How To Draw A Spur Gear

Fourth dimension to read: 7 min

Say y'all're 3D printing a robot, and you're designing a sweet gearing system to brand your robot move smoothly. What to do about the fact that near CAD programs don't have a "create involute gears" button? Welp, you lot'll accept to create these geometries manually. In this tutorial, I'll walk you through the process in SolidWorks, and you tin employ a similar organisation for any other plan.

Creating involute gears in a CAD program is tricky, merely if you follow the steps below, the teeth will come out right every time. Go slowly and brand certain that y'all follow each stride carefully, and soon yous'll have a great gear set up for print!

Step 1

For our example, we want to create a 19-tooth 32-pitch gear. Nosotros know that the pitch diameter of the gear will be xix/32 inches, which equals 0.59375 inches, but because we can keep equations in CAD, we'll simply create our first circle with a diameter of "=19/32", as shown in the picture below. (I recommend using the pinnacle plane for all these sketches.)

Step ii

We want to create the border of the molar equally if information technology were a point on the imaginary cord unwinding from our post. To practice this, in a new sketch on the aforementioned plane, nosotros beginning create a horizontal line at the top of the circle, and so create a line with the pressure angle (xx degrees, since that'south common) which passes through the top of the circle, so we end upwardly with a sketch that looks like the 1 below.

Stride 3

In the same sketch, create a circle inside the first (concentric) that is tangential to the xx-degree (pressure level angle) line, and then make another line from the center of the circles to the intersection of the force per unit area angle line and the inner circle. (Both circle and line are highlighted in blueish below. The circle from this step becomes the "base circle": The imaginary post around which the cord is wound.)

Footstep iv

In this step, nosotros'll finally create the "string" for the involute, imagining the edge of the tooth to be this cord unwinding. In some other new sketch on the same plane, create a line along the pressure bending line from the base of operations circle to the pitch circle, as shown below, and dimension it with a driven dimension. (The actual length of this is determined from the pitch and number of teeth of your gear, so it must be a driven dimension, but we'll demand the dimension on there to use in equations in the adjacent steps.)

Step 5

At present, we'll imagine the string unwinding from our base circle and encounter the curve a point on the string would make. This will be an approximation only will be close enough for a printed gear, and you tin can brand the approximation more accurate by choosing smaller increments for your approximated points.

Describe an arc that goes from the indicate where the "cord" contacts the base circumvolve to a little to the left, coradial with the base circle. Dimension this arc with an arc dimension (select both the end points and then the arc itself, otherwise yous'll end up with a chord dimension, which just measures the straight-line distance between the arc endpoints) and requite it the length of the increment you want for approximating the involute curve. (I recommend using a length about the pitch or module, in this case 0.03, though remember that smaller increments create more accuracy, and larger increments are fine for rougher approximations.)

Footstep 6

Draw a construction line from the left end of the new arc towards the correct, and make the line tangential to the base of operations circle (as well tangential to the arc). We'll telephone call this line the "string plus i" line.

Step 7

Dimension this new line. In the dimension box that pops upwardly (non the area on the left), type "="; click on the dimension for the first directly piece of string (in this case 0.10153723); type "+"; and click on the dimension for the arc.

The resulting box should wait similar the i below; click on the green cheque marking to accept. (The reason for this is that the arc represents the string unwinding from the cylinder, so the end of the string gets longer by that amount equally it unwinds to this new location.)

Step 8

Create several more than arcs on either side of our current arc, each with the same arc length as the first. To do this quickly, draw the arcs; dimension the arcs (selecting each end and and so the arc itself); type "=" in the pop up box; and click on the dimension of the beginning arc.

Step 9

From the next arc to the left, create some other structure line tangent to the base circle. This represents the cord unwinding but a little more, and so it should be the length of the "string plus one" line from steps 6 and 7, plus the length of the arc.

Dimension it past clicking on the line, typing "=" in the box that pops up, clicking on the dimension for the "string plus one" line, typing "+", and clicking on the dimension for the arc. This line will be chosen the "cord plus two" line.

Step 10

Repeat step 9 for three new unwinding strings to the left. Each of these lines should exist the length of the next string to its right, plus the arc length between them. Because these represent the string unwinding, this makes sense with the image of the cord around a cylinder.

Step 11

Now we need to create the lines for the string winding from the original location onto the cylinder till it ends. From the next arc to the right of the original line, create a construction line tangential to the base circumvolve. Because the string is winding more tightly, the length of this line needs to be the original string line minus the length of the arc betwixt them. Click on the line' type "="; click on the dimension for the string line; blazon "-"; and click on the dimension of the arc.

Step 12

Repeat step eleven for the two additional arcs to the right of the original. If y'all are using most the diametric pitch for the arc length, so three arcs to the right will bring the stop of the "string" almost in contact with the base of operations circle; our imaginary cord has been completely wound around the cylinder.

Stride 13

Zoom into the tail of the final "cord" and draw a pocket-size, vertical midpoint line from the finish of the string, with the midpoint on the base circumvolve, so that there is now a point within the base circle straight below the end of the string. Because nosotros can't wind the string into the cylinder, the 2d betoken of this line gives united states of america a point inside the base circumvolve for finishing our gear molar.

Stride 14

Open a new sketch on the same plane and depict a spline through the points from the uppermost (where the string is most unwound) to the lower correct (where the string is tightly wound), plus the point inside the base circumvolve created in pace thirteen. Yous now have one side of the tooth fatigued.

Footstep 15

Draw a construction line to correspond the centerline of the tooth. For a 19-tooth gear, there are 19 teeth poking out and xix spaces between the teeth, then we need the centerline of the molar to be the whole circle (360 degrees) divided by 2 (the molar and valley) divided past 2 (half the tooth) divided by 19 (the number of teeth). Dimension the bending equally "=360/4/nineteen".

Step 16

Mirror the spline about the molar centerline.

Step 17

To ascertain the exterior of the gear, create a circumvolve around the pitch circle. Draw a radial line from base of operations circle on the right manus side to the pitch circle and another from the pitch circumvolve to the new circumvolve (the outside). Make these ii lines equal length, so the outside circle is the same radial length larger than the pitch circle as the base circle is smaller.

Step 18

At present we take all the lines that volition ascertain our gear. In another new sketch on the same plane, draw a concentric circle with extends to the inside finish of the spline (just barely smaller than the base circle, allowing a small amount of clearance). Extrude this circle to the desired gear thickness.‍

Step 19

In a new sketch on the same airplane, utilise "outset entities" and a dimension of "0.00" to copy the right hand spline into the new sketch. Repeat for the left paw spline.

Stride xx

In the same sketch every bit above, use "offset entities" and a dimension of "0.00" to copy the circle from step xviii. Then repeat for the outermost circle from step 17.

Stride 21

In the same sketch, use "trim entities" -> "power trim" to cut off the parts of the spline which extend beyond the exterior circle. (If you hide the body from step 18 and all the other sketches, the tooth will go visible.)

Stride 22

Extrude the sketch above to the aforementioned length equally the circle from footstep 18. Click in the "selected contours" box of the extrude dialogue, and so click inside the tooth surface area to highlight the tooth region.

Pace 23

Click on "linear blueprint" -> "circular design" to bring upwardly the round blueprint dialogue box. For the rotation, click on the exterior of the extruded circle from step xviii. Type in "nineteen" for the number of instances and select "equal spacing", and and so click on the tooth for the "features and faces" to pattern.