Replies

1. 
   ring | Aug 01, 2005 03:50pm | #1

   Mark,

   No new router bits should be leaving burn marks, no matter what wood you're using.  I generally buy Amana, and have not seen a new bit do this at all.

   DR

1. 
   jazzdogg | Aug 01, 2005 08:35pm | #3

   "No new router bits should be leaving burn marks, no matter what wood you're using"

   Ring,

   I'm not sure your statement is absolutely accurate, even though it was expressed in rather absolute terms.

   I've experienced burning in cherry, and some other particularly resinous species, especially in end grain, even with brand new cutters (used at a variety of feed rates). This has been particularly true on inside corners, as when routing cathedral arches, when changing grain requires one to change direction of feed to prevent tearout.

   Not trying to pick a fight; just my observation over the last 30-odd years,

    

    -Jazzdogg-

   "Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie

1. 
   WillGeorge | Aug 01, 2005 10:28pm | #4

   especially in end grain, even with brand new cutters (used at a variety of feed rates). ..
   I agree for what that is worth..
   Even with NEW Whiteside bits I have had burning on more than one wood.Purpleheart will burn in a second if you stop for just moment.. Not every stick but many times.. Maybe just one side or end of a stick.. Other side/end will cut well...???White Oak.. Sometimes..
   Red Oak.. Hardly ever
   Ash/Hickory.. Sometimes...Bit speed does not seem to mater that much.. Feed rate the killer but sometimes you JUST HAVE to..Wood is very mysterious!

2. 
   philip | Aug 02, 2005 09:46am | #7

   Jazz, you are quite correct-some timbers are absolute turkeys with this problem-as well as cherry I can mention Zambesi Redwood (Baikiaea plurijuga)and Wenge.
   The problem can usually be overcome by taking a very fine final cut and not "hovering " in corners or towards the end of the cut. Variable speed routers are useful too.
   If the timber is not an abrasive one, and you are an oldtimer, you may just have a sharp high speed steel cutter.... which gives a better finish than carbide.

1. 
   mikegagne | Aug 03, 2005 07:07am | #20

   you are quite correct-some timbers are absolute turkeys with this problemDont ya just hate it when yer ebony burns like that? And you cant even sand it out!!;-)

3. 
   ring | Aug 02, 2005 02:00pm | #8

   Seems like nothing gets everyone's backs up like an absolute statement.  Well... for anyone willing to "hover around inside corners" just to prove the exception, don't bother.  I concede the possibility that one can burn some  wood species some of the time, but SPEAKING IN GENERAL a new bit should not burn. 

   Better?

   DR

1. 
   jazzdogg | Aug 02, 2005 08:24pm | #11

   "Better?"

   Ring,

   This time it was a misquote. Last time it was a false absolute statement. No, not better.

   "Seems like nothing gets everyone's backs up like an absolute statement"

   That's probably because absolute statements are so seldom accurate or absolutely true; too much hyperbole, not enough credibility.

   Sorry, but you asked,

    -Jazzdogg-

   "Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie

4. 
   mike4244 | Aug 04, 2005 12:17am | #25

   Chery will burn easily , I use a powerfeeder when milling cherry. This eliminates the burn marks from stop and start to advance the piece. If a person does experience burning, clean the profile with the same bit, take it out of the router and scrape like it was a scratch stock.Protect your fingers with a folded rag, the bits can cut you.

   mike

2. 
   nikkiwood | Aug 01, 2005 04:01pm | #2

   A new bit should be sharp, so I would try increasing your feed speed.

   ********************************************************
   "I tend to live in the past because most of my life is there."
   -- Herb Caen (1916-1997)

3. 
   Jellyrug | Aug 01, 2005 10:33pm | #5

   Increase the feed rate and the burn marks will go away.

4. 
   silver77 | Aug 02, 2005 02:14am | #6

   My hunch is you're trying to take too much off at once. Try 1-3 cuts and if you leave 1/16 to 1/32 as your final cut, it will help to reduce burn marks. 

   mo silver

5. 
   charlesm | Aug 02, 2005 02:17pm | #9

   Burning is usually the result of either a dull or gummed cutter or improper feed rate. With a new, clean bit the prime suspect is feeding (of course a bit without proper cutting angles or one that is just improperly ground can also be a factor). You should either try feeding faster as mentioned or slow the cutter. Reducing the RPMs is my recommendation since you will sometimes have to dawdle in tricky cuts and the slower speed allows more margin of error for the feed rate.

   Charles M

   Freud America, Inc.

1. 
   ram | Aug 02, 2005 08:50pm | #12

   Charles, thanks for another clearly explained principle.

   I have a variable speed 3 1/4 hp motor in my router table. I confess I have utterly no clue what speed to choose under what circumstances. Are there guidelines that cover many or (faint hope) even most circustances? Is "go slower when in doubt" a valid fallback?

1. 
   Samson | Aug 02, 2005 09:46pm | #13

   Good bit speed info:

   http://www.newwoodworker.com/rtrbitspds.html

    

1. 
   ram | Aug 03, 2005 12:04am | #14

   Nice link, thanks. I'd seen that before and forgot to bookmark it.

