Homemade plastic gears. Making a plastic gear (video tutorial)
One of the most complex and yet widespread mechanical systems is the gear train. It is a great way to transfer mechanical energy from one place to another and a way to increase or decrease power (torque) or increase or decrease the speed of something.
How to make a gear with your own hands? The problem is always that creating effective gears requires quite a lot of drawing and math skills, as well as the ability to create complex parts.
For a hobbyist there is no need to have maximum efficiency, so we can get a much easier system to make, even with the tools at hand.
A gear is a series of teeth on a wheel. (Note in the diagram above, they labeled the wrong number of teeth on the gears - sorry)
Step 1: Formulas and Calculations
Formulas for drawing and making gear teeth can be found in abundance on the Internet, but for a beginner they seem very complicated.
I decided to simplify the problem and the solution works very well on both large and small scales. On a small scale it is best suited for machine cutting using laser cutters For example, very small gears can be successfully manufactured in this way.
Step 2: Easy way
So, the shape of the prong, to put it simply, can be a semicircle.
Step 3: Determine the dimensions
Now we can define the parameters to make the gear:
- How big/small the gear teeth will be (diameter) - the smaller the gear, the smaller the teeth should be.
- All the teeth that are assembled into the mesh (connected) must be the same size, so you need to calculate the smaller gear first.
Let's start with 10mm teeth.
I want a gear with 5 teeth so that the circle is 10x10mm (in circumference) = 100mm.
To draw this circle I need to find the diameter, so I use math and a calculator and divide the circumference (100mm) by Pi = 3.142.
This gives me a diameter of 31.8mm and I can draw this circle using a compass and then draw exactly 10 circles of 10mm diameter on its circumference using a compass.
If you have the option, it's easier to do everything using drawing software. If you are using software, you will need to be able to rotate the circles of teeth around the main circle, and you will need to know how far to rotate each tooth. It's easy to calculate: divide 360 degrees by the number of circles. So for our 10 circles, 360/10 = 36 degrees for each tooth.
Step 4: Making a Scalloped Shape
Remove top part one circle and bottom part next round. To do this you must have an even number of teeth
We have the first gear. It can be cut from wood or metal using basic tools, saws and files.
This process is easy to repeat for as many gears as you need. Keep the size of the circle consistent and they will fit together.
Step 5: Get the Gear
Since these semi-circular gears are easy to cut, you can make them using a tool and a jigsaw or saw.
I used to make a 9 or 10 tooth template on plywood and used that as a guide for my hand router and cut the gears without any problems.
If you have access to a laser cutter, they can be cut from 3 or 5mm thick acrylic and come in very small sizes.
Nowadays, there are a lot of mechanisms around us that use plastic gears. Moreover, these can be both toy cars and quite serious things, for example, an antenna lift in a car, a spinning rod gearbox, etc. The reasons for gear failure can be different, of course, most of them are related to improper operation, but that’s not about that now. If you find yourself in such a situation and a couple of gear teeth are broken, then there is a way out: not to pay for an expensive part, but to restore it in a simple way.
Needed for recovery
- Unnecessary toothbrush.
- Detergent.
- Two-component epoxy adhesive - cold welding for plastic.
Restoring a plastic gear
Preparation
The first step is to prepare the surface of the gear. We wash it several times warm water With detergent, actively working with a toothbrush. Our task is to degrease and remove grease from all edges.After degreasing is done, dry it dry.
Preparing the glue
Now let's prepare the glue. Mix the components on a small piece of cardboard in the proportions 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 different manufacturers these data may differ radically.
If the consistency turns out to be liquid, let it stand for a while until it begins to harden.
Restoration of teeth
In my case, several teeth were ground off, the situation can be corrected. Apply glue to the place that needs to be restored. The glue should be very thick, but flexible.
We make a kind of tubercle.
We place the gear on an improvised stand so that the glue thickens even more. Again, everything is individual, I personally needed 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 hairdryer and start heating the glue on the gear.
Restoration of teeth
Now the most crucial moment is rolling the teeth. The unit where the gear was used, namely the other gear with which our broken one was in direct contact, must be generously lubricated with grease, grease or lithol.We install the broken gear and roll it over the other one several times.
As a result, another gear will roll the track on the thick glue.
Now you understand that the epoxy glue on the gear needs to cure to the consistency of hard clay before rolling the teeth.
Thanks to the lubrication, the glue will not stick to the other gear.
