Internal keyway tolerance

[cuttergrinder]

Yesterday I was setting up to machine 2 internal keyways 180 degrees apart in a large roller of some kind. The bore is metric but around 11". I wish I would have taken a picture but the drawing was in German and it has symbols in the keyway tolerance that I am not familiar with. The keyway is 63mm wide and the part is about 22" long. The keyway had a tolerance of F7 which I understand but then it had a symbol that was 3 parallel lines with the center one being longer than the other two and then it said .025 and had the letter A. I assume this means it has to centered in the bore within .025 mm but thats only about .001" . I have to mill these keyways with a right angle head on a bullard boring mill. It cuts pretty well but holding the keyway to size and centered to the bore within .001" is going to be tough. Does anyone know what the 3 parrellel lines and the .025 A actually means?

 

[Erich]

I believe that symbol is Symmetry. A is the datum reference, Assuming that is the 11 inch bore.
The .025 is the WIDTH of the tolerance zone. The center of the tolerance zone is the theoretically perfect center of the bore.
Units are whatever the drawing is in. I assume mm. Yep that is a tight tolerance on a large part.

 

[EmGo]

For future reference, all keyways are internal. Keyway goes in bore, keyseat goes in shaft.

 

[gbent]

Then why do keyseaters cut keyways instead of keyseats?

 

[cuttergrinder]

Then why do keyseaters cut keyways instead of keyseats?

I was wondering the same thing.

 

[eKretz]

Then why do keyseaters cut keyways instead of keyseats?

Good question. Most people just call both keyways these days. And yes, OP, you need to hold center pretty close on keyways or step keys will need to be fitted.

 

[EmGo]

Then why do keyseaters cut keyways instead of keyseats?

A good question Because keywayers sounds dumb ?

The other weird case is, how about leadscrews ? When the key is in the outside part, how does that work ?

But you'll notice, Dumont broaches are never called keyseat broaches ....

Like the English language, sometimes things break the rules

 

[John Garner]

Somwhere along the way, someone tried to teach me that a keySEAT held a fixed key, while a keyWAY alowed the key to translate.

 

[cuttergrinder]

We always call both an internal and an external a keyway. I would more apt to call a woodruf keyway a keyseat but what do I know. I do know one thing, it would take a hell of a broach to cut a 63mm wide keyway 22" long. lol

 

[Dan from Oakland]

Anyway-------- yes, thats probably a symmetry symbol and the bore should have a reference to the A datum. The .025 is the total width of the tolerance zone that the centerline of the keyway must fall into. Probably not the 1st time an engineer pulled a number out of his back side. What is the bore diameter tolerance on the drawing? is it stupid as well???

 

[cuttergrinder]

Anyway-------- yes, thats probably a symmetry symbol and the bore should have a reference to the A datum. The .025 is the total width of the tolerance zone that the centerline of the keyway must fall into. Probably not the 1st time an engineer pulled a number out of his back side. What is the bore diameter tolerance on the drawing? is it stupid as well???

I'm not sure about the tolerance on the bore diameter. We didn't machine the bore. I will post a tomorrow when I go back to work

 

[cuttergrinder]

Where did these symbols come from. I've been a machinist for 38 years but have never seen this before.

 

[just Dave]

You have to see machined parts from the assemblers point of view sometimes to understand the need for the specs. You are possibly dealing with a bad design but a tolerance needed to make the design possible to assemble. One flat key of proper size would likely carry the load but it would still need to be well centered. An 11 inch shaft is pretty big to have to beat- press- prey togather with a wonky keyway.

 

[EmGo]

Here's another reason to prefer inches to metric - 2" is bad enough, can you imagine a 100mm key ?

https://www.isccompanies.com/wp-content/uploads/2017/01/Keyway-and-Key-Size-Dimensions.pdf

 

[???]

Where did these symbols come from. I've been a machinist for 38 years but have never seen this before.

Zee Germans. They are still pissed off about the 2 nil score.

 

[gregormarwick]

Where did these symbols come from. I've been a machinist for 38 years but have never seen this before.

38 years and you've not encountered GD&T before?

It's everywhere...

 

[cuttergrinder]

38 years and you've not encountered GD&T before?

It's everywhere...

I have not

 

[gregormarwick]

I have not

That's genuinely interesting - what kind of industry do you work in?

It's really rare for me to encounter a drawing that doesn't use GD&T to some extent.

 

[???]

38 years and you've not encountered GD&T before?

It's everywhere...

When I worked in the Toyota toolroom I had to press punches into punch holders on a hydraulic press. After the second flange cracked a piece out a miked them. Way out of the spec. Called over the turner and showed him the measurement and the drawing. Pointed out that there was a ISO limit and fit on the size. He says what's that so I showed him the relevant page in my Zeuss pocket book and explained how it's easier to make the shaft the correct size than the hole on these items
Asked the foreman where did you find this guy. Cement factory.

 

[cuttergrinder]

That's genuinely interesting - what kind of industry do you work in?

It's really rare for me to encounter a drawing that doesn't use GD&T to some extent.

I have done mostly work for overhead cranes or steel mill parts. One crane company we do parts for is Morgan Engineering. I assume they are pretty well known around large shops and steel mills.