Big holes on a mill ?

[Ray C]

For ~3" holes, I've had good luck with with AL plate up to 2" thick by first using the DRO to drill a tight circular pattern of holes followed-up with a bi-metal hole saw (the kind used to drill door knob holes). Of course, you have to start-out undersized and bore-out afterward. For smaller holes, I have drill bits up to 1-1/2 so that is the starting point followed by traditional boring to size.

Ray

 

[Frank Ford]

Don't forget your old pal, the rotary table. . .

 

[Splat]

I recall a question like that back in 1968 from my HS Metals shop teacher. He showed us the how scribe lines using a compass, then drill holes around the 2nd line scribed just inside it, Then milled on the Bridgeport as close to the outside line and filed the last bit. If I had to do it now I would rough it out that way and then use a boring head to make the final cut and file the sharp edges. In wood shop we used a coping saw and file. Back then it was fun. :lmao:

Guess I'm old school then because that's the way my father taught me to do big holes in metal. Hey, if it works....

 

[RandyM]

Guess I'm old school then because that's the way my father taught me to do big holes in metal. Hey, if it works....

The thing you have to realize is that all of these methods will work. Some better than others depending what you are trying to accomplish. Some more accurate, some will be faster, and yet others will not apply depending your equipment and project. I myself, like all the options. Thanks gang.

 

[rammed]

I have used both the circle cutter and a hole saw. Depends on which one I come across first. Cut it undersize and then bore.

 

[nightowl499]

thanks guys for all the good info i now have a plan several options here.

I have used both the circle cutter and a hole saw. Depends on which one I come across first. Cut it undersize and then bore.