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What is a slitting saw, and what is the use of a slitting saw in the home metalworking workshop?

A slitting saw, along with the fly cutter, is one of the most terrifying accessories found operating in the home metalworking workshop.
slitting saw on morse taper arbor

A usable slitting saw setup consists of a thin disk of metal – the saw itself, plus a holder of some sort. The disk of metal has a toothed edge and is available in bewildering array of thicknesses, diameters and tooth counts. In the middle of the disk is a hole to fit on the holder, usually with a keyway cut in it.

The holder section – we might well call it an arbor – has two parts – one end is a Morse taper, R8 or whatever is required to attach to your mini-lathe or micro-mill or mini-mill or whatever. The other end has the hardware to hold a slitting saw disc onto the end so that it is concentric and perpendicular to the rotational axis of the machine toll you are mounting it on. A poor quality slitting saw arbor will fair in both these respects making the tool very difficult to use.

I personally think the arbors that hold the slitting saw using a keyway are less than ideal for the beginner. If you do not have a keyway holding the slitting saw disk, then, if you make a mistake and the saw bits into the work to hard, the saw will just stop turning and spin it the arbor – if a keyway was locking the saw to the arbor, then more damage would result.

I personally think the arbors that hold the slitting saw using a keyway are less than ideal for the beginner. If you do not have a keyway holding the slitting saw disk, then, if you make a mistake and the saw bits into the work to hard, the saw will just stop turning and spin it the arbor – if a keyway was locking the saw to the arbor, then more damage would result.

A lot of home metalworking workshop websites say that making a slitting saw arbor is a good project to do. Rubbish – you can buy a slitting saw arbor for £10 or so, and it will be better than any you will make. Cutting a Morse taper on the arbor will also be a long and tedious process on a mini-lathe. I think a slitting saw arbor is one of those items where it is more sensible to purchase, rather than make, because you are better of spending your time on something more interesting than making a slitting saw arbor on a mini-lathe.
dismantled slitting saw and arbor

It is very difficult to find good advice about what sized slitting saw you need. Avoid very thin slitting saw disks. These are likely to bend under use, and “walk” in the cut in such a way that it becomes difficult to cut in a straight line.

The key with cutting on home machine tools with a slitting saw is to go slowly. The slitting saw has a much larger diameter than, for example, an end mill. Therefore the cutting surface will be moving at a much greater speed for a given rpm on the mini-mill or micro-mill. Therefore go very slowly. Take shallow cuts as well. If you go too fast, you will learn another attribute of slitting saws – they blunt very quickly if made to cut too fast – always go slow.
slitting saw teeth

As suggested by the name, slitting saws are used for cutting narrow slits in metal. In my metalworking workshop, the two most common uses of a slitting saw is marking graduations on a control knob, or making a slit in a clamp ring. So far I’ve not found a use for the slitting saw on my mini-lathe – mainly because the mini-lathe cross slide does not have T slot for clamping down jobs.

I have also found the slitting saw useful for making very thin disks of small diameter. Clean up some round bar in the lathe and then use the slitting saw on the mill to take small slices off the top. If you need several such slices, it is a million times easier than doing all that parting on a mini-lathe.

And of course – be very careful with using a slitting saw on a mini-mill or micro-mill – they are very unforgiving on naked flesh – keep fingers move out of the way than usual!

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