Cutting a Perfect Circle in Aluminum


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Old 02-16-14, 11:59 AM
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Cutting a Perfect Circle in Aluminum

I need to cut circles in 1/8" aluminum or probably 3/16" 5" diameter I tried the jigsaw in 1/8" but even after sanding you can see some imperfection. Would an adjustable hole cutter on a drill press do a good clean job? it's for a show piece so the rounder it is the better it will look. I was thinking of screwing the aluminum on a piece of ply and at slow speed cutting the hole with one of those hole cutters.

Adjustable Circle Hole Cutter | Princess Auto
 
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Old 02-16-14, 12:06 PM
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That link shows an adjustable circle hole cutter but does not appear to be used on metal.

You can buy a 5" holesaw that will cut a perfect circle but will leave burrs that need to be removed. The best way to make perfect clean holes is to use a punch. A punch can be very expensive.

How many do you have to make ?
 
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Old 02-16-14, 12:11 PM
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So far just 2 or 3 circles and it's for a prototype If it would be more I would send it to a shop, If it cuts wood you think it will cut 3/16"Al at slow speed? My worries is the blades flying off!!!!
 
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Old 02-16-14, 03:19 PM
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I would suggest rough cutting it out about 1/8" oversized. Then cut it to final size using a router table with a straight cutting bit (carbide) and a compass jig. The jig would need a nail, or some other small hole in the middle that you would spin the material on rotating it into the bit.
 
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Old 02-16-14, 03:51 PM
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There are inexpensive fly cutters similar to your link that are intended for metal and they work pretty well on aluminun. If careful you can use a cordless drill that has a clutch but will leave a center hole. If you don't want a center hole clamping the material to a sturdy drill press or mill can make the cut without a center pilot hole. You have to make doubly sure to keep your hands out of the way as a fly cutter can really bite you. You are correct that you will want to turn it slow as the cutter's speed will be relatively high because of the circle's diameter. An aluminum cutting fluid or other lubricant would also help.

Another option is to check with metal fab or machine shops. A few circles are pretty easy for any CNC machine. Punching is possible but fewer shops will have so large a punch.

You can make a simple fixture to hold a router. A piece of masonite or scrap metal with the center screwed to the center of your circle and the router at the appropriate distance to make the circle. I would firmly attach the material to a backer board. Make sure to secure both the outer portion of material and the circle so it does not spin or move and catch the router bit when you complete the cut.
 
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Old 02-16-14, 05:14 PM
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What kind of store would sell fly cutters? I looked at the usual stores and they don't carry anything like that. Also I'm not sure what fly cutters are a search on google leads me to something similar to those adjustable hole cutters.
 
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Old 02-16-14, 06:46 PM
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I found the following adjustable cutter on eBay.
I'm wondering if the one in your link can handle aluminum even though metal isn't listed.

Circle Hole Cutter Adjustable Cuts Metal New Free Shipping Included | eBay
 
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Old 02-16-14, 07:40 PM
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I think it would maybe not 3/4" thick but with lots of lubricant it should easily do 3/16" and 1/8" Too bad that guy wants $20.00 for shipping on a $20 item.
 
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Old 02-17-14, 06:40 AM
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Here is one available from Aircraft Spruce though it only lists going up to 4" diameter. Search their site as they may have ones that go larger. This is similar to the one I have and it's still going strong after almost 20 years. I have mostly used it on 2024 Alclad up to .064 thick but have done a few holes in 6060T6 1/8" thick.

Because of the beveled shape of the cutter it takes a wider cut, removing more material the deeper you go which makes it harder and slower as you penetrate deeper. On thicker material it helps to cut half way through on one side then flip the material and finish on the other side. You also want to turn the cutter so the beveled face is away from the part you want to keep as it will leave an angled cut. If you want a disk turn it opposite of what's shown in the photo.
 
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Old 02-17-14, 09:38 AM
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Thanks Cool trick on reversing the material. I was thinking the same thing about reversing the blade so the outer cut of the circle is straight.
 
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Old 02-17-14, 09:45 AM
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The circle that I need is exactly 5 3/4" I was gonna go to Princess Auto today to buy this unit ( Adjustable Circle Hole Cutter | Princess Auto ) cut some 3/16" at low speed with lots of WD40. In the specs it says it cuts holes from 1-1/8 to 4-5/8. Would only using 1 cutter by sliding the ruler part more on one side. basically what I'm saying is the centre section shank and body where the pilot drill is welded to the ruler?
 
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Old 02-17-14, 11:16 AM
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It's hard to tell if that cutter will let you slide the bar out to one side. I assume it will though as I've never seen one that was welded together.

You will have to be careful. Fly cutters are some of the most dangerous tools for causing severe boo-boos. Don't wear any loose clothing, hair or anything that can drape down and get snagged into the cutter as it spins especially if using a drill press. The cutter that far from the center has a lot of leverage to grab and spin the material so have it clamped well. If using a hand drill use a cordless with a slip clutch set to a manageable torque so it will slip if the bit catches.

