Flush trimming against the grain, best technique?

[Michael Drew]

I just had a piece of hickory jump on me while attempting to follow a patten with a flush trim bit on my router table. I'm wondering what might be a better way to accomplish what I'm trying to do.

I'm building a shelving unit that's going to be a spice rack for a friend. It's all 3/4" and 1/2" hickory. The shelves are 1/2" thick about 10" wide by 5" deep and they fit into the verticals with sliding dovetails. I wanted to put a small 3/4" X 1/2" lip on the leading edge of the shelves to keep the little jars somewhat secured. This isn't a big deal for most of the shelves, but the center shelves are radiused to give the cabinet a unique look. I planned to just cut the lip pieces and glue them to the shelves and this works fine for the straight shelves, but not so simple for the curved shelves.

I figured I'd make a curved template the same size as the required lip pieces to match the radius of the shelves, then rough cut the little trim pieces with the band saw, then stick them to the template with some double sided tape and flush trim them on the router table. This has proven to be a not-so-brilliant idea. As soon as the bit starts to cut against the grain, it grabs the piece and wants to send it across the room. I've been thoroughly spooked. I was using good rubber souled push blocks, safety glasses, was standing away from the projectile zone but still, I got the the piss scared out of me. I've tried sneaking up on it, and going with a smaller, 1/4" bit, but that didn't work either. I have a few of these to make and didn't really want to have to change from a bottom bearing bit to the top bearing bit on every board, which would allow me to flip the pieces over and go with the grain. I'm not coming up with a better idea that this though. Figured I'd ask you guys how you would do this. I do not have any spiral bits, and have not ever used them. Would they be better suited for this type of cutting??

[Neil Brooks]

Would you be comfortable with climb-cutting (http://www.newwoodworker.com/clmbcuttng.html) it -- feeding the stock in the other direction ??

[Bas Pluim]

There are flush trim bits that have two bearings, one on top and one on the bottom, like the Freud 50-509. You'd still have to change the bit height when flipping the piece, but that doesn't take too long.

http://ecx.images-amazon.com/images/I/31FG7Y693ML._SL500_AA300_.jpg
And yes, I share your apprehension of flush trimming small pieces against the grain. Scary stuff...

[Kent Chasson]

Climb cutting could work if you can do it safely.

A spiral bit would be a major improvement but they are hard to find as pattern bits with a bearing. I have one that is essentially a helical power plane cutter with a bearing guide. It's perfect for stuff like this but it's expensive, big, and scary all by itself.

Have you considered bending, either steam or cold bent laminations?

[pat warner]

Forget the tape, the worst of all clamps in the hold-down manual.
Use real clamps, pins, fences and stops. After that consider a plunger, collar and sharp straight bit. With this ensemble you can climb/anticlimb cut through, all sorts or grain, provided you stage cut.
There is always some modest depth of cut that will not tearout whether you rout CC or CCW. May take longer but, alas, the price to pay for success.

[Michael Drew]

It doesn't seam to make much of a difference if I climb cut or not. The curve on the board is too aggressive I think, which is why I can't bend the wood either. I wasn't expecting such a violent reaction as I've done similar flush trimming several times before and it cut smoothly as long as I had the piece firmly held and took my time.

I think I know the answer, and that's to just swap bits and flip the piece.

Good to hear the spiral bit might work better. I have a list going right now for additional bits.

Good excuse to take a break and put the Christmas tree together. I can't even look at that router table now without thinking of blood and lost appendages. I should probably change my shorts too.

[David Cefai]

I think that what would work is "bump cutting".

Charles O'Neil has a video on it but essentially it works like this.

When you came to the problem area move your bit away from the wood. Then approach the wood at 90 degrees, take a bite out of it and move away.

Repeat along the length of the piece so that now you have what looks like a sawtooth edge.

Now revert to routing along the template. Since you've broken up the work into little pieces the bit does not have the chance to grab the work.

[glenn bradley]

Bas has the answer I use. I always route downhill whenever possible. The top/bottom bearing pattern bit make this possible in most situations. I the styles I enjoy there are often symmetrical arches and such so without the top/bottom bearing bit I would be in your situation very, very frequently ;-)

[Michael Drew]

Bas has the answer I use. I always route downhill whenever possible. The top/bottom bearing pattern bit make this possible in most situations. I the styles I enjoy there are often symmetrical arches and such so without the top/bottom bearing bit I would be in your situation very, very frequently ;-)


Ya, I agree. I'm shopping for some bits now. I have always wondered just what the heck I'd ever need a top / bottom bearing bit for and never thought to buy one. Now I know.... I suppose the old saying about "never can have enough clamps" also tends to be true with router bits as well.

The 'bumping' technique has been tried too. Damn thing 'bumped' right back at me, violently.