Safety and Burn-Free Flutes

A long discussion about how to make flutes without burn marks at the end, and without injury. February 16, 2006

Any suggestions for getting rid of the burn marks in the end of my mahogany flutes? All the fluting was done with a brand new bit, however, a lot of the ends are burned.

Forum Responses
(Architectural Woodworking Forum)
From contributor F:
Grind yourself a scraper to the profile of your flute. I have a small triangular scraper with a handle that kicked around my toolbox for years unused until I thought of grinding a flute radius profile on one of its corners and using it to scrape out flute burns. If you don't have one of those, grind the corner of a card scraper to the radius you need. When it comes to burns, nothing gets past the damage like a burr scraper.

From contributor B:
The burning at the end is a result of friction/heat generated by the bit spinning and not moving along in the cut. Don't hang out in the corners and you might try plunging in and starting the run. Near the end, shut off the router for the last inch or so of cut. This slows the bit down enough not to burn. A variable speed would come in handy here also. The handheld routers run at about 22,000 rpms. That's a lot of speed.

From contributor R:
If it's the entry or exit, pare it out with a gouge. It's quicker and it won't bulb on you. Put a screw in a block of wood and grind the head sharp. Makes a quick scraper for the length.

From contributor K:
I have a set of drive punches for leather that I use to make small sanding disks in the size range of 5/8 to 2" out of the 6" adhesive back Norton stick and sand for random orbit sander. They work great in a small right angle die grinder. For a pad, I have sprayed the end of a little diamond wheel that is about the size of a dime on the end of a 1/8" arbor that I have sprayed with several coats of high-tack contact cement. The contact gives a little resilient pad to the rigid face of the disk and keeps the paper on better than it would on a normal rubber disk at these high rpm's. You have to peel right after use, or the high tack will cause the paper to tear down the middle. You might be able to use a Dremel, but I like the right-angle grinder better for control.

From contributor V:
Just get a quart or two of "burn" colored stain, and make the rest of it match. Just kidding. In the future, stop all flutes 1/2" or 1" short and finish them out by hand. When you start sanding and scraping, a little blending cushion won't hurt. Flutes don't look too good when they flare off crooked on the ends.

From contributor S:
The question you asked, "How do I get rid of burn marks?", has been answered with some good suggestions. But wouldn't you rather want to know "How do I stop burning the ends of my flutes?"

If you are using an off-the-shelf HSS core box bit, you can eliminate the burning by grinding away the heel on both wings up to as close as you dare to the actual cutting edge. The manufacturers never engineer enough, if any, clearance on these bits. Knowing how to fix mistakes in wood is a good thing; knowing how to not make those mistakes is even better.

From contributor O:
I just use my Dremel with a bit that matches the size of the flute. It's also great for matching up the ends of the flutes.

From contributor D:
Burning can be completely eliminated by fluting with a molder head for the tablesaw. Faster, safer, higher quality, nicer looking, burn free flutes every time.

From contributor G:
If you plan to use a scraper, a piece of hacksaw blade shaped to the flute works good - just grind it like a normal scraper.

From contributor E:
Re contributor D's solution: One of the worst accidents I have seen in the shop was from such a setup with dado/fluting head, and the piece kicking back and removing (obliterating) an index finger tip. These types of tooling are illegal in Europe due to their ability to make hamburger. There is no way to make them safe. Historically, these flutes, made properly, terminate in their own radius and don't wizzle out in a long tapered flute like the large diameter cutter head makes.

From contributor M:
I agree that it's much easier to not burn them in the first place, hence no need to repair. My method for doing this is with a router table set up with a fence that has marks on it showing where the core box cutter starts and where it ends. I'm moving the board forward as I drop the board down onto the bit. When it reaches the end, I immediately back the board up so as not to burn the end, then go back and do the starting end, working up to the other mark, then pulling the board back once it's reached so that it's not burned either. As was said, it's a lot easier if you don't have to repair it in the first place.

From contributor P:
I don't understand why all the trouble. I did 2000 2 long flutes perpendicular to the grain, yesterday. No burn, etc. I set up the router, and it took about an hour.

From contributor G:
Where do you get a blade for a table saw to do fluting? Sounds like a good idea to me. I can't see where you could get hurt doing fluting on a table saw any more than doing dados. I feel, with a good sharp blade and common sense, a table saw would be the safest
way to go. If you use a router, and get burns, then turn down the speed. Practice on a piece of scrap.

From contributor D:
The molder head I referred to is made by LRH. The RPM's of a table saw make for a very smooth, very tame operation, and the cutterhead is beneath the work piece. Furthermore, with a proper throat plate, only a tiny amount of cutterhead is actually penetrating above the surface of the tablesaw. Of all the woodworking operations done in a typical shop, this one has got to be one of the safest.

From contributor K:
So it would seem, however I have two good friends who thought the same thing with a dado head, who now have parts missing and badly mangled parts remaining. I guess it seems so safe that they just did a hand over hand walking motion, and never knew when the board disappeared. Whatever method of feed you use, never use a feeding force where the effort in your hands is directed into a cutter if the work should seize and kick out.

From contributor G:
Contributor K, I'm sorry, but I don't follow your train of thought. The way you describe it, it's unsafe to use a table saw, router, or shaper, no matter what you are doing. The cutters or blades are always going to tend to push the piece back at you.

