Do Kreg joints weaken under vibration?

[Bob Jones 5443]

Here I go with another long one.

Not sure if this is heresy on the Creek (it would be in the Neanderthal Haven!), but I actually pulled out my Kreg jig this week. I bought it when I was a rank beginner in woodworking, and I can count on one hand the number of times I've used it for a project since then.

I needed to build a new table extension for my new router lift, with a now-standard 9-1/4" x 11-3/4" plate. The original router plate is a 20-year-old Rousseau at 9" x 12". So, new table.

I built mine from a 3/4 Baltic birch top on a frame of 2 x 3 pine, on edge. The top edges of the pine members were carefully jointed to be flat against the plywood. The two long members run the 42" length of the extension, and the 7 cross pieces butt into the long members.

I used the Kreg to make butt joints on all the cross pieces, mostly for stability of the frame during assembly, not for strength. After all, the width of the extension will be held together by the saw's rails.

But I also placed an array of Kreg joints between the tops of the frame members and the plywood, to hold the plywood firmly against the frame –– and reduce vibration. I carefully and gently torqued those top screws so that I could not slide a sheet of paper between the top and a frame member. I don't believe I stripped any of the screws.

Here's the question: Should I have glued at least the top Kreg joints? (The butt joints don't need it.) I wonder if the vibration from the 3-1/4 HP Porter Cable 73182 will eventually loosen the screws in the pocket joints. If so, this would lead to gaps, that would produce noise, that would in turn lead to more vibration, etc.

I know the answer: yes, of course I should have used glue. I'm so tortured by the question that I'm considering unscrewing everything and redoing it with glue. Augh. What do the sages here say? I'll sleep on the decision as I await the wisdom to come.

Boy, I hope I don't have to undo all this screwing. But knowing me, I probably will do it anyway. Talk me out of it?

[Richard Coers]

I bought a K2 jig around 1991. I've NEVER done a dry joint. Just the seasonal movement of wood is enough to change the crushed fibers under the screw head. I'd assume the vibration will do the same thing.

[Bob Jones 5443]

Yikes. I suspected I'd hear that. Any more of you want to pile on?

[Greg Parrish]

I wouldn’t be ashamed of using it. I have hand tools, power tools and numerous ways of making joints but regularly use my little kreg jig for fast work. As long as the joints are hidden and the item is not a piece of fine furniture I’ve got no issue using it when it makes sense. Especially when making quick shop jigs or other shop items. If time allows or the piece requires it, I’ll use other joints and different methods. That said I do use glue with it so the way I view it is the kreg system is really just my clamp until the glue dries.

[Mark Daily]

Use it for awhile and see if the joints loosen up. If not, great- if they do then break out the glue.:)

[Bob Jones 5443]

Epictetus would be proud of your advice.

[Marc Fenneuff]

I did something similar with MDF for the router table in my mobile base in 2010

http://www.yamato72.com/sawcreek/20100626_8345.jpg

http://www.yamato72.com/sawcreek/20100626_8346.jpg

http://www.yamato72.com/sawcreek/20100626_8348.jpg

I have not had any trouble with the joints coming apart. I did cover the top with a plastic laminate though.
Coincidentally, I have the same Rousseau plate

http://www.yamato72.com/sawcreek/20100711_8636.jpg

...and now need to work with a Kreg router lift which is a bit smaller. I'm going to build a dedicated mobile base for the router this time, though, instead of keeping it with the TS.

[glenn bradley]

Often in joinery discussion it is a matter of the chosen method being “strong enough” for the task. Except for a production shop I see no reason why one would not use glue in a lot of joints, especially weaker joinery methods. That being said, I bet you’ll be fine. (Fingers crosses)

[Mike Cutler]

If it makes you feel any better, nothing you can do with screws and glues will withstand the effects of vibration forever. Get the wrong, or right, vibration frequency going and it won't matter.
That said, it is a shop made jig for making more permanent projects. You will make 10 different router table adaptions for it before you make another router table top. In the end though, no one ever makes just one router table in their life. Some of the best jigs I've ever made were cobbled together on the fly. Some of the biggest failures had a lot of time and effort put into them, before they hit the recycle dumpster., or went into the wood stove:o
The closest you'll ever get to a "one and done" router table, is when you move up to a shaper. ;)
Hey,,,, you were looking for someone to talk you out of redoing it.

