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I'm having some issues with burn marks in the corners on maple when pattern routing. The bit is almost new and I know the feed rate needs to be fairly quick but the direction change always seems to leave some burn marks. I was considering changing routers to a variable speed (Milwaukee) and slowing it down a little bit to see if it helps. I know maple and cherry are notorious for burning but I'm tired of trying to scrape/sand burn marks out of corners.
Any thoughts from those of you who have done more pattern routing than I have?
Mike
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What brand of bits? How big? How much stock are you removing? Straight or profile?
Need more info.
Ed
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Pattern bit (top bearing) 1/2" shank straight cutting bit in maple. I usually drill out (forstner bit) the majority of the waste and route the edges against a pattern. Maple is 1 3/4" and I'm making an open topped box. As I say, most of the waste is gone so I'm just doing the inside profile of the box against a pattern. Bit is a 2 flute, 1 1/4" cutting depth but I take it in small bites.
Probably a lot more than you asked for, sorry.
Mike
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IME making a second pass that is very light is more effective than slowing down the bit
to me it seems you can negotiate the corner quicker
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Not sure from your description, but wood's more likely to char when you find endgrain. Guess it's because it doesn't cut/lift straightaway, but lays it over a bit and rubs. I cheat, using templates/collars/spiral bit. Where unable, my pattern bits have a bit of skew in the knives. Lowers the effective cutting angle. End grain likes a block plane, after all.
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Maple, cherry, and the Sapele I've been using frequently lately all like to burn. Lowering the speed seems to help, but taking a light final pass and never stopping moving the router seem more important.
John
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+1. I do a lot with cherry, and find that taking more passes to get to the final profile minimizes the burn.... rpm depends on the bit, going below the recommended rpm can have other consequences like tearout which I experienced when I first got into routers; nothing scientific, just what I recall.
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(07-17-2017, 10:31 PM)JGrout Wrote: IME making a second pass that is very light is more effective than slowing down the bit
to me it seems you can negotiate the corner quicker
Yes, do the majority of the work, saving just that light pass and you will finish smooth, and clean. Even on Cherry, of course if it is Soft Maple, they both have the same hardness, and most of the same working attributes, though IMO Cherry burns more readily.
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GW
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Yes, ABSOLUTELY it does. It is harder to test and control when hand routing, but with CNCs you control the feed speed and the rpm, so you can instantly see the results of slower rpm and higher feed.
Higher rpm means that the bit encounters the wood more often, increasing friction which generates heat. Either reducing the rpm, increasing the feed rate or both creates fewer contacts, larger chips, and those chips remove heat as they lily from the cutting area.
With a hand router, it is important to plan your cuts so that you do not pause anywhere. Keep the router moving steadily as fast as you can. If you need to pause in a corner or at the end of a cut, get into the habit of pulling the bit slightly away from the part. It only takes a fraction of a second's pause to cause burning.