I like to "chuck up" the cutter so there is a minimal amount protruding beyond the holder and rod to minimize tool chatter. Wear safety glasses because chatter, even ultrasonic that you cannot see or hear can fatigue the bit or mount causing it to shatter.

WD-40 is better than nothing but it's not the best lubricant. In aluminum I use Rapid Tap Aluminum which is about $10 a can. It's not needed but will help extend the life of the cutter.

 
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Old 02-17-14, 01:57 PM
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Cool thanks for the tips I know that product Next time I go to a "good" store I'll buy some. For aluminum I use bee wax but for that project I'll need something with a straw that I can shoot the lubricant as I'm cutting I'm gonna screw the aluminium to a sacrifice piece of ply then clamp it to the drill press table go slow with low pressure as I'm spraying while it's cutting. Now I need the freaking cutter P.A was closed today!!!
 
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Old 02-17-14, 10:11 PM
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I finally found one that does light metal up to 6"

Mastercraft Circle Hole Cutter | Canadian Tire


I wonder what the white "rubber" thing above the cutter is? Protection?
 
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Old 02-18-14, 05:56 AM
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That's just a plastic cap to protect the sharp cutter tip during shipping.

You don't need a sprayer for lubricant. You can just put a small puddle on the material. Each time the cutter head passes by it will distribute it through the groove it's cutting. Or, you can use a disposable acid or paint brush to dab on the oil.
 
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Old 02-18-14, 05:40 PM
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OK so I bought the cutter and tried it on 1/8" The thing I was talking about is the silver thing on the side It's actually just part of the locking mechanism. Would be nice to be able to reverse the cutter it creates a huge bevel on 1/8". I really had a hard time with 1/8" my drill press doesn't have enough power it took almost 15 minutes to cut and actually had to stop it but luckily I was able to punch out the circle. Towards the end the press would just get caught every half turn I don't want to increase the speed as I have to clue what could happen safety wise. Right now it's at 600RPMS next speed up is 1500RPMS. Would it still work without the pilot drill in the middle?
 
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Old 02-19-14, 06:39 AM
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Are you certain you can't reverse the cutter. Just slide the big silver bit holder off the end and install it in the other orientation. Either that or is there a set screw holding the cutter in the silver holder?

If your platform is rigid and the material is firmly clamped you don't need the center pilot. If there is movement in your platform the center bit will help keep the material & platform from getting pushed around. If you want to flip the material over so you're only cutting half depth then the center pilot is almost required.

What aluminum are you cutting? Slower is generally better when cutting a large circle. A good general maximum cutter speed for aluminum is about 500 feet per minute cutter speed. A 4" diameter circle has a circumference of about 12 1/2" so every revolution the cutter is moving a bit over a foot so shoot for a maximum speed of less than 500 rpm. If using a standard three jaw drill chuck I usually slip the chuck before the drill press runs out of power because it's geared so low at that rpm.

Basically ignore the thickness of the material. As long as there is metal under the cutter it does not know how thick the material is. It just cuts. Thicker material takes longer to cut through but it has nothing to do with the drill press' power.

Cutting large circles is slow because the circumference of the circle is so large you have to remove a lot of material. It's made worse by the bevel of a fly cutter that removes more material the deeper it goes... making it even slower. And, you've only got one cutter working. Even a standard spiral drill bit has two and a hole saw has hundreds so that one cutter bit has to do a lot of work. They are handy, versatile and cheap tools but fly cutters are slow.
 
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Old 02-19-14, 10:31 AM
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I've cut thin aluminum with a wood-cutting fly cutter and I don't think you'll like it without the center pilot. Even a large industrial drill press has a measurable amount of run-out in the quill (drill press shaft) and in the attachment of the chuck--removing the pilot will allow all these inaccuracies to shift and guarantee it will stick on every revolution and cause a rough cut.

The only way I can think of to end up with a disc with no hole is to attach a sacrificial layer on top and shorten the pilot so it doesn't touch the aluminum while the cutter is working.

Another--and safer--way would be to use a large hole saw to cut a hole in a piece of plywood, then remove the pilot bit and clamp the plywood over the aluminum and let the hole guide the saw. Downsides to this are cost and limited size choices.
 
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Old 02-19-14, 09:26 PM
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It seems that the aluminum bunches up in the channel made by the cutter on the pervious spin and when the comes back to the same spot it cannot seem to cut the nik it created and the drill press just stalls. Ive managed to reverse the blade but now I need another piece of aluminum something much thicker than 1/8" as it is too thick for that project. But I think I can manage to get it done eventually!! I just need more scraps tp practice on.
 
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Old 02-19-14, 09:29 PM
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I've looked at a hole saws But I am just short of 6" and they usually go in increments of an inch
 
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Old 03-01-14, 03:13 PM
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A regular 5" hole saw would do it
 
 

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