Need to make a big hole in Aluminum plate

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I need some suggestions please, I need to 'bore' a 2-2.5" hole in 1.5" aluminum plate.

I'm working on a steady rest, my lathe didn't come with one. To that end I have acquired a piece of 1.5" aluminum (6061-t6 I think) which is 6x10", as well as some brass 'fingers' for the rest. I have pretty much worked out the steps I need to do everything but make the 'big hole'. I have a 12" Logan lathe and a RF30/31 mill to work with.

I think what I need to do is drill then bore it to size on a mill. Trouble is I have no boring head or tooling. Is there another way? Or do I need to bite the bullet and buy a boring head to do it?

Scott
 
Let me be a bit crude, but could you drill a series of holes around the circumference of the hole and then cut out with a jig saw, and finish in the lathe?

David
 
The drill holes and use jig saw method of David S. could work, but you need to go slow with the jig saw. I tried using my jig saw on some 1/2in aluminium and within seconds the blade gullets were filled with cold weld particles. I had to pick these out one at a time then go much slower.

Another option is to grind a trepanning tool.

A Tom Lipton (Oxtool) video on this topic.

Tom Lipton video on trepanning tool
 
I don't think turning the piece itself on the lathe is an option, at least not the way I am planning on making it. I could possibly make a tool on the lathe to cut the hole in the mill though.

The drill and jigsaw idea would likely work, but I'd rather do a more elegant and precise method if it's available.
 
The drill holes and use jig saw method of David S. could work, but you need to go slow with the jig saw. I tried using my jig saw on some 1/2in aluminium and within seconds the blade gullets were filled with cold weld particles. I had to pick these out one at a time then go much slower.

Another option is to grind a trepanning tool.

A Tom Lipton (Oxtool) video on this topic.

Tom Lipton video on trepanning tool
One should always use a lubricant to avoid chip welding with aluminum; kerosene is the old standby but Magic Tap works well and is not so smelly.
 
You could also use a hole saw, though the surface finish won't be the greatest. Drill/Hole Saw then boring would get you the nicest finish. If you get a boring head for your mill, as long as it doesn't have a fixed arbor, there are a variety of additional uses, such as a ball turner or as a means to further offset your tail stock, that you can use it for.
 
That could work, (doing it on the rotary table) but likely you'd need to cut from both sides due to the thickness, same would go for trepanning. A hole saw is a option, also going at it from both sides.
 
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