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How to repair a broken gear tooth

In the mechanisms of previous years of production (machines, gearboxes, drives), gears and gears were often made of gray cast iron, which at low and medium loads were not inferior to steel counterparts, and the casting process was simpler and cheaper than steel.
How to repair a broken gear tooth

But cast iron is brittle, and in the gears and gears with a sharp change in load or its increase, the teeth broke, and the whole mechanism failed. Of course, it would be better to replace a gear or gear with a missing tooth with a new product, which is not always possible. Then it remains to try to restore the tooth in another way.
How to repair a broken gear tooth

One of the options is related to the mechanical preparation of the place of a broken tooth, surfacing of a material suitable for strength and other characteristics, and the processing of surfacing to obtain a new tooth with an exact geometry.

Necessary equipment, devices and materials


For work, we need:
  • grinder and mini-drill (drill);
  • oxygen-acetylene welding torch;
  • ticks;
  • biomeasure (measuring head);
  • lathe;
  • sandpaper;
  • a shaft with a nut and a tubular stop for the gear block and gear;
  • a cutter for forming a profile of the cavity between the teeth;
  • axis of a mill with turnkey capture;
  • dividing head milling machine;
  • measuring tool (vernier caliper, micrometer), etc.

To fill the gap between two adjacent whole teeth in relation to a broken tooth, we need:
  • silicon (silicone) bronze rod;
  • flux (main part: borax with a small admixture of magnesium);
  • fiberglass welding blanket;
  • rags, cloth napkins, etc.

The process of restoring a broken tooth


It consists of three stages:
  1. Site preparation and filling (sealing) of the gap between two adjacent whole teeth with respect to the missing one.
  2. Making a holder for a gear-cutting mill and an axis for fixing the gear block and gear on the machine during processing.
  3. The formation of the tooth profile by sampling the deposited material with a special cutter on both sides.

Preparing the soldering point


How to repair a broken gear tooth

Since gray cast iron is difficult to machine mechanically, it is almost impossible to do this with a mini drill. It is better and faster to grind a broken tooth using a grinder.
How to repair a broken gear tooth

In the end, you can roughen the base with a drill to roughen the base. This will provide a more durable connection of the deposited material with cast iron.
How to repair a broken gear tooth

How to repair a broken gear tooth

Brazing process


How to repair a broken gear tooth

It begins with a thorough and uniform warming up with a gas-acetylene burner, both the soldering place and the adjacent parts of the gear. Otherwise, the likelihood of cracking in the cast iron part increases.
Then the place of soldering and a slightly silicon (silicone) bronze rod are warmed up red, which after heating is lowered into a container with flux, consisting mainly of borax with the addition of a small amount of magnesium.
How to repair a broken gear tooth

Next, a silicone bronze rod coated with a flux is placed above the cavity and melted using the flame of a gas-acetylene burner. This operation continues until the siliceous bronze solder fills the entire volume of the cavity between adjacent whole teeth.
At the end of this stage, so that the soldering does not crack from rapid cooling, we cover the restored part with a fiberglass welding blanket and leave it to cool slowly for the required time.
How to repair a broken gear tooth

The process of machining the ends of the gear with soldering


How to repair a broken gear tooth

We clamp the gear wheel into the chuck of the lathe and, using the measuring head, set the block with the smallest possible runout, knocking the gear from one side or another with a mallet if necessary.
How to repair a broken gear tooth

Then with the help of cutters we remove the influx of soldering, protruding beyond the ends of the gear. At the end of the grinding with sandpaper, we grind the processing sites.
How to repair a broken gear tooth

How to repair a broken gear tooth

Preparation of the block and milling cutters for work


How to repair a broken gear tooth

The gear block and gears are mounted on a lathe on a pre-prepared axis by tightening the nut and cylindrical stop.
How to repair a broken gear tooth

To make a holder for the milling cutter, we take a steel rod of a certain length and a little bit larger in diameter than the hole in the tool. We clamp it in the chuck of the lathe and from one end we first drill a small hole with a center drill, which we then expand with a spiral drill to the required size.
Next, in the tailstock of the machine, we fix the tap and insert it into the hole on the end of the rod. Take the headstock back and cut the thread by hand, rotating the tap with the knob. In the resulting thread, we screw a homemade bolt with a flat cylindrical head and two symmetrically located rectangular cutouts relative to the center of the rod for gripping with a special key.
How to repair a broken gear tooth

How to repair a broken gear tooth

Then we end the rod on the other side and drill it to the required length under the diameter of the spindle of the milling machine. Turning is carried out with a periodic check of the diameter so as not to weaken the size. At the end, we grind the turning area with an emery tape and wipe it with a cloth.

Tooth profile formation


How to repair a broken gear tooth

We fix the holder of the cutter in the spindle of the milling machine and grind the rod to the size of the hole in the mill, periodically measuring the diameter with a micrometer. At the end, grind the groove with sandpaper and wipe with a rag.
We put the cutter on the holder and fix it on the end with a fixing bolt, first by hand, and at the end with a special key with a screwdriver. Install the dividing head and tailstock on the milling machine desktop. Clamping a perfectly even steel rod between them, we expose these nodes to ensure maximum alignment in the vertical and horizontal planes. To do this, use the measuring heads and adjust the position of the tailstock relative to the dividing head. After exposure, these nodes are securely fastened to the table of the milling machine.
The most important operation is the precise alignment of the cutter with respect to the gear being restored. For this we use a caliper, a micrometer, a metal ruler.
How to repair a broken gear tooth

