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Old 26th May 2008, 03:41 PM   #1
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Default cut aluminum with regular router bit?

Any of you had experience cutting Aluminum with regular router bits, such as a rabbit bit?

I want to countersink overlapped tweeter/woofer.

At best, I imagine, the bit will be dulled faster. At worst, a piece of carbide will break off and turn into dangerous shrapnel...

I'll probably route into the plastic tweeter faceplate instead of the Al woofer frame, but, if I have to cut the Al, maybe I'll get a special spiral upcut solid carbide bit made for cutting Aluminum.
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Old 26th May 2008, 04:54 PM   #2
rlabomb is offline rlabomb  United States
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Default Cutting aluminum

I have been doing cabinet work and wood/metal work for about fifteen years. You can cut aluminum with any carbide tipped tool. If you can, slow the motor speed down and use a cooling fluid. Be sure to wear eye protection and long sleeves as the metal chips will be flying and they will be hot! I regularly cut 1/4" aluminum on the table saw with a normal wood blade. Just take your time and use a sharp bit. If you are careful and use a cooling liquid, the carbide will last just as long as with hardwoods.

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Old 26th May 2008, 05:20 PM   #3
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Do *NOT* use a cooling liquid with carbide unless you can ensure that it will be completely quenched for the duration of the cut. Moderate amounts of coolant with a HSS bit is OK, but if you're using a carbide bit -- especially solid carbide, it's all or nothing.

And now with that out of the way...


Every material has a cutting speed, which is essential in calculating the ideal RPM that your cutter must rotate at in-order to achieve safe, and acceptable results. Therefore, if you're machining aluminum with a carbide bit, you would use an approximate cutting speed (CS) of 1000-2000.

Now you plug that figure into the formula used to calculate the RPM of the tool:

r/min = 4 x CS / Diameter of cutter

So if you were using a 1/2" carbide cutter, and wanted to run on the safest side of the speed requirements:

r/min = 4 x 1000 / .500

r/min = 8 000


Admittedly, that cutting speed range allows for a very large window of spindle speeds, but you'll just have to start slow and work your way up until you find the sweet spot where the bit doesn't chatter or burn in relation to your feed and depth of cut (shallow passes are ideal).

~Hope some of that helps!
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Old 26th May 2008, 05:33 PM   #4
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To carry on the above idea, you have to be able to completely flood the cutting tool and work piece in order for the cutting fluid to do it's job. Not possible unless you have a machine tool designed for this.

The carbide bit is not the problem. Carbide is used to cut steel and aluminum in the machining industires, however the cutting tool must be designed to handle the forces involved and a wood cutting bit is not designed as such. I would not attempt this with hand tools as the cutting forces are much larger than with wood. And any vibrations increase the cutting forces. If you have a table that is sturdy you may be able to do it with several shallow repeated cuts of no more than .010 deep at a pass.

But the biggest problem with wood working tools is that they are not designed to secure the work piece while cutting and feed the work piece into the cutter at a precise feed rate.
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Old 26th May 2008, 05:59 PM   #5
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Purely anecdotal, but a friend bought a Unisaw from Boeing surplus that had evidently spent it's first life cutting aluminum exclusively.
After a weekend of cleaning, the machine was introduced to wood.


7/10

BTW; I accidentally cut a 1/2"wide x 3/32"deep swath out of the steel extension table on my saw when I miss clamped a work-piece and routed right through it. I didn't even realize it until I finished the cut...
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Old 26th May 2008, 06:34 PM   #6
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I have used a chop saw with a carbide blade to cut 80/20 type aluminum extrusion before no problem. goes right through it like butter!
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Old 27th May 2008, 02:51 AM   #7
GlennS is offline GlennS  United States
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Probably not the best idea if you're doing it freehand. Aluminum is very soft & aggressive cutters can grab if you're not careful. I'm not sure what the rake angle of a router bit is compared to an end mill, but I've seen it recommended that one use a negative rake saw blade to reduce the tendency to grab. That said, I've cut aluminum all day with a high-speed steel cutter (on a mill) without any problems or coolant. As far as RPM, even the slowest speed on a router is way higher than I've ever spun an end mill while cutting aluminum. Just find a speed that doesn't cause chatter, take light cuts with some sort of guide if possible & you should be OK.

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Old 27th May 2008, 02:51 AM   #8
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Ok, so it sounds like using a table/miter saw to slice of a bit of the aluminum speaker frame is going to be simple and easy, but, trying to use a rabbit router bit (which has only two cutting surfaces vs the many on the saw blade) is much more likely to go wrong and cause damage to either the tool, the speaker being cut, or the person doing the cutting...

Using a spiral upcut bit and a template is probably much more likely to work well than trying to use a rabbit or two flute straight cut bit...

I'm guessing that w/a CNC machine that 1/4" wide cuts in 1/4" thick Al plate can be made in one pass?
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Old 27th May 2008, 03:53 AM   #9
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Quote:
Originally posted by critofur
Ok, so it sounds like using a table/miter saw to slice of a bit of the aluminum speaker frame is going to be simple and easy, but, trying to use a rabbit router bit (which has only two cutting surfaces vs the many on the saw blade) is much more likely to go wrong and cause damage to either the tool, the speaker being cut, or the person doing the cutting...

Cutting aluminum on a tablesaw is probably the most dangerous thing anyone does on this forum, that includes other dangerous things like playing with high voltage. The potential for serious injury is VERY high.
Use of an ordinary carbide blade for cutting wood is NOT a good idea for cutting aluminum. The rake angle on the teeth is too aggressive and can grab and kick the metal back. Metal cutting blades (with the proper rake angle on the teeth) are not much more than regular ones, and aren't your fingers worth it?

Router bits will cut aluminum, but you need to watch out and not cut too quickly or the bit will "chatter" and could break.

I think it would be a bad idea to cut out part of the woofer frame anyway. This is the structure, and it will be weak in this area after. Better to notch the tweeter.


Some aluminum I've machined:
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Old 16th July 2008, 09:00 PM   #10
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I was just about to order some aluminum plates for my amp projects, but I am not sure which one to order.

So when you guys are talking about cutting or machining aluminum plates, say making some holes for tube sockets, sawing of rectangular holes for IEC, which aluminum and thickness is the best?

Onlinemetals has different aluminum alloys, my guess work suggests 6061 alloy 0.065" sheet, but I am not so certain.

Doug
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