Woodworking: does speed matter with drill presses?

[Make Things]

For years I’ve seen the charts, heard that there are speeds that must be followed to ensure a good cut. Is there any truth to it? I did some experiments to check!

[Paul Alciatore]

While a clean hole is definitely a big concern, I fear you have missed other factors that also are influenced by the speed of a drill bit. I work with metal as well as wood. In fact, I work with many other materials. And all of these will, at one time or another, need to be cut and to have holes drilled in them.

Wood is fibrous: it has fibers. Those fibers will tear apart from each other more readily than the grains of a metal or the homogeneous structure of a plastic. So wood tools are run fast to deny the fibers the opportunity of tearing apart instead of being cut by the tool. This is much like the use of a machete to chop through dense vegetation. A swift stroke with the machete will cut cleanly through the grass and vines while a slower stroke would only nick them, pushing them aside a short distance, perhaps bending them, but leaving them mostly uncut.

On the other hand, when metal is cut there is a region where that metal actually flows. A tool that is cutting metal can cut at a wide range of speeds from slow to faster and the metal will still be cut. The surface finish may vary, but the metal will be separated in any case.

Heat is a factor when cutting something. Wood is a soft material which is easily cut. So a high cutting speed does not generate excessive heat and the use of a coolant is rarely needed. However because metals are generally harder, more energy will need to be extended when cutting them and, like in so many other physical processes, that energy will become heat. That heat will be generated at and near the actual cutting edge. Tools for cutting metal have evolved from simple tool steels to alloys like HSS (high speed steel), tungsten carbide, and even diamond. HSS is a steel alloy that is effected less by the high temperatures associated with the cutting of metals at higher speeds. Tungsten carbide is more so. Coolants are frequently used when cutting metal.

The life of the tool before resharpening is another factor. The heat as well as abrasion acts to wear away the sharp, cutting edge of all cutting tools. The amount of abrasion depends on the material being cut while the heat depends on that and on the linear speed of the cutting edge. Cutting metals will generate a lot of heat at slower speeds than when cutting wood but wood can also generate heat. All of us have seen wood become burned along the cut due to a dull blade.

All of these factors and more have gone into the published tables of speeds to be used when cutting different substances. These tables are ONE person's SUGGESTED cutting speed, not some kind of absolute rule that must be followed. Wood tools generally cut better when used at high speeds. But, a good wood plane which is properly sharpened is used at a very low speed and can produce some of the most perfect surface finishes in all of wood working. Each type of metal (steel, aluminum, brass, bronze, even different steel alloys) will have a different suggested cutting speed. For metal cutting these tables will lean in a compromise between tool life (between sharpenings), time needed for the cut, and factors like surface finish and quantity and size of burrs. Plastics often can be cut at higher speeds but some will generate too much heat and melt if the speed is too fast.

The point is these published tables are only a STARTING POINT for any particular cutting job. The wood worker, the machinist should take them as such and make any adjustments that are needed to obtain the desired outcome. And that outcome is not always just a clean cut.

[Make Things]

Thanks, Paul, I appreciate the feedback. I'm not disagreeing with anything you've mentioned. I agree wood tears. The answer I tried to prove in the video is that even at very slow speeds that end result can be achieved. I've done a million things with wood in the last 3 years with all sorts of exotic woods from around the world. It was actually about 4 years ago that I started working with metal and switched to the lowest speed because of the heat. Out of laziness, I never switched it back. What I found, in those 3 years (and you can go to both my Make Things video account as well as my Let's Make Things and see a lot of my exotic projects) is that at 300RPM's, I'm able to do everything that needs to be done.

To sum this up, I guess I'm not disagreeing with you to the nature of wood, I'm disagreeing with the speed needed. I've also shown that with a rusty bit with very little sharpness to it it can achieve the same results, if you allow the drill bit to cut instead of trying to wedge the bit into the wood as fast as you can. This is personal experience that I've dealt with, not some idea that I came up with a week ago.

Of course, maybe there's a little magic in my ridgid drill press that's not present in other drill presses, as this is the only large drill press I have ever owned.

I'm not suggesting that these manufactures are trying to rip us off. Maybe 50 years ago it was necessary to use these types of speeds due to the way drill bits were cut back then...but now, it hardly matters. I think a clean hole can be had easily at a minimum speed of 300RPM, so long as you're willing to let the press do its thing and the bit do its thing.

Thanks for responding!

[katy]

FWIW, I usually run my drill press at a slow speed, I don't know the RPM, just slow (moderate?). Also when turning stuff in the (metal) lathe I do it at a moderate speed, I've been criticized by a machinist friend for that doing that and I just say that I'm not in a hurry. I took machine shop at night school many, many years ago and I don't remember if the instructor talked about "proper" speeds or not.