Gearbox and Helical Ratios

I'm afraid that the question as you have presented it is basically meaningless.

You say that you are going to change the gearbox with one that has the same gear ratio.

In which case it will have exactly the same gear ratio of 64:1

4:1 x 3 stages = 64:1. Output will rotate in opposite direction to input. If same rotation is required, 4:1 x 2 + 2:1 x 2 = 64:1 in 4 stages.

Yes, the individual ratios are higher with perhaps some disadvantage, but I think not out of the question if a 8:1 x 8:1 is used.

That too might be possible, but I don't remember if the 8:1 ratio is too extreme.

If the approximate ratio of 63:1 is acceptable, I think there are cycloidal reducers that can do this in one stage (same direction of rotation), and certainly in two.

thank you very much for the suggestion. Actually i want to change it in helical gearbox becaause i am suffering serious problem of wearing of worm wheel. Can i use any other material of worm wheel in the place of phospher bronze. The input worm is of EN-9 material which causes rubbing of worm wheel. Can we prepare it in any steel grade????

Worm wheels are highly inefficient, and aside from the proper choice of materials where I would have thought that the rule "one unit hard, one unit soft" might apply as for bearings, a focus on the adequacy of the lubrication being used could be productive.

As to using helical gears....they are more sophisticated and expensive and quieter than spur gears - both being more efficient with minimal losses compared to a worm and wheel. Your choice depending on the application.

Silicon Bronze

As noted above, One Hard, One soft where the part that is lower cost and and easier to replace part is the soft one.

As I said before, for the 'soft one' a very high grade of Silicon Bronze is harder, tough and adds considerable wear resistance as well as the capacity to withstand higher temperatures. Heavy duty Diesel pistons have up to 25% silicon in them just for these reasons and is definitely NOT like machining most brass / bronzes.

Depending on how thick and strong the teeth are for the soft' gear, if they are heavy and beefy enough that they have substantial strength because of this, 'Oil-Light' which is commonly used in bushings especially where there is lubrication is scarce. It is Sintered brass that is quite porous and full of (microscopic) interconnected hollows through it which is (easily) permeated with oil/lubricant before it is installed and thus remains lubricated for (considerably) longer than it otherwise would. It is not that tough or strong of a material though and as such is usually only used in sleeve bushings where it is well supported and constantly has full contact with a rotating shaft, thus my questions about 'how thick and beefy' the teeth of the 'soft gear' are.

For the 'Hard' gear, 4340 is a very good selection: It is very tough, fairly common and can be (case) hardened: quench it in heated oil.

Another possibility is to utilizing 'wear hardening materials' that are just what the name implies: as they get 'worked' the surface actual hardens considerably from being worked. When machining these materials be sure to use sharp tools and a good feed rate as if you let it 'rub' the material will harden (quite quickly) and becomes substantially harder to machine; possibly to the point where you have to scrap it and start over again because it has become to hard to machine by normally machining methods, even with carbide tools. These apply to machining 4340 as well as it is a very tough material and a LOT of (case hardened) gears are made from it.

The 'Machinist's HandBook' is a very good reference source of a wide range of information for these types of problems, applications and questions.

Machining 'Oil-Light (bushings): This not a real tough brass with high tensile strength; thus it is quite malleable. Thus when finish machining it, one wants to be sure you have a VERY sharp tool with a very small nose radius to cut it cleanly and finish it so that the pores are not sealed up. Especially on the side of the bushing that is the bearing surface.

At all times, Oil-Light (bushings) does not necessarily our of Brass or alloys of Copper. It is only a thin film of Oil which works under Bearing Pressure and hence used as journal. Many times Oil-Light (bushings) are sintered for porosity; as in M&M Sintered Bushings, India. Thanks to my teacher Mr. Razak Shaikh for explanations in Journal Bearings and thin film Oil Lubrication inside journals.

Case or surface hardening is preferential over completely hardening the whole gear to the point where the faces of the gears are hard enough to withstand the heavy friction loading. Things that are very hard are quite brittle, including metals. Thus with case or surface hardening the gears you get the best of both: you retain the significant strength and toughness of the 4340 and the hardness you get on the face of the teeth that you can retain as you don't need to temper it afterwards so that they majority of the body of the gear is still tough and gives you the strength you need, but then you lose the hardness that you need on the face of the gear teeth when it is tempered.

There are sometimes reasons of safety that a worm gearbox MUST be used, are you sure that this is not the case here.

Wrong lubrication and/or too heavy a load are reasons for excessive wear & tear.....

Go for planetary : High reduction, compact High efficiency and reliable.

At 64:1 may be (I am not sure) you may have to go for double stage planetary. You may check the globalspec for suppliers and ratio (of course select with respect to the power transmission, duty and shock loading)

hope the alignment of worm wheel with respected to worm shaft checked before considering for type change.

thanks all of you for your valuable suggesstions.