Calculation of max. torque 1

[vinerunner]

Hello!

I would like to ask the following:

What are the calculation formulas for maximum allowable torque on the attached cross section at a shaft-bore connection (minimal bore length?)?

Probably I have to calculate surface pressure but I don't exactly know which surfaces and radiuses matter.

I have very limited space available at a shaft-bore connection, the torque is 25Nm-s and I'm trying to figure outthe exact minimu length of the bore.

Please advise.

http://files.engineering.com/getfil...185d-45f6-b92e-a0689c138672&file=crosssec.png

 

[rb1957]

you're going to have to give us more to answer sensibly. Lots of toothpicks will transfer 25 Nm (well maybe). I'd've thought the maximum section would be round.

btw, dimension or torque are Nm

another day in paradise, or is paradise one day closer ?

 

[vinerunner]

The question is as simple as I asked:

I have a hub and a shaft, the hub should be removable, I don't have space to insert a key so I would like to mill the end of the shaft to a rectangular shape but I don't know how to calculate the sufficient hub length. The diameter of the shaft is 14 mm the milled rectnagular end is 10mmx10mm. I've calculated ~4 mm for the minimum bore length with ~60MPa surface pressure but I'm not sure that I've used the correct formula. So the questio is simple, you have a rectangular shaft end and a hub, the torque is given, how do you calculate th min, bore length. I don't want to use a key.

 

[drawoh]

vinerunner,

You need to examine your shaft bore connection and look for possible modes of failure. You must analyze each and every one to see where it will fail. Either that, or hand this thing off to an engineer.

--
JHG

 

[Jboggs]

vinerunner, I read your descriptions three times. I looked at your diagram. I've designed machines and their details for decades, and I have no clue what you're talking about. You say you have a 14 mm diameter round shaft which you want to machine down to a hex shape to mount a hub. OK, I get that. But then I see a square shape also in the diagram. In your description above you say you have a shaft of 14mm diameter, which means round, but then later you say you have a "rectangular shaft". Which is it? Is the shaft round or square or rectangular? And if it is not round why are you machining a hex shape onto it? You also did not mention the material of the shaft or the hub.

 

[SnTMan]

1) Doubt it is a surface pressure problem, 2) Units don't make sense, "..torque is 25Nm-s.."

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[vinerunner]

Hello!

Sorry I was rushing and I was quite confusing. I attached a basic model about the problem. How do you calculate the width of the white arm? If I would use key connection than I would calculate surface pressure on the side of the key, but in this case?
First I'm interested in a rectangular connection, and than second I'm interested in a hex connection (I think the method would be the same).

I'm looking forward to your answer!

 

[SnTMan]

Torsional Strength
and Shear Strength

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jlnsol]

Hello vinerunner,
You talk about a removable hub. So play between the hub and the square shaft is a given I would say.
Given that play a torque would try to rotate the hub at the shaft resulting in a maximum of 4 pressforces close to the shaft corners.
But based on dimension tolerances it is possible that only 2 forces do the job alone.
These forces will create stresses locally close to the shaft corners.
To be able to remove the hub only elastic deformations are allowed I would say.
So in any case stresses should lower than the yield stress value of the materials used.
How are the tolerances between hub and shaft?