How to repair a broken gear tooth

Divide the characteristic of the head by the number of teeth and get the number of revolutions of the handle per 1 tooth. Usually a fractional number is obtained. Then this value is on the circle of the divider.
Now you can turn on the spindle of the milling machine and begin to form one of the cavities of the restored tooth. This is best done in 2-3 passes, so as not to damage the surfacing. When forming a tooth, it is necessary to remove particles of the material being cut from the cutter and lubricate the tool. Next, we retract the cutter and turn the gear exactly one step with a dividing head and repeat the previous operation again.
How to repair a broken gear tooth

How to repair a broken gear tooth

One comment


Why take silicon bronze to form a tooth on a cast iron gear? Is it not more reliable to brew a cavity between the teeth with a cast-iron electrode and then process it with a gear-cutter?
If you do this, then due to the high temperature, the cast iron “bleaches” and areas are created that are practically not amenable to mechanical processing. Silicone bronze is similar in strength to gray cast iron, and in tensile strength even higher. Moreover, its processing, as we have seen, is not difficult at all.

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Comments (16)
  1. Guest Sergey
    #1 Guest Sergey Guests March 29, 2019 2:57 p.m.
    1
    Can i ask you? How much is this gear on sale? not good to buy? and this method is not new, they also welded a broken tooth, then brought it into the hand, even without a modular cutter, made a tooth profile template and finished the tooth to the final one, the rest is rolled by the mechanism
  2. Sergey K
    #2 Sergey K Visitors March 29, 2019 16:05
    20
    Cognitive, but little applicable in practice at home ...
  3. Guest Sergey
    #3 Guest Sergey Guests March 29, 2019 11:02 p.m.
    1
    I tried electrolytic deposition of iron at home. According to smart books, the strength is almost like that of 45 calcined steel (the resource of the restored crankshaft is ~ 80%). I did not finish the process - I could not maintain the temperature of 85 degrees (poorly prepared). When I tried to cut the applied layer with a file, there was no exfoliation - it was cut as a whole with the base. In my opinion, at home, building iron in place of a broken tooth is easier than surfacing.
  4. Andrew
    #4 Andrew Guests March 30, 2019 10:08
    1
    Red heat is approximately 800 degrees. Too much. You can do with heating 200 degrees, or even without heating. Smelted the first deposited layer in small sections with an electrode such as Monel, Cupronickel, Komsomolets. If in small areas, then you can not warm it, if you weld the first layer at once, it is better to warm up to 200 degrees. Further layers are fused fused with conventional electrodes UONI 13/45. Cool down to make slow. In practice, they act even easier. Surfacing is carried out with UONI electrodes with copper wire wound around it.
  5. Guest Sergey
    #5 Guest Sergey Guests March 30, 2019 11:26
    0
    It’s easier to make steel. Cut the crown and center it with the gear - not a problem. And if there is st45 or any instrumental, then adding 40 units, it will be eternal. (Referring to the above equipment).
    1. Guest Alexander
      #6 Guest Alexander Guests April 4, 2019 07:27 AM
      0
      I heard that there are such disciplines: metal science, sopromat?
  6. Guest Pavel
    #7 Guest Pavel Guests March 30, 2019 12:28
    1
    Vaughn Alexander Oblivin restores welding and grinder
    1. guest 27
      #8 guest 27 Guests April 3, 2019 2:31 a.m.
      0
      It was easier to saw off the old gear and boil the new one to the hub!
      1. Guest Alexander
        #9 Guest Alexander Guests April 4, 2019 07:18
        0
        So with your automatic transmission you will do so!
    2. Guest Alexander
      #10 Guest Alexander Guests April 4, 2019 07:24
      0
      What is unique here? One operated the unit without lubrication and with overload, and the other, from hopelessness and poverty, is forced to treat this on his knee.
  7. Guest Andrey
    #11 Guest Andrey Guests March 30, 2019 2:39 p.m.
    0
    even new technology can be fucked up with such specialists. Well, you would read the old gear repair literature, you look and would do it right from the point of view of mechanics
  8. Ivan
    #12 Ivan Guests March 31, 2019 07:38
    1
    As an option, you just need to take into account that the teeth are usually coated (cementation, cyanidation, etc.) and for this the hardness of the teeth is more than the core, and not how it turned out it is not clear how long the “temporary” patch will live
    1. Guest Alexander
      #13 Guest Alexander Guests April 4, 2019 07:15
      0
      It’s clearly said to you: it’s a CAST IRON!
  9. Chekantsev Vyacheslav
    #14 Chekantsev Vyacheslav Guests April 4, 2019 12:43
    1
    restoration of teeth with a method of surfacing with various metals does not always give the necessary effect. In my opinion, it is much simpler and more efficient, in the presence of a lathe with a dividing head, to make a new gear from steel of the corresponding grade and weld it instead of broken one, while ensuring the necessary alignment due to manufacturing seats
  10. Guest Andrey
    #15 Guest Andrey Guests April 4, 2019 11:53 p.m.
    3
    If your incandescent lamp burns out, do not rush to throw it away! Carefully separate the base and cut off the upper part of the cylinder, using microwelding, restore the integrity of the tungsten filament.Burn the melted part of the glass with a burner, restoring the tightness of the lamp bulb. Cut the "nose" at the bottom of the bottle, pump out the air and melt the nozzle again. Now attach the base.
    The light bulb will still serve!
  11. Guest Alexander
    #16 Guest Alexander Guests April 5, 2019 07:57
    2
    This is how people suffer when there is no gear cutting machine.)
    But seriously, with such a set of equipment it’s easier to make a new gear. It will turn out faster and more reliable.

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