Boston Gear - why helix angle changes and the pitch diameter doesn't? 1

[wagnergear]

In the Boston gear Catalog, in the worms and worm gears section, they have single, double and four threads. All with the same pitch diameter but very different helix angles. Doesn't the helix angle change the P.D.? Thanks

 

[Occupant]

You are using the same wormgear regardless of the number of leads. The only thing that changes is the lead angle on the worm because they have to spread the "threads" apart to accommodate the additional leads. So where does the helix angle come in?

 

[wagnergear]

Sorry, I was talking about the worm wheel,

 

[mfgenggear]

wagnergear

the single, double & quad leads are surely for the
worms & not the worm gears.

it would be interesting to calc out the worms.

MfgEnggear

 

[wagnergear]

For a 12DP worm and wheel.
1 thread worm / mating gear 4.766 degree, 60T 5.000 PD
2 thread worm / mating gear 9.466 degree, 60t 5.000 PD
4 thread worm / mating gear 18.433 degree, 60T 5.000 PD.
Thanks for the help

 

[drawoh]

wagnergear,

The pitch diameter is a function of the number of teeth and the pitch of the teeth, specified as diameter pitch or metric module. The lead angle has no effect on this. The lead angle is driven by the worm's pitch diameter and the number of leads.

The worm wheel is cut for a specific pitch, number of teeth, worm diameter and number of leads. Worm wheels are not interchangeable unless you are making a very crude, sloppy worm drive.

JHG