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What problems can occur when dowelling?

What problems can occur when dowelling?

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Image of a target to show that dowelling must be accurate at all times Dowelling can be a tricky process as it requires accuracy at all times.
Image of a DIYer running up a hill as a reminder never to give up when learning how to make effective dowelling joints It’s easy to make mistakes but don’t be put off! Being aware of potential problems can help you to avoid running into them during your dowelling project.


Illustration of how drill holes can be inaccurate

Uneven drill holes

If you find that the holes you’re drilling are not perfectly round then it’s likely that your drill bit is not straight.

Image of a badly bent drill bit that is no longer suitable for use in dowelling projects Once a drill bit becomes bent, it will need to be replaced as it can no longer drill holes accurately.
Image of a dowel joint that won't connect because the dowel holes are not straight

Uneven joint

If you find that your joint does not connect properly, or that the two pieces of wood you are joining are not lined up properly, there may be a problem with the way your holes have been drilled.

DIYer drilling at 90 degrees to the work surface If dowel holes are not drilled at 90 degrees to the wood’s surface, the pieces of wood you are joining will not meet up properly and you will be able to see your dowel pegs in the resulting gap.
Image of a DIYer pulling a joint apart to check the angle of the dowel holes If this is the case, then you need to disassemble your joint, check which piece of wood has been incorrectly drilled and replace it with a new piece of wood with correctly drilled holes.

You may need to start the joint again from scratch.

Misaligned joint

Misaligned boards that have been badly joined due to the inaccurate drilling of dowel holes If the edges of your joint are not in line, it’s likely that your dowel holes were drilled incorrectly in your second piece of wood.
Dowel holes being redrilled in a piece of wood with more accurate guidelines Fixing this is a little easier. You can do it by disassembling your joint and re-drilling your holes in the correct place.

For more guidance, see How to accurately align dowel joints.


Image of a wooden plank that has cracked open due to hydraulic pressure caused by an unfluted dowel peg

Cracked wood

Making a dowelling joint can sometimes cause wood to crack. This is usually because of something called hydraulic pressure.

Diagram to illustrate hydraulic pressure Hydraulic pressure is caused when something pushes down on liquid that is already in a confined space. The pressure that is being put on the liquid is then transferred to the material that contains it.
Image of a crack along the grain in the surface of a guitar The added pressure on that material can cause it to break along any weak points. For example, wood would break along the grain.
Image of a wooden dowel with flutes cut along its length to allow glue to escape and avoid cracking caused by hydraulic pressure This can be avoided by using fluted or grooved dowels, or by cutting nicks into plain dowels to allow the glue to escape the joint.

It can also be avoided by drilling a hole 1mm wider than the dowel you are intending to use.

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