From contributor K:
I know it seems safe enough, that you could turn your brain off and do the work on automatic pilot. There is so little cutter sticking above the table, that you just hour after hour stand there feeding the board by walking with your hands to feed the board across the cutter.

If you make the habit of feeding with the force of your hands directly over the cutter, eventually the board is likely to get off to the side, or maybe it is bowed up and gets too big of a bite with plenty of stock behind for it to take off on. The work will just disappear. If you are feeding with the force of your hands right at the cutter, I am sorry to say that your hands will also disappear.

Always try to feed with the pressure of your hands off to the side, or fore and aft. The two guys that I know that lost part of their hands said "I was doing it the way I always do. I have been doing it that way all of my life, and suddenly… Boom. I knew better. It just seemed so safe."

You can do the same job just as well and fast by letting the effort of your hands be to the side rather than into the cutter.

From contributor G:
I'm sorry, but I still don't follow your train of thought. Your mind can wander while using
a hand drill and drill a hole in your finger. Sounds like these guys were listening to the radio or something. If you decide to "turn your brain off," then you probably better turn the lights off and go home for the day.

From contributor L:
I disagree. Contributor K's point is basic: You establish a work process/habits that - when an accident happens - maximizes your chances of walking away unharmed. He isn't advocating inattention; he's suggesting that you hedge your bet.

From contributor E:
I am curious as to why people defend proven bad practice in the face of overwhelming evidence to the contrary. Or why one would choose to walk so close to the line as to present imminent danger, and not cut wide around such a process. This goes well beyond our chosen careers, but is a basic human trait that we all seem to have little understanding of. Old habits? Retirement portfolio in table saw molding head companies? Defensive/threatened just on general principles? Why would dado heads and table saw molding heads be banned in European Union countries? To make life difficult for their industries? If logic is to be questioned, it should be applied across the board (pun) and not to just one area.

From contributor D:
Am I hearing correctly? Dado heads should be banned? Molding heads should be banned? The molding head we use to cut flutes is so easy and so safe, you'd truly have to be an idiot to hurt yourself. Is there truly a cabinetmaker out there that feels dado heads are one of the more dangerous tools we use? How do you build anything? Do you clamp everything prior to every cut on your chop saw? Do you never push anything past the tablesaw freehanded? Have you never stood directly behind a planer, even for a second?

From contributor J:
Preventing burns at the end of flutes is done by using the right feed technique. No matter what machine you use, if you pause the cut, it will burn. You would be hard pressed to "have your hands disappear" with 1/2" diameter cutter sticking 1/4" out of the table saw. I can't take a moulding head for a table saw seriously - too few cutting edges (knives) per revolution, causing too many problems to list, way more weight on the arbor of your 10" saw than it was ever intended for, etc. As mentioned above, flutes should terminate in their own radius, sometimes flat at the bottom, so use a router, preferably a CNC.

From contributor D:
Actually, the molder head by LRH is no heavier than a typical saw blade. As for the lack of cutter heads, the flutes come out looking perfect, requiring very little sanding. I understand the issue of terminating in their own radius, but we do so many flutes, and I looked so long for a solution that when someone asks for a good method I feel obligated to tell them about it.

The tapered ends of our flutes have never been questioned by a client, designer, architect, or builder, and I've seen them offered by many very respected millworking companies. You get the same look by ramping with a CNC router. I'd much rather have a tapered looking flute than a piece of cut molding, which is the other typical way I've seen it done.
In the end, using the molder head is faster, safer, and provides a higher quality flute than any other method we've tried.

From contributor T:
Do it on the shaper. Grind your own profile using HSS slip knives. The small radius of the collars make a nice round entry and exit. Use a guide with a tall enough face, and attach temporary extended stops to the setup at each end. Begin a pass by resting the work piece end against the stop on the infeed side, hold the edge of the work down tight to the shaper table, and feed into the cutter gently till against the guide face tight. Then just feed through till you contact the stop on the outfeed side, being always conscious of where your hands will be, should the piece lurch. This is an old millwork standard procedure that I have done hundreds of times without a problem. The only time I've seen this go wrong was when someone tried to cowboy a cut by skipping the end stops. If there is even a little play available for the piece to back up, allowing the cutter to grab and climb, there will be catastrophic results.

If you plan properly by leaving some extra length on your work stock, you can do double runs on each piece by flipping end over and rerunning, then trim ends to final size. I save time and retain depth of cut by making a tick mark where the guide face and table meet on the infeed side, move the guide out, go to the next cutter setting, turn on the shaper and pivot the guide into the cutter until the tick mark shows and clamp. This way the guide opening is zero clearance so the cutter is less likely to tear out.

If you are not experienced enough, or simply cannot be comfortable with this or any machine setup, don't do it. Keep thinking about it and make whatever changes it takes to be sure all is safe. No deadline is as important as meat and bone. Like Dirty Harry said, "A man's got to know his limitations."

From contributor X:
The original question was what to do about the burned flutes. I would re-cut the burned part of the flute, or the whole thing slightly deeper, with a stop-block set to let the bit go past the previous cut 1/16", and maybe 1/16" deeper. By moving quickly, and pulling up and/or back (you could actually have a four-sided guide jig to keep the router from moving sideways), the cut would be cleaned up nicely. Don't allow the bit to stop moving at the end of the cut.

In the future, I would do fluting on a CNC machine, if you have one - there is never any chance of burning in a properly programmed cut. Maybe even jobbing this out next time would be cheaper and faster than doing it by hand.