# How To Cut A Key Slot In A Shaft Without End Mill



## Pmedic828

Does anyone know how to cut a key slot in a shaft without using an end mill?  Watched various youtube videos watching machinists work and on more than 3 sites, the machinists said not to cut a key slot in a shaft with an end mill because the end mill would either chip because it is hitting 2 sides at the same time, or it will wonder and not produce a straight slot.  They, however, didn't explain how to do it with magic?  Can anyone enlighten me?


----------



## JR49

Pmedic828 said:


> the end mill would either chip because it is hitting 2 sides at the same time, or it will wonder and not produce a straight slot.


             You can use an end mill that is smaller than the width of your key slot,  then trim each side separately to bring the slot out to proper dimension.  Good luck,  JR49


----------



## T Bredehoft

If you can figure out how to hold the shaft, you can do it with a woodruff cutter.

Last week I used JR's method. 5/64 two flute to make a 3!6 keyway. And where did I get a 5/64 2 flute cutter, I bought about 50 of them on Ebay for $16.00, free shipping.


----------



## joshua43214

The mill should not chip just because it is hitting two sides. Milling a slot is after all one of the things mills do...

JR49 and Tom nailed it, either plow the groove and widen, or use a key cutter
http://www.use-enco.com/CGI/INPDFF?PMPAGE=115&PARTPG=INLMK3&PMITEM=367-2100

Key cutters are regarded as being better because they add less of a stress riser, but plenty of shafts are keyed with a mill.


----------



## JimDawson

I've keyed a lot of shafts with end mills, in fact that the only way I have ever done it.  Never had one chip.  But you want to use a sharp 2-flute.  A 4-flute will pull sideways and make the keyway oversize.  Or as said above, use a smaller cutter and step over.


----------



## Bill C.

Pmedic828 said:


> Does anyone know how to cut a key slot in a shaft without using an end mill?  Watched various youtube videos watching machinists work and on more than 3 sites, the machinists said not to cut a key slot in a shaft with an end mill because the end mill would either chip because it is hitting 2 sides at the same time, or it will wonder and not produce a straight slot.  They, however, didn't explain how to do it with magic?  Can anyone enlighten me?



   I never heard that one before.  If you use a milling machine be sure to tighten the cross feed clamps. Helps to snug the table feed clamps so the cutter doesn't pull itself.  I have used to many used milling machines.
   Now the old school method, early 1900's, those machinist would drill a series of on size holes drilled  to the requires depth leaving material between each hole. Then using a flat chisel and ball-pein hammer cut out the remaining material.  Then they would use a flat smooth file to cleanup the slot.  If you ever tear down a old drive shaft and see a series of drill bits hole that how they cut their slots.


----------



## kingmt01

Bill C. said:


> If you ever tear down a old drive shaft and see a series of drill bits hole that how they cut their slots.


I've seen this a few times.


----------



## Whyemier

We usta, that was in the dark ages, chuck the shaft, tube, bearing, whatever, up in the lathe and drag an appropriately sized tool bit, set up in a boring bar, tediously centered, down the inside of a tube or the outside of a shaft to cut the keyway. Got a lot of spring in the bar but it worked after a fashion. (Hmmmm? That was a long sentence.  Guess my grammer etc. ain't that good.)


----------



## jeff_g1137

Whyemier said:


> We usta, that was in the dark ages, chuck the shaft, tube, bearing, whatever, up in the lathe and drag an appropriately sized tool bit, set up in a boring bar, tediously centered, down the inside of a tube or the outside of a shaft to cut the keyway. Got a lot of spring in the bar but it worked after a fashion. (Hmmmm? That was a long sentence.  Guess my grammer etc. ain't that good.)



It was a long keyway LOL


----------



## Ulma Doctor

i have used small diameter slot cutters on the horizontal mills to success ,
woodruff key cutters &  2 & 4 flute endmills on the vertical mills, 
use an endmill smaller than required for final dimension, 
make multiple passes to creep up onto dimension if you are unsure. 
it's easier to remove metal than it is to put it back!
good luck


----------



## Paul in OKC

Always done them with and end mill. First shop I worked in, we did them by plunge cutting first, about .05 per step, to just shy of depth, then set the quill and ran a pass to finish things up.


