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

[jmarkwolf]

Hole needs to be approx 1/2in - 5/8in dia.

I'll be starting the hole on the center line of the stock, and would like the hole to pop out the far side on center as well, without walking, deflection, etc. Will be using my full-size milling machine. How best to accomplish this?

 

[mmcmdl]

Make sure your head is trammed and drill away .

 

[markba633csi]

The trick is finding the exact center of the workpiece. This is where an edgefinder comes in handy. Then with a little math you can position the spindle exactly over the work.
Drill first with a center drill or spotting drill. Use oil. I often will use two drill sizes for example 5/16" first then the final size.
-M

 

[mickri]

Milling a small flat for the drill to start on can also help to keep the drill from wandering on a round surface.

 

[aliva]

Agree with mickri use a 1/4" end cutting end mill then a center or spot drill. Of course find center first.

 

[Al 1]

my question is : can cold rolled harden if drilled improperly? Al

 

[BGHansen]

No on the hardening for CRS. Key factor for hardening is carbon content. Low carbon steel like 1008 or 1018 won't harden.

Bruce

 

[mickri]

If you don't have an edge finder you might be able to find the center of the flat with a dial indicator. Start on one side just before the flat. Note the position when the DI stops moving. Then move across the flat until the DI changes. One half of that distance should put you in the center of the flat.

 

[JimDawson]

Start on center, center or spot drill. Drill about 1 inch deep with 0.340 or so drill. Then plunge with a 3/8 endmill to the 1'' depth, this will straighten the hole, then drill through with a 3/8 drill, the milled hole will act as a drill guide. Now you should have a pretty straight hole. The finish size drill bit should follow the starter hole.

 

[jmarkwolf]

OP here:

Excellent ideas everybody, thank you.

I do have edge finders and commonly use them to find the center and either center-drill or spot-drill initially.

Admittedly, I hadn't thought of plunging an end mill to "clean up" the hole. Any reason I couldn't just drill the complete through-hole with a 3/16in or so, then plunge a 1/4in endmill the entire depth, then thereafter drill with successively larger drill bits to final size? The endmill will have established the "trajectory" of the hole. Subsequent drill bits will just follow, correct?