What kind of circular saw blade is best for safely cutting aluminium?

I have some long sections of aluminium, actually hip beams from a dismantled conservatory, that are roughly T-shaped and 40 x 70 mm in section. As they are very rigid I plan to cut these to a standard length to use them to support shelves in my garage workshop.

I don't have a chop saw, mitre saw or band saw, but I do have cordless Dewalt DCS391N circular saw (takes 165mm diameter blades). I'm thinking I could cut them relatively safely with this if I clamped the pieces in a cross-cut jig, and if I had the right blade.

From what I've read, I think I should use a blade with a low tooth count, a low kerf width and a low or even negative rake angle. But how low is low? And what kind of problems will I get if the blade is too thin?

My local retailer stocks these two 165mm Dewalt tungsten carbide-tipped blades and claims they will both cut aluminium, but which is better and why?

  • 36 teeth, 1.5mm kerf, +3 degree rake
  • 18 teeth, 2.4mm kerf, +10 degree rake

UPDATE: this is the kind of jig I intend to use to keep the work secure and the circular saw aligned, but my jig is wider to make it easier to clamp the work on both sides of the cut. (Source) enter image description here

  • 1
    Search for "DIABLO 7-1/4 in. x 56-Tooth Aluminum/ Laminate Metal Cutting Blade" reviews indicate it easily cuts 1/4" aluminum. Jun 22 '20 at 12:30
  • Have you considered buying a cheap jigsaw and a couple of long metal-cutting blades? Jun 22 '20 at 13:48
  • Thanks, maybe a jigsaw is my best option. They don't seem to make particularly long metal-cutting jigsaw blades, but a 70mm blade might just be long enough.
    – mikeagg
    Jun 23 '20 at 8:06

For blade selection the higher tooth count makes for smaller chips which is a good thing as each chip cut is an impulse against the work and the tool, and smaller impulses are better.

Circular saw blades tend to grab in aluminium I wouldn't risk it hand-held: when using a drop saw a slow feed rate is essential else you stall the blade or distort the work. A hand-held circular saw is likely to be uncontrollable.

If you're persistent a hacksaw will work.

  • I second this. I have mitre saw which claims to be able to cut non-ferrous metals as well as plastics, with the supplied blade. I had it on slow speed, with the Aluminium clamped, and went at it very gently. It still grabbed the workpiece, ripped it out of the clamp and bent the fence. I was extremely glad not to be using a hand-held circular saw
    – SiHa
    Jun 22 '20 at 8:56
  • I would use a hacksaw if it was only one or two cuts, but I want to cut at least 24 lengths, maybe as many as 32.
    – mikeagg
    Jun 22 '20 at 10:20
  • @SiHA Why is a slow speed better? Would the saw be less likely to grab the workpiece when it's running faster? (I'm quite new to power tools).
    – mikeagg
    Jun 22 '20 at 11:03
  • I'm no expert, but yes in general, fast speed means less likely to grab, I think. It also means more kinetic energy though, which increases with the square of speed. So when it does grab it's more messy.
    – SiHa
    Jun 22 '20 at 11:44
  • can you get the vendor to cut it for you?
    – Jasen
    Jun 22 '20 at 13:16

Jasen brings up a great point in his answer, and especially the comment on it about the blade grabbing the material and bending a miter saw base. You don't want your hands near that kind of force!

You might consider a "toothless" blade designed for cutting cement.

These blades don't really "cut" as much as they abrade with the diamond impregnated surface. I've used them in hand-held circular saws for cutting block, and they work quite well for that.

I cannot imagine any reason why the blade would not also work its way through the aluminum, and it would eliminate the possibility of a tooth being able to catch the metal and yank something out of your hands. I'd suggest that you'll want to cut slowly to avoid overheat your aluminum - you do want it cut, not melted. You might need to experiment with a squeeze bottle of water to keep the metal cool.

You may also want to make a test cut or two (if you're cutting 100mm off the end, start with a 30 mm cut) just to get the feel for it and to ensure it's going to work the way you want. That way, once you've perfected your technique, you can make a final cut at the final length on your test piece without wasting any material.

  • Better and less costly would be an abrasive metal-cutting blade made for cutting aluminum (and no need for pricy diamonds.) Don't forget your hearing protection. I SAID, DON'T FORGET YOUR HEARING...oh, nevermind, too late ;-)
    – Ecnerwal
    Jun 22 '20 at 13:13
  • THANKS FOR SHOUTING!!! Yeah, hearing protection is good! (Too much time with the headphones cranked as an invincible teenager...) An abrasive metal cutting blade would be just fine, too. I was surprised - my concrete cutting blade wasn't all that spendy, so it would be a valid option if the specific metal cutting blade isn't immediately available.
    – FreeMan
    Jun 22 '20 at 13:20
  • I'm certainly not going to use an abrasive disk on aluminium. I don't know much about power tools but I know chemistry, and aluminium powder is nasty stuff.
    – mikeagg
    Jun 23 '20 at 7:58

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