reduced worm backlash effects

[5347]

Hello,
I have some concerns on making a design change for the worm and worm gears. The purpose of the design change is to reduce the backlash between the worm and worm gear. The centre distance between the two is currently set at 1.75inches(1/2 of sum of the pitch dia.) If the distance is further reduced, what will be the effects on efficiency, locking ability, noise and duriablity (wear)? Pleae also provide recommendations on reduce the centre distance between worm and worm gear under 1/2 of sum of pitch dia.
p.s the normal operating RPM is around 3000. All metal gears.

 

[EnglishMuffin]

Although not quite on topic, this thread might be of interest to you:
thread406-67911

 

[5347]

Many thanks to EnglishMuffin!! Thank you for your reply.
I've read Thread406-67911. I'm wondering if you could further explain your following comments on that Thread.

"1. Simple radial adjustment of worm shaft center distance.
Depending on the type of worm and amount of adjustment, this can have problems in some cases."

I'm particularly interested in the POTENTIAL PROBLEMS for adjusting worm shafts center distance.
Some additional information for our application: Only 1/3 of the worm gear is used at any time. The lab testing to simulate 10 years of usage is 140,000 cycles. Frequent rotational direction change is required. Correction for RPM posted last time. 3000RPM for the motor no load and 20RPM for worm gear shaft turning.

Any tip or comment is appreciated!

 

[5347]

I also have a few questions for JRCD's following comments to Thread406-67911.
"Backlash reduction by center distance decrease is not good solution. Firstly because put in contact worn with not worn flank surfaces. Secondarily, throat-form radius surfaces, in single or double enveloping worm gear no more contact well. If the transmission shaft angle is not orthogonal other troubles will arise."
My questions are
1. Why is it not a good solution? What are the performance risks involved and how would you quantify them?
2.What does JRCD mean by his/her first reasoning? "Firstly because put in contact worn with not worn flank surfaces."
3.Please explain what causes the shaft angle to not be orthoganal and how that relates to the backlash. What specific troubles would arise and how would you quantify them.

Could JRCD give some further explainations on those issues? Anyone else's comments or thoughts are greatly appreciated as well!

 

[EnglishMuffin]

Unlike ordinary involute gearing, the geometry of single and double enveloping worms is such that it is only theoretically correct at the designed center distance. If one designed a very accurate single enveloping worm for zero backlash, however, it is conceivable that very small adjustments in center distance could be employed to fine-tune the actual backlash without serious detriment to the correct contact patch configuration. On the other hand, a non-enveloping worm/wormwheel could be arranged to accommodate considerable backlash adjustment by changing the center distance, provided the correct involute tooth form were used.