Replies

1. 
   SgianDubh | Dec 19, 2010 12:44pm | #1

   Slow down the peripheral rotatiing speed of the cutter (drill bit or router cutter), or increase the speed at which the tool passes along the cutting path, or both: but bear in mind that with the router you need to balance peripheral rotating speed of the cutter with tool travel speed to get a good and clean cut. Also, small diameter router cutters cut most effectively at high speed, ie, at about 22000 to 24000 rpm. This applies to pretty much all cutters under 25 mm (1") diameter. Greater than this diameter and you need to start reducing peripheral speed of the cutter to prevent burning.

   In using the pillar drill (drill press), you can't adjust the travel speed of the machine, you can only adjust the tool's peripheral speed. However, you sometimes need to adjust the rate at which you feed the drill bit into the wood to reduce or eliminate burning. Large diameter Forstner bits will burn if they aren't advanced into the work swiftly enough, or the peripheral speed of the bit is too fast, or both. Slainte.

1. 
   esc | Dec 19, 2010 01:41pm | #2

   Ok thanks. I actually thougth the opposite, that is I need to push slower on the drill press. I will try what you say and see what happens. By the way my drill and router bits are 16 mm for my job.

   Thanks Enrico

1. 
   SgianDubh | Dec 19, 2010 05:55pm | #3

   Sometimes with large diameter drill bits, if you don't keep them penetrating into the work at a steady rate they just rotate in the existing hole and the wall of metal around the circumference will burn the wood. This is particularly the case with Forstner type bits. If they are dull the burning is even more likely because the bit won't shear fibres efficiently at the bottom of the hole to create a route for the rest of the bit following behind. Slainte.

2. 
   DonStephan | Dec 19, 2010 08:14pm | #4

   Somtimes I get burning in cherry.  I've been told that resin buildup on the cutting edge and a dull cutting edge will both produce burning, in addition to a bad feed rate.

1. 
   SgianDubh | Dec 20, 2010 03:35am | #5

   Don, some wood species are particularly prone to burning. Maple is one and cherry another, but there are more whose names escape me right now, but will no doubt spring to mind after I've finished typing. Maple, for instance, often has a high sugar content, and we all know what happens to sugar when you put some in a pan on the cooker ring and heat it up... don't we? Slainte.

1. 
   joinerswork | Dec 20, 2010 12:19pm | #7

   Richard,

   The little bit of purpleheart I've worked was very prone to scorching, whether due to high sugar or just plain cussedness (I suspect the latter) I don't know.

   Re: maple's sugar content, I was reminded of a cartoon I saw a long tome ago, from a trade journal, in which a shop owner is on the phone to his lumber supplier: "Well,I won't say that that last 1000 feet of maple you sent me was green, but we ended up with 800 feet of lumber, and 20 gallons of syrup!"

   Happy Boxing Day,

   Ray

1. 
   SgianDubh | Dec 20, 2010 03:17pm | #8

   Ha, ha Ray.

3. 
   swenson | Dec 20, 2010 10:14am | #6

   When I try to go to full depth in one pass with a Forstner bit I get burning.  I like to go down in stages, raising the bit to clear chips and then lowering for more cutting.  This is for deeper holes of course.  Shallow holes don't need this.  If a lot of holes are being done at once, the bit heats up quite fast.  I work mostly with cherry and usually make multiple passes on the router table with the router at slow speeds and when the cherry is splintering I even climb cut for the final pass.

4. 
   roc | Dec 21, 2010 12:58am | #9

   Sharpen (and a bit o' candle wax)

   I work purple heart to the max and never have any burning problems.  Yah right.

   I find VERY OFTEN that even quality drills for wood are poorly sharpened.  Often the cutting edge can not get fully engaged in the cut because there is not enough clearance behind the cutting edge; stuff like that.  Just rubs and gets hot.  Gets hot and swells.  Swells and gets hotter.  Like that.

   Very frustrating when I pay decent money for a good bit and still have to sharpen the forstner or brad point bit before it cuts right.

   So . . . study bit sharpening, buy diamond sharpening hand files, not that expensive if you shop around.  If you don't shop around you may get your lips ripped off.

   You have had some great advice and I agree with the speed of cutter and speed of travel recommendations.

   The only thing I would add is use some candle wax.  Let the bit get warm and touch the candle to the cutter every once in a while.  IF IT IS SQUEALING IT IS SAYING "WAX ME".

   The stuff that makes purple heart burn seems to be a tar like resin.

   In the pics I added here you will see a brad point bit and an extension I made for it to drill all the way cross ways through my solid purple heart work bench for the all thread to tie the shoulder vise to the main body of the bench.  I used up about all the length and drilled through no problem.  Note the wax still on the bit and extension.

   Sharp bit

   Wax

   Kept clearing the wood chips.