What causes Router Burn Marks?

[Chris Tsutsui]

I have a Ryobi 1/4" radius roundover bit in a router table that was burning the round part in the corners of a maple end grain butcher block. Only in the corners...

This never happened with my other 1/4" radius bits so I'm wondering if the Ryobi bits are just not that good?

I did move the bit slower around the corners because I'm afraid of chipout. Are there any secrets because having to hand sand the corners is something i'd like to avoid in the future.

[Todd Burch]

Burns are from heat. Heat is from friction. Friction is from dull cutting edges or too much pressure or moving too slow.

[Chris Padilla]

Uh, yeah, what Todd said. Typically, I think, it is from moving too slowly and letting the cutter slice too many times in one spot but certainly, dull blades burn just as nicely. :)

[Darrin Davis]

Carbide bits don't burn like high speed steel bits.

[Tom Hintz]

Cheap bits, dull bits, dirty bits and moving even good bits too slowly can all cause burning. Using good quality, sharp bits, keeping them clean and learning to keep the router moving all help. The speed thing takes some practice but isn't that tough once you get the hang o fit.

[Bill Huber]

Maple will burn really easy and so will some of the other hardwoods. Purpleheart will burn if you just blink your eye.

As has been stated the speed is one of the big things, you can take a brand new bit and it will still burn if you go to slow. There are times like going around a corner it is just really hard not to slow down and that's when you will get the burn.

About all you can do then is sand it off.

[Joe Jensen]

If your sharp bit is burning, reset to cut shallower and do more passes. To keep some woods from burning you have to move the router pretty quickly. You can get good clean cuts as long as you are not trying to remove too much material at once. I like to always have a 1/32" or so "cleanup cut" when routing.

With the shaper and feeder I've never burned, not sure why, maybe the larger cutter cools enough? Anyone here ever burned woodwith a shaper and sharp cutter?

[Chip Lindley]

Besides moving the router too slowly, pitch build-up on a bit causes burning also. Clean the bit frequently with one of the *many* solvents mentioned in these threads. Take care to keep the solvent away from the ball bearing!! A touch-up with a diamond grit stone (equal strokes on each edge) keeps a fresh edge on bits!

[Chris Tsutsui]

This was on a brand new bit right out of the cheap set so it wasn't dull or dirty.

I guess I have to experiment with speed in cutting corners because I've had chip-out before and personally I'd rather have some burn marks to sand off than a chunk of wood get broken off and lost... heh

If I move the bit too fast the roundover part feels more rough from tear-out, so I am doing 21K rpm on a 3-1/4hp PC router moving at a rate of about 2 inches per second on the sides, though much slower than that on the corners.

Am I supposed to go around an edge in a single motion? It's not like i can route the entire perimeter of the panel at once, so I do one side at a time and I overlap at the corners. Now that I think about it, that's probably what's causing the burning is starting and stopping on the corners slowly... :D

Should I be overlapping the router strokes on a straight edge?

[Paul Atkins]

Another reason - not enough back grind on the bit.

[Joe Jensen]

Chip,
I would do a roundover in 2 passes on wood that doesn't burn easily, and 2 or 3 passes on one that does. I rarely have chipout problems when take a very light cut (final pass).

What wood was it? Cheap bits could cut badly even when new. I haven't bought any cheap carbide bits in 15 years so they may have improved, but I swore them off 15 years ago.

[Myk Rian]

I don't run the router at high speed, even for small bits. No need to. High speed makes more friction and that burns. Slow it down and move the stock faster.

[Bill Huber]

If I move the bit too fast the roundover part feels more rough from tear-out, so I am doing 21K rpm on a 3-1/4hp PC router moving at a rate of about 2 inches per second on the sides, though much slower than that on the corners.



That I think is one of the problems, slow the router down and I think you will have much better results.

[Clifford Mescher]

I like to hog out most of the wood with conventional passes and finish it up with a final climbing pass. Clifford.

[Chris Tsutsui]

Those are some good ideas. I like the multiple pass ideas. Should be easy and convenient with a router lift, I don't know why I was lazy to try and just do everything in one pass. I guess I thought it was just a small 1/4" roundover so no need for more than one pass.

One thing I learned is never route anything that has a hair line crack in it. The high speed bit and vibrations can catch on that crack and cause it to chip. :rolleyes:

[Brian Peters]

Ryobi and all those borg router bits are junk. Carbide on the label doesn't necessarily mean good carbide if at all. I would say burning comes almost always from dull bits or cheap cutters or pausing and rubbing the cutter up against the same area for more than a few seconds. Buy better bits though, Amana, Whiteside sell some of the best.

[Chris Tsutsui]

The Ryobi set was $40 for 20 router bits at the Borg, so I knew they were going to be "cheap" bits, but I also didn't know what bits I would use the most.

I am looking at getting the whiteside roundover bit set and pattern straight bit. Those are the two I use the most.

Holbren had a sale a while back where their 3/4" whiteside straight pattern bit was only $27, but now it's back up to $33 or so.

My collection of brands is Ryobi, Woodriver, Bosch, Dewalt and Holbren's $2 dado bits. I like the woodriver bits better than Ryobi and can't wait to try whiteside.

Will have to hold off for a while though and make do with the cheapo bits I have due to $$$ reasons. :)

[Justin Holt]

chris,
to avoid the chipout, why dont you just rout the end grain first, then rout the sides? This will cut away any chipout you might have from routing the end grain. Also, I've read where you can use a small plane to remove burn marks. This might be better than sanding, which can tend to round over crisp edges. Havent tried it yet, but I'm about to. I just burned some curly maple! :( First time working with it and I didnt know it burned so easily.

[Cliff Rohrabacher]

Burns are from heat. Heat is from friction. Friction is from dull cutting edges or too much pressure or moving too slow.

or too high a cutter speed or any of the above.

Try slowing the cutter speed, or taking a lighter pass or increasing your feed rate.

If none of that helps toss the cutter in the trash and get a new one.

[Bob Genovesi]

Most of the time it's caused by moving the cutter too slow therefore increasing friction and burning the wood.