How Are Slotted Keyways Squared Off?

Riaan

Riaan

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Gentlemen,

I've always wondered about this. Assuming you have milled a slot in a piece of stock:

1) Using an end mill cutter, the inner end of the slot will be round when viewed from the top.
2) Using a milling cutter, the inner end of the slot will have a ramp when viewed from the side.

(I hope my terminology is acceptable!)

How would one go about achieving perfectly squared inner corners? Also, is there some sort of machine that does the job first time?

Thanks!
Riaan
 
An example of what I'm on about. How would one get rid of the sloping metal so that the slot is perfectly cuboid?

I've been tryin to suss this problem and have no idea.
 
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Use a shaper.

You could also make the slot with chisels as I did recently, but I don't recommend that.
 
Hey Riaan welcome to the forum! The corners do not need to be squared off as long as the slot is long enough to accommodate the key. Many times they are cut with an endmill with a square profile. You would still have a radius at the end of the cut, but the bottom would be flat.
 
Thanks for the welcome! This question was purely out of interest. I'm guessing it's possible to reduce the radii in the lower corners to small sizes with a combination of vertical and lengthwise milling (assuming of course you can fit the workpiece vertically), amirite? :)
 
The short answer is "You don't". Seldom if ever is there a real need for that type of slot, and there are not many ways to achieve it. A shaper won't really do it because it needs a relief at the end of the slot for the chips to break into, or the chips will pack up and either push the part back or break the tool. You get closer if you use an end mill, but the radius is still there, simply in a different plane.

If cost is no object, you can get that shape by means of a sinker type EDM, but I can't think of a practical way to machine it. If you can stand a relief at the end of it, then some options open up.
 
EDM, that's spark erosion?

ETA: Could a shaper surmount the problem of swarf by scraping down and "pulling" towards the open end of the slot?
 
Once again , you don't as it is not necessary.

"Billy G"
 
That's understood, but I am tickled by the theory behind it.
 
I assume that the keyway can't just run through the length of the shaft and no end. So if you had to have a square end, you would cut it with an end mill and stop short, then make a broach to knock out the corners squaring it up. It would entail making a special purpose tool and maybe a jig to hold it in place to get anything close to accurate.

Or, you could set the shaft up in a lathe with the 4-jaw chuck indexed to the position of a tool and take very light incremental cuts (.001) with a sharp tool in the compound, manually bumping towards the chuck, literally scraping the ramp off. It would have to be untreated steel to remove material this way. I've seen this done in some threads before.
 
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