Use it, enjoy it, make nice things with it.:D

[Peter Kuhlman]

I really see no issue here. My router table is all screwed together although not using the Kreg method - no glue. It is about 15 years old now and no issues. I have the big PC 7518 router in it. I would use it as is and in the future when you build a new fancy one you can glue it if you feel the need.

[Bob Jones 5443]

If it makes you feel any better, nothing you can do with screws and glues will withstand the effects of vibration forever. Get the wrong, or right, vibration frequency going and it won't matter.
That said, it is a shop made jig for making more permanent projects. You will make 10 different router table adaptions for it before you make another router table top. In the end though, no one ever makes just one router table in their life. Some of the best jigs I've ever made were cobbled together on the fly. Some of the biggest failures had a lot of time and effort put into them, before they hit the recycle dumpster., or went into the wood stove:o
The closest you'll ever get to a "one and done" router table, is when you move up to a shaper. ;)
Hey,,,, you were looking for someone to talk you out of redoing it.

Use it, enjoy it, make nice things with it.:D


Mike, that's an honorable go at dissuading me from taking everything apart. Well played.

This is my second table. On the first one, I think I must have screwed the top down onto the frame members. It looks like I used two thickness of laminate over the top. In any case, I can't feel any bumps through the laminate. Maybe that prevented them from coming loose. You can read between the lines that I have no memory of my process from 2001.

Still, that first one held a 690 at 1-3/4 HP. It seems possible that the 3-1/4 HP beast in the new table could be a different matter where the intensity of vibration is concerned. Not to mention weight: 14 pounds for the 75182, 11 for the Mast-R-Lift, and the frame members all add up to over 30 pounds. That's a sag waiting to happen.

I've decided to compromise and glue the final two cross members, and the other two I'll add between them at right angles –– the ones that surround the router plate itself. That will give me a screwed and glued perimeter around the router. Come on: that has to be enough, right?

[Bob Jones 5443]

I really see no issue here. My router table is all screwed together although not using the Kreg method - no glue. It is about 15 years old now and no issues. I have the big PC 7518 router in it. I would use it as is and in the future when you build a new fancy one you can glue it if you feel the need.

Alright, that does it then. Thanks for the eyewitness account. Sounds like a perfect surrogate for mine. Away I go. I'll probably soon forget I was even thinking about this.

Love the Creek.

[Mark Daily]

Alright, that does it then. Thanks for the eyewitness account. Sounds like a perfect surrogate for mine. Away I go. I'll probably soon forget I was even thinking about this.

Love the Creek.

Thinking about what?

[jeff norris 2011]

Yes vibrations will weaken the joint. Question is will it weaken it enough to fail?

Rare I use pocket screws, but when I do I typically glue and screw and less I need to take it apart later

[Alex Zeller]

When I got my used PM66 the extension table was some sort of phenolic material resting on a very basic wooden frame. The shop that owned it before me used 3/4" x 1 1/2" pine to make the frame and brads to hold it together. They used 1/4" bolts to secure it to the fence rails. When I removed it it was falling apart just leaning against a wall. When in place it was fine. I didn't reuse it because I wanted to make something that I felt more confident owning. I can tell you that the router and extension table were both well used. I'm assuming you also have heavy duty steel rails for your fence. How you attach the wood that the 3/4" birch will rest on is going to be the real strength. I don't think seasonal movement is going to come into play like it would on a cabinet door. Since you are going to replace the 3/4" birch I would glue that down to the 2x3 frame and a few screws and call it good.