Standard tolerancing on stainless keys and keyways 1

[CristianF]

Hello all,

I am looking for some feedback regarding a request from a supplier.
One from our supplier is requesting that shaft keys and keyways be toleranced on our prints in such a way that the keyways would *always* be bigger than the keys. For instance, if standard tolerancing on stainless keys is, say, 0.250 +0.000 / -0.004, then the shaft keyway should be 0.251 +0.xx / -0.000 so that there is no possibility that the key and keyway would be the same. (We were shown a drawing where a key was 0.250 +0.000/-0.004 with a keyway of 0.250 +0.xx/-0.000 so it’s possible that *both* could be 0.250, still be in tolerance, but not fit.)

My argument is that the standard (I believe is ANSI B17.1) should be followed as we have now on our prints. Is anyone else having this issue?

Regards,
C

 

[CristianF]

Hello all,

Thank you for all your input!
I will try to answer some of the questions.

Is not the customer who is pushing the change. The manufacturer is concerned that a drawing where a key was 0.250 +0.000/-0.004 with a keyway of 0.250 +0.004/-0.000 so it’s possible that *both* could be 0.250, still be in tolerance, but not fit. Galling it was not presented as an issue.
I also told them that if this situation occurs, running the key twice on a scrub pad will solve the problem. I was asked, so who will do that? The manufacturer or the customer? Since we are a customer oriented company, we do not want to "upset" them and we rather go the extra mile and do odd things.

C

 

[desertfox]

If galling isn't an issue then I would say the fit should follow the design requirements and not what the manufacturer thinks is correct.

 

[dgallup]

Never force anything. Get a bigger hammer.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[hydtools]

As a customer, I have never been upset with a line-to-line key fit.
As a manufacturer, I have never been worried about the odds of a max key fitting a min keyseat.

Ted

 

[mfgenggear]

Just my two cents.

It's easier for the manufacturer to grind the Key's flat. & hold .250 -.001/-.004
as a matter of fact it should be a piece of cake to hold .250 -0005/ -.0010

it's always easier to machine the key than to mill out a keyway, on a shaft. its very easy
to broach a keyway in bore with in .0005" tolerance with no problem

if the manufacture is milling the key width it should be easy to maintain .001" tolerance

The manufacture is making excuses. for bad manufacturing practices.



Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[Cockroach]

From an earlier post: "You need 0.250 +0.002/-0.000 inch on the Key and 0.255 +0.000/-0.002 inch on the keyway."

So 0.252/0.250 inch on the Key, 0.253/0.255 inch on the ways. What's with the size-on-size or that 0.250 inch coincidental measure?

Regards,
Cockroach

 

[kingnero]

You need 0.250 +0.002/-0.000 inch on the Key and [highlight #EF2929]0.255[/highlight] +0.000/-0.002 inch on the keyway. Done deal.

Did a typo slipped in there?

Holding 0.250" on a 2 thousands tolerance can easily be maintained on both machining the keyway and grinding the key.

Just to clarify (again),
You need 0.250 +0.002/-0.000 inch on the Key and 0.250 +0.000/-0.002 inch on the keyway. (copied and adjusted the answer from Cockroach).

 

[mfgenggear]

Just to clarify (again),
You need 0.250 +0.002/-0.000 inch on the Key and 0.250 +0.000/-0.002 inch on the keyway. (copied and adjusted the answer from Cockroach).

yes but I would manufacture the key to .249-.248"
& the keyway I would hold to .252-.251" so that it would assemble easily.
& no engineering design change required. It would fall into the original tolerance.

at the worst conditions there is .002" or .001" per side. which works fine.
or .004" or .002" per side.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[kingnero]

I prefer them to have a p6/P6 fit (which is a ISO/metric tight fit, for 6mm this means +12/+20 mu and --/-17 mu, very near the small values I quoted above).

 

[kingnero]

edit above: -9 / -17 mu

 

[mfgenggear]

I prefer them to have a p6/P6 fit (which is a ISO/metric tight fit, for 6mm this means +12/+20 mu and --/-17 mu, very near the small values I quoted above).
edit above: -9 / -17 mu

Ya that's cool when it needs to be tight. :>)

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.