Homemade propeller

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swedtug
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Homemade propeller

Post by swedtug » Wed Jan 13, 2016 7:14 am

I have long played with the idea to build a propeller and finally made a try. find the results where good. the only thing that was a little difficult was to twist the blades. I did it with a small hydral press . the blades were made of 15 mm steel.

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tacking upp the blades

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the plane is to make it a 30"x46" propp

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lots of cutting and sanding

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swedtug
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Re: Homemade propeller

Post by swedtug » Wed Jan 13, 2016 7:24 am

Image

balancing

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a little primer

Now let's see if it will fit also

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old and too smal propp

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It's close but I think it should work

Johan
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fredrosse
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Re: Homemade propeller

Post by fredrosse » Wed Jan 13, 2016 7:22 pm

What a great job you have done on that propeller, and a very good cost saving for sure!

For a propeller that size with perhaps up to several hundred horsepower at a few thousand RPM, self building is not a reasonable option, but for a steam launch carrying well under 100 horsepower at a few hundred RPM, it is a very good possibility, and from the looks of things you have a first class piece of work.

One potential issue is the root of the weld securing the blades to the shaft sleeve. When the weld cools metal shrinkage tends to produce tension stress on the surface of the weld, and sometimes this leads to cracking at the weld. Once a crack has formed, repeating stress cycles lead to crack propagation, and often a failure.

In this case there are two well proven methods of eliminating this troublesome stress condition. 1. Thermal stress relief of the entire propeller, commonly done at shops all over the country for a low price and overnight completion, in the USA probably less than $50 for this job. The propeller is placed in an oven, slowly heated to the proper annealing temperature, then cooled slowly, relaxing all of the locked-in stresses. 2. Shot peening of the areas which have tensile surface stresses. This is done with thousands of hard steel balls, shot at the surface with compressed air at bullet speed. As the hard balls strike the surface, the weld metal is deformed again and again, with the end result a compressive residual stress on the surface of the metal, and much less tendency for crack initiation. Shot peening of welds is common practice for several applications.

With common steel construction the thermal stress relief is the best method here, shot peening is most often used where the material cannot be annealed without affecting previous heat treatments to the part, which it is desired to retain. Crude, but often effective treatment with an air hammer, or hard needle scaling gun on the surfaces can be done with equipment that many of us have access to. Just hammer away with the pneumatic tool until the entire surface has been deformed by the blows.
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Akitene
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Re: Homemade propeller

Post by Akitene » Wed Jan 13, 2016 7:36 pm

Awesome job! Quite a hefty prop.

BTW, thermal stress relief, definitely.
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swedtug
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Re: Homemade propeller

Post by swedtug » Wed Jan 13, 2016 9:21 pm

I may not have the largest whistle but I have a big propeller :D

I'm not so worried about cracks in the weld, so long as you don't weld to long welds and keep the temperature down during the process so the risk is minimal, it is not as welding cast iron or cast steel .
the Centre is probably not entirely around anymore but don't think there is any problem, It seems to be a good fit on the shaft still.

Johan
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Re: Homemade propeller

Post by TahoeSteam » Fri Jan 15, 2016 1:25 am

WOW I am truly impressed.

I'm going to have to send this to my dad!

The new prop looks more hydrodynamic also with the smaller diameter hub and such.

Great work
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swedtug
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Re: Homemade propeller

Post by swedtug » Fri Jan 15, 2016 6:51 am

Thank you very much, to build its own propeller can be a very economical option.
I even felt that it was easier than I had imagined to build
but I still do not know if my Engine has the strength to spin it. but the advantage of steel is that I can twist and cut and weld on the propeller how much I want to, if the diameter or the pitch is too much or too little.

Johan
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swedtug
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Re: Homemade propeller

Post by swedtug » Mon Jun 27, 2016 6:45 pm

I finally gott the shance to test the propeller thoroughly, and it works perfekt.
it makes more than a knots diferense. and the Engine seams quieter and smother.
the RPM is ruffly the same as Before, about 200, the boiler is a bit too small but i can keep a higer presure in the boiler now,
about 8,5 kg and Before 7 kg, very happy whit it :D

Johan
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Re: Homemade propeller

Post by TahoeSteam » Wed Jul 06, 2016 9:33 pm

Johan, That's great to hear! I'm glad it worked out well!!

What would you charge for a 48x60"? :D :D
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swedtug
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Re: Homemade propeller

Post by swedtug » Thu Jul 07, 2016 10:01 pm

I am afraid that the transportation cost should exceed the manufacturing cost :D
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