It appears that Robint has taken his free-wheeling bolt hobs and gone home. What a pity.

The mildly interesting part of that thread (to me at least) was the idea of using a common ISO bolt to generate gear teeth. Since the sides of an ISO thread are flat, the flanks on the teeth are involutes and should have all their advantages - conjugate action as the teeth roll on each other, constant pressure angle, ability to tolerate slight changes in mounting, etc. The distance from the tip of an ISO thread to its pitch line is 3/5 of its height, so a gear tooth generated with a thread should have a bit of clearance at the root (where the thread tip ends up), so that works too.

Looking deeper, the dimensions of a gear tooth generated with an ISO bolt would be:

Pb = bolt pitch (Robint used a M24-3.0 bolt when illustrating his passion here, the pitch is 3 mm)

The pressure angle of an ISO-bolt generated gear tooth would be 30°. This large pressure angle makes the gears less efficient in transmitting force and torque, increases (by about 46% over a 20° pressure angle) the radial forces that push the gears apart and do no work transmitting motion or torque, but on the upside it allows fewer teeth on a gear before undercutting takes place (minimum of 8 teeth with a pressure angle of 30°, minimum of 17 teeth with a 20° pressure angle).

N = Number of teeth (Robint used 28 teeth in a couple of now-deleted example photos, we'll use it here too)

Dp = pitch diameter = diameter of the pitch circle = N * m where m = the module of the gear (1 / diametral pitch)

Circumference of pitch circle = N * Pb = Dp * pi, so the module of Robint's gear is

m = Pb / pi = (3 mm)/pi = 0.955 mm

Which gives the pitch diameter as N * Pb / pi = 26.74 mm

The addendum (distance from the pitch circle to the tip of the tooth) of a gear generated with an ISO bolt is

a = (1/4) * sqrt(3)/2 * Pb = pi * sqrt(3) m /8 = 0.68*m,

which is 32% shorter than the addendum of a standard AGMA gear tooth (1.0*m). The addendum diameter, the size of the blank we need to start the generation process, is

Dp + 2*a = [N/pi + sqrt(3)/4]*Pb = 28.04 mm in our example.

The dedendum (the distance from the pitch circle to the root of the tooth) of a gear tooth generated with an ISO bolt is

d = (3/8) * sqrt(3)/2 * Pb = 3 * pi * sqrt(3)/16 * m = 1.02*m

or 18.4% shorter than the dedendum of a standard AGMA gear tooth (1.25*m).

The height of an ISO-bolt generated tooth is

a + d = 5 * pi * sqrt(3)/16 * m

or 24.4% shorter than a standard AGMA gear tooth (2.25*m)

With all of this in hand, I drew a perfect ISO tooth form and the proper sized blank and rolled them together on the pitch line/circle, deleting the intersection on the blank, just like hobbing a gear, to generate the space between the teeth. An extrusion and circular pattern later, I had the gear below (the facets are due to rotations with fairly coarse 5° steps - I was interested in seeing what would happen, but not overly obsessed):

So we have cute little (seriously little) involute gear teeth cut into this blank (the gear is 28 mm is diameter, about 1.10"). Two such gears appear to mesh along the pitch circle as they should (the centers of these two identical gears are one pitch diameter apart), and may be vey happy playing with other similar (same bolt pitch) gears of the same parentage.

The geometry of these gear teeth certainly precludes them from ever meshing with a standard AGMA gear of any common pressure angle. Even comparing to a 28T, 26.6 DP AGMA 30° gear (same pitch diameter as the gear above and no, this doesn’t exist in any catalog but you can define it and draw it, it’s the green one shown below) the flanks seem to match well but the tips and roots would prevent proper meshing.

The geometry seems to work out, and some might be tempted to generate gears for themselves in this way but executing this idea in actual material would, I think, prove difficult. First, you’d have to find or make a perfect ISO bolt, no small task. Bolts are made of steel that is chosen and processed to make good bolts, not cutting tools, so I’d expect using bolts would be good only for soft materials such as plastics, maybe aluminum. Bolts do not come in a large range of thread pitches, so most of the teeth are going to be very small (think small modules or large diametral pitches), requiring both very precise machining and mounting.

