Methods for the manufacture of gears, cogwheels. Making a plastic gear (video tutorial) Making a gear at home
For the manufacture of gears, the following materials are used: iron, cast iron, bronze, simple carbon steel, special steel compositions with an admixture of chromium, nickel, vanadium. In addition to metals, softening materials are used: leather, fiber, paper, they soften and noise-free engagement. But even metal gears can work silently if their profile is made with precision. For rough gears, "power" gears are produced, they are made by casting from iron and steel without further processing. “Working” gears for high-speed gears are made on milling or gear-cutting machines, followed by heat treatment - carburizing, which makes the teeth hard and resistant to wear. After carburizing, the gears are processed on grinding machines.
Run-in method
The rolling method is the most common gear manufacturing option, since this method is the most technologically advanced. In this manufacturing method, the following tools are used: a cutter, a worm cutter, a comb.
Break-in method using cutter
For the manufacture of gears, a gear shaping machine with a special cutter is used (a gear equipped with cutting edges). The procedure for manufacturing gears takes place in several stages, since it is not possible to cut off the entire excess layer of metal at a time. When processing the workpiece, the cutter performs a reciprocating motion and after each double move, the workpiece and the cutter turn one step, as if “running” over each other. When the gear blank has made a complete revolution, the cutter performs a feed motion towards the blank. This cycle of production is carried out until all the required layer of metal is removed.
Rolling method using a comb
The comb is a cutting tool, its shape is similar to the gear rack, but one side of the comb teeth is sharpened. The workpiece of the produced gear produces a rotational movement around the axis. And the comb performs a translational movement perpendicular to the axis of the gear and a reciprocating movement parallel to the axis of the wheel (gear). Thus, the comb removes the excess layer across the entire width of the gear rim. Another variant of the movement of the cutting tool and the gear workpiece relative to each other is possible, for example, the workpiece performs a complex intermittent movement, coordinated with the movement of the comb, as if the profile of the cut teeth is engaged with the contour of the cutting tool.
This method allows you to make a gear using a worm cutter. The cutting tool in this method is a worm cutter, which, together with the gear blank, produces a worm gear.
One gear cavity is cut with a disk or finger cutter. The cutting part of the cutter, made in the form of this cavity, cuts the gear. And with the assistance of the dividing device, the gear being cut is rotated by one angular step and the cutting process is repeated. This method of manufacturing gears was used as early as the beginning of the 20th century, it is not accurate, the recesses of the produced gear wheel are different, not identical.
Hot and cold rolling
In this method of gear production, a gear-rolling tool is used, which heats a certain layer of the workpiece to a plastic state. After that, the heated layer is deformed to obtain teeth. And then the teeth of the gear being manufactured are run in until they acquire the exact shape.
Manufacturing of bevel gears
For the manufacture of bevel gears (bevel gears), a running-in variant is used in the machine engagement of the workpiece with an imaginary producing wheel. The cutting edges of the tool in the process of the main movement cut off the allowance, thus forming side surfaces future gear (gear).
In today's time, there are a lot of mechanisms around us that use plastic gears. Moreover, it can be both toy cars and quite serious things, for example, an antenna lift in a car, a spinning gearbox, and so on. The causes of gear breakage can be different, of course, most of them are associated with improper operation, but this is not about that now. If you have already found yourself in such a situation and you have broken a couple of gear teeth, then there is a way out how not to pay for an expensive part, but to restore it in a simple way.
Required for recovery
- Unused toothbrush.
- Detergent.
- Two-component epoxy adhesive - cold welding for plastics.
Plastic gear restoration
Training
The first step is to prepare the surface of the gear. Rinse it several times in warm water detergent actively working with a toothbrush. Our task is to degrease and remove grease from all faces.After degreasing is done, dry it dry.
Cooking glue
Now let's prepare the glue. Mix the components on a small piece of cardboard in proportion as in the instructions. Mix well.In general, before opening the glue, I recommend that you carefully read its instructions, especially with the time of complete and partial hardening, since these data can differ dramatically from different manufacturers.
If the consistency turned out to be liquid, let it stand for a while until it begins to harden.
Tooth restoration
In my case, a few teeth were ground off, the situation is fixable. We smear glue on the place that needs to be restored. The glue should be very thick, but plastic.
We make such a kind of tubercle.
We put the gear on an impromptu stand so that the glue thickens even more. Everything is again individual, it took me personally about 20 minutes for the consistency to noticeably thicken.
You can speed up the reaction and reduce the thickening time by heating. For example, take a hair dryer and start heating the glue on the gear.
Tooth restoration
Now the most crucial moment - rolling the teeth. The unit where the gear was operated, namely the other gear with which our broken one was in direct contact, must be liberally lubricated with grease, grease or lithol.We install a broken gear and roll it several times over another.
