Need to make a big hole in Aluminum plate

Last year I cut two holes through 1" aluminum with a 6" hole saw with a DeWalt wrist-snapper hand drill. It was a hell of a job. It was on a piece of large equipment that would have had to be completely disassembled and sent off for machining, very costly. So we decided to try the hole saw first. I didn't think it would work, but it did. Went at it with plenty of WD40 and stop when the drill gets too hot to hold (or starts smoking from the motor, whichever comes first) then take a 10min break. Repeat.

The surface finish was crap, but would have been better if done in a rigid machine and not by hand.

If it can be done with a 6" hole saw by hand, then surely a 2.5" hole should be no problem for any machine you have access to.
 
Yes I would use the lathe itself to cut it, so I would rough cut the hole first then build a temporary mount and fasten it to the carriage. Then I would build a large flycutter with an adjustable tool bit, mount it in the spindle and start taking light cuts through the hole, running the carriage back and forth, adjusting the flycutter each time.
Painstaking, but will give a beautiful machined surface if you use the power feed. I've used this technique to cut largish holes in 1/8" and 1/4" aluminum.
Also, for a project like this, I would make a fairly detailed drawing since there are many little details to work out and many different design ideas.
Mark
 
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If you have the mandrel a hole saw will cost you under $10, use lube, peck drill and have a vacuum cleaner pointed at cut. Swarf is what kills holesaws.
Run at very slow speed as to fast is killer No. 2.
2 - 2.5" is not a big hole and 1.5" thick can be handled by a standard saw if you buy a long series blade. If you need to extend one just part in lathe and weld in an extension of ERW tube. Make sure the outside is cleaned smooth when done.
Clean up with a sanding drum and file the edge if you want a really flash finish.
 
I'm assuming you don't know anyone with a cnc mill or this question wouldn't be asked. If you do or can track someone down who does it would be a fairly simple operation.
 
coherent said:
I'm assuming you don't know anyone with a cnc mill or this question wouldn't be asked. If you do or can track someone down who does it would be a fairly simple operation.
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You're right, I don't know anyone with any equipment whatsoever.

derf said:
Here's one I made for my 10" SB, and then an adapter for my 13". It's been a long time ago, but I think I just drilled some 3/4" holes and freehanded the rest on the mill.
View attachment 269526
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This is pretty close to exactly what I plan to do. I don't plan to make it hinge, just a solid rest. My plan is to take the plate and put it on the mill table flat/horizontally on risers and true the bottom with an endmill. Then to remove that set up, and measure/mark the "V" way and put it back in the mill, this time vertically at a 45* angle. Then to plunge down with the spindle and make the "V" way cut through the length of the bottom. Then it goes onto the lathe.

On the lathe, I plan to make a center point held in a 5C collet in the lathe. The plate will be placed on the bed and softly mark the center of the hole. Off the lathe and use the marked hole placement as well as the true bottom on the rest to lay out 3 slots for the brass fingers 120* apart. Back onto the mill, again on risers and line up the slot and cut with flat end mill, check for fit of finger, and while still set up drill and tap the hole to hold the fingers so it is in the center line of the slot. Repeat for each finger.

Off the lathe, mark the hole better, then use hole saw to make the hole.

I think that will work nicely for what I need, but I don't know what I don't know so if anyone has suggestions I'm open.
 
I would suggest that the hole in the SR should be at least as big as the size of a part that can swing over carriage.
 
I use a hole saw for aluminium often.
I clamp the aluminium to a plywood backing and clamp the whole (pun intended) lot onto the drill press table.
Directed wd40 spray and pecking at the drills slowest speed works for me.
Heres some I did earlier.
https://www.hobby-machinist.com/threads/the-giant-binocular.55688/page-3
last post.
I have another sheet to do soon so I will show the actual drilling.
 
I once had to cut 6 holes in 1/4 " hot rolled steel plate, from 3" to 4". I used a fly cutter in my mill to do the job...
 
kd4gij said:
50 BMG will blow a pretty big hole in that plate.
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Well a .500" hole. It reminds me when I was a teenager and got my first highpower rifle a .303 Enfield. I shot it at some aluminum plate and was astonished to see the lands and grooves of the rifling perfectly reproduced around the inside of the hole.
 
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