Building a Two-piece Aluminum Canoe Pole Without a Machine Shop
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Around here in the northeast US the almost universal aluminum canoe pole is 12 feet long made from a high temper corrosion resisting tube (this usually means something like drawn 6061-T6.) with an outside diameter (OD) of 1.125" and wall thickness of 0.058" Drawn tubing usually has better dimensional control and (depending on where you look) better mechanical properties.
For this project, the basic materials were 6063-T832 drawn aluminum tubing, available (in UPSable lengths of 6 feet) from Texas Towers http://www.texastowers.com/aluminum.htm). In May of 2005, they were charging $1.35 a foot for the 1.125"OD stuff, and you'll be hard pressed to do better at your local metal store, even if they do let you in off the street.
Material note: 6063 is usually referred to as an "architectural grade" - code I think for appearance being more important than mechanical properties, but at T832, the properties of 6063 (hardness, strength, ductility, etc) are so close to those of 6061-T6 (a "proper" structural grade) that the differences are practically meaningless.
The 1.125" OD x 0.058" wall tube gives a nominal 1.009" inside diameter, so a short inner sleeve of 1.0"OD x 0.058"wall tubing is usually used at the joint.
The length of the inner section is up to you. I used 12". I dunno whether Texas Towers will sell you just a foot of it.
Here's an end view of the two main tubes and the smaller inner tube.
Here's a picture of the 1.0" OD section telescoping into the 1.125"OD main tube.
Between the tubes, there's a nominal 0.009" diametral gap, and this may or may not feel like a problem to you. I decided that it was a problem.
You can get an idea about how sloppy the joint is with a simple model. If you look at the tubes as rigid bodies then this schematic shows how much one end of the pole will move if you clamp down the other.
The inner sleeve can tilt up an angle 2*(0.009)/6 = 0.003 radians, and the right pole section can tilt up an equal amount. So the total tilt is 2*0.003 = 0.006 radians. At the end of a 72" long pole section, this is a distance of 72*0.006 = 0.4" slop.
This sounded like a lot, so I decided to do some things to reduce it.
First, I decided to bond the inner sleeve into one end of the pole. This cuts the slop by two.
Maybe it was an example of the Engineer's Disease (deciding to sweat some detail that turns out to be trivial), but I decided to wrap the inner sleeve with a piece of 0.005" shim stock when I bonded it into the outer tube.
I used general-purpose hardware-store epoxy. To prep the surfaces, I used fine steel wool, and everything cleaned up with denatured alcohol.
It was a mess getting all those things together at the same time. Fortunately, I had masked off everything (including myself), and the result turned out ...
reasonably well after I ground off the protruding shim stock.
So the sleeve was done. Next was the mechanical connection.
Valco http://www.valcocleve.com/snap-buttons.htm) is a Cleveland company that apparently makes a living making and selling the snap buttons that secure telescoping tubes. They produce a bewildering variety of button assemblies, many of which would work fine for canoe poles.
This picture shows a sampling of styles and sizes from some paddle ferrules. They have solid or stamped buttons. The leaf springs can set in the tube longitudinally or tangentially. They can be carbon steel or plastic or stainless, and on and on ...
But Valco has a $50 minimum order (for snap button assemblies that might cost around a buck or so), so I decided to roll my own.
This lashup required a half a dozen trips to a distant hardware store plus about $10 worth of stainless parts that didn't work, so I would have been ahead ordering from Valco and scrapping or giving away the 49 extra buttons.
Most snap buttons consist of a cylindrical button cap formed from or rivetted to a leaf spring. Mine consisted of a #8 x 3/4" long stainless hex socket head cap screw (the head of which forms the button), a nut for it, a helical spring, and a body whittled on a drill press from a piece of 7/8" (standard hardware store) birch dowel to keep everything contained and aligned.
Before insertion into the inner sleeve, the snap button assembly looks like this.
More reflexively than anything, I put a couple of coats of spar urethane on the wood part.
The pole sections were telescoped together and taped. Then I measured up 4" from the joint and drilled a radial 9/64" hole through outer tube and inner sleeve. It helps to remember which end is epoxied and which end gets the drilled hole and snap button. The head diameter of a #8 is close enough in size to a hole left by that drill that the head works as a snap button after some light file work.
Here's a schematic cross-section of the joint.
and here's the finished joint apart ...
... and together. The green duct tape marks the pole's balance point.
Next were the pole ends.
Here's where you usually turn to your trusty lathe and turn out stepped nylon plugs to press into the end of the aluminum, but if your girlfriend is using the lathe to make garden tools, you can root around your local hardware store (look in that section where there are racks of trays and shallow boxes for specialty parts) for some 1" pipe plugs like these. They consist of rubber donuts that get squeezed by throughbolts to seal inside tubes. Their downsides include:
1. The throughbolts aren't long enough to leave a useful projection on the end of the pole, and
2. Once installed, these things can be easily pried out 'twixt thumb and forefinger.
The fix for the first is easy. The throughbolts are replaced with 5/16" carriage bolts. For the first version of this, I used stainless bolts. Not only were they ridiculously expensive, but they seemed to be too hard, not giving decent purchase on rocks.
My advice is to save your money and use carbon steel. They wear away or you lose the pole long before there's a corrosion problem.
The fender washers here are part of the solution to the second problem ...
... which involves inserting a washer that registers between throughbolt and pole tube and that prevents pryout.
To work, the washer has to have a tight fit on both the OD and the ID. I found some 1/4" fender washers (mild carbon steel, again) that could be drilled out to fit the 5/16" bolt and chucked into a drill press and the ODs filed down to a tight slip fit with the inside of the pole tube.
This picture is a schematic of the assembly.
The way this pole gets put together, it's reasonably well sealed, but it will eventually waterlog and sink.
To slow things down some, I cut strips of pipe insulation foam and inserted them into the tubes before I assembled the snap button and the pole ends.
Here are the assembled pole ends.