As a result, another gear rolls a track on thick glue.
Now you understand that before rolling the teeth, the epoxy glue on the gear must harden to the consistency of hard plasticine.
Thanks to the lubrication, the glue will not stick to the other gear.
hardening
We carefully remove the restored do from the mechanism and leave it for final hardening, usually for a day.
like this in an easy way it is quite easy to repair broken gears.
What is a substitute for epoxy?
If you have not found the glue, I can recommend that you make a slightly similar composition.For this you will need:
- Epoxy resin with hardener.
- The cement is dry.
In the proportion indicated in the instructions, mix the components to obtain the right amount of glue. Add cement. Only not a cement-sand mixture, but pure cement. The proportions are about two to one. That is, two parts of glue and one of cement. And mix everything very carefully. The glue is ready, and then everything is as per the instructions above.
This material is a general guide for designing and printing plastic gears on a layered 3D printer.
A light switch on gears is a tricky example of what you can design yourself after reading this article.
Optimum materials for plastic gears
What is the best material? The short answer in terms of the quality of finished gears is as follows:
Nylon (PA) > PETG > PLA > ABS
- Please note that the "Personal Use Only" license, i.e. the result cannot be distributed, sold, changed, etc.
- When assembled, the design has a diameter of 15.87 cm. Largest printed part - 14.92 cm in diameter
Print all parts with at least 3 perimeters on all sides and bottom, 15% coverage. We recommend a layer thickness of no more than 0.3 mm. Any material will work - as long as it is possible to avoid distortions of parts, which will render the device unusable.
The handle part is the only one that will require support.
Assembly instructions (read before starting work)
- Use a blade to clean the teeth of the gears so that they line up well, then install them on the plate with the same direction of rotation in which they were printed (center gear pin on the right, driven gear hook on top center).
- Secure the main gear by inserting the pins into the holes.
- Apply some dry glue (glue stick works well) to the working end of the lever and install the lever on the side with which it matches the pins. Glue is needed in order to secure the lever to the pins. The lever also presses the main gear against the structure.
- Heat up and soften the clamps. This is enough to reveal them. Align the edges of the clips with the holes on the back of the plate and crimp the gear in a circle. (The holes on the back of the plate may need to be cleaned - a knife will help, it all depends on how good your printer is). Press the clamps until hardened. This ensures that everything will hold securely.
Special Benefits of Layered Printing and Examples of Using Gears
So, what is the advantage of 3D printing gears over traditional methods of making them, and how durable are the gears?
Printed plastic gears are cheap, the process is fast, and you can easily get a customized result. Complex gears and 3D variations print without issue. The prototyping and building process is fast and clean. Most importantly, 3D printers are widespread enough that a set of STL files from the Internet can provide thousands of people.
Of course, printing gears with common plastics is a compromise in surface quality and wear resistance when compared to cast or machined plastic gears. But if you design everything right, printed gears can be quite effective and reasonable option, and for some solutions, ideal.
Most work applications look like gearbox, usually for small electric motors, knobs and winding keys. This is because electric motors work great at high speeds, but they have problems with a sharp decrease in speed, and doing without a gear drive is problematic in this case. Here are some examples:
Specific Issues of Layered Printing
- Printed gears usually require a little post-processing before use. Be prepared for "wormholes" and the fact that the teeth will need to be processed with a blade.
Reducing the diameter of the center hole is a very common problem even on expensive printers. This is the result of many factors. This is partly due to the thermal contraction of the cooling plastic, and partly because the holes are designed as polygons with a large number of corners that contract around the perimeter of the hole. (Always export gear STL files with a large number of segments).
Slicers also contribute, as some of these programs can choose different points to bypass holes. If the inner edge of the hole will draw the inner edge of the extruded plastic, then the actual diameter of the hole will have a slight shrinkage, and it may take some effort to insert something into this hole later. So the slicer may quite intentionally make the holes smaller.
In addition, any discrepancy in the layers or discrepancy in the width of the intended and actual extrusion can have a rather noticeable effect, "tightening" the hole. You can deal with this, for example, by modeling holes with a diameter of about 0.005 cm larger. For similar reasons, and in order for the printed gears to fit next to each other and be able to work, it is recommended to leave a gap between the teeth of approximately 0.4 mm in the model. This is some compromise, but the printed gears will not get stuck.
- Another common problem is getting a solid fill, which is quite difficult for small gears. Gaps between small teeth are fairly common, even when the slicer is set to 100% infill.
Some programs are relatively successful in dealing with this automatically, but manually you can solve this problem by increasing the overlap of the layers. This task is well documented on RichRap, and the blog provides various solutions to it.
- Thin-walled parts are fragile, overhanging parts need support, the strength of the part is much less along the Z axis. The settings recommended for printing gears do not differ from the usual ones. Based on the tests already carried out, a rectangular infill and at least 3 perimeters can be recommended. It is also desirable to print as thinly as possible - as far as equipment and patience allow, because then the teeth are smoother.
