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How to Dimension Timber Accurately using a Planer Thicknesser

This guide explains why a planer thicknesser is an essential tool for accurately sizing timber.

Author: Record Power

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How to Dimension Timber Accurately using a Planer Thicknesser Most woodworkers, whether amateur or professional, will invariably at some point need to use a planer thicknesser. There are various reasons for this: Cost - Rough sawn timber can be bought at a lower price than pre-planed and can then be dimensioned to the exact size required for the project. Even when paying a premium for pre-planed timber it is often irregularly sized or warped and so needs further preparation. Most projects require timbers to have adjacent edges at 90º, particularly when jointing is required. Often pieces must be exactly the same size as each other when used for jointing. A question we are often asked, particularly at woodworking shows and demonstrations, is why we need to use a planer as well as a thicknesser to achieve the above. Many woodworkers decide they can make do with a standalone thicknesser. These machines have a great deal of appeal to those relatively new to woodworking as they are less costly than a planer thicknesser and can be bench mounted. However, as can be seen below, a standalone thicknesser is simply not capable of dimensioning all four sides of a piece of timber accurately.
The Diagram opposite shows an exaggerated cross section of a typical rough-sawn piece of timber which will be used to illustrate the different results that can be achieved using both a standalone thicknesser and a planer thicknesser.
How a Thicknesser Works
1 Firstly, surface A will be cut to be parallel with surface C. To achieve a planed finish to surface C, the workpiece is rotated 180º and passed through the thicknesser again.

2 Now these opposite faces are parallel, we can see by turning either surface B or D face down on the table that we are only able to plane them parallel to each other but never at 90º to surfaces A or C.

3 It can now be seen that no matter which way the timber is turned, only a parallelogram profile can be achieved.
How a Planer Thicknesser Works
1 Plane surface C to be flat using the machine in the planing mode.

2 Place surface C against the fence, which is set to 90º, and plane surface B until it is at 90º to surface C.

3 Once we have two adjacent faces at 90º to each other, the remaining opposite faces can be thicknessed parallel by using them as a reference.