A drop in maximum speed or an uncharacteristic vibration of the body when moving is often the first signal that the body is moving. propeller Many small boat owners mistakenly believe that the problem lies in the carburetor or ignition system, while the root of the evil is hidden under the water. Dulled edges of the blade can not "slam" into the water stream with the desired force, creating excessive resistance and reducing the overall efficiency of the engine.
Recovery of the screw geometry is not just a cosmetic procedure, but a necessary technical operation that requires accuracy and understanding of the physics of the process. Aluminum alloysThe throttle, which is the most budget-friendly screws, is quite soft and easily deformed when hit by sand or rocks, but even a slight deformation or loss of sharpness of the front edge can eat up to 15% of the engine's thrust.
In this article, we will take a closer look at the technology of manual and mechanical blade processing, examine the necessary tools and point out critical errors that can permanently put the part out of action. gearboxReduce the load on the bearings.
Diagnosis of the condition of the blades and search for defects
Before you pick up a file or grinder, you need to make a thorough visual and tactile diagnosis. Often owners try to sharpen the screw, which has cracks or irregularities in the geometry of the pitch, which is a gross mistake. First, the part is cleared of algae, dirt and oxides, then conduct a careful examination of each blade in good light.
And you have to pay special attention to the front edge, which is the main impact of the movement, and this is where the most common bullies, chips and characteristic burrs are formed. blade-figure It also checks for cracks from the base of the blade or from holes under the mount bolts.
- 🔍 Visual inspection for deep scratches and chips along the entire length of the blade.
- ✋ Tactile check of the front edge for the presence of burrs and uneven wear.
- 📏 Verification of the diameter and pitch of the screw with the data-sheet figures of the model (in the presence of serious deformations).
- 🛠 Checking the landing place and sliches for production or corrosion.
⚠️ Note: If a through crack or deep metal (shell) is found on the blade, sharpening of such a screw is strictly prohibited. Operation of the damaged part can lead to its destruction at high speeds and a serious accident.
To accurately assess the degree of wear, you can use a rod by measuring the thickness of the blade at different sites. If the difference in thickness between the blades exceeds the permissible norms (usually 0.5 mm for small motors), you will need not just sharpening, but full restoration of geometry or replacement of the unit. Balancing It also plays a role, but it is checked after machining.
Necessary tool and workplace preparation
The quality of the sharpening depends on the equipment used. aluminum screws Some tools are suitable, while for stainless steel It requires more powerful equipment and specialized abrasives, and the wrong tool selection can lead to overheating of the metal and changes in its physical and mechanical properties.
The main tool for rough processing is a corner grinder (Bulgarka) with adjustment of turns. However, to finish the finishing and give the correct shape to the edge, it is better to use a hand file or a flat grinder, which allows you to control the metal layer that is removed without disturbing the metal layer. cross-section.
☑️ Screwing kit
And personal protective equipment, metal shavings and abrasive dust fly in all directions, so glasses and gloves are mandatory, and you also need a reliable fixation of the screw: a vise with soft sponges or wooden pads will help avoid accidental scratches in already treated areas.
Manual sharpening technology: a step-by-step algorithm
The process of restoring the cutting edge requires consistency and patience, and the main task is to restore the angle of attack and make the front edge sharp, while maintaining the overall geometry of the blade, and always start with removing large bullies and leveling the surface.
First, with a coarse-grained abrasive or a coarse file, you take the base metal from the front of the blade, and you make a new bevel, and you have to move from the root of the blade to the end, following the natural curve, and you don't overdo it, and you don't take off too much metal, because that's going to change the way you move. screw-step.
- 📐 Marking the working area with a marker to control the removed layer.
- 🗡 Handling the front edge at an angle of 20-30 degrees (depending on the type of screw).
- ✨ Polishing the back surface to reduce friction against water.
- ⚖️ Control of symmetry of processing of all blades.
Nuances of stainless steel processing
Stainless steel is highly viscosity and prone to sticker, and you can't overheat it, otherwise it will float, use only special stainless steel circles and take frequent breaks to cool it down, and water or a special spray will help reduce the temperature in the cutting area.
