Dealing with tearout - Woodworking Talk

thekctermite · 11-12-2008, 11:08 PM

I'm building a bed from African mahogany. Until now, everything has gone pretty well. I laminated a piece of 4/4 to a piece of 5/4, as I'm doing for all the stretchers on the footboard and headboard (the design of the bed is such that the glueline will not show).

Tonight I roughed out the curve for the bottom footboard stretcher on the bandsaw and then used a brand new 2" pattern bit in the router to follow a plywood template to remove the remaining 1/16-1/8". I went nice and slow but got some pretty ugly tearout when climbing the curve into the grain. There's some really freaky curly grain on the entire length of the 5/4 piece. The bit's edge grabbed pretty hard two times...One resulted in me tilting the router slightly, which put a little gouge in the wood...Nothing I can't get rid of with a card scraper and light chisel work. Plus, it is on the underside of the footboard near the floor.

In hindsight, flipping the workpiece and reversing the template would have worked quite nicely to avoid having to cut uphill into the grain.

So, tonight's events have me worried...
I have to plow a 3/4" wide x 1/2" deep dado on the top edge of this thing (the left side in the picture) into which the slats will go, and any tearout would be catastrophic. I've attached a picture of a similar bed I built a few years back to illustrate.

I'm looking for ideas on how to prevent the tearout, or at least big chunks of curly grain from popping out. I pretty much planned on using the stack dado to cut the groove with the board on edge. Now I'm thinking that I'm going to run a saw kerf to define the edges of the dado with the tablesaw before taking the stack set to it. Does that sound do-able? Or would I be better off with a router and a carbide spiral bit???

I'm open to any ideas anyone can offer! Sorry for the long-winded post.

thekctermite · 11-12-2008, 11:10 PM

The curly-grained piece is face down in the pics by the way.

Tony B · 11-13-2008, 09:14 AM

By the way: that was a great description. Most often there is not enough of description.
Anyway, I would go with the stacked dado over the router anyday. The rotating motion of a router would be more likely to tare out chunks then the different angle of attack you will get from the dado.
I'm not sure how much table saw kerfs will help, but they certainly couldn't hurt if all goes well. Anytime we add additional steps to a project, we are also introducing more chance of a screw-up.
I'm sure someone here will suggest using masking tape, I never have for a dado cut. If you do, make sure you put strips in different places so the board don't rock back and forth.
Personally, I think all will go well and I'm not just saying that for encouragement.

Do you have a any scraps with the curly grain in it where you can make a test cut and see how smooth it cuts? Sometimes in woodworking we just have to be wasteful.

BTW: As for your router jumping, you may want to change your technique and work backwards in VERY short strokes when 'climbing'. Its just a matter of practice and your router will tell you when you are doing it wrong.
Problem may also may be caused by a light weight router. I used to have a very heavy router - about 13 lbs - just for things like this.

mmwood_1 · 11-13-2008, 09:38 AM

I'm in agreement with Tony on this. The dado should do a fine job, as long as your blades are sharp. Definitely preferable over the router for this cut.

I had a similar problem with tear-out on some maple which I was cutting, using a pattern and router. I had to do exactly what you thought of, which was to flip the thing over for half of it and rout that half from the other direction. This entailed removing the pattern and replacing it on the opposite face of the wood, so I had to have very precise reference points for the placement of the pattern. It worked pretty well, but was slightly nerve-wracking. Also, I set my depth of cut at about 1/4" at a pass, and repeated passes until I got through the 2" maple.

bradnailer · 11-13-2008, 10:44 AM

If you know exactly where your dado will hit, then you could also take a sharp utility knife and scribe the wood about 1/8" deep which should eliminate the tear out.

dbhost · 11-13-2008, 10:54 AM

Scribe the line like the poster above stated, AND run your rabbet (Did I read that right, you wanted a rabbet right?) in multiple passes, nibble deeper each time until you reach your depth.

Never tried it with mahogany, but it works great for me on Quarter Sawn Red Oak. (And Pine, and Cedar...)

Al B Cuttn Wud · 11-13-2008, 11:31 PM

Just curious, what kind of pattern bit did you use? I do a lot of pattern cutting and quit using the blade style and only use the spiral style, either up cut or down cut depending on if I am using my table or free handing. The spiral bit isn't as violent as the bladed style. I still get a little tear out every now and then but very minimal that I have been able to sound out without noticing.

thekctermite · 11-14-2008, 05:14 PM

Quote:

Originally Posted by Al B Cuttn Wud

Just curious, what kind of pattern bit did you use? I do a lot of pattern cutting and quit using the blade style and only use the spiral style, either up cut or down cut depending on if I am using my table or free handing. The spiral bit isn't as violent as the bladed style. I still get a little tear out every now and then but very minimal that I have been able to sound out without noticing.

I went looking for a spiral pattern bit but couldn't find one long enough...Or any for that matter. I needed it ASAP, so settled for just a regular carbide tipped "straight" pattern bit 2" long.

I've decided that I'm too scared to use the router or the dado on cutting this dado to receive the vertical headboard and footboard slats. The piece is long, heavy, and the grain goes in all directions.

Soooooo,

This is a good excuse to buy a good self-centering doweling jig. I've decided that two dowels per slat (two top, two bottom) will be a very strong joint, and much less risky. Laying it out should be a breeze as well, but it could make for an interesting glue-up with all the slats I have to do.

Tony B · 11-14-2008, 05:37 PM

would be dowels. As a matter of fact, dowels wouldn't even be on the choice list. Thats an aweful lot of slats to line up. You will need forstner bits or other styles that wont wander in the end grain of the slats nor in the gnarley grain of the board. Unless you have the accuracy of really good machining equipment your next post will be......."If I wallow out the holes to get everything to fit together loosely so it can be assembled, what glue should I use?" the answer would be to get some earth powders and color your epoxy before assembly.
I hate to sound like the prophet of doom and I do wish you luck. It can be done, but with extreme care and a really good jig.

Tony B · 11-14-2008, 05:45 PM

Spend about a half of a day making a jig for your router that will allow you to make individual mortise holes for the slats. Then make tenons on the slats. If you have to adjust any of the tenons or mortise holes, the tenon shoulders will hide all of this.
This should ultimately be faster and easier than dowels.

thekctermite · 11-15-2008, 01:30 AM

Well, I got a really good quality self-centering dowel jig at Woodcraft ($60). I'm thrilled with the results I got on pieces of scrap. Using new brad point drill bits, I'm getting very clean holes. Two dowels at each end of each slat is going to do the trick...But yes, the glue-up is going to be a real challenge.