Worm Gear Design 1

[DVE]

Hello All,

I have 2 right-angle shafts to connect, the driven must rotate at half the speed of the driver one.
Worm gears are generally recommended for big reduction ratio. So, can I use a worm gear with the small ratio (2)in this case ?

The distance between shafts is 45 mm. So, I found the following values.
modulus = 3
Worm Wheel
Z - teeth 10 20
Root diameter 23.89 53.89
PCD 30.00 60.00
Tip diameter 35.09 65.09
Width 46.2 18.4
Helix angle = 32.0°
mn = 2.54

Could you comment these figures ? Are they practicaly acceptable ?????

Thank you,
DVE

 

[Iskit4iam]

I'd use bevel gears or right angle meshed helicals.

 

[diamondjim]

If you have space limitations,
the worm design might be your
answer. What kind of material
are you suggesting? Will this
operate without lubrication
for a space project?

 

[DVE]

Hello Diamondjim,
Hello Iskit4iam,

To a answer your questions, material should be something like BS817M40 (34 CrNiMo 6) or equivalent with the necessary heat treatment. Lubrication should be by splash, the design allows the use of a cooling system and, up to now, I don't know about the grade ... so let's say it is not an issue in this case.

Both of you seems to prefer the cross-helical gear choice for such a small ratio or if packaging is not an issue.
In this case, the two gears have contact only in one point; contrarily to worm gears where the contact is line-wise. Cross helical gears are then more subject to pitting and not so safe in terms of fatigue... (how to evalute this ?)

... So, yes, maybe I should make the calculations for both solutions but this will not answer my first question : is it allowed to have a ratio of 2 with a worm gear system ???

Thanks,
DVE

 

[sacem1]

Hello DVE:

The answer to your question is that it is not practical to manufacture a 10 lead worm to mesh with a 20 teeh gear as you asked.

REASONS:
First: It would be very difficult to make a 10 lead worm with accuracy,
Second: the resulting angle would be very high for both the worm and the gear, you would get to "slanted" teeth meshing would be at so high a pressure angle that a very high loss of power would result.
Third: All power loss would be turned into heat so you would requiere to install oil cooling devices or get a very low life on the worm and gear
Fourth: The side pressure upon the gear made by the worm would tend to push it sideways with the resulting high load on the gear bearings and a high abrasion would destroy in a relatively short time your gear.

RECOMENDATION: Use a conical gear, the relation 2:1 or 1:2 is easily achieved, the cost is low, setup is simple and high power can be transmited in a compact package. The mayor drawback of this setup would be a higher noise level.

If the noise is a problem then you could use a helical conical gear, but this type of gear requieres special equipment to make so your next choice would be 2 helical tooh gears crossing at 90º between axis.

Definitly forget the worm-gear option because you would not be able to use the self braking capability of a worm gear set up as the angle would not block the movement of the gear with the worm.

Hope you got your answer

SACEM1