I want to cut some holes(4") on aluminum plate using a jig saw. is this a good idea?

If eye-ball accuracy is all you need, and the aluminum isn't too thick (up to 1/2" shouldn't be a problem), or a wierd hard alloy, you'll be fine. Just make sure you are using a metal blade, and maybe add some oil or other lube.

My new makita jig saw just went through a 3/4" bar of aluminum last night, no problem.

-Jeff

As Jeff stated, if precision is not an issue it works fine. I will however disagree with Jeff on one thing. Use a 6 or 8 tpi blade, not a metal blade. The aluminum will clog up the metal blade very quickly. The 6 or 8 tpi blade will stay clean and cut quickly.

Really? I'll give it a try this weekend. I assume I should use a "rip" tooth rather than a "crosscut" tooth?

Thanks!

-Jeff

I tried a more coarse blade.... seemed to work a little better, but it didn't seem night and day. I need to get some of those Bosch blades.

-Jeff

which jig saw do you have? I'm planning to buy the jig saw next week.

Bosch makes the best jig saw I've ever used.