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Things to consider when choosing an engineer’s straight edge

Things to consider when choosing an
engineer’s straight edge

Shop for Engineer’s Straight Edges

You should take careful consideration of several factors when deciding what engineer's straight edge is best to use When deciding which engineer’s straight edge is best for you, consider the following:

  • The accuracy you require
  • The shape and size of the workpiece
  • Whether you want to check for levelness

The accuracy you require

You should always use a straight edge that has the required accuracy for the job you are doing Your first consideration when selecting an engineer’s straight edge should always be the accuracy that you require. You should select the appropriate accuracy grade of straight edge for the task you intend on using it for. This may have an affect on the other factors as to which straight edge you decide to use.
It's important to select a suitably accurate straight edge for the job, aluminium might not be accurate enough if you require a grade 00 straight edge For example, if you required a grade 00 accuracy straight edge of 3m (9′ 10″) long, then you would not be able to use an aluminium straight edge, as they are not produced to that accuracy. This might mean you have to use a straight edge that is heavier than you would ideally like.

The shape of the workpiece

Knife edge or triangular straight edges are required for checking the straightness of machine tool dovetails If you are checking a large flat workpiece for straightness, then you can use any type of engineer’s straight edge. If you need to check the straightness of dovetails on a machine tool, then you will need either a triangular straight edge or a bevelled straight edge. It is important that the triangular prism angle or bevel angle on the straight edge is the same as the dovetail you want to check.
If the area you need to check for straightness is in a narrow recessed channel, then you may require a thin rectangular or knife edge straight edge for this task.

The size of the workpiece

When deciding what type of engineer's straight edge is best to use you need to weigh up the pros and cons of each type Where possible, you should always use a straight edge long enough to cover the area of the workpiece you need to check. This is because using a shorter straight edge cannot guarantee that the entire length of the area you want to check will be straight.
If you have to use a large straight edge its best to use one that has weight saving holes Very long straight edges can be heavy. If you need to use a long straight edge you may want to use one that has weight saving holes or one made from aluminium to make it easier to lift and manoeuvre.
Just like people engineers' straight edges come in a variety of different sizes

What engineer’s straight edge lengths are available?

Engineer’s straight edges range in length from 100mm (4″) to 5m (16′ 4″)¬†depending on what they are designed to check.

Longer straight edges are used for checking the straightness of machine tool beds and have to be lifted by crane due to their size and weight.

Smaller ones are used to check and calibrate other tools such as rulers and squares.

Checking for levelness

Spirit levels can be used in conjunction with I section and rectangular straight edges If you need to check a workpiece is level as well as straight (such as in a machine tool bed), then you’ll want an engineer’s straight edge that has two parallel working faces, such as an I section or rectangular straight edge. This will allow you to use the bottom working face to check the workpiece is straight, whilst enabling you to place a spirit level on the top working face to check that it is level at the same time.

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