The mildly interesting part of that thread (to me at least) was the idea of using a common ISO bolt to generate gear teeth. Since the sides of an ISO thread are flat, the flanks on the teeth are involutes and should have all their advantages - conjugate action as the teeth roll on each other, constant pressure angle, ability to tolerate slight changes in mounting, etc. The distance from the tip of an ISO thread to its pitch line is 3/5 of its height, so a gear tooth generated with a thread should have a bit of clearance at the root (where the thread tip ends up), so that works too.

Looking deeper, the dimensions of a gear tooth generated with an ISO bolt would be:

Pb = bolt pitch (Robint used a M24-3.0 bolt when illustrating his passion here, the pitch is 3 mm)

The pressure angle of an ISO-bolt generated gear tooth would be 30°. This large pressure angle makes the gears less efficient in transmitting force and torque, increases (by about 46% over a 20° pressure angle) the radial forces that push the gears apart and do no work transmitting motion or torque, but on the upside it allows fewer teeth on a gear before undercutting takes place (minimum of 8 teeth with a pressure angle of 30°, minimum of 17 teeth with a 20° pressure angle).

N = Number of teeth (Robint used 28 teeth in a couple of now-deleted example photos, we'll use it here too)

Dp = pitch diameter = diameter of the pitch circle = N * m where m = the module of the gear (1 / diametral pitch)

Circumference of pitch circle = N * Pb = Dp * pi, so the module of Robint's gear is

m = Pb / pi = (3 mm)/pi = 0.955 mm

Which gives the pitch diameter as N * Pb / pi = 26.74 mm

The addendum (distance from the pitch circle to the tip of the tooth) of a gear generated with an ISO bolt is

a = (1/4) * sqrt(3)/2 * Pb = pi * sqrt(3) m /8 = 0.68*m,

which is 32% shorter than the addendum of a standard AGMA gear tooth (1.0*m). The addendum diameter, the size of the blank we need to start the generation process, is

Dp + 2*a = [N/pi + sqrt(3)/4]*Pb = 28.04 mm in our example.

The dedendum (the distance from the pitch circle to the root of the tooth) of a gear tooth generated with an ISO bolt is

d = (3/8) * sqrt(3)/2 * Pb = 3 * pi * sqrt(3)/16 * m = 1.02*m

or 18.4% shorter than the dedendum of a standard AGMA gear tooth (1.25*m).

The height of an ISO-bolt generated tooth is

a + d = 5 * pi * sqrt(3)/16 * m

or 24.4% shorter than a standard AGMA gear tooth (2.25*m)

With all of this in hand, I drew a perfect ISO tooth form and the proper sized blank and rolled them together on the pitch line/circle, deleting the intersection on the blank, just like hobbing a gear, to generate the space between the teeth. An extrusion and circular pattern later, I had the gear below (the facets are due to rotations with fairly coarse 5° steps - I was interested in seeing what would happen, but not overly obsessed):

So we have cute little (seriously little) involute gear teeth cut into this blank (the gear is 28 mm is diameter, about 1.10"). Two such gears appear to mesh along the pitch circle as they should (the centers of these two identical gears are one pitch diameter apart), and may be vey happy playing with other similar (same bolt pitch) gears of the same parentage.

The geometry of these gear teeth certainly precludes them from ever meshing with a standard AGMA gear of any common pressure angle. Even comparing to a 28T, 26.6 DP AGMA 30° gear (same pitch diameter as the gear above and no, this doesn’t exist in any catalog but you can define it and draw it, it’s the green one shown below) the flanks seem to match well but the tips and roots would prevent proper meshing.

The geometry seems to work out, and some might be tempted to generate gears for themselves in this way but executing this idea in actual material would, I think, prove difficult. First, you’d have to find or make a perfect ISO bolt, no small task. Bolts are made of steel that is chosen and processed to make good bolts, not cutting tools, so I’d expect using bolts would be good only for soft materials such as plastics, maybe aluminum. Bolts do not come in a large range of thread pitches, so most of the teeth are going to be very small (think small modules or large diametral pitches), requiring both very precise machining and mounting.

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