Saturday, June 25, 2011

Cutting Choices

Today, I finally came across an image I made of the broken round stock shear I described in May, so there it is - the price of unnecessary quenching of mild steel or failing to keep mild steel rod and tool steel rod segregated.

Most decisions about cutting stock are intuitive and don't take a lot of consideration of alternatives although of all the shop operations it has the greatest number of tools and methods to consider. I originally set up the entire work environment so I am throughly familiar with the possibilities but when a new helper is working they need some instruction so I prepared these thoughts about cutting strategies. The choices largely depend on stock size and whether we are working cold or hot.

I estimate that I use the small bandsaw most often for cutting. This is largely determined by the most commonly used stock which is flat bar 1/2" thickness or less, round bar under 3/4", square bar 1/2" or less, angle under 2", etc. It is set up at bench height, quiet and can be left unattended while cutting. It has the advantage/disadvantage of a 90º clean cut surface finish. The large bandsaw is reserved for cutting thick stock or gang cutting multiple pieces.

If the stock is really small I may use the hydraulic forging press with a cold cut die with 1/32" stop. I like the quiet operation and the "V" pinched sever line which is ideal for welding or tapering. The stop prevents complete separation for good control and leaves the thin connecting point which is easily snapped.

Four cold shears are available. The Edward's floor shear is seldom used but the vise mounted round rod shear is used often - frequently with a stop to assure multiple cuts have the same length. It is quiet and good for cold work, leaves a 90º end but can only admit stock up to 3/8" diameter. The throatless shear is used for cutting prototype patterns with curved lines in sheet metal up to 14 gauge. Above 14 gauge I use a torch or plasma cutter. There is also a bench mount straight blade shear which is used infrequently.

The oxyacetylene torch is used several times in a typical day and it would be hard for me to imagine being without it. It is one of those systems where redundancy assures no down time, two torch outfits, multiple industrial gas cylinders, etc. In my hands the cut end always needs cleanup.

A Zip disc in an angle grinder is used at least as often as the torch but almost entirely for small pieces in the vise.

I seldom use the chop saw unless the cut is 45º because that is where it is set. I don't like the noise and the abrasive dust.

Likewise, I seldom use the 14" cold saw. Again, the noise and also I reserve it for stock which has at least 1/2" minimum thickness and it seems best suited for large rounds. It is very accurate and cuts cool leaving chips and no dust similar to a bandsaw cut. Seldom do I have projects which use large round material.

When working hot we use the hardie hot cut a lot and use a handled chisel under the treadle hammer a lot. The hydraulic press recently fitted with one of Old World Anvils scissor tools works well. I have another one set up to use with the power hammer.

Since tapering is probably the most frequent operation, I try, as often as possible, to sever stock at an angle to help avoid cold shuts when drawing out. Stealing a phrase from the fabric working industry I call this “cutting on the bias.”

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