Gear template generator help The gear template generator is a program to calculate and print gear shapes for involute spur and pinwheel gearing.

Gear type and properties

Tooth spacing

Specifies the center to center tooth spacing, as measured along the gear's pitch diameter (this valuie is also known as circular pitch)

Type

This selects what type of gear teeth to draw. The gear's teeth can be spur, pinwheel, or protractor.

Involute

This specifies involute spur gears. Involute spur gears are the most commonly used type of gear. Any two gears that have the same tooth spacing (or pitch) and the same contact angle (also known as pressure angle) will mesh and run smoothly.

Pin

For some applications, it is desirable that one gear be comprised of just a ring of pins. Such gears are also known as "lantern" gears. The pins are typically held together by two discs on either side, so that the whole structure could be said to look like a "lantern". Such a gear may or may not have a shaft passing through the middle of the pins.

The primary advantage of this type of gear is that it's possible to make gears with as few as three teeth that will still run smoothly.

For pinwheel gearing, the gear on the right will always be the pinwheel and the gear on the left will always be cycloid shaped to mate with the pinwheel.

Protractor

Sometimes it's useful to be able to create a template that divides a circle into a specific number of intervals. For example, to divide a circle into 23 equal parts with a protractor would be tedious and error prone. Using this program you can print a template that divides the circle as specified.

Shaft spacing

This field always displays the calculated shaft spacing value. The shaft spacing is the sum of the pitch radii of both gears. Pitch radius is calculated from the pitch circumference. Pitch circumference is equal to the number of teeth times the tooth spacing.

You can also enter a new value in this field and the gear's tooth spacing will automatically be recalculated to produce the desired center to center distance for the two gears.

Contact angle

This field specifies the contact angle, also known as pressure angle, for involute spur gears. Larger pressure angles produce gears that have more triangular looking teeth. Larger pressure angles work better for gears with a small number of teeth, but the overall result is lower efficiency due to higher friction in the gear set.

This field is only applicable for involute spur teeth and is hidden if other types of gear teeth are selected.

Pin diameter

This field specifies the size of the pins for pinwheel gearing. This field is only applicable to pinwheel gearing and is hidden if other types of gear teeth are selected.

Gear properties

Show

Selects whether the gear is visible. Note that for pinweel gears, the properties of the pinwheel affect the shape of the mating gear, so even if the right gear is hidden, its properties still affect the gear on the left.

Spur

Selects a regular spur gear. That is, a round gear with teeth on the outside.

Ring

Selects a ring gear. A ring gear is a gear with teeth on the inside. Ring mode can only be selected if the other gear is a spur gear. Ring gears are useful when making planetary gear sets

Rack

Selects a "rack" type gear. A rack is essentially a gear that has been unwrapped. Rack and pinion mode is only currently available for involute tooth types.

Teeth

Specifies the number of gear teeth.

Odd shaped gears generated by setting the right side gear addendum to zero.

Addendum

Spokes & more tab

Diametric pitch

Some people prefer to use diametric pitch, as opposed to tooth spacing (also known as circular pitch). Diametric pitch is equal to 2 * π / tooth spacing. Some people prefer the program do this calculation for them, so on the "Spokes & More" tab, diametric pitch is shown. You can enter a value in the diametric pitch, and the circumferential pitch on the main tab will automatically be updated.

Pitch diameter

The pitch diameter is the diametric pitch times the number of teeth. The pitch diameter is useful for working out gear spacing. The ideal center to center distance of a pair of gears is equal to the sum of the pitch diameters, divided by two. Note that the shaft spacing in the "Gear properties" tab already shows the center to center distance as "shaft spacing".

Overall diameter

This displays the overall diameter of the gear, from tip to tip.

Spokes

Specifies the number of spokes. Only spur gears above a certain number of teeth are large enough to have spokes.

Shaft hole diameter

Specifies the shaft hole to draw. For pinwheel (lantern) gears, this specifies the size of the shaft in the middle of the pins. The gear teeth of the mating gear will be kept short enough so as not to interfere with the central shaft. Specify zero to omit the center shaft or shaft hole.

Chain & Sprocket mode

Block chain

Roller chain

The gear template generator can produce both block chain sprockets, and roller chain sprockets.

Nearly all modern metal drive chains, such as those used on bicycles, are of the "roller chain" variety. Roller chains have a cylindrical roller on every pin joint, with two sets of links on either side to join them together.

Block chains are an older, obsolete style of drive chain. Block chains are much simpler to make, and lend themselves well to wood. In a block chain, the sprocket engages bocks in the middle of the chain. Each block has two holes, to which the links on either side attach. An example use of a wooden block chain can be seen in this tank thread vehicle

If the blocks of a block chain are not rounded on the corners, then the corners tend to scrape the sprocket where the chain engages and disengages the sprocket.

The gear template generator will generate sprocket shapes that make allowances for this "undercut" next to the teeth for this, but the sprockets are still somewhat ugly and inefficient.

A much better solution is to put a bit of a round or chamfer on the edges of the chain blocks. The sprocket at left is very similar to the previous sprocket, but with blocks that have chamfered corners. Note that the teeth have much less undercut.

