Mini Metal Lathes.

people why not get band saws i have picked up 4 of them from craigs list for around 50$ with blades. you can use wood blades on aluminum btw.
i know its a bad idea but you can use a nice finer toothed wood saw and just put it on the lathe at the slowest speed.
Black & Decker 74-591 Navigator Wood Saw Blade
Some thing like this would work you can rig up something to hold it and it should work we did something like that back in HS.
its deep enough that it wont snap and fine enough and strong to cut aluminum.

I've been a trained machinist since 1980 and grew up playing on one at Dads shop since I was a tot.

Parting tools are mostly used for machining parts off of long pieces of stock, too long to pull out and chop-saw off.
They are also used for o-ring grooves, thread reliefs and flat belt pulley tracks.

Due to the nature if the tool you need a fairly large maching as the chatter you experience is from small lathes flexing. It can also be from not feeding the tool fast enough into the work. You want the chips to peel off like a apple peeler.
Unless its a VERY short work, you will need to run the work between centers.

These tool have to be spot-on dead center, otherwise they will allow the work to roll up and over the tool at the last part of the cut, or if lower than center will rub and deface the tool.

I've found the best way is to use it right up to the center then finish the cut with a hack-saw. Just be sure to move the tool out of the way as the back is normally as sharp as the front. I have a nice scar where the work broke and my hand jammed the back of the cut-off tool. Clean to the bone.

Abit off topic... I would like to see Jayrob do one of these on his lathe. A heatsink I mean.