Hardening
Carefully remove the restored product from the mechanism and leave it for final hardening, usually for a day.
In this simple way, you can quite easily restore broken gears.
How to replace epoxy glue?
If you haven't found glue, I can recommend you to make a slightly similar composition.For this you will need:
- Epoxy resin with hardener.
- The cement is dry.
In the proportion specified in the instructions, mix the components to obtain the required amount of glue. Add cement. Just not a cement-sand mixture, but pure cement. The proportions are approximately two to one. That is, two parts glue and one part cement. And mix everything very thoroughly. The glue is ready, and then everything is as per the instructions above.
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 reduce noise. But metal gears can also operate silently if their profile is made with precision. For rough gears, “power” gears are produced; they are made by casting from cast iron and steel without further processing. “Running” gears for high-speed gears are manufactured on milling or gear-cutting machines, followed by heat treatment - carburizing, which makes the teeth hard and resistant to wear. After carburization, the gears are processed on grinding machines.
Running method
The rolling method is the most common option for manufacturing gears, since this method is the most technologically advanced. In this manufacturing method, the following tools are used: cutter, hob cutter, comb.
Rolling method using a 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 one time. When processing a workpiece, the cutter performs a reciprocating movement and after each double stroke, the workpiece and the cutter rotate one step, as if “rolling” over each other. When the gear blank makes a full revolution, the cutter performs a feed motion towards the workpiece. This production cycle is carried out until all the required metal layer has been removed.
Rolling method using a comb
The comb is a cutting tool, its shape is similar to a rack, but one side of the comb teeth is sharpened. The blank of the gear being manufactured produces a rotational movement around its 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 option for the movement of the cutting tool and the gear blank 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 engaging with the contour of the cutting tool.
This method allows you to produce a gear using a hob cutter. Cutting tool In this method, a hob cutter is used, 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 shape 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 at the beginning of the twentieth century, it is not accurate, the cavities of the produced gear are different, not identical.
Hot and cold rolling
In this method of producing gears, a gear-rolling tool is used, which heats a certain layer of the workpiece to a plastic state. After this, the heated layer is deformed to obtain teeth. And then the teeth of the gear being manufactured are rolled until they acquire the exact shape.
Manufacturing of bevel gears
For the manufacture of bevel wheels (bevel gears), a variant of running in the machine gearing of the workpiece with an imaginary producing wheel is used. The cutting edges of the tool, during the main movement, cut off the allowance, thus forming the side surfaces of the future gear (gear).
This material is general leadership on designing and printing plastic gears on a layer-by-layer 3D printer.
The gear light switch is a clever example of something you can design yourself after reading this article.
Optimal materials for plastic gears
What material is the best? The short answer in terms of the quality of the finished gears is as follows:
Nylon (PA) > PETG > PLA > ABS
- Please note that the license is “Personal Use Only”, i.e. the result cannot be distributed, sold, changed, etc.
- IN assembled form the structure 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% infill. 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 supports.
Assembly instructions (read before starting work)
- Use a razor blade to clean the teeth of the gears until they fit together well, then install them on the plate with the same direction of rotation as they were printed (center gear pin on the right, driven gear mesh top center).
- Secure the main gear by inserting the pins into the holes.
- Apply some dry glue (a glue stick works well) to the working end of the lever and install the lever on the side where the pins match. Glue is needed to secure the lever to the pins. The lever also presses the main gear against the structure.
- Heat and soften the clamps. This is enough to open them. Align the edges of the clamps 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 require cleaning - a knife will help, it all depends on how good your printer is). Press the clamps until they harden. This ensures that everything will hold securely.
Special advantages of layer-by-layer printing and examples of the use of gears
So, what is the advantage of 3D printing gears over traditional gear manufacturing methods, and how strong 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 are printed without problems. The prototyping and creation process is fast and clean. The most important thing is that 3D printers are common enough that a set of STL files from the Internet can supply 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 designed correctly, printed gears can be quite an effective and reasonable option, and for some applications, ideal.
Most working applications look something like this: gearbox typically for small electric motors, handles and winding keys. This is because electric motors work great at high speeds, but they have problems with a sharp decrease in speed, and in this case it is problematic to do without a gear transmission. Here are examples:
Specific problems of layer-by-layer printing
- Printed gears usually require 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 central hole is a very common problem even on expensive printers. This is the result of many factors. This is partly due to thermal compression of the cooling plastic, partly because the holes are designed in the form of polygons with a large number corners that fit around the perimeter of the hole. (Always export gear STL files with a large number of segments).
