Sawing metal

If you make things out of metal, you’ll typically be cutting lots of it. Steel bar, rolled hollow section (RHS), pipe, tube – and so on. So how do you cut it?

There are these major approaches:

• a friction cut-off saw (that abrades its way through the material)

• a ‘cold’ saw (that uses a slowly rotating blade and mills its way through the material)

• a bandsaw (that uses a flexible teethed blade and chews its way through the material)

• a power hacksaw (that is just a very big brother to a hand hacksaw and works in the same way)

• a hand guillotine (it shears the material like a big pair of scissors)

Friction cut-off saw

By far the cheapest approach to chopping metal is to buy a friction cut-off saw. The most common and lowest priced of these machines use cut-off discs that are 355mm (14 inches) in diameter. (Note that more serious versions of these saws use larger blades of 400mm diameter. They are a lot more expensive though.)

Friction cut-off saw are cheap, will abrade their way through nearly anything (even, if you have enough time and spare discs, thick steel sections), and can usually be adjusted to do angles – eg 45-degree cuts.

But they also have some significant disadvantages.

The first disadvantage is that they are incredibly noisy. If you work in an urban area, that straightaway limits how much you can do at night. You should also always wear good quality ear muffs – and get anyone else nearby to wear them as well.

The second disadvantage is that a friction cut-off saw is not a precision machine. They used pressed steel baseplates (rather than castings) and invariably the blade will not be perfectly square to the baseplate – and there’s no adjustment.

A final disadvantage is that the material being cut gets hot – really hot. If you remember that, it’s not a huge problem – but you certainly will need to quench the material after cutting it.

Advantages? They can cut hardened and stainless steels – materials that normally cause problems (or fast blade wear) in other saws.

Another advantage is that they can cut tubes largely square - at the lowest cost. For example, if you are making a car exhaust or the plumbing for an intercooler, a friction cut off saw is the easiest way of cutting the thin-wall tube square, so that it can be butt-welded together with no gaps. (Yes you can use a hand hacksaw, but take it from me – for its very low cost, a friction cut-off saw is worth buying for even just one of these types of jobs.)

If you’re on a budget, at the time of writing, a cheap 355mm friction saw costs only about AUD$135. A brand name, good quality one will be about double or triple that. Over the years, I’ve used both the no-names and the brand-names: the brand-names last longer before the chassis breaks or the motor fails, but the advantages of the more expensive units is not any greater than that.

Cold saw

A cold saw is a much more serious bit of gear – and the price reflects that.

It typically uses a full cast chassis and a geared-down electric motor that turns the metal-cutting blade quite slowly – eg 40 rpm. These saws also use a coolant system, where lubricating and cooling fluid is pumped over the blade. As with the friction cut-off saw, 45-degree cuts can be performed.

Interestingly, motor power in cold saws is typically less than that of friction saws – eg 1kW versus 2 or 2.2kW of a friction saw. However, as is appropriate with these higher quality machines, the motors are usually induction motors, versus the brushed universal motors of the cheaper saws.

If you need to cut with great precision, or work quietly (when compared to a friction cut-off saw), a cold saw may be the answer. However, for most home-based hobbyists, a cold saw is just too expensive. How expensive then? Prices start from AUD$1500 or thereabouts.

Bandsaw

Think ‘bandsaw’ and most people think of a vertical bandsaw, where the blades travels vertically. But metal-cutting bandsaws are, these days, most often horizontal designs. In this approach the bandsaw blade, its associated wheels and the motor are all mounted on a pivoting assembly. The whole assembly pivots downwards (rather like the friction drop saw) as the blade chews its way through the material.

A major differentiator of horizontal bandsaws is the feed mechanism. Some use the weight of the assembly (partially balanced by a spring) to apply downwards pressure on the blade, while others use a more sophisticated adjustable hydraulic system. Some bandsaw also automatically turn off the motor when the material has been fully cut, while others stay running until the operator switches off the machine.

Most bandsaws are highly adjustable – ball-bearing rollers guide the bandsaw blade and these rollers are adjustable to keep the blade square to the work. The tension of the blade can be adjusted and the amount of blade that is ‘free’ (ie not guided) can also be changed to suit the size of the work.

Making angled cuts is done in one of two ways - it depends on the design of the machine.