After the bevel is formed, the back (back) part of the blade must be treated to remove the burrow formed when the front edge is sharpened, this is done by light movements of a fine-grained skin or a velvet file. Sharp edge It should be clean and smooth along the entire length of the blade.
Working with CSM: risks and features of mechanics
The use of a angular grinding machine greatly speeds up the process, but requires a high level of skill of the operator. The high speed of rotation of the disk creates a risk of local overheating of the metal, which is especially critical for light alloys. If the metal turns blue, then its structure is broken, and at this point the screw will become brittle.
When working with a power tool, you need to strictly control the angle of the disc, and uneven pressure can cause one part of the blade to become thinner than the other, which will disrupt the balance. Vibration. At high speeds, this is the direct result of this asymmetry, which will quickly disable the lower unit bearing of the motor.
| Parameter | Hand sharpening | Mechanical (MSM) | Professional machine |
|---|---|---|---|
| Speed. | Low. | High. | Medium |
| precision | Depends on skill. | Low (risk of overheating) | High. |
| Risk of overheating | Minimum | Highly | Medium. |
| Cost | Low. | Medium | High. |
To minimize the risks when working with CMM, it is recommended to use petal circles with a grain content of at least P80 for finishing, they soften the metal and heat the surface less. The movements should be smooth, without pressing the tool against the part.
The main principle of machining is "it is better to remove less, but check more often." Overheating of metal irreversibly changes its properties.
Geometry control and post-sharpen balancing
The final step is to check the geometry and balance, and even perfectly sharpened edges will not work if the screw hits when it spins, and you can check the balance at home by placing the screw on a special cone or simply hanging it on the thread behind the central hole.
If one of the blades is heavier, the screw will turn around, and the heavier part will fall down, and to eliminate the imbalance, you need to carefully remove the metal from the back of the heavier blade in the thickening area at the bushing, and do this in minimal portions, constantly rechecking the result.
⚠️ Warning: Never try to balance the propeller by adding solder or other materials to a lighter blade, which will disrupt aerodynamics and cause the load to be taken off during operation. Only removing the metal!
It is important to check. screw-step The angle of the blade at the root and the end must be factory specifications, and if you hit the angle in the process of sharpening, the screw will work inefficiently, creating cavitation.
To test the step without special devices, place the screw on a flat surface (glass or sheet of metal) and measure the gap between the edge of the blade and the surface at different points.
Common errors and impact on operation
One of the most common mistakes is sharpening the screw under the knife, where the edge is made too sharp, ignoring the radius of rounding. In reality, the blade profile has a certain thickening at the front edge, and completely removing it will lead to rapid dying of the metal and loss of strength.
Another mistake is the uneven handling of the blades, so if you sharpen one blade harder than the others, the balancing will inevitably break, and this will cause the motor to vibrate at high speeds and the thrust will be uneven. Cavitation in this case, it will destroy not only the screw, but also the anti-cavitation plate.
- ❌ Removing too much metal, which reduces the diameter of the screw.
- ❌ Ignoring the back edge, leaving burrs.
- ❌ Violation of processing symmetry, leading to a beat.
- ❌ Use of rough abrasives for finishing polishing.
Timely and competent sharpening saves fuel and engine life. A smooth, balanced screw with the right geometry provides better bulk and higher maximum speed. Regular inspection and maintenance of the propeller is a sign of a professional approach to the operation of water technology.
Can I use a sleeve in the field?
Yes, it's possible if you don't have a power tool at hand, you can take off the burrs with a file and adjust the geometry a little bit, but it's going to be very difficult and long to repair a badly damaged edge by hand. Use a fileboard for hard-to-reach areas.
How often do you need to sharpen the screw?
The frequency depends on the operating conditions. If you often walk in shallow water, sand or rocky bottom, you need to check every 10-15 hours. When operating at depth and clean bodies of water, you need to check at the beginning and end of the season.
Does the scaling affect the guarantee?
Self-machining of the screw is usually not a warranty for the screw itself, if it is new. However, if due to poor balancing after sharpening the engine fails, the warranty repair of the engine may be denied, citing a violation of operating conditions.