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Drilling Into End Grain
Question
Forum Responses
For accuracy I would use a brad point style bit. If accuracy is not important I would try a spade style bit. It can be reground to be more effective by grinding the cutting edges to a steep angle from the spur to the outside edge. Machinists also have a special type of step drill that bores a smaller diameter on the first end of the bit, followed by a diameter of the required finished size. The same principle can be employed by boring a hole to approximately .8125" with a brad point, and then with the same drill press setting, running a .875" twist drill bit into the hole. Machinists may even drill a .0625" hole carefully through their material and then let that small hole be a centering device for boring the larger hole. If you can control the speed, the old fashioned auger style bits are still made today and are used by electricians and plumbers. I have bought at least a hundred used ones over the years and they are easily sharpened with an auger file. Use caution as they have a threaded lead screw which pulls the bit through the cut like a screw. I would be very cautious about trying to use one in a drill press.
From contributor B: You might try a router bit used to cut mortise slots. You can get them to move chips up or down. From contributor C: I personally would go with a Forstner bit. That bit won’t break the 1/2 in. wall between the first holes. For clearing chips, I would drill in more than one shot. I wouldn't drill a smaller hole first. That removes the material necessary to keep the final bit centered by its point. Those bits may not reach 6 1/4 in. deep without using a shaft extension. From contributor D: Boring end grain material with a standard brad point drill with outlining spurs can be a problem because the spurs are not needed. The spurs drag in end grain. Modify the drill by grinding the spurs off following the existing back clearance. Then, regrind the cutting edge with a 7 to 15 degree angle from the od of the drill, tilting downwards to the point, again following the existing back clearance. This is called an acme cut. Now the brad point enters the material followed by the outlining od (where the spurs were), which sizes the hole without dragging. You will still require a 6-1/2 to 7" twist length to clear the chips. Use 1700 to 1725 RPM. One note - the modified drill will not work as well boring cross grain.
From contributor E: I have had good luck using my horizontal boring machine (doweling machine) with a bit from Nordic Inc. They have an amazing variety of drill bits. They have a great catalog. You may have to drill most of hole with the machine and finish by hand.
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