The simplest machines use a vice that changes in angle, allowing the angled cut to be made. Two downsides of this approach exist. Firstly, the moveable vice jaws are usually not as rigid as fixed jaws, and so inaccuracies can occur with sloppy positioning. Secondly, with this approach, the material must also swivel if it is to be angle cut. If the material is long (eg a 6-metre length of square tube), then clearance in your working space can become problematic.

The more complex (and expensive) machines use a swivel head to make angle cuts. The vice can then be more rigid in design and there’s no need to have material going off at odd angles within your work-space – the material is always on the one plane.

Bandsaws down at the home workshop end of the field are typically low in motor power - eg 375W – 1kW of induction motor power. (To put this another way, they use efficiency rather than brute force.)

Bandsaws vary substantially in the maximum size of material they can cut. Therefore, if you are looking at cutting – say – 100mm tube at 45 degrees, check these ‘size’ specs carefully.

A bandsaw does not cut as accurately as a cold saw, but if set up carefully, it can still be sufficiently accurate for almost all purposes that don’t require machined (or ground) surface accuracy.

Bandsaw blades vary in teeth per inch, construction (cheaper carbon steel versus bi-metal) and quality. It is not hard to destroy a bandsaw blade, so if you’re to achieve a good blade life, care needs to be taken in terms of selecting speed, blade type, feed rate and lubrication.

Talking of lubrication, many bandsaws have pressure-fed cooling of the bandsaw blade via a pump and nozzle. If the saw does not have this, cooling lubricant should be manually applied via a suitable fluid in an oil can.

With the range of pricing available (horizontal, metal-cutting bandsaws start from about AUD$500), and the versatility and the ability to set up the saw for accuracy, a bandsaw is a good step up over a friction cut-off saw.

Power hacksaw

Power hacksaws comprise a motor and a crank that drives a reciprocating blade. The blade is like a hand hacksaw but longer - and much thicker and stronger. The mechanism usually incorporates a function that lifts the blade slightly on the return journey. Power hacksaws usually have force-fed lubricant/cooling of the blade, and may have variable speeds. Most will turn themselves off when the cut is complete.

Power hacksaws are going out of fashion a bit because when compared with the competition of horizontal bandsaws (and cheap friction drop saws), their advantages of being able to cut very thick sections of steel is no longer the winning factor it once was. Downsides include expense, weight (they tend to be very heavily made) and an inability often to perform angle cuts.

That said, if you have a need to cut railway line, piece after piece, nothing will beat a power hacksaw. However, for a typical home workshop, a power hacksaw is usually over-kill.

Power hacksaws are now hard to find new at amateur prices, but second-hand are available from around AUD$200. A real bargain unit, working well and priced at less than this, is still worth carefully considering.

Hand guillotine

A hand guillotine (sometimes called a hand shear) works rather like a large pair of scissors. A heavy-duty blade, typically operated by a long handle, moves closely past another (fixed) blade, so shearing the material.

A hand guillotine can be used only with solid material (so not pipe, tube or RHS) and typically is able to work with material that is relatively thin (eg less than 5mm soft mild steel) and about 150 – 200mm in width (depending on the model).

However, these specs are a bit misleading. Typically, if you are using the full width of the shearing jaws, you’ll be cutting material only 1-2mm in thickness. On the other hand, if you’re working with flat bar, you might be able to go to full 5mm thickness – but only for material perhaps 25mm wide.

Hand guillotines are quick to use and are typically not that accurate. They’re perfect though for cutting off 25mm x 3mm bar stock (eg to make a 100mm long bracket), for shearing small pieces of aluminium sheet to size, and the like. The major benefit is the speed – it takes only moments to make the cut.

If you do lots of ‘little’ work – making brackets, cutting sheet steel patches for bodywork repairs, working with small pieces of aluminium sheet – then a pair of hand shears will be very useful in your home workshop.

Note: while not dangerous in terms of potential ear or eye damage, a pair of hand shears will easily remove fingers. Always lock the hand guillotine when it is not in use – especially if children are ever in the home workshop.

Pricing starts from around AUD$120 for small units – well worth it.

Conclusion

The approach you choose to take depends on what you are doing and your budget. If you are on a tight budget, go for the friction saw and also buy excellent eye and ear protection. If you can afford a bit more, the horizontal bandsaw is a good bet. Alternatively, if you’re working largely with thin material, a pair of hand shears will speed up your work. And, if you stumble across an old power hacksaw at giveaway prices, grab it! Cold saws? One to think of in the future if you need expensive precision.

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