It seems every time I use one of these bits it burns a lot, and gets dull easy. Any suggestions? Maybe speed? I can get my lathe down to 800 rpm but have been drilling about 1500. I get the same thing in a drill press. The bit seems to cut ok for maybe 2 or 3 holes, then it starts to burn.
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Forstner Drills
- Thread starter LANKFORD
- Start date
...and I thought I was way too fast with my lathe at 600 rpm. It does the same burning thing at 600. My next Forstner bits will be carbide.
Hopefully by then I'll have added an index hole to slow my lathe to 300 rpm.
Stoppy
Hopefully by then I'll have added an index hole to slow my lathe to 300 rpm.
Stoppy
Richard Baker
RIP
If you're drilling hardwoods, that's way too fast. A sheet in the Delta drill press owners' manual has the following for hardwoods: 1/4"--3/8", 700 rpm, 1/2"--1", 500 rpm, 1-1/8"--2", 250 rpm. Much faster is ok for drilling soft pine.
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- Leopold Victoria Australia
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- www.cwsonline.com.au
Forstner bits are made to be run at very slow speeds. ie 150rpm or a little bit more.
You have a large cutting surface which has to be allowed to cut if the speed is too high it just glazes over the top of the hole and generates heat and blunts the bit.
They are easily resharpened on the front face of the cutter with a flat file and if it is the sawtooth type you can use a triangle file to resharpen the teeth.
The forstner type are a little harder to do but I run a diamond lap around the outside and use a small stone in my dremel to touch up the internal part.
There is different qualities of these bits ranging from the general purpose chinese variety to the German stubia and you do get what you pay for. Most guys get away with the cheaper variety but if you find you are using a certain size a lot I would reccomend getting one of the better ones as they hold there edge a lot longer.
Like all drill bits there is optimum working speeds. Small is fast and as you go bigger you go slower.
You have a large cutting surface which has to be allowed to cut if the speed is too high it just glazes over the top of the hole and generates heat and blunts the bit.
They are easily resharpened on the front face of the cutter with a flat file and if it is the sawtooth type you can use a triangle file to resharpen the teeth.
The forstner type are a little harder to do but I run a diamond lap around the outside and use a small stone in my dremel to touch up the internal part.
There is different qualities of these bits ranging from the general purpose chinese variety to the German stubia and you do get what you pay for. Most guys get away with the cheaper variety but if you find you are using a certain size a lot I would reccomend getting one of the better ones as they hold there edge a lot longer.
Like all drill bits there is optimum working speeds. Small is fast and as you go bigger you go slower.
2 Suggestions
1. Before you sharpen, clean your bit(s). Because of their wide surface contact area, Forstner's tend to load up on pitch, lignin and sugars quite easily. Even if you sharpen, the sticky film will smoke and drag in the hole. A little oven cleaner takes it right off, then water rinse and dry.
2. Consider using a spade bit instead. "They wander and don't cut straight," she said. Ah, all too true when the bit's off center. "Huh?" he said. If you carefully examine the grind and wings on many such bits, you'll find a number are not ground properly (even fresh from the factory) with the cutting wings a) with 1 spur point longer than the other, b) with one side at a different angle from the centerline, c) one side longer than the other putting the point and shaft off center in the hole, d) , one side sharper than the other, e) all of the above, any one of which will cause the bit to "wander as you wonder."
If you regrind a bit (part pun) the tool will cut straight without the hassels you have with forstners.
m
1. Before you sharpen, clean your bit(s). Because of their wide surface contact area, Forstner's tend to load up on pitch, lignin and sugars quite easily. Even if you sharpen, the sticky film will smoke and drag in the hole. A little oven cleaner takes it right off, then water rinse and dry.
2. Consider using a spade bit instead. "They wander and don't cut straight," she said. Ah, all too true when the bit's off center. "Huh?" he said. If you carefully examine the grind and wings on many such bits, you'll find a number are not ground properly (even fresh from the factory) with the cutting wings a) with 1 spur point longer than the other, b) with one side at a different angle from the centerline, c) one side longer than the other putting the point and shaft off center in the hole, d) , one side sharper than the other, e) all of the above, any one of which will cause the bit to "wander as you wonder."
If you regrind a bit (part pun) the tool will cut straight without the hassels you have with forstners.
m
The forstner has some advantages over the spade bit, It doesn't 'wander' like a spade bit; It doesn't have the long point at the center like a spade bit does.