Slicers also contribute, since some of these programs can select different points to bypass holes. If the inner edge of the hole draws the inner edge of the extruded plastic, then the actual diameter of the hole will have a slight shrinkage, and it may take some force to insert something into this hole later. So the slicer may quite intentionally make the holes smaller.
In addition, any discrepancy between the layers or the discrepancy in the width of the intended and actual extrusion can have a significant impact noticeable effect, “sealing” the hole. You can combat this, for example, by modeling holes with a diameter of approximately 0.005 cm larger. For similar reasons, and to ensure that the printed gears fit next to each other and can operate, it is recommended to leave a gap of approximately 0.4mm between the teeth in the model. This is a bit of a compromise, but the printed gears won't get stuck.
- Another common problem is getting a solid fill, which is quite difficult for small gears. Gaps between small teeth are quite common, even when the slicer is set to 100% infill.
Some programs deal with this relatively successfully in automatic mode, but you can manually solve this problem by increasing the overlap of layers. This problem is well documented on RichRap, and the blog provides various solutions.
- Thin-walled parts turn out fragile, overhanging parts need supports, and the strength of the part is significantly 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, we can recommend a rectangular filling and at least 3 perimeters. It is also advisable to print in as thin a layer as possible - as much as your equipment and patience allow, because then the teeth will be smoother.
- Though, plastic is inexpensive, but time is precious. If the problem is critical or you need to replace a huge broken gear, you can print with continuous filling, so as not to leave a chance for any other ambush other than wear.
Most Common Reasons for Printed Gear Failures
- Grinding of teeth (from long-term use, see Step 10 about lubrication).
- Problems with fitting onto the axle (see Step 7 about fitting).
- Broken body or spoke (these are rare failures that usually occur if the gear is poorly printed, has insufficient padding, for example, or is designed with spokes that are too thin).
About the importance of involute
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 along some contour. In technology, the involute of a circle is used as a tooth profile for gear wheels. This is done to ensure that the rotation speed and engagement angle remain constant. A well-designed set of gears should transmit motion entirely through rotation, with minimal slippage.
Modeling an involute gear from scratch is quite tedious, so it makes sense to look for templates before taking it on. Links to some of them will be given below.
Subtleties of tooth modeling. Optimal number of teeth
Think about it: if you want 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 friction coefficient (the number of teeth meshing at once) and provide smoother rotation. Increasing the number of teeth means that each of them must be smaller to fit the same diameter. Small teeth are more fragile and more difficult to print accurately.
On the other hand, reducing the number of teeth provides more volume for increased strength.
Printing small gears on a 3D printer is like painting fine lines in a coloring book with a thick brush. (This is 100% dependent on the nozzle diameter and the horizontal resolution of the printer. Vertical resolution does not play a role in the minimum size restrictions).
If you want to test your printer by printing small gears, you can use this STL:
The printer we tested performed everything perfectly. top 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 warnings from the program about having too few teeth, and also avoiding intersections.
There is one more thing to consider when choosing the number of prongs: 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 continually bump into each other, creating wear points.
More correct solution- 15 and 31. (This is the answer to the question at the beginning of the section).
In this case, the proportion is not observed, but uniform wear of the pair of gears is ensured. Dust and dirt will be distributed evenly throughout the gear, as will wear.
Experience shows that it is best if the ratio of the number of teeth of the two gears is in the range of approximately 0.2 to 5. If a higher gear ratio is required, it is better to add an additional gear to the system, otherwise you may end up with a mechanical monster.
How many teeth are there?
Such information can be found in any Mechanic's Handbook. 13 is the minimum recommendation for gears with a pressure angle of 20 degrees, 9 is the recommended minimum for 25 degrees.
A smaller number of teeth is undesirable because they will intersect, which will weaken the teeth themselves, and the problem of overlap will have to be solved during the printing process.
Subtleties of tooth modeling. Pressure Angle, and How to Make Strong Teeth
Pressure angle 15, pressure angle 35
Pressure angle? Why do I need to know this?
This is the angle between the normal to the tooth surface and the diameter of the circle. Teeth with a larger pressure angle (more triangular) are stronger, but have poorer grip. They are easier to print, but during operation they create a high radial load on the supporting axis, produce more noise and are prone to kickback and slipping.
For 3D printing good option is 25 degrees, allowing for smooth and efficient transmission in palm-sized gears.
