Under the Choko Tree By Nevin Sweeney

Hand Tools - Cold Chisels

Thirty years ago and old friend of wrote a series of articles on buying, doing up and looking after hand tools. Bill was a manual arts teacher at one stage, very skilful with his hands and knows all that there is to know about hand tools (among other things). His articles are available here. I will also be submitting my comparatively poor contribution on hand tools which I have used over the years. This article is part of that contribution.

Cold chisels are used for working metals and sheet metal. There are six different types which used to be in current use but some have become rarer over the years.

Types of Cold Chisel

Flat Chisel – This is by far the most common type of cold chisel you are likely to meet up with at a “Trash and Treasure” market, second hand shop or your local hardware. It is also the most versatile, being used for general metal working duties. It is capable of being used to cut off rivet heads or rusted nuts and bolts, cutting rods or bars to length, cutting sheet metal such as a 200 litre drum or chipping back thicker metals. The edge is usually ground straight but may be given a convex cutting edge if particularly hard or soft metals are being cut.

Crosscut or Cape Chisel – This chisel tapers back from the cutting edge to prevent binding in a groove and is used to cut keyways in shafts or pulleys or for cutting grooves in wider surfaces.

Round Nose Chisel – This is used to cut oil grooves in bearings etc but can also be used cut a small groove to bring a drill bit back into the centre of a hole where it has drifted off while starting a hole on thick metal.

Diamond Point Chisel – The diamond point chisel is used for cutting vee shaped grooves in metal such as in large diameter metal pipe or metal plate to enable material to be broken off them. It is also used to prepare metal parts for welding and chipping out welds as well as squaring corners.

Side Cutting Chisel – The side cutting chisel is used for getting into those pesky corners to chip out metal or to access places which would inaccessible to a straight chisel. They are also used to true up keyways cut by the crosscut chisel.

“C” Chisel or Gouge – This is used where a half round surface is being cut or to enlarge circular holes.



Second Hand Cold Chisels

The following comments mainly apply to the more common “flat” cold chisel but could be adapted to the other types if you find one you are interested in. As previously mentioned, the flat cold chisel is the most versatile of the cold chisel family and is also the one most likely to be on offer, sometimes for as little as a dollar or two in places where second hand tools are found. Due to their versatility they can also see some pretty heavy service and by the time they get to you they may be in poor condition. That’s OK because with a little time, skill and access to a bench grinder you can get them looking new again (well almost!).

Mushrooming

While cold chisels are made from carbon steel, only the business end is hardened and tempered, the other end is left soft so that it can absorb the hammer blows without shattering. This is all well and good but if the people who owned the tools before you didn’t look after them it is highly likely that the metal on this end will be deformed by said hammer blows into a mushroom shaped end.

An example of mushrooming

The mushrooming on the end of a cold chisel is undesirable for two reasons, the first is that the mushrooming has jagged edges which can slice open a finger if you are not carful. Secondly a lump of the mushroomed metal can come adrift while hammering and cause damage, particularly if it were to hit an eye or other sensitive bit.

The same chisel after grinding off the mushrooming

To fix this problem, you need access to a bench grinder and it is easier if the grinder has a 25mm wide or wider wheel, the little 12mm wide ones are a pain to use. Hold the chisel horizontally and with the shaft at about 45⁰ to the face of the wheel and the mushroom head towards the wheel. Start up the wheel and rotate the mushroomed head against the face of the wheel, ensuring you move the mushroomed head across the face of the wheel so that you don’t cause gouges in the face of the wheel.

Removing mushrooming from a cold chisel using the bench grinder

Continue this process until all of the mushrooming has been removed and the top of the chisel is chamfered at a roughly 45⁰ angle. If you repeat this process regularly to remove the burr before it graduates into mushrooming it will be a quick as easy job and your cold chisels will always be safe to use.

Sharpening

Depending on the life story of your particular chisel, it may have been used for everything from chiselling out bricks to breaking up rocks so the cutting edge is likely to be pretty blunt. This is pretty easily corrected but also requires access to a bench grinder like the one mentioned above. As always, wear eye protection while grinding, preferably goggles or a face shield.

The cutting edge of the chisel has been hardened and tempered so it is very important during the sharpening process not to overheat it, ruining the temper and causing the overheated area to become soft. To prevent this take plenty of pauses and have a container of cool water next to the grinder to dip the blade into if it starts to get too hot.

Sharpening a cold chisel using the bench grinder

Turn on the grinder and lean the chisel against the tool rest and place the cutting edge of the chisel so that the bottom facet of the cutting edge of the chisel lies flat against the face of the wheel. Move the chisel from side to side across the face of the grinder, turning the chisel over regularly so that metal is remove equally from both sides of the cutting edge. Don’t forget to cool the chisel down so it doesn’t over heat.

The included angle of the cold chisels cutting surface should be 60⁰ or thereabouts, so make sure it does not become too narrow or flat during the sharpening.

A regular sharpening will only take a minute or two and will keep your cold chisels in good working order for their lifetime. A wipe over with an oily rag once in a while will also discourage surface rust. Surface rust is a cosmetic issue only but if it bugs you, run the rusty areas against a wire wheel (which is also fitted to a bench grinder) to remove it, then give it a wipe over with the oily rag. It will be good as new!

 

 

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