----------



## Wreck™Wreck

Pmedic828 said:


> Does anyone know how to cut a key slot in a shaft without using an end mill?  Watched various youtube videos watching machinists work and on more than 3 sites, the machinists said not to cut a key slot in a shaft with an end mill because the end mill would either chip because it is hitting 2 sides at the same time, or it will wonder and not produce a straight slot.  They, however, didn't explain how to do it with magic?  Can anyone enlighten me?


That is a good deal of misinformation right there, a side milling cutter works well for long external key ways also. You mention watching videos of machinists on youtube, are these people that do it for a living or hobbyists?

As far as magic goes yes it exists, it is easily done with a ram EDM with high accuracy and surface finish at great expense, no one would do this for a simple keyway in mild steel however if it could be milled, EDM will produce an excellent slot in a carbide shaft for instance. One may also produce a key slot on a surface grinder if so inclined but this is also a laborious process.


----------



## kd4gij

I cut key seats on a horizontal mill almost every day. What ever you use it should have a radius on the sides at the bottom..


----------



## kingmt01

kd4gij said:


> radius on the sides at the bottom..


Can you explain this? I'm just not able to picture what your saying.


----------



## kd4gij

A corner radius.


----------



## kingmt01

So you cut the key slot with a radius on the conners?


----------



## joshua43214

kingmt01 said:


> So you cut the key slot with a radius on the conners?


it is best practice to have a radius in the corner because a sharp corner is a potential failure point.
In practice, you can use square corners with fractional horsepower with no issues most of the time. You can probably even get away with it up to 3 HP as long as the load on the key is fairly constant.
If you start looking around at key ways, you will probably find a lot of commercial made ones have square bottoms unless they are under some kind of heavy to severe duty.


----------



## kingmt01

Thanks guys. That is good information. I was thinking the only slots I've seen had sharp corners but then again I don't think I've ever looked close.


----------



## royesses

A sharp edged notch increases stress 4 to 16 times. This increases the possibility of fatigue fracture failure. This was part of the metallurgical failure analysis classes I took at Caterpillar.


----------



## planeflyer21

royesses said:


> A sharp edged notch increases stress 4 to 16 times. This increases the possibility of fatigue fracture failure. This was part of the metallurgical failure analysis classes I took at Caterpillar.



Is there any standard/guide as to when the notch goes from having a ever decreasing radii to being sharp?  Asked another way, is there a radius that is too small that is effectively a sharp angle or is it material dependent?


----------



## juiceclone

Whyemier said:


> We usta, that was in the dark ages, chuck the shaft, tube, bearing, whatever, up in the lathe and drag an appropriately sized tool bit, set up in a boring bar, tediously centered, down the inside of a tube or the outside of a shaft to cut the keyway. Got a lot of spring in the bar but it worked after a fashion. (Hmmmm? That was a long sentence.  Guess my grammer etc. ain't that good.)



Yes..been there, done that.  tedious, but if it's just one keyslot, what the heck, it'll get er done.  :>))


----------



## royesses

According to the metallurgists who taught our classes the radius must be smooth with no steps. There is still increased stress due to the notch. I don't recall any formula given for the radius dimension. Even striations that you can feel with a fingernail act as a stress raiser. Polishing to a mirror finish also reduces stress raisers. Many mechanics radius and polish the base of gear teeth on differential gears to help prevent failure, mainly on circle track cars.


----------



## MUSKRAT

This is my first post, saw this and thought I would share this picture of shaft failure due to the sharp edge key way. the break always starts at the edge. thanks for all your post.


----------



## bfd

an endmill is supposed to cut slots if it chips get another end mill to finish up the slot. taking light depth of cuts will help to ease this from happening. cutting keyways with an endmill is the only way I have done it on shafts might have broken an and mill or two. oh well. bill


----------

