A solution for blind internal keyways in long parts?

[Mook]

Had to cut an internal keyway in a part too tall for my mill & too long for my lathe so I made this.

[DIYer]

Thanks Mook! We've added your Keyway Cutting Tool to our Machining category,
as well as to your builder page: Mook's Homemade Tools. Your receipt:

Keyway Cutting Tool by Mook

tags: keyway, cutter

[metric_taper]

I thought the OP was trying to make a 1 meter long keyway, that I would like to see.

That's a radial mill. What I've done with long parts, is to rotate the milling head and it's extension. Put a tall angle plate on the table bolted to the edge of the mill table top, and mount the part on the angle plate with clamps.
I was able to bore out the cylinders on an Onan opposing twin engine block that would not have been possible with the clearance between the spindle and table at it's lowest.
I've also bored holes in 4x4 wood (Douglas fir) stair banisters for the stair rail. They were 1-1/2" holes that I used a forstner bit on a 12" extension shaft to make deep holes, so I could mount these on steel pins that were mounted under the floor. It was to make these banisters structural, as well removable when big stuff had to be moved up or down the stair well.

And of course, you're still limited to the height of the table to the floor below. But 1 meter is not a problem.