How to machine difficult timbers

Words and photos: Charles Mak

Rough-sawn wood gives us better value, more choices and better control over the stock dimensions and even the final appearance of the wood we can use – if you know how to machine it properly. Some rough-sawn boards are harder to flatten than others and the techniques needed to handle them are usually not found in the jointer’s user manual. Let me show you how to deal with three common but challenging scenarios. First of all, I will share some workshop tips that will give you better control of the jointing process.

1. Select the most suitable stock

The first line of defence against difficult timbers is, of course, just to avoid them. That is, pick wood in the best condition – boards that are least twisted, least bowed and least cupped. If that is impracticable, use the least twisted for the longest parts of your build and the rest for smaller parts. This allows you to get the best surface and yield from the timber.

2. Let the moisture content settle

Where possible, try to mill stock that has been stored in the workshop for a few weeks so its moisture content is similar. And also, try not to dress your stock until you know you will be using it relatively soon.

3. Cut stock to rough size

Where possible, rough cut boards to approximate sizes as that will reduce cupping or bowing. This will in turn result in thicker boards or longer pieces after the jointing process. The exception is that you should keep short pieces long enough to handle safely and with ease on the jointer.

4. First place the bowed side down

In general, to flatten a cupped or bowed board, place the concave face or bowed side on the jointer to prevent rocking. Apply light pressure on the cupped stock and once the front has passed the cutter, shift one of the pads onto the outfeed side. You will, however, see an exception or two to this guideline later in the article.

5. Compromise with difficult grain

We all know that we should try to joint or plane with the grain. But, what if the grain reverses on the same side or edge? One should be more concerned about the severity of the tear-out than the amount. As a compromise I will feed the stock in the direction that will produce the least severe tear-out. Planing mostly with the grain may cause less tear-out but may also result in more serious chip-out.

6. Don’t overdo it

When pushing, use gentle downward force to avoid flexing a board as it will spring back. Finally... Always remember to clear the infeed and outfeed tables of any shavings after each pass. Now, let’s looking at flattening some difficult boards.

Dealing with long and badly bowed boards

If you run a severely bowed board that is longer than your infeed table, you’ll end up with a tapered piece as the rear end rises up onto the table. The trick is not to start with the front of the board on the infeed table, but rather place the board with its front end on the outfeed side and the other end on the infeed table, planing the trailing end first as shown above. Then reverse the board and plane the other end in the same manner.

Repeat the process to increase the jointed surface on each pass until the board is relatively flat and then make a couple final passes with the grain in its full length.

What if a cupped board is slightly wider than the jointer?

We usually plane a board cupped or concave side down on the bed, but when the cupped board is wider than the jointer’s table, I handle it differently. I place the board convex side down and roughly centred on the jointer’s bed. I then place the push pads on the centre area of the stock to keep it steady and remove the middle spot on the convex side, see above. As soon as the convex face does not rock, you can flatten the opposite surface on the thickness/surface planer and then the convex face with the same machine.

What about twisted boards?

Twisted boards are more difficult to handle. Some woodworkers place a push pad on the centre of the board to balance the twisted face on two diagonal corners and then push the board towards the outfeed table. This balancing act is difficult to perform as one has to keep the opposite high corners off the table by an even amount.

Instead of balancing the board free hand, I shim the high corner or edge at the end of the board on the infeed table with some paper towel or wood shavings so the board rests on three points. Then hold a push pad down on the board near the centre end and make a pass.

Using just one push pad, applying pressure on the board near the end of the infeed table to make a pass. If the twist is not removed, repeat the same shimming and passes. Once the twist is gone, the board can be planed as usual using two push pads with steady pressure on the outfeed bed after the board passes the cutter.

Square and flat stock is fundamental to straight line, tight joinery and fine work. Knowing these jointing tricks and techniques should give you a head start for any project.

Charles Mak lives in Alberta, Canada and enjoys authoring tricks of the trade, teaching workshops, and woodworking in his workshop.