- Though, plastic is inexpensive and time is precious. If the problem is critical or you need to replace a huge broken gear, you can print with a solid fill so as not to leave a chance for any other ambush, except for wear.
Most Common Causes of Printed Gear Failure
- Tooth grinding (from prolonged use, see step 10 for lubrication).
- Problems with mounting on the axle (see Step 7 for mounting).
- Body or spoke failure (these are rare failures that usually occur if the gear is badly printed, underfilled, for example, or designed with too thin spokes).
On the importance of the evolvent
Bad way to make gears
Quite often in amateur communities you can find incorrectly designed gears - gear modeling the matter is not so simple. As you might guess, poorly designed gears do not mesh well, have excessive friction, pressure, kickback, and uneven rotation speed.
An involute (involute) is a certain kind of optimal curve described by some kind of contour. In engineering, the involute of a circle is used as a tooth profile for gear wheels. This is done so that the speed of rotation and the angle of engagement remain constant. A well-designed set of gears should transmit motion solely through rotation, with minimal slippage.
Modeling an involute gear from scratch is pretty tedious, so it makes sense to look for templates before you start it. Links to some of them will be given below.
Subtleties of tooth modeling. Optimal number of teeth
Think about this: if you need a 2:1 gear ratio for a linear mechanism, how many teeth should each gear have? Which is better - 30 and 60, 15 and 30 or 8 and 17?
Each of these ratios will give the same result, but the set of gears in each case will be very different when printed.
More teeth give a higher coefficient of friction (number of teeth engaged at the same time) and provide smoother rotation. Increasing the number of teeth means that each one must be smaller to fit the same diameter. Fine teeth are more fragile and more difficult to accurately print.
On the other hand, reducing the number of teeth gives more volume to increase strength.
Printing small gears on a 3D printer is like painting thin lines in a coloring book with a thick brush. (This is 100% dependent on nozzle diameter and printer horizontal resolution. Vertical resolution does not play a role in the minimum size limit.)
If you want to test your printer printing small gears, you can use this STL:
The printer we tested did everything on highest level, but with a diameter of about half an inch, the teeth began to look somehow suspicious.
The advice is to make the teeth as large as possible, while avoiding the warning from the program about too few of them, and also avoiding intersections.
There is one more thing to pay attention to when choosing the number of teeth: prime numbers and factorization.
The numbers 15 and 30 are both divisible by 15, so with that many teeth on two gears, the same teeth will constantly meet each other, forming wear points.
A more correct solution is 15 and 31. (This is the answer to the question at the beginning of the section).
In this case, the proportion is not respected, but uniform wear of a pair of gears is ensured. Dust and dirt will be distributed evenly throughout the gear, wear too.
Experience shows that it is best if the ratio of the number of teeth of the two gears lies in the range from about 0.2 to 5. If a larger gear ratio is required, it is better to add an additional gear to the system, otherwise you may end up with a mechanical monster.
Few teeth - how many?
Such information can be found in any Mechanic's Handbook. thirteen - minimum recommendation for gears with a pressure angle of 20 degrees, 9 is the recommended minimum for 25 degrees.
Fewer teeth are undesirable because they will overlap, which will weaken the teeth themselves, and the printing process will have to deal with the problem of overlap.
Subtleties of tooth modeling. Pressure angle, and how to make strong teeth
Pressure angle 15, pressure angle 35
pressure angle? Why should I know?
This is the angle between the normal to the surface of the tooth and the diameter of the circle. Teeth with a high pressure angle (more triangular) are stronger, but less interlocking. They are easier to print, but in operation they create a high radial load on the bearing axle, make more noise and are prone to kickback and slippage.
For 3D printing good option is 25 degrees, which ensures smooth and efficient transmission in palm-sized gears.
What else can be done to strengthen the teeth?
Just make the gear thicker - this will obviously strengthen the teeth as well. Doubling the thickness doubles the strength. Good general rule states: the thickness should be three to five times the pitch of the gear.
The strength of a gear tooth can be roughly estimated by considering it as a small cantilever beam. With this approach, it is clear that the addition of an overlapping solid wall to reduce the unsupported area greatly enhances the strength of the gear teeth. Depending on the application, this calculation technique can also be used to reduce the number of engagement points.
Axle Mounting Methods
Tight nozzle on the axis with notches. This simplest method is not very common. Here you need to be careful with the skew of the plastic, which over time will worsen the transmission of torque. This design is also non-separable.
Axle on the fixing screw in the plane of the gear. The locking screw goes through the gear and rests against a flat area on the axle. The locking screw is usually driven directly into the gear body or through a recessed nut through square hole. Each method has its own risks.
