Tongue & Groove mistake - how to fix?

[Mark Cook]

Folks, I'm brand new to the forum and I come seeking help from more experienced woodworkers.

I'm building a roll-around computer cart and am building the sides out of 1" oak (actually 2 1/2" pieces laminated together.) To build the sides tall enough, I'm using tongue & groove to join 3 pieces edge-to-edge vertically. The middle piece has both the grooves. The top and bottom piece will each have the corresponding tongues. This will be the same for both the left and right side panels of the cart, although they will be mirror images of each other. That should be enough design background.

I've cut the grooves on both edges of both middle pieces (left and right side) to my satisfaction (on my router table.) I spent the better part of an afternoon and countless test cuts to get the tongue created properly on scrap oak (leftovers from the 3 actual side pieces), using a 1/2" straight router bit and flipping the wood over to do each side of the tongue separately. After getting a test piece exactly the dimensions I wanted, I held my breath and cut the first actual piece of the project. Once done, I test fit it to one of the completed grooves and discovered to my horror that one side of the tongue was cut too deep. I couldn't understand how this could have possibly happened until I checked my router and discovered that, after many dozens and dozens of test cuts without moving, the router bit had "walked" up out of the chuck just prior to the final cut. This left one side of the tongue at the correct depth and the other side too deep. (I have no idea why the bit choose that exact time to move, but can only assume that I failed to tighten the chuck sufficiently and it just took that long for it to slip.)

Here's what the mistake looks like:

344453

The correct (test) piece is on the right, the screwed-up actual project piece is on the left.

So, after all that exposition, I've got two (obvious, I hope) questions.

1. Aside from my failing to tighten the chuck sufficiently, is there any other possible reason why the bit would have moved and, if so, how do I prevent it in the future?

2. More importantly, how do I fix my mistake? I can't easily start the entire piece over, as it's cut in a fairly complicated (for me) shape which would be difficult to reproduce exactly. Can I glue an oversized shim along the length of the tongue (on the incorrect side) and then re-router it to the correct dimension? From a practical standpoint, that's what I'm inclined to try, but given that the joint will be moderately load bearing, I am somewhat concerned about the strength of the repaired joint. Will it be strong enough, or is there a better way to fix the mistake?

Any and all suggestions are greatly appreciated.

- Mark C.

[John TenEyck]

First, welcome to SMC.

OK, now to your problem. Was the bit completely bottomed out in the router when you tightened it? That often leads to problems. Always make sure the bit is off the bottom before tightening the collet.

Yes, you can glue an oversized piece onto the tongue and then reroute it. But next time I suggest you forget about those T&G's altogether and just butt glue your wood together to make the panels. Edge glued panels are as strong as the wood itself; adding splines, dowels, whatever, are OK for alignment but don't increase the strength of the panel.


John

[mreza Salav]

+1 to everything John has said.

[pat warner]

If the slots are all in the same place, I'd waste the tongues and spline every stick.
What happened? Is the stock the same thickness?
If you used a spiral cutter then it's crystal. They screw themselves into the stock.
Pulling the cutter from the collet, albeit & common.

[David Eisenhauer]

Easy fix. The guys above already told you what to do. If that is the worst screw up that comes off your bench, you are golden. It is recommended to fully seat a router bit, then pull it back up out of the collet approximately 1/8" or so to prevent the bit from pulling out some during heavy use. Some anal types put 1/8" diameter O-rings on the shanks (seated down low next to the upper end of the cutter edge) of their bits to automatically account for the recommended 1/8" lift. I don't use anything when edge joining individual pieces to create a panel, but some folks do more for better face alignment of the boards rather than for extra strength. Your call.

[Lee Schierer]

Others have told you how to fix the off center problem. Here's a suggestion for before assembly. Remove the sharp corners from your tongues with a small hand plane. Just a slight chamfer. This will do two things. First it will allow your tongues to bottom out in your grooves. It will also relieve some of the hydraulic pressure from places where there is excess glue allowing it to move out of the joint a bit.

[Rod Sheridan]

Mark, if I understand you correctly, you're using tongue and groove joinery to glue up 3 boards to make a wide panel?

If so just glue them together, making sure you align the surfaces, there is no reason to use any joint, biscuits or dowels on a panel glue up.

As for routers, don't own one or use one however it sounds like the bit slipped in the collet.

Regards, Rod.

[Andrew Gibson]

Nothing wrong with tongue and groove. The easy fix is to add a strip of material to glue a strip to the over cut tongue and route it again.
A little trick I like to use with the router table is to drop a spaceball down into the bottom of the collet to keep the router bit from bottoming out. If you don't have any spaceballs handy for making raised panel doors, an O-ring will also do the trick, then you can drop the bit in and tighten without worrying about the bit bottoming out.

It sounds like when you are done you will have a bomb proof computer cart.

[Mark Cook]

Thanks to everyone for the advice. I glued an oak shim the length of the over-cut tongue and re-routered it. It looks like it'll work just fine now. FYI, I did have about 3/16" of margin on the bit shaft (above the collet) before the error occurred. I'm fairly certain now that I simply didn't tighten the collet nut sufficiently. I'll be sure that doesn't happen again!

[Lee Schierer]

I'll be sure that doesn't happen again!

I usually route a scrap piece before cutting the finish pieces and recheck the tightness of the nut.

[pat warner]

Was it a spiral cutter?

[Doug Hepler]

Mark

It's good that you could correct the mistake. Now, how to prevent the bit from coming out of the collet. Others have advised not to bottom out the bit. That's good advice. You said that you had allowed clearance, so that probably was not the cause. After that, I believe that feeding the work too aggressively can cause the router bit to vibrate, which exacerbates any other problem such as a bit of oil on the shank of the bit or on the inside of the collet, using a spiral bit, or not tightening the collet sufficiently. This is especially true for 1/4" shanks.

I have ruined a few cuts despite my efforts to tighten the collet sufficiently, when cutting too aggressively using a bit with a 1/4" shank. (It was with a trim router that had a spindle lock instead of a collet requiring two wrenches.) Vibration can, over time, also cause a 1/4" shank to break, which is dangerous. Listen to the sound of the cutter in the wood. If you hear a "zing" it might be from vibration. I greatly prefer 1/2" shanks for this reason.

I hope this is useful

Doug

[mreza Salav]

Pat has a valid point too.
Be extra careful with spiral cutters and take light passes. They are full of surprises...