snaps to the nearest whole tooth count
count · hole Ø · circle Ø (BCD)
Pick a chain size and a tooth count, get a manufacturing-correct DXF ready for the laser, waterjet, or plasma table. Real ANSI B29.1 tooth form, true arc entities, tips truncated at catalog OD the way a real sprocket is. Free, no signup.
A sprocket tooth is not an arbitrary shape. ANSI B29.1 defines the space between two teeth as a specific chain of four elements, and every one of them is derived from just two numbers: the chain pitch P and the roller diameter Dr. Get those right and the tooth form falls out of the standard.
The seating curve is the pocket the roller actually sits in. It is an arc of radius R centered on the pitch circle, swept A degrees either side of bottom dead center. Where it ends, the working curve takes over — radius E, swept through B degrees, internally tangent to the seating curve so the roller rolls off the seat without a step. That is the surface that carries load as the chain articulates off the sprocket. From there a short tangent flat of length yz runs out to the topping curve, radius F, which rounds the tooth tip. The topping curve is tangent to the flat at one end and its center sits exactly 1.4·Dr from the roller center — that last relationship is the check that proves the construction closed correctly.
Constants are in inches, which is why the generator converts metric input to inch,
solves, and converts the coordinates back out. Note that the seating radius makes
the seat diameter 1.005·Dr + 0.003 — the standard's nominal minimum.
Production sprockets are usually cut a thousandth or two looser than that, still
inside B29.1 tolerance, to keep the roller from binding on a tight pocket.
Finally, the tips. The pure construction produces a pointed tooth, but real
sprockets are machined from a blank turned to OD = P(0.6 + cot(180°/N)),
which cuts the point off. This generator does the same thing: it solves for where
the topping curve crosses the blank OD and caps the tooth there. That is why the
teeth come out with slightly flat tips, and it is why the OD in the readout matches
a catalog sprocket instead of running large.
A generator that produces a plausible-looking tooth is easy. One that produces the correct tooth has to be checked against something real, so here is exactly what was checked and what came back.
The published check case. The American Chain Association works a #25 chain, 30-tooth example all the way through with published intermediate values. This generator reproduces every one of them. It also lands the topping-curve center on the standard's own W/V datum to about 1 part in 1016 — the construction and the datum agree to machine precision, not just to the four decimal places the standard prints.
Overlay against a commercial part. A #40, 18-tooth profile was generated and overlaid in SolidWorks against a published CAD model of the same catalog part. Arc for arc, the profiles matched — working radius 0.4079" and topping radius 0.2582", identical to four decimals.
Repeating that overlay at #60, 11 teeth did not match, so the difference got traced rather than assumed away. The model's tooth form turned out to be driven from a 0.312" roller — the #40 size — rather than the 0.469" roller a #60 chain actually uses.
That is worth knowing generally, and it is why the check is described here at all. Downloadable CAD models are usually supplied for fitment and visualization, not as manufacturing geometry, and the tooth form does not always get rebuilt for every chain size in a family. If you are cutting a sprocket from a model you downloaded, open the sketch and confirm the roller diameter driving the tooth form matches your chain. It is a thirty-second check that catches a part you cannot use.
A console self-test runs the ACA check case on every page load. If it ever fails, it says so in the browser console rather than quietly handing you a bad file.
Pitch and roller diameter for standard ANSI single-strand chain. These are the two numbers the tooth form is built from, and they are what the preset dropdown loads.
| Chain | Pitch (in) | Pitch (mm) | Roller Ø (in) | Roller Ø (mm) |
|---|---|---|---|---|
| #25 | 0.250 | 6.35 | 0.130 | 3.30 |
| #35 | 0.375 | 9.53 | 0.200 | 5.08 |
| #41 | 0.500 | 12.70 | 0.306 | 7.77 |
| #40 | 0.500 | 12.70 | 0.312 | 7.92 |
| #50 | 0.625 | 15.88 | 0.400 | 10.16 |
| #60 | 0.750 | 19.05 | 0.469 | 11.91 |
| #80 | 1.000 | 25.40 | 0.625 | 15.88 |
| #100 | 1.250 | 31.75 | 0.750 | 19.05 |
| #120 | 1.500 | 38.10 | 0.875 | 22.23 |
#25 and #35 are bushed chain — they have no rollers, and the listed diameter is the bushing OD, which is what the tooth form is cut to. #41 is a narrow, lighter-duty chain that shares the 1/2" pitch of #40 but uses a smaller roller, so a #40 sprocket and a #41 sprocket are not interchangeable.
An R12 DXF containing real ARC, LINE and
CIRCLE entities. Nothing is flattened into polylines, so the curves
stay curves when your CAM software reads them. R12 is the most widely accepted DXF
version there is — every cutting service and every CAD package opens it.
The file is a plain, closed-contour R12 DXF, which is the format all of them ask for. Units are tagged in the header (inch or millimeter, matching whichever you generated), so the part should come in at the right size without scaling. As with any DXF, check the dimensions in their quoting preview before you pay.
7 through 400. The tooth form itself stays valid well outside that range — it only breaks down mathematically around 4 teeth — but 7 is a sensible practical floor, since chordal action and chain articulation make very small sprockets a poor drive. The ceiling is about file size and preview speed rather than geometry: a 400-tooth #40 is already over five feet across. If you need a bigger diameter, the answer is usually a larger chain pitch, not more teeth.
Yes — enter a target outside or pitch diameter and the tool picks the nearest whole
tooth count and tells you how far off you landed. Diameter is quantized, because tooth
count has to be an integer: consecutive tooth counts are spaced P/π
apart in pitch diameter, about 0.16" for #40 chain and 0.32" for #80. Remember that
chain drive ratio is purely tooth count — a diameter target is about fitting the
sprocket into a space, not about the ratio.
Yes. Switch the units toggle to mm and all inputs and outputs convert, including the DXF header. The geometry is still solved in inches internally because the standard's constants are inch-based, but that is invisible to you. For British standard chain (08B, 10B, 12B), use the Custom preset and enter the pitch and roller diameter directly — the math handles it.
Because manufactured sprockets have flat tips. The tooth is cut from a blank turned to a specific outside diameter, and that diameter is smaller than where the pointed construction would end, so the point gets removed. If the tips came out sharp, the sprocket would be oversize compared to a catalog part.
Not yet — the generator produces the plate: tooth profile, center bore and an optional bolt circle. That is the flat-cut part. A keyway is a straightforward addition in any CAD package afterward, and it is on the list for a future version.
Yes, and there is no signup. It runs entirely in your browser — nothing you type is sent anywhere, and no file leaves your machine except the one you download.
These tools are free because we make the TNB roll out wheel — a truck-mounted pipe positioner that lets you weld solo, in the field.
See the roll out wheel