Drilling a cross-hole thru 2.5in of cold rolled round stock

[JimDawson]

then plunge a 1/4in endmill the entire depth

You have a 1/4'', 2.5'' flute length endmill? I think an endmill that long and skinny would be like pushing a piece of string, you could probably drill around a corner with it.

If it were not for your concern about having a perfectly straight hole, I would just suggest plunge through in one pass with the 5/8 drill bit, no pilot holes needed, it would probably come out fine. The suggested 3/8 endmill/drill operation was to insure a straight hole.

 

[markba633csi]

You never get a perfectly straight hole no matter how you make it- it's a matter of what kind and how much error you can accept.
Using an end mill helps a great deal overall, but I rarely do it.
Modern CNC machinery with modern cutting tools can bore the hole in one pass to very tight tolerance. Most of us can't do that, so we have to use stone-age methods. Be thankful you don't have to use a bow-drill
-M

 

[tq60]

Get a dial indicator and place it in your chuck, hold it by the cover for the opposite end as the pointer.

Carefully place on stock that is in vise, drilling off end of vise or on parallels to provide clearance on bottom.

Move table to get the center via the peak on indicator.

Get a 2 flute sharp end mill and place in mill, in chuck will be fine.

Touch off work to make a small flat spot.

Next either center drill or SHORT small drill placed in chuck with minimum stick out.

Set rpm a bit high and come down with a gentle tap, this will make a dimple.

Set rpm correct and drill deeper.

Change to larger bit, maybe 1/4 and drill through.

Question, do you have end mill final size?

If yes, next drill hole ONE size smaller than final size and use end mill for final.

That will insure straight and round hole.

Or drill to final then us end mill to clean up.

We Mahe a wheel hub interface that had 8 3/4 inch holes on 7 inch circle.

Made test part in wood and drilled with end mill, it fit so did steel part.

Drilled via a few steps, final drill with drill bit final size, then end mill.

One would think it would not cut much but a lot of material was removed by the mill.

Part was perfect fit.

No photo of end mill pass...

Sent from my SM-G781V using Tapatalk

 

[FOMOGO]

Depending on the accuracy required, you can always drill under size, and bore to your final demension. Mike