I have a few 8-9m lengths of 200x100 rectangular hollow section (5mm) and 150x150 equal angle (10mm) sitting outside. These are to be used to maintain the strength of a brick wall which is having openings cut in it. (The steel has been specified by an engineer and the engineer's design has been signed off by the local authority.)

I'd like to explore cutting this steel to length myself. I have a 100mm angle grinder and 80mm cut-off tool, both air powered, and a suitable compressor. I suspect both of these may be undersized for the steel I am working with.

I am willing to obtain tools and learn skills in order to do this, if it's reasonably practical.

What's the best way to cut 5mm and 10mm steel safely and in a reasonable period of time? Although the steel is currently sitting outside I am able to run an air line or electrical power to it easily.


6 Answers 6


Your tools are quite large enough, since none of the shapes you are dealing with will require you to make a cut more than 10-15mm deep.

Use a square and chalk or soapstone or a paint marker to mark the cut lines on the outsides of the angle and on all 4 sides of the square section. Don eye protection, ear protection, and wear boots that come far enough up your legs that your pants come down over them (hot sparks in the shoes can be quite miserable - nylon sneaker fabric melts quite nicely in the face of sparks...)

Support the steel well on both ends so that it will not sag and pinch the disk as you cut through the last of it. Cut one side and turn to cut the next. Use thin cutoff disks (1/16" or about 1.6mm - next usual choice is 3.2mm - the thinner the disk, the less steel you have to cut, the faster it goes) and go at a speed that does not bog the tool down (if you push too hard, the cut actually goes slower, and things heat up more, and you are more likely to break the disk.) Let the disk cut. Beware of twisting in the cut, as that will break your disk as well. Cutoff disks are often sold in packs of 10 or more, and that's the way to buy them, so breaking one won't put a crimp in your day.

Grinder sparks can travel far and hold heat for a while, though you are probably fine outside - they are responsible for many construction fires when steel is cut inside on a construction project and nobody sticks around for firewatch, as they skitter off into the same corners where sawdust accumulates and can smolder quietly for hours. If you are cutting outside, you might want to water the area after you are done cutting (and also before you start if it's abnormally dry.)


Grinder is best tool for this job....maybe even you can use the one that you have just make sure you have several plates in order to complete the job. If your grinder isn't enough 115mm one is big enough for sure....When you cut it don't just go straight down like you are cutting a butter but once you cut through wall on one side rotate your beam (or column, whatever that might be) for 90 degrees and repeat this for all 4 sides. But be really careful grinder is really dangerous tool unless you are skillful. It can be heavy and can slip from the thing you are cutting which may lead to injury. Also be extra cautious about the sparks....they can set things on fire, so make sure that anything flammable isn't around.

  • Grinding can heat steel and cause tempering. I wonder if that can be a problem for structural beams.
    – sharptooth
    Jun 2, 2015 at 9:05
  • No....tempering is not that extreme, plus it only appears locally (near cutting points), and if you want to be extremely cautious you can make brakes between short cutting periods. Jun 2, 2015 at 11:43
  • ...and if that would be truth no one could weld anything (welding causes even higher temperature)...ever -->Look at the golden gate bridge ;) Jun 2, 2015 at 12:07
  • 2
    @sharptooth Structural steel is (quite intentionally) not hardened and tempered. As steel is hardened it becomes more brittle as well - and you want structural items to fail, when and if they fail, in a non-brittle manner, that is, to stretch and bend rather than snap.
    – Ecnerwal
    Jun 2, 2015 at 12:42
  • When I've cut steel with an angle grinder / cutoff wheel I've never noticed discoloration at all of the steel, which I think should mean the temperature rise wasn't very significant. Feb 5, 2020 at 13:08

Torch cutting

These types of cutting tools use high temperatures, and/or pressures to cut through the material.

Oxy Acetylene

Cost: Medium-high
Speed: Fast

Acetylene Torch

An Oxy Acetylene torch ignites a mixture of oxygen and acetylene, to produce a flame that burns between 5800°F to 6300°F. The resulting flame is used to melt a cut through various metals.


Cost: Medium-high
Speed: Fast

Plasma Torch

A plasma torch uses a mixture of gas(es) and and electrical arc to generate a plasma, which is hot enough to melt through the material to be cut.


