Big holes on a mill ?

[nightowl499]

ok how many ways to make a big hole with a mill ? im thinking about 3 inches
cut through aluminum plate, would be for mounting gauges and such


ok guys how many ways would work

 

[DMS]

1) Interpolated hole if you have a CNC machine
2) Hole saw
3) Boring head
4) Chain drill, then boring head.

Probably others, but that's what I came up with on the top of my head, oh, and the coup de gras

5) 3" twist drill

 

[OrangeAlpine]

If the plate is over 1/8" tick, hole saw only if chip relief holes are drilled.
Bill

 

[GK1918]

Just did one in a piece of truck chassis, Hole saw but a good one.

 

[RandyM]

I agree, hole saws are great for this though there are things to consider.

First, go at a nice slow speed, I run on the slowest rpm of the machine.
Second, constantly clear the chips, and I mean constantly.
Third, use cutting oil.
Fourth, make sure you consider the size properly, a hole saw will cut oversize. If you need an accurate hole use a smaller saw and bore to size.
Fifth, if the plate is thicker than the depth of the saw, flip the work piece over and finish from the other side.

Hope this helps, good luck.

 

[OldMachinist]

1) Interpolated hole if you have a CNC machine
2) Hole saw
3) Boring head
4) Chain drill, then boring head.

Probably others, but that's what I came up with on the top of my head, oh, and the coup de gras

5) 3" twist drill

6) Circle cutter/trepanning tool

 

[RandyM]

6) Circle cutter/trepanning tool

So, how well do they work in metal?

 

[OldMachinist]

I've used them many times in steel(up to 3/32") and aluminum(up to 1/4"). They work quite well with the right speed, a ridgid machine and having the workpiece secured.

 

[Richard King]

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:

 

[kd4gij]

So, how well do they work in metal?

I have used mine in AL up to 1/4" thick works great. Mine has a HSS cutter. Low RPM and lots of WD40.