How do I ?

[FM44]

Hello,
Can any one, please, help me with the following series of questions:
1) can I use a set of worm and worm gears (both plastic) for an adjustable arm, which will support a load at the other end (T=300 In-Lb) ?

2)Can a worm/worm gear move in reverse ?
(The screw might be required to rotate either way to adust the angle of the long arm, which is connected to it.)

3) If the answer to #1 and 2, is YES, then:
can I use a spur gear instead of worm gear, since the mold will be too complicated ?
Or should I consider using a combination of worm & helial?

Thank you, in advance for your help.

FM44

 

[Timelord]

FM44

Yes and Yes. A worm & wheel gear set typically cannot be back driven i.e. driven from the wheel side, but there is nothing that prevents it from being driven both directions from the worm side. Certainly spur gears can be used, but you cannot get a very large ratio in as small a package as with a worm & wheel set. Whether you can use plastic gears will depend on the localized forces in the gear set and must be checked. Your questions seem very specific with very few details supplied so my answers are based on little or no knowledge. Take them for what they are worth.

Timelord

 

[unclesyd]

Take the above advice and watch the loads on the arm.
Depending on your precision there could be a little impact loading upon reversal. I've seen this on some small winches that were using pot metal in the gear train.

All small worm gear winches do this everyday. For free spooling they usually have a clutch and brake.

 

[MikeHalloran]

3. You can drive a spur gear with a worm. You have to skew the worm shaft to account for the helix angle. It will probably be noisy.



Mike Halloran
Pembroke Pines, FL, USA

 

[FM44]

Thank you ALL, Robointern, Timelord, unclesyd, and Mike Halloran, for your replies. I will take your advise and use a combination of worm and spur gear for raising and lowering a 20 Lb weight. All action is manual and very slow speed. I am using the worm screw to simply give me a constant angular change of the arm, rather than using a toothed sleeve, which will give me an incremental change of angle.
Thanks, again!

FM44

 

[whitetop]

Be cautious MF44, not all worm/worm wheel sets are self locking and according to "Murphy" if you are relying on them to lock, they will back drive. NEVER count on a worm/worm wheel set to not be over powered by the load and when safety is involved ALWAYS use a braking system to secure the input worm when you cannot tolerate any output rotation. Also, the more spur ratio you add to the system the more likely it will be able to be back driven.