making a drawing of a standard key 1

[duk748]

hello - i was recently told i did not know what i was talking about when i specified a standard metric key instead of making a drawing of the key - the keyways in the hub & shaft are standard keways -
the machine that i have the standard key in has 2 arms on the shaft - one arm is sitting higher then the othew when it was put together - i was told that because i did not make a drawing of the key that
they could have used any old thing as a key even though the description on the drawing calls for a standard metric key 20 x 12 for a 75mm dia. shaft - anyone else have any opinions about this - just wanted to make sure that if i was wrong i can correct this practice in the future - thank you

 

[KENAT]

Did you reference some kind of standard or document for this "standard metric key 20 x 12 for a 75mm dia. shaft"?

If not then the people who told you you didn't know what you were talking about - while perhaps being a tad harsh - did possibly have a point.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

duk748,

A "standard metric key" ought to have a part number, and probably a manufacturer too. Failing that, you need a fabrication drawing with dimensions and tolerances.

I figure that a clerical level person should able to take your parts list and order the parts on it such that you can assemble the system and it will work. This drives the quality of information on your parts list.

--
JHG

 

[MintJulep]

Well...

I Googled "Standard Metric Keys" and the first hit I got told me that for a 75mm diameter shaft the "standard key size" is 22mm wide x 14mm high.

That is different from 20 x 12.

 

[Keith1029]

Perhaps if the size, shape, tolerance, material and finish of the key was given on a specific "standard" and that specific standard was quoted when the key was specified, then no problem. But that still means a single unambiguous drawing of the thing exists and we are just making a distinction between "here is the drawing" and "here is where to go to look up the drawing". One of those has to be supplied though.

 

[duk748]

hello again & thank you for the help - in the part number i specified that the key should be a certain companies number or equal along w/ the material- my chart from roy mech shows a 75 dia should have a 20 x 12 key - maybe i am wrong - after i looked at the parts together my observation is the the keyways are machined wrong - we have a lousy manufacturing plant across the pond anyway - thank you again

 

[MintJulep]

One of the problems with "standards" is that there are so many of them - often for the same thing - and they are rarely all the same.

 

[MintJulep]

To fully and unambiguously define a (rectilinear) key you need:

Width
Height
Length
Material
Hardness
Finish (plating)

It is not clear to me from your two prior posts that you accomplished that.

It is not clear from your second post what may be included in the "certain companies number". Very often keystock is sold in some arbitrarily long length - a foot, or a yard, or a meter - with individual keys cut to length from that stock by the user.

It seems very possible to me that you did not provide a complete and unambiguous definition that allowed whoever chastised you to buy or make the key. The way to avoid this - or similar mistakes - in the future is to always provide complete and unambiguous information. Or to say it another way - answer every possible question about the part before it can be asked.

 

[CheckerHater]

One of the problems with "standards" is that there are so many of them - often for the same thing - and they are rarely all the same.

Or, in more precise terms: two major metric standards for Rectangular and Square parallel keys are ANSI B18.25.3M and ISO 773, and they are NOT interchangeable.
We are not even going into tapered, low profile, woodruff, etc., etc. keys.

 

[Tunalover]

CheckerHater-
Does e.g. ANSI B18.25.3M specify only geometry or does it also the rest of the necessary information including materials and finishes? I don't have either standard.

Tunalover

 

[pmarc]

ANSI B18.25 is a group of 3 standards:
B18.25.1 - Square and Rectangular Keys and Keyways;
B18.25.2 - Woodruff Keys and Keyways;
B18.25.3 - Square and Rectangular Keys and Keyways: Width Tolerances and Deviations Greater Than Basic Size.

It is true that these ANSI standards define different products than ISO specs. For example, in terms of tolerances products manufactured to B18.25.1 will meet ISO standards (ISO R773 & ISO 2491), but not vice-versa (because tolerances defined in B18.25.1 are tighter than in ISO documents). Per B18.25.1 corners of a key are allowed to be chamfered or rounded - per ISO only chamfer is acceptable.

There is no interchangeability between B18.25.3 and ISO at all.

Regarding unambigous key designation, according to the ANSI a key shall be designated by the following data:
a) ASME document number;
b) product name;
c) nominal size;
d) form;
e) hardness (if other than non-hardened).

As for material of a key, all three standards state that: "Standard steel key shall have a hardness of 183 HV minimum. Hardened keys shall be alloy steel through hardened to a Vickers hardness of 390 to 510 HV. When other materials and properties are required, these shall be as agreed upon by the supplier and customer." There is nothing about surface roughness in the documents.

And there is one more thing to be mentioned:
In terms of dimensioning and tolerancing of keys and keyways the standards focus solely on aspect of size of features, without paying any attention to other important geometric characteristics, like orientation and location of a keyway relative to axis of shaft and housing. These characteristics have to be somehow controlled to make everything working properly. (What is even worse, some dimensions given in the standards, like depth of a keyway in shaft (t1) and housing (t2) are nonverifiable.)