|Morse Taper #6 to 5|
|MT6 Morse Taper live center|
|Live Center MT6|
If you do any work with machine tools, you will learn about tapers. There as several sizes of them and a variety of types. Morse invented the twist drill during the civil war, and quickly learned of the need to be able to hold the drill true. A unique feature of the twist drill is that it is self aligning. It really want's to drill true, but it needs to be set true. A taper fit is the natural way to join two pieces of steel and have them true to one another. The challenge is figure out the right amount of taper, and of course the male and female mating parts must be of the same taper. Morse defined a taper of approximately 5/8's of an inch to the lineal foot as a suitable taper because it will generally jam together, and 'stick' tightly enough to transmit the needed power for drilling.
Ultimately 8 sizes of Morse Tapers were defined as national standards. While the exact taper varies a little for each one, all adhere roughly to the 5/8's inch per foot taper specification. These are the measurements in inches of the 'big end' of the taper. If you are looking at the female end, this will be the diameter of the hole.
Other tapers include Brown and Sharpe, Jacobs, Jarno. The Jacobs taper can be the most confusing because It is also used for drilling. Generally you will encounter the Jacobs taper in mounting drill chucks to arbors. Many drill presses have a Morse taper in the end of the spindle, and if you want to use a jawed Jacobs chuck for holding straight shank bits (typically smaller sizes), this is often accomplished by means of an arbor with a male Morse taper on one end (to fit the drill press spindle) and a male Jacobs chuck taper on the other end to match the selected chuck. The crucial thing is to not mix up the numbers, because a Jacobs 6 and a Morse 6 are not the same.
For most modertely heavy work you will see and most commonly encounter the MT#5. It is the norm on drill bits up to 3" in diameter, and is a standard found in tail stocks of many larger lathes. Indeed all three of my larger (but older) lathes have a MT #5 in the tail stock and a MT#6 in the headstock. The larger size in the headstock is for convenience to providing a larger spindle hole than would be permitted by the #5. What I have shown in the first frame is an extension adapter that is #5 on the male end and MT #6 on the female end. Use of this adapter will allow MT #6 tooling to be installed on the Radial arm drills that have a #5 spindle hole, and also on the tailstock of lathes with a MT#5 compatibility. One thig to remember is that the MT design usually has a 'tang' on the end of it--i.e. a flat portion that sticks in a slot that will positively prevent the taper from spinning. Lathes do not have the slot in the back of them so they will spin out---andif allowed to spin will destroy the tailstock of the lathe. Thus when drilling with a lathe you need to make alternative plans to keep the bit from spinning out. The normal solution is a Dog clamp on the bit resting on the compound.
Another issue that is of signifcance when thinking about Live centers is that their quality and weight ratings (and prices vary radically). For example, in connection with writing this artical I looked through the catalog of one tooling supplier and they had MT #6 live centers rated from 6,000 lbs (work weight) to 22,500 lbs (work weight). Thet message here is that if you are turning fairly heavy weights on live centers give some thought about the center.