   I think it may be only part of the story, though ... what about "difficult" woods such as those discussed in this thread? Does slower by definition mean more likely to burn? How do you judge feed rate? The link's discussions make sense but don't go into those factors.

   Please excuse my newbie ignorance. Maybe I should sign up for one of routerman's classes ;-}.

1. 
   Samson | Aug 03, 2005 12:30am | #15

   I'm hardly a router expert compared to many of the folks around here, but I have used my router a good bit (pun intended) so FWIW my thoughts:

   what about "difficult" woods such as those discussed in this thread?

   In my experience, the species is what matters most as far as burning.  Dense and resinous stuff burns more easily.  Cherry is really easy to burn in my experience.  Others in the thread have given good advice:

   - Make some test runs on similar stock to get check your feed rate

   - Keep the router moving as best you can as pausing or altering the feed tends to be when burns happen.

   - Take most of the waste in incremental passes and then do a crisp final pass to get the last 1/32nd - with almost no resistance you can make a quicker cleaner pass with little risk of burn.

   Does slower by definition mean more likely to burn?

   I'm not sure what you mean by slower, but I'll assume RPM (as opposed to feed rate).  As the article discussed RPM does not translate linearly to cutter speed depending upon the bit.  At the end of the day, the trick is to find an RPM speed and feed rate that together give a smooth burn free cut.  If you think about why you get burns it may help - the blades get hot form friction under normal use and when you linger on an area the heat transfer burns the wood - also the blade can get abnormally hot when placed under the strain of removing too much wood in a single pass which causes even more friction and really heats up the cutter (ever rip 8 quarter cherry or maple on a 1.5 hp contractor saw? Even a minor pause in the feed rate can give you a burn no matter how well the fence is set) 

   How do you judge feed rate?

   Results from test cuts and experience.

2. 
   ram | Aug 03, 2005 01:16am | #16

   Samson, thanks again.

   I did mean feed rate as I agree the web article you gave seems a good treatment of bit speed and RPM. You covered my questions, much appreciated.

   Edited 8/2/2005 6:18 pm ET by ram

3. 
   charlesm | Aug 03, 2005 03:18pm | #22

   Samson,Your post is very good and pretty much on the mark.Burning is due to the cutter rubbing in the cut instead of cutting. If you can imagine the cutter at slow enough speed that you could see it working it might make it easier to envision. If each cutter wing is cutting an ideal size chip there will be very little friction. If the size of the chip is reduced by slowing the feed rate in relation to the cutter speed the friction increases proportionately. Conversely, if you feed faster the chip becomes too large and gullet loading will occur. I agree with multiple passes in terms of safety when a large amount of material is being removed but when a small amount is removed you are really causing premature wear to cutter (i.e. a 10' cut turns into 20', 30' or more). Sometimes the wood species dictates that a final light pass is required for a smoother finish but the real key to this "burning issue" is to lower the rotational speed and provide a larger margin of error for the feed rate.IME, the more prone the wood is to burning and/or splintering the slower the bit should be turning. You have to experiment with the wood you are using but 20% slower than the recommended RPMs is a good starting point. The resulting feed rate can sometimes be tediously slow but this is still faster than several multiple passes.
   Charles MFreud America, Inc.

   Edited 8/3/2005 8:18 am ET by CHARLES_MC

4. 
   Samson | Aug 03, 2005 04:32pm | #24

   I knew an expert would show up sooner or later!

   Thanks for the very detailed and (unlike mine) coherent explanation. 

   I love my Freud bits, by the way.

2. 
   jazzdogg | Aug 03, 2005 01:41am | #17

   Samson,

   Inspired by your post, I threw together a simple Excel spreadsheet to post in the workshop.

   I have attached a copy of you're interested.

    -Jazzdogg-

   "Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie

   
1. 
   Samson | Aug 03, 2005 02:44am | #18

   Thanks, very cool. 

   I'll post a copy near my router table.

2. 
   jazzdogg | Aug 03, 2005 08:04am | #21

   You're welcome. Glad you found it interesting.

    -Jazzdogg-

   "Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie

6. 
   forestgirl | Aug 02, 2005 07:22pm | #10

   Mark, see Charles' reply for sure, but also, please let us know what kind (or at least quality) bits you bought.  Bargain basement bits probably don't have the kind of shear angle built into them that help bits cut more efficiently.

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
   Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

7. 
   mikegagne | Aug 03, 2005 07:03am | #19

   Mark, if you have a speed controlled router, try that. Otherwise move either faster or slower and note the difference. Koa wood does that and amazingly, if I move the router faster than I normally would it does not heat the lignans in the wood and turn them black. Each species has its own point-and you get to find it. aloha, mike

8. 
   Dave45 | Aug 03, 2005 04:24pm | #23

   When I get burn marks, it's usually when I stop moving the router (or workpiece) while I change my stance, turn a corner, etc.  I can often reduce (or eliminate) the problem by making a "dry run" before I turn the router on.  The "dry run" shows me where I may have problems.  I'll often stop cutting before I get to a problem area, adjust my stance, then restart the router.