Heavy duty aluminum cutting recommendations please

I made some similar cuts on a large heatsinks a year ago using a cordless reciprocating saw.

I held the heatsink vertically in a vice and cut downwards across the fins. I used a 6" metal cutting blade, plenty of cutting fluid and let gravity do the work.

The cuts weren't perfect but not terrible either. Serviceable enough.

Probably not the best way to do it but it certainly worked and wasn't too sketchy or dangerous.
 
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For a nice clean cut, see if there's a metal workshop nearby that has one of these. The proper tool for the job.
 
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I am not interested to invest metal cutting power tools, i just go to to nearest metal workshop and let the Pro do their job. Alum, Steel, Copper plate is not an issue with them. straight, polished, and clean result instead of doing it by my self which will be messy job.

majority of metal workshop around me is working on ship or truck parts, our DIY parts are peasant for their machine 🙂
 
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The most important thing when cutting alu is to keep the metal cool, or else it will adhere to the cutting blade and things get funny very fast.... Spray a mist of alcohol when cutting and You can use almost whatever kind of saw You can find. I've cut with band saw, miter saw, hack saw, table saw, all works (when building boats). With some care, an angle grinder with alu cutting disc will do the job(dont use alcohol).
 
I've done this in the past and I took the heat sinks to a metalwork shop and they sliced some off the top with their giant hacksaw, similar to the one pictured above. It ran pretty slowly, so it took some time to fully cut through the heat sink.

The result was OK, but not as smooth and nice as I would have liked. Certainly not as good as the factory cut edge. So my conclusion after all this was just to buy appropriate sized heat sinks, you'll end up with a far nicer finish!

Doing it using a hand hacksaw is a non-starter, it's impossible to keep it straight. It'll have more curves than Robin Hood's bow.
 
White Dragon is correct, wood is easier to machine than steel, aluminum is more difficult than steel to machine.

We worked on wood turning lathes then moved to steel as we got more experienced in Engineering college.

I don't bark at dogs, particularly stupid dogs with idle minds.

Wire EDM can do a lot of things, and is worth reading up about.
Here the charges are very low, about 10 cents per square centimeter, and the finish....well, there must be videos in the net, all I can say is polish will be rarely needed, it is that clean.

When you are machining aluminum, there are many grades and densities (cast vs. forged vs. extruded, alloy differences), and the metal tends to stick to the blade, a bit difficult for the inexperienced.
And power tools can be unforgiving, you can lose fingers for example.

Best get it done by a professional workshop.
It is their choice, based on facilities available and complexity of the shape, which is where wire EDM is great (water jet size is more), wire EDM is usually done with a 0.3 mm wire on a CNC table, some shops use 0.4 mm.
Water jet cuts will be 4 mm or maybe more.
Laser may work on thin sections.
Hand held hacksaw with 24 or 30 teeth per inch flexible blade, with experienced user, can give good results.
 
NareshBrd,

I had a few heatsinks cut with wire EDM a few years back; very nice and clean cuts.

However, after doing those few, the wire EDM shop said that they would not be willing to take any more orders for cutting aluminum heat sinks - according to them, the cutting wires degrade faster when cutting aluminum, and they had instances of the wire breaking; the wire lasts longer cutting harder materials like steel, and they were unwilling to provide the service.
 
Older machines were once use wire, later ones have reusable wire, cheaper to operate, finish is not as good on hardened steel.
Wire EDM allows cuts on carbide tools and hardened tool steel, where you would otherwise need diamond coated tools, and for complex press tools (for example) it is the only practical way, (you can use a diamond file, will take weeks instead of hours).

The charges used to be 0.25 Indian Rupees per square millimeter, now about 0.10 with a reusable wire machine, taper cut is 20% higher charge.
The wire speed, current, machine condition, additives in the water, all those are factors, and the wire breaks due to factors like kinks, high current, too much tension and so on.
But for them to refuse...must be low price, poor machine, inexperienced operator, or simple laziness, thay may be having series production, one off needs more attention at times.

Reusable wire machines start at only 400,000 Indian Rupees, cheap Chinese ones, assembled from table, controller and so on here.
Decent ones are 1.2 milion, and the highest is about 4.5 million with a larger table size and many added functions in the control unit.

If needed, find another shop....