drill presses...morse tapers...lateral forces?

[gerhard]

To underline Brisbanefitter's point how subtle this fitting system is, i found a worthwhile description in Wikipedia, called "Machine taper". I extracted some pics and a dimension diagram from that article. The taper angle is less than 1.5 degree, measured from heartline to side and less than 3 degrees in total (measured from left to right side). That is very little and the entire grip and torque transfer is a result of friction between the outer and inner cone surfaces. It doesn't take much dirt or unevenness between those surfaces to loosen this grip. As a comparison, the only slightly less tapered B12 or B16 cones for fitting chucks, will be much harder to pry loose. It may even take heating or freezing or brute force to separate B-type inner and outer-cones after years of service.

So the Morse-type was designed as a compromise between high torque transfer , easy fitting and good centricity, combined with easy removal without excessive force. There are also MC- or MT- outer cones with partly recessed surfaces, as shown in the left upper pic. I never quite understood why this is done. Maybe to achieve yet easier loosening, or does anyone know a better reason?

Brisbane also pointed out that there is never a certainty that a morse taper will not get unstuck when subjected to lateral load. Indeed the moment that it happens can be a surprise. It happened to me even in quality machines like a Metabo/Flott drill press (immaculately finished inside taper and very good steel) and in a large handheld Eibenstock 32 mm drill (MT3!). Bits or chuck adapter shanks fell out now and then even when i thought i had fitted them well.

But it is possible to minimise those occasions. I've stored my MT drill bits for some time now in a purpousmade box, where they are arranged side by side like colour crayons. No banging them on top of each other in some tool chest compartment, but keeping them utterly clean and rustproof and scratch- or dentfree. I oil them lightly like sawblades and wipe them dry prior to use. I also clean the machine's inner taper (this is often forgotten). Since then dropping out or loosening happens only seldomly. There is also the issue of choice for quality manufacturing of all the components involved, but apart from that there is little else you can do.

greetings

gerhard

[gerhard]

correction: a large part of torque transfer is achieved by the flat tang, of course, and not entirely by surface friction. I didn't reread my text before uploading, sorry about that!