If you drive the screw directly, you can break the fragile plastic threads. The sunken nut method solves this problem, but if you're not careful and apply too much force when fastening, the gear body can break. Make the gear thicker!
The addition of special screw-in thermal inserts will significantly improve the strength of the axle attachment.
Recessed hexagon - a hexagonal mortise in which sits a hexagonal nut for a hexagonal screw. Enough solid layers should be printed around the hexagon so that the screw has something to hold on to. In this case, it is also useful to use a fixing screw, especially when it comes to high speeds.
Wedge found in the world of amateur 3D printing infrequently.
Axle as a single unit with a nut. This solution resists torsional loads well. However, it is very difficult to achieve it on a printer, because the gears have to be printed perpendicular to the table surface, and any axes with this solution have weakness along the Z axis, which manifests itself under high loads.
Some types of gears
External and internal spur gears, parallel helical (helical), double helical, rack and pinion, bevel, helical, flat top, worm
Spiral gear (herringbone). It is commonly seen in printer extruders, which are difficult to work with but have their advantages. They are good for high coefficient of adhesion, self-centering and self-levelling. (Self-leveling infuriates, because it affects the operation of the entire structure). This type of gear is also not easy to make with conventional equipment like hobby printers. 3D printing knows much simpler methods.
Worm gear. Easy to model, there is a great temptation to use it. It should be noted that the gear ratio of such a system is equal to the number of gear teeth divided by the number of worm openings. (You need to look from the end of the worm and count the number of beginning spirals. In most cases, it turns out from 1 to 3).
Rack gear. Converts rotational motion to linear motion and vice versa. Here we are not talking about rotation, but about the distance that the rack travels with each turn of the gear shaft. Here it is very easy to calculate the density of the teeth: you just need to multiply their density on the rail by pi and by the diameter of the gear. (Or multiply the number of teeth on the rack by the density of the teeth on the pinion).
Lubrication of 3D printed gears
If the device operates at low loads, at low speeds and frequencies, you don’t have to worry about lubricating plastic gears. But if the loads are high, then you can try to extend the life by lubricating the gears and reducing friction and wear. Anyway all gear functions are more efficient when lubricated, and the gears themselves last longer
For objects such as 3D printer extruder gears, heavy lubrication may be recommended. Litol, PTFE or silicone-based lubricants are perfect for this. The lubricant should be applied by lightly rubbing the part with toilet paper, a clean paper towel or a non-dusty cloth, evenly distributing the lubricant by turning the gear several times.
Any lubricant is better than none, but you need to make sure it is chemically compatible with the given plastic. And you should always remember that WD-40 grease sucks. She does clean well though.
Tools for making gears
High-quality gears can be made on free programs alone. That is, there are paid programs for very optimized and perfect gear connections, with finely tuned parameters and optimal performance, but they don’t look for good from good. You just need to make sure that the same mechanism uses gears made by the same tool so that the connections mesh properly. Gears are best modeled in pairs.
Option 1. Find an existing gear model, modify or scale it to fit your needs. Here is a list of databases where you can find ready-made gear models.
- McMaster Carr: extensive array of 3D models, proven solutions
- GrabCAD : a giant database of user-submitted models .
- GearGenerator.com generates SVG files of spur gears (These files can be converted into importable ones. However, some programs, such as Blender, can import SVG directly, without dancing with tambourines).
- https://inkscape.org/en/ - free program vector graphics with an integrated gear generator. A decent guide to creating gears in Inkscape - and .
STL file editors
Most gear template generators output STL files, which can be annoying if you need features that the generator doesn't offer. STL files are the PDFs of the 3D world and are intricately difficult to edit, but editing is possible.
TinkerCAD. A good elementary browser-based CAD program, easy and quick to learn, one of the few 3D modeling programs that can modify STL files. www.Tinkercad.com
meshmixer. A good program for scaling source forms. http://meshmixer.com/
Non-FDM 3D printing
Most people, even hardcore hobbyists, don't have immediate access to other 3D printing technologies for making gears. Meanwhile, such services exist and can help.
SLA- excellent technology for professional gear prototyping. The printed layers are not visible, and very fine details can be obtained as a result of the process. On the other hand, the parts are expensive and somewhat fragile. If you use this process for prototyping a future cast model, there will be no problems with its extraction. Make the part solid, otherwise it will certainly break!
SLS- a very precise process resulting in durable parts. The technology does not require props for overhanging structures. You can create complex and detailed products, preferably with walls up to a quarter of an inch thick. The print layers are also almost invisible... BUT, the rough surface (because the technology is based on powder printing) is extremely prone to wear. A very powerful lubrication is required, and many do not recommend SLS gears at all for long-term applications.
Technology BinderJet good for detailed and accurate multicolor decorative or non-structural details. Good for crazy color parts, but very brittle and grainy, so not what you need for functional gears.