For clarity, I changed the links to be very thin, but the links do not actually engage the sprocket, so only the link's length, not its actual shape contributes to the sprocket shape.

The gear generator can generate shapes for workable sprockets down to three teeth. However, these sprockets are inefficient and will run very rough. If you use the "Animate" function in the gear template generator, you can see that the chain has quite a bit of side-to-side motion.

The shape of the teeth also doesn't engage the chain very well, as the teeth need to be very sloped to allow the chain to engage and disengage the sprocket.

Sprockets with larger number of teeth will run much more smoothly.

To better see how the chain meshes, parts of the chain and sprocket can be hidden. The image at left, for example, has the chain links hidden. You can also hide the chain entirely. Hiding the chain is useful when making a printout of the sprocket template shape to use when cutting the sprocket out of plywood.

The image at left also has the "Show pitch diameter" turned on. The blue lines represent the pitch diameter, and the lines crossing it indicate the centers of the tooth undercut radii. If you have the right size drill, you can start by drilling out the undercut circles, which will make it easier to cut out the rest of the sprocket with a bandsaw

Specifying the chain dimensions

The shape of the chain blocks and links is specified in terms of length and width. Please note that the specified length is the length between the two holes. The program automatically adds some length to the link to allow for material around the holes.

An additional parameter, "Chamfer" determines how much to remove from each corner of the blocks and links. If "Round chamfers" is selected, the chamfer is replaced by a round with a radius equal to the chamfer measure.

Display parameters

This part of the panel selects which aspects of a gear to display.

Show pitch diameter

When selected, a circle is drawn indicating the gear's pitch diameter.

Show line of contact

For involute teeth, this shows the contact angle (pressure angle) and base radii of the two gears. If you think of the base radii as being two spools, a point along a string unwound from the right gear's base radius and wound onto the left gear's base radius would exactly follow the path along which both gears touch.

Show center

Show a crosshair in the center of each gear.

Grid

Draw a grid. The grid is useful for getting a sense of scale, for checking that a printout was scaled correctly, and to help align multiple pages together when pasting together multi-page printouts.

Grid diagonals

Draw diagonal lines on the grid. Diagonal lines are very useful to help align the sheets of a multi-page printout when gluing the pieces of paper together. The diagonals grids work so well, I later wrote BigPrint to allow other types of images to be pasted together this way.

Animate

Slowly turn the gears. This allows you to examine how the gears mesh. Note that spur gears with less than 10 teeth and low contact angles will often cause interference. For gears with very few teeth, try pinwheel gears.

Wobbly

I implemented "wobbly mode" for the evaluation version of the program. The eval version can do everything the full version can do, but all output is distorted. The distorted gears would not work in real life.

I found the distorted "wobbly mode" fun to watch, so I have added this "feature" as an option to the full version as well, just for fun.

Show rotated

This field causes the gears to be displayed rotated. The angle is specified as one hundredths of a tooth. Specifying 25, for example, will cause the gears to be rotated by one quarter tooth interval.

This feature is useful if you want to check that spur gears mesh without interference. It's especially useful if you use the up/down buttons, and zoom in on the meshing point by reducing the value of the "screen view width" field.

Screen view width

This field indicates how wide an area the screen represents. This value defaults to 20 cm, or about the width of the printable region on a normal piece of paper.

Note that this value is in whatever units you chose. If you change the units to "inches" then the visible region would change to 20 inches, along with all other dimensions. The display would not change, but when you print it, it will now be much larger as it's now sized in inches.

Saving

Units

Printing

Grid lines, especially when combined with diagonal grid lines, are very useful to help precisely align the pages when gluing them together.

It's advisable to do a print preview before printing your gears. The dimensions you have specified might result in gears that span a surprisingly large number of pages.

Printing parameters

Printer scaling

You may find that your printer prints just slightly larger or smaller than it should. If you find that 10 grid lines of a one centimeter grid are actually 10.1 cm, you can compensate for this by telling the gear generator to scale output to 99%.

Page overlap

If you print gears that span multiple pages, the gears are printed with no overlap. You may prefer to have a slight amount of overlap from page to page, to give you more confidence in aligning the pages. Use this field to specify that you want overlap.

You may also find that its quite easy to align the pages even without overlap when grid diagonals are enabled.

Exporting

No printer pagination will be applied to export.

3D gear drawn from gear outline in SketchUp

DXF (for CAD)

The DXF export does not include units. Programs that import DXF typically allow you to specify which units the DXF file actually uses. For example, if you used inches to design your gear, but the importing program assumes the units are millimeters, the imported gear will be much smaller than you expect.

SketchUp

When you import a gear into SketchUp, it will be imported as nested objects. Keep opening the objects until you have opened the gear outline. To turn the outline into a surface that can be extruded, draw a rectangle around the whole outline, then delete the outline of the rectangle. If your gear has spoke and center holes, select these with a double click, copy them, delete them, then paste them in place. After that, you will be able to delete the surface inside the spoke holes. I don't think SketchUp works as well as they say it should in this particular regard, but the above procedure has worked for me.

HPGL

CSV (for spreadsheet)

Displaying gears in a spreadsheet is not particularly useful, but it's a good starting point if you wish to manipulate the X-Y points in some way for your own purposes.

Any other questions?

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