9

Commercially available dowel pegs come with a spiral groove around their outside surface. How important is this grooving?

This comes to bear in the case when using smooth dowel stock to make ones own dowel pegs. Should one always buy the commercial grooved pegs or are DIY smooth pegs just as good?

2

It probably doesn't make much difference, but I suspect it also depends on your application. If your joint must withstand more shearing force, I would expect the smooth dowels to be slightly stronger at resisting shearing, all else being equal. If you have a single dowel that must withstand rotational force (such as in a knob), maybe a grooved dowel is better (like treaded vs. bald tires). If the joint must withstand pulling or racking force along the length of the dowel, there may not be much difference at all, but I would somewhat expect the grooved dowel joint to be weaker since glue on its own is not a good filler and the insides of the grooves are just open space with no mating surfaces.

I've always thought the grooved dowels were simply designed to be easier to push in. The grooves provide reduced contact area between the dowel and the walls of the hole, and at the same time they provide channels for any excess glue if you didn't drill the hole slightly deeper than the dowel. This also means you won't get an air-tight seal that causes compressed air and/or glue to push dowel back outward.

On the other hand, perhaps the grooved dowels are slightly oversized, and they deform inside the holes so they remain compressed and tight-fitting at all times. But you could just as easily make a tight fit using a smooth dowel.

| improve this answer | |
  • I think you have a point regarding the glue escape. I've had problems with smooth dowels acting like a piston in the hole where it was impossible to properly seat the ddowel due to glue trapped behind it. In a number of cases I had to resort to slitting a groove along one side of the dowel with a razor knife or flatten one side by sanding the peg. – Michael Karas Mar 19 '15 at 4:30
6

The main reason for for the grooves in the pegs is to increase the surface area for the glue to adhere to. You get a lot more surface area, which gives more bonding strength. My dowels have straight lines.

Cutting long dowels down to peg size is fine as well. It partially depends on how much strength you need and you can often add in an extra dowel to get the same effect.

| improve this answer | |
  • 1
    This, exactly. The main reason for using a dovel is to create "long grain contact surface" because end grain doesn't glue well. The grooves greatly amplify that effect. – Damon Mar 18 '15 at 16:31
  • 2
    I follow the part about the grooves adding more surface area, as well as more glue surface adding strength, but there's a jump in between those two pieces of conventional wisdom where I get lost. My understanding is that glue does not add strength when acting as a filler, and in the end the glue would just be filling the grooves in the dowel unless you also managed to make perfectly-mating grooves around the inside of the matching hole. Do you know of any studies in which grooved dowels were proven to make stronger joints than smooth dowels? – rob Mar 18 '15 at 23:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.