Basic Keyway/Slot Cutting

[BladesIIB]

Had someone ask how large a keyway/slot I could cut in steel on my round column Jet JMD-18 Mill Drill so I did this quick video for them. Thought others may be interested as well.

 

[benmychree]

I'd be interested in how the "keyways" measure for size; call me skeptical that one could hold an accurate size for a keyway with this method.

 

[BladesIIB]

I'd be interested in how the "keyways" measure for size; call me skeptical that one could hold an accurate size for a keyway with this method.

Should only vary by the runout of your spindle? Making one pass at full depth with the key size end mill. Any backlash in the machine should get pulled out at the start of the cut. As I mentioned in the video, I should not have fed back on the ¼ inch key, that will affect the size, and just measured and that slot was an extra .0015 wide. The 3/8" and the ½" measured fine with my digital caliper. This is the only way we cut keys in the shop I worked in years ago. What is your method?

 

[benmychree]

Should only vary by the runout of your spindle? Making one pass at full depth with the key size end mill. Any backlash in the machine should get pulled out at the start of the cut. As I mentioned in the video, I should not have fed back on the ¼ inch key, that will affect the size, and just measured and that slot was an extra .0015 wide. The 3/8" and the ½" measured fine with my digital caliper. This is the only way we cut keys in the shop I worked in years ago. What is your method?

I would generally use an undersize mill and make multiple passes, or preferably use a plain milling cutter without side clearance or a woodruff keyseat cutter.

 

[BladesIIB]

I would generally use an undersize mill and make multiple passes, or preferably use a plain milling cutter without side clearance or a woodruff keyseat cutter.

All good methods. The one shot, one pass method does work as well and cuts down on time. With a 2 flute plunge mill also works in the middle of a shaft.

 

[benmychree]

a bit hard to achieve a tight fitting key, in my experience, especially with worn tool holders such as I was brought up with.

 

[Nutfarmer]

This is where resharpened end mills are handy to have. Being undersized they will work out well for cutting a keyway.

 

[benmychree]

This is where resharpened end mills are handy to have. Being undersized they will work out well for cutting a keyway.

Yes, I quite agree; where I worked, resharpened cutters of all types were all that there was. The grinding room was kept busy with all the cutters in use in the shop.

 

[RaisedByWolves]

Should only vary by the runout of your spindle? Making one pass at full depth with the key size end mill. Any backlash in the machine should get pulled out at the start of the cut. As I mentioned in the video, I should not have fed back on the ¼ inch key, that will affect the size, and just measured and that slot was an extra .0015 wide. The 3/8" and the ½" measured fine with my digital caliper. This is the only way we cut keys in the shop I worked in years ago. What is your method?

That is a no.

Spindle runout and backlash are the least of your worries. Every set of ways whether locked or not will have some give, the quill will add to this and all the castings flex to a degree. Plus, your endmill, unless carbide will flex.

Even the vaunted Bridgeport is considered a limp noodle in todays world of CNC machines.

Im curious as to why you had to re-center for the 3/8" if nothing moved?

 

[BladesIIB]

That is a no.

Spindle runout and backlash are the least of your worries. Every set of ways whether locked or not will have some give, the quill will add to this and all the castings flex to a degree. Plus, your endmill, unless carbide will flex.

Even the vaunted Bridgeport is considered a limp noodle in todays world of CNC machines.

Im curious as to why you had to re-center for the 3/8" if nothing moved?

Don't disagree with any of your flex points. IMO, once you start the full cut it tends to pull all that flex and then continues the cut at the width of the cutter. The reason you want to cut the key in one pass full depth to get all that flex the same for the full pass. I had to recenter the 3/8" most likely because I centered the ¼" before taking a heavy cut. Once it cut the ¼" key it likely did shift over the backlash on the bed and I adjusted to that on the 3/8". No comparison of this machine to heavier or more rigid machines, just trying to help someone who asked see what it could do.