Cutting Large Diameter Holes in Aluminum Plate

[barkster]

What is the best way to cut say a 3 or 4" hole in a 1/2" aluminum plate. I'd been using a jig saw but my lathe won't chuck the piece so I can't really clean it up. I have a Mini-mill but really don't know how to clean them up there either? Fly cutter? Never used on but thought that might be what I need? Thanks

[Rekd]

You should be able to cicular interpolate it using IJK or R values, depending on your controller. You could use a hole saw. You could use a fly cutter if it's adjustable.

There's several ways, and the best way will depend on your tooling, controller/machine etc.

'Rekd

[barkster]

My mill isn't cnc

[Rekd]

DOH!

How close is the tolerance? You could scribe your circle and trace along it manually if it's not too critical. Or if you have a fly-cutter, the type with the cutter held in with set screws, you can approximate the dia and bore finish bore it with that. Or you could get a hole saw.

'Rekd

[DR-Motion]

A 3 or 4" hole... hmmm that's a pretty big hole to cut with a flycutter on a small machine. The best that I've managed are 1 1/4" holes x 1 1/2" deep using a boring head on my old chinese mini mill.

This was at the lowest speed setting and it still cause a bit of squeeling and low frequency rumple (not good because I was living in an hi-rise apartment at the time)

The problem is that a 3" hole has a circumference of almost 9 1/2" and at only 100 rpm spindle speed you end up with the cutting tool travelling at over 78 feet per minute.

This means that you have to take very light cuts because the cutting tool is held so far away from its rigid support.

Of course a cnc'd hole is relatively easy if you don't have too much backlash in your setup.

Good luck.

[barkster]

Looks like it may not be too much fun. I've used hole cutter for about 1.25" but never any larger. I'll figure something out. Thanks

[Rekd]

Good luck. Let us know how it turns out.

'Rekd

[pminmo]

Do you have a router? If co use a carbide straight bit with a bearing and cut out a circle using particle board, masonite... as a template for a good finish.

[avsfan733]

rotary table?

[barkster]

Thats an good suggestion pminmo. Thanks

[oldguy]

Believe it or not, use a good hole saw. With aluminium use a faster speed than you would for steel. Drill press (or mill) is best but a good angle 1/2 inch hand held drill will work. Clean chips frequently. Add some lube and have a good long handle to prevent winding up the hand held drill. I have cut large holes up to 4 inches in diameter in 1/2 steel and 1 inch aluminium as well as in stainless thinwall stainless steel with this method. Keeping chips cleared and tool cool is a must for tool life. An eye for perpendicular is also important when doing it hand-held to avoid catching on the cut through at the end of the cut. Of course a pilot hole for guidance is essential. Sometimes it is advisable to predrill a pilot hole and then to replace the hole saw's pilot drill bit with a piece of the same size drill rod notched to fit the locking set screw. The smooth drill rod won't enlarge the pilot hole as a drill bit may and keep the hole saw cutting trueer than would otherwise be the case, especially if you do not keep the process perpinduclar. Also, be sure to stop the saw from revolving before you remove it to clean chips. Then do not begin turning it until it is back in the cut. Do not rush it. Clean chipe often. But, do not be afraid to put some pressure on the down cut as a continuously cut chip is easier on the saw teeth than constantly wearing without really cutting, which builds up heat, but gets little progress. Remember, a lot of the heat is carried away with the chips, just like with a drill bit. The hole saw has more trouble clearing the chips, though. You hjave to help by stopping and removing them. Keep the saw cool. You will develope a feel for the right feed pressureis you have a mechanical affinity.

But, I have one more caution: Ease up on the downward pressure as you near the end of the cutting depth. It is also possible to turn the piece over to cut in from the opposite side, but I would advise against it. The two seldom align as well as a one-sided cut and cleanup is always needed. If extreem accuracy is not needed hand-held works well. Clean up can be accomplished with cartrige rolls, sanding sleeves or large cross pads (all are abrasive tools.) Of course if you have a mill or slow turning drill press you can use a fly cutter for clean-up. But, NEVER HAND HOLD A FLY CUTTRER! And they are for enlarging holes, not for making them. If you have a mill or drill press a hole cutter that uses a cutting tool similar to that in a fly cutter, but held at 90 degrees to the bar (parallel to the hole axis) will work if you are careful with the feed rate.

Good luck!
oldguy

[barkster]

So you use a standard bi-metal hole saw to cut your aluminum, say from home depot?