Consider the following statements regarding improvement of efficiency of worm gear drive
1. Efficiency can be improved by increasing the spiral angle of worm thread to 450 or more
2. Efficiency can be improved by adopting proper lubrication
3. Efficiency can be improved by adopting worm diameter as small as practicable to reduce sliding between worm-threads and wheel teeth
4. Efficiency can be improved by adopting convex tooth profile both for worm and wheel. Which of the statements given above are correct?
(a) 1, 2 and 3 (b) 1, 2 and 4
(c) 2, 3and 4 (d) 1, 3 and 4