How to resolve off-center router cuts
I wanted to cut a 1/4″ grove down the middle of a length of a piece of stock. I didn’t measure the width of my stock before hand. I assumed it was 1.5″, but it was 1/8″ narrower than that from the yard. Anyway, in my ignorance, I set the position of a 1/4″ router bit to make a centered groove down the length of the board, using a height gauge set on its side against the fence. I checked it by eye. It looked a bit off, but who am I to criticize the accuracy of a device that can measure to 1/1000 of an inch? I made the cut.
Hey! It isn’t centered! D’oh! (Yes, yes, I know… The idiocy doesn’t stop there, though.)
Now, how to fix this problem? I first thought, well I can turn the piece around and cut the same groove from the other way. It will now be centered and a little too wide. I’ll cut the corresponding piece to match. Unfortunately, this violates the standard rule against climb cutting. Some articles here say you can do that to avoid tearout, and I’ve gotten away with it a few times before. I’m now pretty sure they were not advocating climb cutting a groove on a router table though! In this case, I am lucky to be (still) able to report this is not a good idea. It is neither good idea to climb cut a groove with the cutting surface away from the fence and a disasterously worse idea to do it with it toward the fence! (This was predicted, but being stupidly obstinate, I had to test…) Three broken router bits and quite a bit of flung wood later, I have become convinced fixing this on the table is probably not possible. Freud will get more of my money.
I ended up fixing it with a knife, straight edge and 1″ chisel and better yet, I got to keep my fingers. The results (in wood) were actually nicer than I expected. However, as always, I seek perfection.
What, dear reader, would you have done to correct the off center cut? And yes, the piece of wood probably cost $2. I had just spend all day milling it and its fellows and was reluctant to surrender the work.
Replies
Can't quite picture the part you are making, whether it shows in the final project, or why the groove would work if it was wider, but that said I think I would have milled a strip to fit in the off center grove, glued it in and reset the router to cut on the center. That would leave the groove with a thin strip of filler on the off center side. I would like to think I would have scrapped the part or done a trial cut on scrap or had cut an extra part just in case, but sometimes I don’t.
The Little Voice: Every time I have done something dangerous or dumb it is because I have ignored the little voice in the back of my head that says "something doesn't feel right about this." I’ve dodged the bullet a couple of times, still have all my fingers, and try to heed the little voice more. Good luck with the project.
measuring and marking
1. I usually measure and mark the end of the piece, so I can double-check the router table setup. Your tale of woe sounds like you forgot to subtract half the bit diameter when you set the distance to the fence.
2. Although I tend to be stingy with my wood, they say it's a good idea to cut a couple of "spares" at the milling stage. If one has a spare part, the logic goes, one is less tempted to "correct" a cut that is off when it is dangerous to do so.
3. Making test cuts on scrap pieces also allows for some fine-tuning of the setup.
Climb Cut
I would have gone with the climb cut but very slowly and only advancing the bit depth an 1/8th at a time.
For centering I like the marking gauge from both ends and when I push the work into the bit or blade I just nick the work - pull it back and see how it contacts my mark before running the length - if possible I rather use the table saw for 1/4 in. grove than a router bit.
SA
SA, there is no need to do a climb cut if the groove has already been formed, but found to be either off centre or not wide enough. You simply reverse the direction the router is either pushed or pulled so that what you execute is a normal cut. Slainte.
Climb
Rich -
He wanted to make it wider going in the opposite direction. I think that would have been OK
SA
do different?
Ah measure twice cut once. Simple phrase. To fix. I would either decide to go with a larger groove and adjust all others that need the groove, I would (if it were expensive) cut a larger goove fill it with a piece to match and recut it, or chuck it. It's just not worth saving most times. Buy extra stock for those necessary fubar's.
Yes, I was thinking last night that a climb cut, removing 1/8" or 1/16" with each pass might work. I was just trying to take off too much wood, which was probably the real mistake, among many.
I did account for the bit radius when measuring. I just assumed that the wood was 1.5" wide when in fact it was 11/8" so I ended up 1/16" off center. It was enough to be visible. However, since the cut doesn't show in the finished piece (at all!) what I really should have done is just adjust the position of the mating rabbet/tenon off center to compensate! I think the real lesson here is to put the part down when you make a mistake and think about it for a while. I am reaping the wages of inexperience.
The part is a middle leg in a cabinet like construction. The groove stops a few inches above the floor, which is why I didn't just turn the piece around and cut it straight-cut from the other end.
Doing a spare for practice cuts and such is good advice. I recall doing that on day 1, but seem to have forgotten about it along the way.
reaping the wages of inexperience
Most of us learn from our mistakes. That's a good thing as long as you end up with ten fingers and your eyesight. Next time if you are using expensive wood, mill some extra parts from scrap wood just for the trial cuts. FWW Taunton Press once published a book called Fixing Woodworking Mistakes, if I remember correctly. It had some neat tricks in it.
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