Gear box RPM

'Simplest way I could think is to turn one side and count how many times the other side turns. However, all this gives you is the gearbox ratio.

If you know or can read the gearbox's brand, you could try contacting the manufacturer and give him a description (i.e., dimensions) of the gearbox and they can check their catalog for the exact part. If they're willing to help, that is.

The gear box does not have a RPM. It has a ratio and torque rating. Output RPM is a Ratio of the Input RPM. By turning the input shaft and counting revolutions until one revolution of the output shaft is obtained you can figure the ratio. Generally the larger the diameter of the output shaft the greater the torque rating. But that is all so limited by the HP of the connecting motor.

Add to this:

Presuming it is a gear reducer, the input and output shafts can be dfferentiated by their diameters. Input shaft dia would be smaller than output shaft.

Also in gear reducers, rotating output shaft by hand, would be difficult than rotating the input shaft.

I'm a gearbox manufacturer and I'm not agree everythig it has been said here.

With the same box (same external dimensions) we have hundreds ratios for each box.

Having a big output shaft doesn't seems to have a big output torque. In fact, some manufacturers sell more the output shaft that the real gearbox characteristics, when the torque supported by this shaft is much bigger than by the gearbox. Normally the output shaft is calculated for the bigger torque of the gearbox model, because of this, normally is a little overcalculated.

The methods described for having the gearbox ratio are correct. It is true that is much more easier to move the input shaft. In fact, if it is a worm gearbox, it could be impossible to move the output one.

You would be the perfect one to give an answer then.

How can our friend determine the ratings (torque, horsepower, maximum rpm, etc) for his unit? He says the name plate has been effectively obliterated so there's no information.

I'm curious to know the answer too. Or would it be safe to just know the gear ratio? Are all gears safe to use at 1800 or 3600rpm (input)?

I've used and maintained gearboxes, hence may be limited with design aspects.

So curious to hear from a manufacturer.

You have said, "Having a big output shaft doesn't seems to have a big output torque."

In a 'gear reducer (step-down gear box)', is not the dia of output shaft bigger than the input shaft?

With out the mfg. specification plate there is no way to determine the RPM rating of the gear box. I use variable frequency drives in most of my applications and if you are running a 3600 RPM motor at 100HZ it is possible to exceed the gear box rating.

Mike

Hi!

I suggest a simple procedure:

Please obtain a suitable sized drill and a tachometer. Attach either shaft, the drive shaft or the output shaft to the drill chuck, run the drill and determine the rotation speed of the free shaft with any type of a tachometer or speed meter. This could be manual, contact analogue type, or the digital type, contact or non-contact, or if you can get hold of a stroboscope, will be much more accurate. The actual speed of the drill can also be determined before using this to turn the shaft. You can do several trials and get the average. The Horsepower rating of the gearbox can be determined by the shafts diameter and referring this to a torque table.

This procedure only assumes that the size of the gearbox you have on hand is not so big. Otherwise you have to innovate and use other means to rotate the shafts.

Without knowing the range of potential ratios' for whatever you have that looks like a gear box it is difficult to determine the method of test to use. If the ratio is small the run the input with any motor and record the input rpm and then record the output rpm. If the ratio is large then put a disc of any sort on the output shaft with many reflectors that are evenly spaced. or

Put a crank handle on the input turn it 1000 times while counting the revolutions of the output shaft.

But all of these concepts are so easy, if you need to ask how to do this then you need to find someone else to do it. You have no skill or ability to think for yourself. I don't believe you are capable of doing this and I therefore suspect that even your question is wrong.

It's RPM is 0, unless you start spinning it.

Guys, the question is:

How can we determine the output or input RPM limit of the gearbox?

An additional question (though not asked) is:

What's the torque or HP rating of the gearbox?

My earlier post just described a way to get the gearbox ratio as did several others. I think our friend already figured that out himself (sorry for making the opposite assumption).

Is shaft diameter a good way to determine the torque rating? I wouldn't know. I think it might be. At least, it might give you a ballpark figure. Maybe, if you have other gearboxes, find one that has the same shaft diameter and assume that it would have at least equal or less torque than the one you have. Or, find a motor that has the same shaft diameter as the input shaft and, maybe, you can use that motor for the gearbox (I'm really unqualified to say that but it seems to make sense, someone correct me if I'm wrong).

As for determining the RPM...well, I can't think of a way to determine that. Only that most motors are either 1800 or 3600 RPM so I would think that most gearboxes would be designed to operate at those speeds.

I think I have my old ROTC helmet here somewhere...

I very much agree with your line of thinking, well said.

In other part of world with 50 cycle power supply, 1500, 3000 rpm are prevailing. Still this marginal change should be matter.

Which ever be the case, comparing the gear box input shaft with the motor is good idea. Speed and torque are automatically taken care by this comparison.

Dear Guest,

Perhaps you might add some information as to what would be your intended use for this old gearbox. The RPM rating will not really matter if you use it for simple speed reduction. It is the speed reduction ratio that may be important to you, or simply that you would want to know what the resulting speed is if you use this gearbox with a standard speed motor. Or it could be possible that you will be using it for driving a winch or other application that may not even use a motor. The gearbox can actually rotate at whatever RPM you apply as input, whether slow or fast, the resulting output RPM will just follow according to the gear ratio of the box..

Finally let us try to help the original Questioner:

What do you NOW want to use this BLACK BOX for?

Input rpm,HP? Motor/Engine you have?

Output RPM you would like to have?

What was the speed ratio found using a Chalkmark and hand-cranking?

Can you give us the Shaft In/Out details?

When (you think) was the gearbox manufactured/installed( the History of the place?)

A photo for all of us to appreciate its pristine beauty?

We will surely say something useful after that!!

I think the gear bos ratio by rotating the one side is known. It islawyas possible the application where similar type of gearbox is used and its mouting pattern. Input RPM can always be taken as 1400 for 50 Hz.Since the rpm's wouldbe muliples it is always better still if you have some doubts connect with a VFD in lab and try to confirm.