router burn!

[David Prince]

Question for the router pros. Probably basic questions, but I am not much of a router person.

I have routers, a router table, and a shaper. My question has to do with burning. I have not had any burning problems with my shaper. I do see some burning with the router.

Is the burning because of the speed of the router bits, the speed of my feed, or heating up of the router bit from use?

And if because of the speed issue, will decreasing the speed of the router a touch help with this?

Do you feel that better bits result in less burn? I can see cheap hss bits causing burn if they rub without a bearing.

Does anyone ever completely eliminate burn? And, certain woods are probably more prone to this.

[Steve Bracken]

Question for the router pros. Probably basic questions, but I am not much of a router person.

I have routers, a router table, and a shaper. My question has to do with burning. I have not had any burning problems with my shaper. I do see some burning with the router.

Is the burning because of the speed of the router bits, the speed of my feed, or heating up of the router bit from use?

And if because of the speed issue, will decreasing the speed of the router a touch help with this?

Do you feel that better bits result in less burn? I can see cheap hss bits causing burn if they rub without a bearing.

Does anyone ever completely eliminate burn? And, certain woods are probably more prone to this.

Router bits, esp. the small ones, are meant to run at those very high speeds and scorching is a real issue. It is more of a problem in very hard, light coloured wood like maple.

Burning is a function of feed rate, principally, so if you are getting scorch marks you are feeding too slowly. It takes some practise, and some confidence to move the router, or workpiece fast enough to cut cleanly. Clean, sharp bits will help.

Try a few test cuts, just putting a profile on the edge of some hard maple until you get the feel for it. It is possible to get burn free cuts, but you often have to rout at a feedrate that feels wrong, until practise shows you that it's right :D

[Dave Wagner]

Depends on the type of wood too.
I would think the sharpness and speed of feed. I usually don't have any problems as long as I go slow with either the router or shaper.

[Gerry Grzadzinski]

Feedrate and rpm work hand in hand. Increasing feedrate is the same as lowering rpm. Either will help to reduce or eliminate burning. Sharpness also plays a part. If the bit is dull, it can't be fed as fast, which leads to burning.

Also, the burning is not because of the bit being hot, it's friction between the bit and wood. In order for it to burn, the cutting edges need to repeatedly rub against the wood in the same spot.

While you can eliminate most burning with sharp bits and proper rpm and feedrates, you may still not be able to avoid it completely, as you may need to feed slower with delicate pieces or changing grain directions.

And yes, different woods make a difference. Cherry probably burns the easiest, but maple is right up there.

[Rick Fisher]

I have had success doing round overs in 2 passes.. First pass makes 95% of the cut, last cut is just a paper thin cut.. Its easier to keep the router moving with (for me) with minor cuts.

[Jerome Stanek]

You will want to make chips not sawdust. The chips will take the heat with them. slow the router speed and move the router faster.

[Bob Carreiro]

Ditto for Jerome's comments. Also, bit sharpness matters. MUCH heat is generated by dull bits, seperate or regrdless of of RPM/feed speed.

good luck, and happy woodworking,
Bob

[glenn bradley]

+1 on feed rate and bit speed as inseparable. If you don't have variable speed, there may be no safe rate fast enough to avoid burning with some wood/bit combinations. On things like cherry and maple, especially the end grain of woods like these, I feed quickly and consistently. I also leave the last 1/32" or 1/64" for a final "clean up" pass. Also, if burning occurs, I find that if I use a card scraper quickly, it cleans up easier and doesn't go very deep.

[Lee Schierer]

Not all router bits are created equal. I have found from experience that cheap router bits are not a good deal. They don't cut as well and leave more burn marks than the better quality higher priced bits. When I started buying router bits Craftsman was about the only game in town. Their HSS bits were okay but their performance improved greatly with a little hand honing. Their carbide bits weren't much better. I bought some blue and yellow colored store brand bits from woodworking stores and none have performed very well. I purchase some "Viper" bits at a wood show and they work better than craftsman. I bought a couple of Freud round over bits and what a difference. The wood came off as fine shavings and not a burn mark to be seen. Now any new router bits that come into my shop are red colored.

Cutter quality and lack of burning has to do with cutter sharpness and speed but is also highly dependent on cutting edge relief or the angle behind the cutting edge. The greater this angle the less burning you are likely to see, because there is less metal in contact with the wood.