Cost: High
Speed: Fast

Laser Cutting

A laser is used to melt through the material.This method is typically only used in industrial applications, so it's not likely you'll use it at home.

Water Jet

Cost: High
Speed: Fast

Water Jet

A water Jet cutter uses a very high pressure jet of water; or water abrasive mixture, to cut through materials. Like lasers, it mostly use in industrial applications. Water Jet is more commonly used for cutting plate materials, but could possibly be used for cutting tube stock as well.

Abrasive cutting

These types of cutting tools "grind" their way through materials, by removing a small bit of material at a time.


Cost: Low
Speed: Slow

Hand Grinder

A hand grinder uses an abrasive disc (or wheel) to cut through a material. This method is often slow and tedious, and will likely require multiple discs depending on the material being cut.

Chop saw

Cost: Medium
Speed: Medium

Chop Saw

A chop saw works similarly to a hand grinder, except that the disc is often larger, and is held an a consistent angle to the material being cut. Since it's not held in the operators hand, it provides a more accurate cut than a hand grinder.

Saw cutting

Like most materials, metal can also be cut using toothed saw blades.

Cold saw

Cost: Medium-high
Speed: Medium

Cold Saw

Similar to a chop saw, except instead of a grinding wheel, the cold saw uses a blade with teeth to cut the material. The blade spins at a lower speed than a chop saw, and uses a coolant to keep the part and blade cool while cutting.

Band Saw

Cost: Medium-high
Speed: Medium

Horizontal Band Saw

A band saw uses a long band with teeth in it, which is rotated around a set of rollers to cut through the material.

  • 1
    Pretty pictures, but not really applicable to the job at hand for the most part. I need to cut a few pieces of steel for my house, I'll just nip out and drop a million pounds/euros/dollars on a waterjet....
    – Ecnerwal
    Jun 2, 2015 at 13:49
  • @Ecnerwal Maybe water jet and laser are a bit beyond DIY, but the others could easily be begged, borrowed, or bought.
    – Tester101
    Jun 2, 2015 at 20:48
  • @Tester101 what would you suggest if you were in a same situation?What do you think is, overall the best solution? Jun 3, 2015 at 8:07
  • @pythonstarter The "Best" solution is subjective. Are you looking for speed, accuracy, cost, ease of use?
    – Tester101
    Jun 3, 2015 at 9:39
  • @Tester101 overall best keeping in mind OP's situation Jun 4, 2015 at 7:34

I am not an iron worker, but from what I understand the best tool for a fixed location job, meaning you have all the beams right in front of you and you can position them however you want, is a horizontal band saw like this:

horizontal band saw

There are band saw blades that are exactly designed for cutting structural steel and they work perfectly for that application.

Iron workers often use oxygen-acetylene cutting torches because they are more portable.

I would not recommend using an angle grinder; it is slow and dangerous.

  • Nice thing except it requires a large table for dealing with long beams.
    – sharptooth
    Jun 2, 2015 at 13:28
  • @sharptooth The beam has to be set up on a horse. The OP should be doing that no matter what method he uses. Jun 2, 2015 at 13:30
  • Okay, but how would you combine this machine with a horse such that they are both on the right height?
    – sharptooth
    Jun 2, 2015 at 13:32
  • @sharptooth If it was me, I would probably use two double stacks of cinder block. Each cinder block is 8 inches high, so five-high is 40 inches which is the height of the table of a band saw. You can alternate the cinder blocks when you stack them, so they are interlocked. It makes a very sturdy platform. You need two such supports obviously when cutting a long beam. Jun 2, 2015 at 13:43

You can simply use a reciprocating saw... You can successfully cut through steel with a 'metal' blade (high tooth count, small teeth) and a good amount of lubricant (WD-40 works well, for example). Get several blades, they will dull and you should put a nice new one in when you see the cutting starting to go more slowly.


There are also portable band saws "porta-bands". A little harder to cut strait, but the work. A band saw (portable or fixed) is your best bet. Second would be an abrasive chop saw. You could probably just rent either one fairly inexpensively. I wouldn't try to use an angle grinder by hand for very many cuts.

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