Calling All Router Experts

[Harvey Pascoe]

Here's my problem: I rout a 3" wide by 3/4" deep trough to create small trays using a 1" wide core box bit with multiple passes finishing up with a very light pass to minimize burning. About half the time I end up with no burning, other times a lot. The thing is, I can't figure out why I am successful part of the time but not others on various types of wood. This is done on a router table.

Question: Is there a way to get consitently burn-free cuts? I think I know the basics of routing but either I'm missing something or this is just wishful thinking?

Yes, I adjust the feed rate and avoid the router bogging. On the final pass taking 1/16" shouldn't be an issue. The one thing I haven't tried is changing the router speed. The bit is new.

[Jerome Stanek]

You have to move faster so the bit doesn't heat up. You should be able the hold the bit after you cut. You want to make wood chips not saw dust. the chips will carry the heat away

[Robert LaPlaca]

Also some woods are more prone to burning, Cherry and Maple come to mind immediately.. I will also agree. sometimes you can move too slow..

[pat warner]

Simply not possible to hand feed stock for an inside excavation on the router table and get perfect results. Too much risk, too much blind cutting, very little control, high demands on material prep, table/fence squareness & flatness.
Must be hand routed, indeed @~1/16-1/8/pass.
Moreover, an inside single diameter cutter pathway kills cutters faster than anything.
I'd bet yours has reached its half/life. Cut the thing to 90% with your dead cutter, switch to a new cutter for the finish cuts. Expect excellence.
(http://patwarner.com/images/prc508.jpg)

[Doug Morgan]

Speed of the feed, types of wood and amount taken on each pass are the major factors along with age, sharpness and type of the bit. Those are the big players on this field. If this is a plunge cut you should be raising the bit a little at a time (if you're using a router lift) lower a little at a time (if its a plunge router) and then take into your calculations the type of wood (maple will dull a bit fast) speed of feed and sometimes even the force at which you feed your wood at. Too big of cut with lots of force = firewood. Plunge cutting is more difficult because the bit is being used more than the normal >1/2.

[johnny means]

What type of bit are you using? Not all straight bits are designed for that type of operation. Your bit should have cutting edges across the bottom to the center and the body should stop shy of the edges. If you don't have a bit like this, it may be that the body of the bit does not have enough clearance at the bottom of your groove.

[Curt Harms]

I am certainly NOT an expert but I saw someone doing something similar. He removed most of the stock with a forstner bit then did the last bit with a router bit. Just another way to defur that feline.

[Doug Morgan]

I am certainly NOT an expert but I saw someone doing something similar. He removed most of the stock with a forstner bit then did the last bit with a router bit. Just another way to defur that feline.

Now that you mention it, I remember some show doing just that. Removing most of the wood with a forstner bit then cut the area to make it smooth using the router and finished with a chisel to clean up any areas necessary.

[Neil Brooks]

Am I thinking of your need wrong, or ... couldn't you do this on the TS, with a dado stack ?

[glenn bradley]

All good info here. Bear in mind that the center portion of such a profile has very little cutter-face speed and pretty much just spins like a drill. If you are getting narrow burn tracks, this can be your cause. Many surface "leveling" bits like dado clean-outs, bowl bits and the like to not have the cutting surface in the center portion. They rely on the leading or trailing outer edge to take care of that. If you are getting full (or nearly full) profile burning, touch up that bit. It is probably not razor sharp.

[Tom Esh]

...On the final pass taking 1/16" shouldn't be an issue. .
1/16 may well be too much if you've had burning. My finish passes are always < 1/64, often much less.

[Larry Edgerton]

If I have to use a core box bit I run a 1/4" or 3/8" straight bit on the same path first to get most of the material out of the center where you have a problem because of what Glen mentioned. The outside of the bit cuts just fine, so by doing it this way you can get it in two passes. I also agree with Pat that it is not a router table thing. You need to be "One with the router"

Larry

[Harvey Pascoe]

My bit is an ordinary radiused 1" core box and I've routed about 100 of these trays so far on the table. I agree, its risky should I mess up my cutting sequence. Only one mishap so far, very early on. As for good, straight, clean cuts, I made a special pusher jig to securely hold the workpiece, plus my table and fence are extra heavy duty, so really getting my shoulder into it is no problem. It usually goes well right up to the end where I get a "bump" due to the fence opening so I just make the piece an inch longer and cut it off.

