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Scratch building Shafts

Drvsft.gif (1702 bytes)This is simple, using what's called the "Three Tube" - Brass Tubing Method. One Brass Tube fits into the other, like a telescoping Antenna. The size of the tubing   required, depends on what your model needs. I use 1/8" rod for shaft, 3/32" tubing for sleeve bearing, and 5/32" tubing for stuffing box and grease tube. For large models with props bigger than 2" you should increase the size of the brass. If you already have props then you will want to start with a shaft that fits the hole in the prop.

 

 

 

shaft-in-stern.jpg (58712 bytes)shaft-construction.jpg (67678 bytes)  LEFT: parts to make a stuffing box.

  RIGHT: stuffing box mounted in hull.

 

 

Scratch building Props

Since I build displacement hulls, I didn't need to buy expensive props that would be hidden most of the time in a kort nozzle. I decided to make my own and can make five props from a sheet of brass that costs around $2.00.

If you have a graphics program you can use this pattern to make your own props.

makeprop00.jpg (69885 bytes)

First I drew a pattern for a left and right handed prop, then I scale it to the size I needed and print it out.

makeprop01.jpg (36336 bytes) After I printed the pattern, I used spray adhesive to stick it to a sheet of brass stock.

makeprop02.jpg (118059 bytes) I trimmed the stock with tin snips as close as possible. Then I used a Dremel Moto-tool with a fiberglass cut off wheel to trim to the outline of the prop.

 

makeprop04.jpg (311325 bytes)makeprop03.jpg (116397 bytes)  After I got the patterns cut out, I took the moto-tool and "polished" the brass. Click on the images and notice how it looks like real turned props on the prototypes. I did this by holding the cutoff disk at an angle and going from the center outward turning the prop a little with every horizontal stroke.

makeprop05.jpg (64320 bytes) Since I build displacement hulls instead of fast planning hulls, balance and pitch is not all that important. I use 1/8" brass rod for my shaft and use a punch to center the hole in the prop and drill it out. I then place the rod in helping hands and get the alligator clamp level to where the prop will sit level on it. Then I put paste on the area to be soldered, used a soldering gun to get it hot and use rosin core solder to solder the prop to the shaft. If you wipe the flux off while it's still warm it comes off easier.

makeprop06.jpg (200844 bytes) After the solder cools, I use the moto-tool to "polish" the solder area and this is how it looks.

 

 

makeprop07.jpg (62879 bytes)When I finish that, I bend a pitch in the prop. The more pitch you have the more thrust you have and more load on the motor. If you use a motor less than 4000rpm or have it geared down, then a sharp pitch is alright. I you run direct with motors above 5000rpm, then you shouldn't bend as much pitch to it. As you see in the photo I use a square to get my angle of each blade the same. Use a piece of 3/32" tubing in the clamps so the shaft can be turned. Angle the helping hands slightly so the top blade won't hit the square. Check the blades at the bottom and bend until all four brush the square the same. I never balance my props because of the low rpm, but if you want to try it, below is a home made setup River Bill uses.

BALANCING - The PROP & SHAFT

Shft-bal.gif (2470 bytes)Use about a 4" length of scrap - block wood, and glue a pair of Single or Double - Edge Razor Blades to each end of the block, as shown in this drawing. Then lay your Drive Shafts & Props, across the balancer to check them ( as shown in the bottom drawing ). The heavy shaft - side, will roll to the bottom. That Indicates a need for weight to be removed, so "Polish Off a small portion of "Solder" around the Prop - in the heavy area, where the fluke is soldered to the bushing & shaft - itself, to gain a better balance. Then rotate and recheck - balance again, to insure its right and repeat until correctly balanced. NOTE ... Be sure the table your using to balance things, is also "LEVEL", before you use this system, it can effect Shaft balancing. And this balance system, is not made to adjust "High Speed" props for Race Boats, but works on the same principle - as theirs do!