Deg Parametric Helical Gears With Catia V5 1d5u5m

Deg parametric helical gears with Caa V5

1 of 5

hp://gtrebaol.free.fr/doc/caa/helical_gear.html

Deg parametric helical gears with Catia V5 Published at h p://gtrebaol.free.fr/doc/caa/helical_gear.html Wri en by Gildas Trébaol on July 1st, 2005. Zipped part: gearbox.zip (728 KB). VRML97 model: helical_gear.wrl (414 KB).

A helical gear can be used with a worm, in a worm / worm wheel gearbox

This tutorial shows how to make a basic helical gear that you can freely re-use in your assemblies.

1 Sources, credits and links The helical gear can be coupled with a worm part. The helical gear is close to the standard spur gear part. The main difference is the inclinaon angle of the teeth relave to the rotaon axis: On a spur gear, the tooth is parallel to the gear axis. On an helical gear, the angle between the teeth and the axis is named ψ . (i.e. the Greek le%er "psi"). The ψ angle of the helical wheel must match the ψ angle of the worm. The lead L of the helix screw corresponds to the formula: L = π * D / tan( ψ ) . The dimension of the helical gear and the worm shown in this tutorial are taken from the page #358 of the part catalog Engrenages H.P.C, June 1999 edion.

2 How to use the same parametric part for spur gears and helical gears The standard spur gear coresponds to a

ψ = 0

.

3/1/2011 8:06 PM

Deg parametric helical gears with Caa V5

2 of 5

hp://gtrebaol.free.fr/doc/caa/helical_gear.html

In that case, L = π * D / tan( 0 ) = ∞ . So we cannot use the helix curve provided by Caa when ψ = 0 . However, whe can use a zero angle when the helix is replaced by a straight line: For ψ = 4.50deg we have L/D = π / tan( 4.50deg ) ≈ 39 . For ψ = 20.0deg we have L/D = π / tan( 20.0deg ) ≈ 9 . Since the L/D rao is large, a straight line is a good approximaon of the helix. Then the spur gear and the helical gear can be generated both by the same parametric part.

3 Make the tooth profile The tooth profile is built using the Caa part shown in the spur_gear.html tutorial:

4 Make the rotated tooth section and the inclined guides The tooth template is a mul-secon surface: The first secon is the tooth profile built previously in the spur_gear.html tutorial. The second secon is a translaon and a rotaon of the first secon on the Z axis. The translaon length corresponds to the wheel thickness e . The rotaon angle φ corresponds to a fracon of the helical lead L : φ = 360deg * e/L = 360deg/π * tan( ψ ) * e/D . The inclined guides are two line segments connected to the ends of the tooth secons.

5 Make the gear surface with a circular repetition of the tooth

3/1/2011 8:06 PM

Deg parametric helical gears with Caa V5

3 of 5

hp://gtrebaol.free.fr/doc/caa/helical_gear.html

6 Make a part body with a filled teeth surface

3/1/2011 8:06 PM

Deg parametric helical gears with Caa V5

4 of 5

hp://gtrebaol.free.fr/doc/caa/helical_gear.html

7 Assemble or intersect it with the main part body The intesecon of the second part body with the main body is advantageous when the main part body is a beveled cylinder.

8 Check that we can generate a spur gear When

ψ = 0deg

, the helical gear becomes a standard spur gear.

9 Make a toy gearbox With the worm shown in the worm.html tutorial, you can make a reducon gearbox: I theory, we should use a worm wheel instead of an helical wheel,

3/1/2011 8:06 PM

Deg parametric helical gears with Caa V5

5 of 5

hp://gtrebaol.free.fr/doc/caa/helical_gear.html

but I don't know how to design a worm wheel... So I use an helical wheel having the same ψ angle as the worm. The distance between the two sha<s is the sum of the pitch radius of the worm and the worm gear. For a pitch m = 1.5mm , a worm pitch diameter D = 20mm and an helical wheel having Z = 22 teeth, that distance is (D + m * Z) / 2 = (20 + 1.5 * 22) / 2 = 26.5 mm . End of File

3/1/2011 8:06 PM