2 keyways, tolerating the angle?

[Qube]

Hello,

Does anyone knows the tolerance of the angle? My keys are at 120°. I've nothing found in the DIN 6885 .Everyone keeps saying "the angle must be as good as possible", but this is no way to go in the shop.

Kind regards.

Jurgen

 

[MechEng13]

Jurgen,

You have to look at how the 2 keyways are going to be placed in the part. If they are broached in a single pass then you +/-110% of the broach tolerance. If they are made on a mill/turn machine, what can you hold there. If they are made in 2 passes on a broach, will it be fixtured each time, locating the 2nd keyway off the first? There are a lot of variables to look at when tolerancing... you have to know the capabilities of your shop.

With more information, more help may be available.

HTH,


Alan M. Etzkorn
Product Engineer
Nixon Tool Co.

http://www.nixontool.com

 

[EdDanzer]

Your tolerance angle will be driven by the manufacturing method used. If the shaft keys are positioned by a rotary axis, then use 2X the stated accuracy of the rotary axis. To broach the keys, the accuracy of broach collar, or broach will determine the tolerance. We have made broaches, 1pass broach holder and broach collars to do multiple keys. Cost in relation to benefit will drive the manufacturing method. Your best bet is to work with the shop to determine what will be the best overall solution. Our experience is that a broach holder for 1 pass broaches is the least expensive for 4 to 20 piece lots. For proto types, a special broach collar is adequate. Larger quantities may justify a custom broach.

 

[funnelguy]

Qube,
Are the keyways internal or external? Are you using 2 keyways to share torsional load between 2 parts or is this a simpler case where you only use the keys to establish angular relationship between 3 parts?

More information about the assembly and its components would be nice. The correct tolerance is the largest tolerance that still assures function. Why does everyone keep saying "the angle must be as good as possible"?

 

[diamondjim]

I assume these are side fit keyways
and the angle would have to be very
accurate to have them work properly.
You have not indicated at all how
accurate you are machining these.

 

[Qube]

Hello everyone,

Thx for the replies, this is the situation (try to explain ;-)

I have redesigned an old (+70 years) transmition. I had to start from an existing shaft,with 2 keyways at 120°. No one knows the accuracy of the angle. We can't measure the angle until we start building the new transmition (with hollow shaft) around it...

So I'm building an calibre to measure the angle over there. Once the angle is measured I can make a special home made key according to the difference of the angle between new/old. The Torque is alway in the same direction, so back clearance of the key is not so important (i guess)

I think, this is going to happen.... After everthing is installed, firt time torque is applied. So the hollow shaft can rotate a bit until one of the 2 keys hit the flange of the keyway. At this time the first key takes all the torque, so it deforms a bit. Due the deformation of the first key, the hollow shaft rotates again a bit, until the cealerance between the other second key is gone. But when the clearance is too big, the first key will deform too much...So what's the max clearance (between keyway flange an key). I thought there were some standards for the angle. with the angle i could maybe calculate the clearance....?


Hope you guys understand the problem ;-), i'm not used to write/speak english

Kind regards

Jurgen

 

[funnelguy]

So we are dealing with making a one of a kind part with a pair of internal keyways for the transmission of significantly more torque than a single key could handle.

If the keyways are or can be through keyways (not blind), then I would wire them in with EDM after a very careful measurement of the shaft. This is your most accurate means of generating the 2 keyways IMO for a prototype.

The good news is that even if you have to resort to shaping or broaching the keyways, you can still fit the keys to give a good sharing of the loads. This is where the prototype quantity works for you.

 

[Qube]

Hi,

The bad news is that the keyways are blind en we can't disassemble the input shaft over there :-(

So it will be measuring over and over again...but I have to now some allowable clearance between 2nd key/keyflange

 

[EdDanzer]

One approach is to mark the hub you are going to broach using the keys on the shaft. It may take a couple of parts to get the angle correct but that will probably be less costly than any other method. Measuring and transferring the position will be less accurate and more costly if you are only doing one part.
If the hub does not have to be removed often, use Locktite Quick Metal to take up any extra clearance and lock the hub to the shaft. Be sure to load the keys before the Quick Metal sets up. This will insure that one key will have metal to metal contact. Quick metal has a load capacity of about 6,000 psi minimum, so a quick area check in relation to the torque will help determine if this method will work.

 

[Qube]

I think Locktite is maybe the best solution in my situation. Due the high torque I really must ensure a perfect fit of the 2 keys.

Kind regards.

 

[diamondjim]

Can you tell us the size of Shaft Dia.,
Key Width, and other particulars? Also the
T and S dimensions that you are considering.
A good vendor would have made the
key very accurate as far as angle
is cut on the shaft unless you have reason
to believe otherwise. Is it an inch series
or metric? Much is based on size of parts.