The burning takes place primarily at the radius with only very slight burning at the center. I think this is because I take overlapping cuts.

The trays I machine are 12" long, too small for hand routing as I've got no way to hold the workpiece. Do you think I'd be better off routing them from a longer board by hand, say four feet, and then cutting them to size? Seems to me the bit would get awfully hot with passes that long. And frankly, I fail to see how I'd get better control by hand with a router with fence. Plus it seems that the numerous changes in setting the fence and depth on the hand held router would take more time, as it take only seconds to set the table fence, and less than a minute on the depth of cut.

I don't do enough of these that I'd want to set up a table saw dado, but what about making a few rips down the center of the work piece, would that ease the load on the router bit, or would it cause nasty chattering?

[Gene Howe]

In addition to using a Forstner first and taking light cuts with a sharp tool, I wet the wood with a damp sponge just before the final cut.

[pat warner]

Clearly you're a table routerer. Notwithstanding your time & skills at such, you and the work are at risk.
A spontaneous mis-feed, an accidental over-bite, a second's worth of hand control loss and it's curtains.
Hundreds of samples?? That cutter is dead; use it for the rough cuts.
Cut x hand? See sample (http://patwarner.com/images/eg_2688.jpg). And yes I'd harvest the work from a larger stick.
With an edge guide on both sides of the work, the risk to you and the work is lowered substantially.
Yep, you'll need to fixture. Hand work requires the work to be stabilized. Router work is jigs & fixtures (& so is all woodwork); they do squat without mechanical assistance.

[Harvey Pascoe]

I was not able to respond to all these great replies because my computer was down yesterday.

Because of the pushing jig I use there is no risk to my hands as they are not even close to the bit. It has the shape of a hand plane with a tall vertical handle. The side of the workpiece is held against the fence with another board by hand pressure.Should the bit catch, the workpiece will go flying past me. And I am on my third bit, the latest of which is new. Besides, all router table work is risky and frankly I fear the table saw more. That is why after 25 years I still have all my fingers. Good old fear.

I would like to be able to follow Pat's advice but unfortunately I cannot as circumstances do not permit.

That aside, I think I found the source of the burning. On the bit resin collects immediately at a point just at the bottom side terminus of the radius on each flute. I scrape it off and its right back again. The wood burning corresponds to these accumulations of resin (from cherry) It looks to me like there is something "off" about the geometry of that bit.The bit is producing fine chips and some dust.

I ran two pieces yesterday taking lighter passes and the result was improved. I could at least fairly easily sand out the burns.

I thank everyone for their thoughtful replies.

[Harvey Pascoe]

On thinking through this further I recalled that there are two basic types of mills. One is where the cutter moves over a stationary workpiece, the other the workpiece moves past a stationary cutter. Both are equally effective.

In order to minimize risk on the router table, which is the later type of milling, the workpiece must be securely held, which is what I was attempting to accomplish but only got part way there as my present jig is not beefy enough. I've had instances where the bit jammed in the wood and stopped the router because the workpiece cocked slightly. This is good because it demonstrates that the jig is strong enough to prevent the bit from throwing the wood and causing a serious accident.

So what I need to do is make my carriage jig heavier and somewhat larger so as to avoid any possible misalignment of the workpiece. This should solve the problem of both uneven cuts AND eliminate all risk. Does this make sense or am I missing something here?

[pat warner]

You're right about machining; you either move the tool or the work.
(& in some cases you move both!)
But in your case, in my view, your assumptions are misguided. Your table fixturing may be durable but you jam & burn stock; it's miracle you haven't been hit x a busted work piece. Moreover, with push sticks (proof you deem the operation risky), you've lost workpiece control. Dead cutters and lousy control are the reasons your results are variable.
If your work was powerfed, its depth of cut intimately controlled, & you had rock solid fixturing, you'd have it.
Surface grinders move the work and change the depth of cut precisely, as good as it gets.
Table routing does not have this facility. You need to see what's going on, change the depth incrementally (leaving a 1% cut for the finish pass), use sharp cutters, control the work with authority.
With router in hand and reasonable fixturing, there is little risk and far fewer problems. The cutting is faster, the chip gets the hell out of the way (otherwise trapped in your config.), the work immobilized, each pass controlled, visible; you can see trouble before you have an accident.
Hand routing is a transfer of problems alright, but it in the end, it is the solution.