Wood Glue vs Dowel Plugs

[oran]

Hi,

If wood glue is stronger than the wood itself, why should I ever use dowel plugs? It seems more complicated and time consuming.

Couldn't find the answer on the internet.

(And let's assume that I don't want to dis-assemble the woods afterwards)

Thanks

[curlyoak]

On 10/1/2023 at 4:39 AM, oran said:

wood glue is stronger than the wood itself,

That is true if a joint between two pieces of wood is properly made. Poor execution will not be saved by glue!

[oran]

On 10/1/2023 at 12:06 PM, curlyoak said:

That is true if a joint between two pieces of wood is properly made. Poor execution will not be saved by glue!

So a direct conclusion from what you're saying is that someone who uses dowel plugs is not that good working with wood glue? Just to be clear, I'm talking about joining two pieces of wood along the grain.

[JohnG]

Your first post was not clear. Generally plugs are considered to be a non-structural, cosmetic piece to fill a hole in one piece of wood. Dowels, dowel joints, or dowel pins are generally considered to join separate pieces of wood together, for alignment or structural aid. That might be getting a bit pedantic, but when no other information is provided in how the dowels are being used, it makes a difference.

Dowels, biscuits, and/or dominos can be useful when jointing boards together by keeping one face of the boards aligned and flat. Especially on longer boards, it is difficult to keep the boards aligned as you are tightening the clamps and the glue is making the boards slip around. 

Dowels, biscuits, and/or dominos do not add strength to the joint in any significant way, when considering a long grain to long grain glue up that is properly jointed. If the boards are not jointed well, then the dowels, biscuits, and/or dominos might start to play a role in joint strength. 

 

[BillyJack]

Plugs..

 

[wtnhighlander]

Wood glue is NOT stronger than the cellulose wood fibers, but IS as strong or stronger than the lignin that binds the fibers together. So, in a joint where the fibers of the mating parts are parallel, such as boards in a panel, a well-formed glue joint will be as strong as the surrounding material. Adding dowels or tenons adds strentgh across the joint, so a fracture will occur in the middle of a board, instead.

Using dowels or tenons to cross the glue joint places the stronger cellulose fibers in position to resist breaking at the joint. Doing this does add strength to joints where the grain of the mating parts is NOT parallel.

[pkinneb]

Alignment for one...but as explained above there are others.

[gee-dub]

I think dowels get a bad rap or become points of contention in conversations due to some apples-to-oranges comparisons.  I think @wtnhighlander identifies one of the main uses for dowels.  Many types of joinery are the better choice when compared to each other for a given situation.

We have a lot of traditional joinery that would resist failure of the glues due to stress.  Some of these continue to provide mechanical connections even if the glue does fail; dovetails, pegged tenons, wedged tenons, etc.  Modern materials and adhesives makes these methods more optional.

There's a ton of joint torture tests out there where the same stresses are performed on various joinery methods.  These are good sources of information but a joinery method that provides good pull strength may not provide good lateral stress resistance. 

Mortise and tenon, dovetails, or dowels don't work best for everything.  We have a Swiss-Army-Knife of joinery options available to us.  Open the blade that works for your specific requirement.

[oran]

OK got it, thank you everyone for your help and detailed answers! :)