy to over-torque and mash the flare (single flare I assume) until it's paper thin...and then it cracks.

Tom... my AC 65-9A (A&P Mechanics General Handbook) says that 5052-O and 6061-T alloy tubing from 1/8 to 3/8 should be double flared. No mention of other alloys.

However, it is an old reference document (first published in 1970) and describes a different type of flaring tool than we usually use now.

The flaring tool described works by striking a tapered plunger into the tube, and forming the flare against the side of the die. The modern flaring tools sort of push the flare out in a rolling motion, and don't rely on impacts. This might make the difference, since the AC document says that a single flare might "cut off the flare and failure of the tube assembly" - perhaps the rolling is easier on the metal than forming it with an impact into a die?

gil A

[chaskuss]

Mike,
I also was taught to double flare. Your suggestion of using a 45 degree flare tool to do the first half of a double flare won't work. That is because the automotive 45 degree tools are made do doing flares on steel tubing. There are serations on the inside of the clamping block of the 45 degree tool. These are meant to grip the steel tubing firmly. However, they will damage the soft aluminum tubing, rendering it un-airworthy.
I was also aghast at the price of 37 degree double flaring tools. I created a "favorite search" on EBay looking for one. After about 4 months, I was able to purchase a "NOS" (new old stock) tool for $137 on EBay. Another route might be to get your local EAA Chapter or RV Builders Group to purchase one as a group tool. My local EAA Chapter has done this for a number of tools, such as electronic scales, Greenlee punches for flight instruments, magneto timing tool, etc.
A flare is weakest where it has been stretched the thinnest (the end of the bell). A double flare rolls the material over, so that you have thicker material to start with. You also don't have a "raw" edge to induce stress risers either.

Charlie Kuss

[Aden Rich]

I debur the inside of the tube prior to flaring
I use a small amount of oil to lubricate the flare so it wont gaul.
I slowly flare the tube and back it out and then back in slowly several times (kind of like tapping a hole)
I then take small file and debur the outside edge of the tube, then inspect the inside for flakes of alum and burrs.

Haven't had one leak yet.

[ThisOne]

There have been several goods points made here in this thread.
The first being that (given the choice and the proper tools), a double flare is by far the best choice for flaring aluminum tubing. But as also noted here the tooling is not only costly but will in fact damage the tubing.
The second being that you must properly prepare the tubing end before you make your flare.
Some of the most common flaring mistakes I have seen (and I have seen a lot of them) are over flaring (this where the flare goes past the nose of the AN male part, thus not making a proper seal and possible leak), and “rushing” the flare it self (Aden Rich nailed that one), by not taking your time and going too fast you take the chance of “thinning out” your flare (thus making it a weak point) and also risk a split in the flare (this is not always seen at first glance).
If you take your time and make your flare the MS33584 spec. your flare will not only turn out fine…but last a long time as well.

MS33584 (old) is now SAE-AS4330

[chaskuss]

Originally Posted by ThisOne

There have been several goods points made here in this thread.
The first being that (given the choice and the proper tools), a double flare is by far the best choice for flaring aluminum tubing. But as also noted here the tooling is not only costly but will in fact damage the tubing.
The second being that you must properly prepare the tubing end before you make your flare.
snipped

MS33584 (old) is now SAE-AS4330

Brett,
Perhaps I was not clear in my first post. The PROPER 37 degree double flare tool will NOT damage aluminum tubing. I was responding to Mike's question regarding trying to create a double flare by using an automotive 45 degree double flare tool to do the first step of making a double flare (rolling the edge over, inboard).
Mike was hoping he could create a double flare by combining the use of both an automotive 45 degree flare tool and an aircraft single flare tool to actually make the flare. I know it won't work because I tried to do what Mike had suggested in his first post. The automotive tool will damage the soft aluminum tubing about 2" behind the flare area. This is caused by the design of the clamping block on the automotive tool.
Charlie Kuss

[tomcostanza]

Mike was hoping he could create a double flare by combining the use of both an automotive 45 degree flare tool and an aircraft single flare tool to actually make the flare. I know it won't work because I tried to do what Mike had suggested in his first post. The automotive tool will damage the soft aluminum tubing about 2" behind the flare area. This is caused by the design of the clamping block on the automotive tool.

Charlie,
Why couldn't you use a 37 deg. single flare tool with the double flare button from a 45 deg. tool? I've never tried it, but from looking at the pics, the button only gets the fold started. It seems angle agnostic to me. Then you would finish the flare with the 37 deg tool. I'd experiment with it myself, but I have the Rolo tool too, and I DON'T think the technique would work with that style tool. The little dbl flare buttons are available separately (I've seen them at Sears), if anyone wants to try. The obvious question of course is, if what I proposed is true, why are the double flare tools so expensive? What am I missing?