What else can be done to strengthen teeth?
Just make the gear thicker - this will obviously strengthen the teeth too. Doubling the thickness equals doubling the strength. good general rule states: the thickness should be from 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 adding an overlapping solid wall to reduce unsupported area significantly improves 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 fitting on the axle with notches. This simplest method is not found too often. Here you need to be careful with the distortion of the plastic, which will worsen the transmission of torque over time. This design is also non-removable.
The axis is on the fixing screw in the plane of the gear. The retaining screw passes through the gear and rests against a flat area on the axle. The retaining screw is usually directed directly into the gear body or through a recessed nut through square hole. Each method has its own risks.
Pointing the screw directly can strip the fragile plastic threads. The recessed nut method solves this problem, but if you are not careful and apply too much force during fastening, the gear body may break. Make the gear thicker!
Adding special screw-in thermal inserts will significantly improve the strength of the axle attachment.
Recessed hexagon - hexagonal insert in which sits a hexagonal nut for a hexagonal screw. You need to print enough solid layers around the hexagon so that the screw has something to hold onto. It is also useful to use a fixing screw, especially if we're talking about about high speeds.
Wedge found in the world of amateur 3D printing rarely.
The axle is a single unit with the nut. This solution resists torsional loads well. This, however, is very difficult to achieve on a printer, because the gears have to be printed perpendicular to the table surface, and any axes with this solution have a weak point in 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, they are complex to operate but have their advantages. They are good for their high coefficient of adhesion, self-centering and self-leveling. (Self-leveling is annoying because it affects the operation of the entire structure). This type of gear is also not easy to produce using conventional equipment such as 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 starting spirals. In most cases it turns out from 1 to 3).
Rack and pinion gear. Converts rotational motion into 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. It is very simple to calculate the density of the teeth: you just need to multiply their density on the rack by pi and by the diameter of the gear. (Or multiply the number of teeth on the rack by the tooth density on the pinion).
Lubricating 3D Printed Gears
If the device operates under light loads, at low speeds and frequencies, you don’t have to worry about lubrication of the plastic gears. But if the loads are high, then you can try to extend the service 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, a heavy-duty lubricant may be recommended. Litol, PTFE or silicone-based lubricants are perfect for this. Lubricant should be applied by lightly wiping the part. toilet paper, with a clean paper towel or dust-free cloth, evenly distributing the lubricant, turning the gear several times.
Any lubricant is better than no lubricant, but you need to make sure that it is chemically compatible with the plastic. And you should always remember that WD-40 lubricant sucks. Although it cleans decently.
Tools for making gears
High-quality gears can be made using free programs alone. That is, there are paid programs for very optimized and perfect gear connections, with finely tuned parameters and optimal performance, but good is not sought after. You just need to make sure that the same mechanism uses gears made by the same tool so that the connections mesh as they should. It is better to model gears in pairs.
Option 1. Find an existing gear model, modify or scale it to suit 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 to importable ones. However, some programs, such as Blender, can import SVG directly, without dancing with tambourines).
- https://inkscape.org/ru/ - free program vector graphics with integrated gear generator. A decent tutorial on making gears in Inkscape - and .
STL file editors
Most gear pattern generators output STL files, which can be annoying if you require features that the generator doesn't offer. STL files are the PDFs of the 3D world, they are intricately difficult to edit, but editing is possible.
TinkerCAD. A good basic 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 original shapes. http://meshmixer.com/
Non-FDM 3D printing
Most people, even dedicated hobbyists, do not have immediate access to other 3D printing technologies for making gears. Meanwhile, such services exist and can help.
SLA- Great technology for professional gear prototyping. The printed layers are not visible and the process produces very fine details. On the other hand, the parts are expensive and somewhat fragile. If you use this process to prototype a future diecast model, you won't have any problems retrieving it. Make the part solid, otherwise it will certainly break!
SLS- a very precise process that results in durable parts. The technology does not require supports for overhanging structures. You can create complex and detailed pieces, preferably with walls up to a quarter inch thick. The printing layers are also almost invisible... BUT, the rough surface (because the technology is based on powder printing) is extremely prone to wear. A very heavy duty lubrication is required and many do not recommend SLS gears at all for long-life applications.
Technology BinderJet good for detailed and precise multi-color decorative or not structural details. Suitable for producing parts with crazy colors, however, very fragile and grainy, so this is not what is required for functional gears.