Thread: Lag Screws/Coach Bolts

Must be good reasons to do things this way.

Maybe this method is stronger an less likely to tear out
or work loose so that the thing develops a wobble.

Originally Posted by Soredust

I am in the planning stages of making a piano stool for my big sister. I am using the plans from a Woodsmith magazine, see picture.

001.jpg

The plans call for lag bolts where the legs attach to the corner of the triangles. They use double thread lag screws, the type you have to use two nuts together to screw into the wood, then remove the nuts, assemble and then fit washer and tighten nut. I assume this is in case you want to disassemble for some reason? I can't see any other advantage of using this type of lag screw over a normal coach bolt, or am I missing something?
Can the wise please put me on the straight and narrow or am I OK to use normal coach bolts in place of lag screws.

Originally Posted by artme

Must be good reasons to do things this way.

Maybe this method is stronger an less likely to tear out
or work loose so that the thing develops a wobble.

my guess is that the suggested lag bolts require a smaller surface hole which in turn can be covered by the plugs used in the design.

Originally Posted by ian

my guess is that the suggested lag bolts require a smaller surface hole which in turn can be covered by the plugs used in the design.

I don't think so, any size hole could be duplicated with the same size coach bolt. The only real reason I can see, and that I could find with my old mate Google, is that you can disassemble a number of times without compromising the strength of the fitting. The magazine article even states not to use glue, but it doesn't mention the reason is for dis-assembly, it just say something like "no need for glue because of the strength of the lag bolts".

Whilst Googling though, I did realise that Lag/Coach are deemed the same and that the one that has two different threads and nuts is called a double thread coach screw.

and the other thing about not using glue with that stool is that you don't need clamps !!