I use forstner bits without problems. The slowest my lathe will turn is 450rpm.; really too fast for the forstner bits, but I take my time; dont hurry the cut-use light pressure feeding the bit; withdraw it freequently to allow for cooling and to clear the hole.
I use forstner bits without problems. The slowest my lathe will turn is 450rpm.; really too fast for the forstner bits, but I take my time; dont hurry the cut-use light pressure feeding the bit; withdraw it freequently to allow for cooling and to clear the hole.
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Since no one else has mentioned it I will, it helps to have a pilot hole already drilled. If you are trying to drill something like a box drilling a pilot hold and then two or three different forstners until you get the size whole you want also helps.
Well, how would a good quality Brad Point Wood Bit (center point and two side cuttting points) be in comparison. I'm thinking my most used would be 3/4" diameter and go about 3 to 5 inches deep. Would this type bit also wander a lot?
Richard Baker
RIP
So, relatively slow rpm. but pay attention to feed rate also. Too slow feed may be worse than too fast. Did a 2-1/8" hole at about 125 rpm tonight to start a candle holder. Nice smooth continuous ribbon from the hole and no problem. Cheapo chinese bit and only one side was cutting, but still got a nice clean hole. Feed rate.
Lankford, A good brad point should not wander in hardwood if the hole is started carefully and well centered. Delta suggests 250 rpm for a 3/4" brad point in hardwood. Retract frequently to clear chips for a hole 3"-5" deep.
Lankford, A good brad point should not wander in hardwood if the hole is started carefully and well centered. Delta suggests 250 rpm for a 3/4" brad point in hardwood. Retract frequently to clear chips for a hole 3"-5" deep.
Last edited:
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LANKFORD said:
In end grain it would go just fine. It would guide on the edges almost like a Forstner, which is really best, BTW, on cross-grain bores. It would also clear dust better with the deep flutes, though you'd be well-advised to draw it a few times to clear when boring deeper holes. Beats the daylights out of a spade bit, which is neither designed for end grain nor edge guided.
I've got a cheap Chinese set (5/8-1")I bought a number of years back for about 20 bucks. I keep a chainsaw file available to freshen them up, as they started with crummy steel, and have not improved with heat.
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I agree with michael a good brad point will get you several inches
According to anyone of the numerous Speed Charts you are going way to fast.
Various information on Speeds etc. can be found here
http://www.laymar-crafts.co.uk/links.htm
Richard
Various information on Speeds etc. can be found here
http://www.laymar-crafts.co.uk/links.htm
Richard
What strikes me funny, they make all these different drill bits, but generally all the drills, drill presses, lathes etc. are too fast to use most of them properly. And they don't tell you that when you buy the bits or the tools.
LANKFORD said:
Most every drill press I've used has had the capacity to change speeds, even if only by stepped pullies, to slow the bit down well below 500 rpm. Can't say the same for lathes.
m
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LANKFORD said:
Actually most lathes are designed so they fit somewhere in that mystical ideal range for turning speeds. Ideally if you multiply diameter of piece by the speed you get a number between 6000 and 9000, this is all well and good for a perfectly balanced piece, however engineers on their theoretical design doodle pad must assume that wood like their designs could never be full of holes or voids.
They also assume that if a turner is smart enough to buy the lathe they should be smart enough to read the directions and do the research on what is and isn't safe.
Engineers ? ?
OOOO, we've gone there before here, but,
Maybe they know about this place where Mr. Lankford, Naval Architect though he may be, could find out about bit speeds and such.
Crafty, dudes, those engineers. 😉
m
TurningDog said:
OOOO, we've gone there before here, but,
Maybe they know about this place where Mr. Lankford, Naval Architect though he may be, could find out about bit speeds and such.
Crafty, dudes, those engineers. 😉
m
TurningDog said:
Actually, if you divide 6000 and 9000 by the diameter of the work piece, you should get a speed range that MAY be safe.
I have 4 or 5 sets of forstner bits, 2 of them being carbide. I find I use them almost always (long as I have the corresponding size). For anything over about 1/2". I think they give a cleaner cut at the same speed as a hss unit.
Paul
Paul
The one thing I've found helpful in addition to feed rate and slower RPM is that I keep the bits clean and polish the outer diameter to a mirror (or so)finish on the bench buffer with polishing compound. My tid-bit for the day. And yes the larger bits do sharpen well. Hats off to anyone though who can put a new edge on a .25" forstner!! 😱