homemade polespear

Looks good!

Please bring it when you come over.

If you build another one, try to find some rems from a fab shop of 7075 tubing, it can be heat treated to T6 condition and then powder coated.
Cheers, Don

Quote from mrmike

Jeff please feel free to give me the old "I told you so" haha

No way. I really wanted it to work out.

If you are going to make the aluminum tube one continuous piece, and you don't intend to get nuts with really heavy bands, then yes, i think that it will probably be strong enough. And you have exactly the right idea by "counter drilling" a little to leave the stainless at the full diameter, and then starting the threads a little deeper.

For what it's worth, and at the risk of letting the inner nerd out, the stiffness of a round tube is proportional to: OD (to the fourth power) - ID (to the fourth power). So if you wanted to compare the stiffness of 5/8" solid rod to 1/2" solid rod (of the same material), for example, then the ratio would be:

(.625 x .625 x .625 x .625) / (.5 x .5 x .5 x .5) which equals 2.44 . So the 5/8" rod is 2.44 times as stiff as the 1/2" rod.

The reason I say this is to emphasize that a small change in diameter can pay big dividends in stiffness. A 5/8" tube can have a thinner wall and be the same weight as a 1/2" tube, but the 5/8" will still be much stiffer.

Mike, I can't give you any numbers, but the JBL hollow alum polespear wall diameter is a fraction of your alum pipe. It's less than the thickness of a dime. And it's plenty rigid to stay straight with a very strong band.

Quote from mrmike

OK is rod or tube stiffer??? I always thought tube was stiffer but maybe im wrong. My Odor is 5/8" rod, my next project will be 1/2" tube with a .120 wall (almost 1/8") again. its about a pound lighter as far as the material goes, but I don't know if it will be rigid enough to use my 1/2" OD band.

Solid rod is stiffer IF it has the same diameter as the hollow tube. Here are some comparisions.

Your 5/8" solid Odor spear weighs about 0.37 lbs per foot. It has no ID, so the stiffness is proportional to:
(.625 x .625 x. 625 x. 625) = 0.152

Your 1/2" OD tube, with a 1/4" ID weighs 0.24 lbs per foot, and the stiffness is proportional to:
(.5 x .5 x .5 x .5) - (.25 x .25 x .25 x .25) = 0.058

So the Odor spear is 0.152 / 0.058 = 2.6 times stiffer than the 1/2" hollow tube.

Let's say that you used 5/8" OD tube, with just 1/16" wall thickness. This would weigh 0.13 lbs per foot, and the stiffness is proportional to: (.625 x .625 x .625 x .625) - (.5 x .5 x .5 x .5) = 0.09

So you can see that the 5/8" hollow tube is half the weight of the the 1/2" heavy wall tube, but still 1.5 times as stiff.

Three words..... Metal Matrix Tubing. great for gun barrels as well . Cost could be a issue unless you work in aerospace and have a BIG lunch box.:nono:

Cheers, Don

5/8" solid rod weighs about 2.2 lbs for a 72" long piece, and has a relative stiffness of 0.152.

3/4" OD tube with a 1/16" wall weighs 0.97 lbs for a 72" piece, and has a relative stiffness of 0.163.

You got it. The 3/4" tube is a hair stiffer, and less than half the weight. Chad and I (well mostly Chad) have been playing with some blue water pole spear designs. After testing the 3/4" prototype, we redesigned it to be 5/8" OD. That seems to be where many of them (like the Odor) end up.

We're still playing with it. It's a heavy spear, though, so may or may not be comparable to what you are trying to do.

Quote from mrmike

WOW 1000mm piece = $1443!!!!!!!!!!!! im sure it would make a fantastic polespear DON but at that price it would take a lifetime to pay for itself. HMMM I do know somebody that works for NASA up at Canveral.... Maybe ill try to make a phone call later this afternoon.

Yeah not something you want pay list $ for, I was in the right place at the right time 20 years ago but I don't have any for sale.

A more backyard approach is to find a golf club fab or repair shop that has cheep Boron/Graphite or Metal Matrix golf shafts their unloading. ( dumpster diving is a sport too):D The shafts can be inserted and epoxied in side appropriately sized thin walled T-6 tubing. A few have found there way in side one of my guns.

I have a experimental gun project for my kid in the works using bonded club shafts called; bundle of sticks .:D

Cheers, Don

You could use a broken golf club for a carbon section. The golfing equipment stores throw them out.