Subject: Tapers: draft FAQ item

From: [email-masked] (James Kirkpatrick)
Date: 14 Sep 94 14:27:17 MDT

Since it does come up from time to time, I have slapped together
an FAQ entry on tapers.  Please let me know of anything I've missed
or anything that I got wrong.

This is from memory, the archives, Machinery's Handbook, and
Machinists' Ready Reference.

Jim

98.  What are the various tapers (Morse, JT, R8, etc.)?

     Unfortunately, there are many different tapers, and not enough
     space to tabulate them here.  For details, consult a good reference
     such as Machinery's Handbook, or Machinists' Ready Reference.

     First, why use tapers?  Two basic reasons.  At shallow angles,
     a tapered rod will tend to stick in a matching socket.  This
     is frequently used to hold tools such as drills or centers in
     a lathe tailstock, allowing rapid change.  At steep or shallow
     angles, a taper allows mating parts to line up very accurately.
     Note that the shallow tapers such as Morse may tend to get
     stuck if too much force is used, and this can turn into an
     interesting problem when you try to separate them!

     Tapers are poor holders for large side-loads, in which case
     you need a drawbolt or drawbar.  Here, a threaded bar is used to
     pull (draw) the tool into the socket and hold it in place.
     This is commonly used in milling machines and for collets.

     Shallow tapers such as Morse are "grabby" and need some force
     to break free.  Beyond a certain angle, a taper is self-releasing
     if the coefficient of friction is less than the tangent of the
     taper angle.

     Tapers can be sensitive to chips and dirt, so keep them clean.
     A gouged taper socket can usually be cleaned up nicely with a
     taper reamer, if you can borrow one.

     Morse:  Very common in lathe spindles and tailstocks.  Different
     standard sizes exist, such as MT1, MT2, and so on.  The actual
     taper varies from one size to the next.  Some examples:
        MT0   small=.252 inch, large=.3561 inch, taper=.052050 in/ft
        MT1   small=.369 inch, large=.4750 inch, taper=.049882 in/ft
        MT2   small=.572 inch, large=.7000 inch, taper=.049951 in/ft
        MT3   small=.778 inch, large=.9380 inch, taper=.050196 in/ft
        MT4, MT 4 1/2, MT5-MT7: see references.
     These values are for the "business" part of the taper, and exclude
     whatever the taper is attached to, such as a drill or a center,
     and also excludes the tang, if any.  Note that there is no overlap,
     making it practically impossible to mate mis-matched tapers (this
     may also explain the different taper rates).  Some MT accessories such
     as drills will have a flat tang on the end, intended to mate with
     a matching slot in the socket, to give a setup better strength
     against rotation; in this case the taper is primarily being used
     for alignment, and to hold the drill from falling out when not
     being used.  Most small home-sized lathes use between MT0 (e.g.
     the Sherline) and MT4.  Larger taper sockets may include a
     sideways slot, intended for a flat tapered knock-out bar to
     facilitate tool removal.  Machinery's Handbook claims that Morse
     tapers are the only type of taper used on drills that have a
     taper shank.

     Morse Stub: a variation of Morse, but less than half as long.
     Same numbers as Morse, and correspond to the large end; that is,
     you can make a Morse Stub #3 by slicing off the end of a standard
     Morse #3 (excluding the problem of making the tang, if any).

     Brown & Sharpe tapers are similar to Morse tapers, but are
     found on some end mills and reamers, and on milling machines
     and grinding machines, also dividing heads.  Sometimes they have
     a tang, sometimes they are drilled and tapped for a draw-bolt.
     Some examples:
        BS1   small=.20000 inch, large=.23922 inch, taper=.50200 in/ft
        BS2   small=.25000 inch, large=.29968 inch, taper=.50200 in/ft
        BS3   small=.31250 inch, large=.37525 inch, taper=.50200 in/ft
        BS4   small=.3500  inch, large=.4023  inch, taper=.50240 in/ft
        BS5-BS18 see references.  Taper varies with number.

     Jarno:  Used on various machines, such as profiling machines and
     die-sinking machines, and on some lathes.  An attempt to create
     a very simple taper: all of them are .6 inch of taper per foot,
     the diameter at the large end is as many eighths, the diameter at
     the small end is as many tenths, and the length as many half-inches
     as the number of the taper (i.e. machinists making tapers didn't
     have to use big formulae or tables).   Some examples:
        2   small=.2, large=.25
        3   small=.3, large=.375
        4-20 see references, or compute from formulae above.

     Jacobs Taper:  commonly used to mount a drill chuck to a machine,
     whether a drill press or a lathe tailstock.  Since most chucks
     use a female Jacobs, such as JT6, and most tailstocks are female
     Morse, an adapter bar is usually used here, with the appropriate
     tapers on each end.  The taper varies quite a bit with taper number.
     Some examples:
        4   small=1.0372, large=1.1240, taper=.62886 inch per foot
        6   small=0.6760, large=0.6241, taper=.62010 inch per foot
     Nubers 0-5 appear to have been original, in that number 6 and
     number 33 (no 7-32!) are smaller than 5, and have a length of
     exactly 1 inch, and thus seem like later additions to the series.
     Number 2 is possibly also supplied in a short version, in addition
     to a standard-length 2.

     R8:  Frequently used on milling machine spindles.  Lots of tooling
     is available for R8.  Requires the use of a drawbar as the angle
     is relatively "blunt" and usage is often vertical with large side
     loads.  The taper is apparently 16 degrees 51 minutes, and the
     relevant diameters are .949 and 1.25 inches.  The drawbar thread
     is 7/16-20

     Others:

       American National Standard Tapers: really several families.
       The "self-holding" series appears largely identical to Morse
       except for details of the tang dimensions:  ANS continue the
       taper all the way down the sides of the tang, while Morse ends
       the taper at the start of the tang, with a straight-sided tang
       that starts out a bit smaller than where the taper left off.
       Some very small tapers are based on Brown & Sharp (they have
       fractional numbers), and some large ones use a taper of
       .75 inch per foot (numbers 200-1200).  They also have a
       separate family of steep tapers, numbered 5-30 in steps of
       5, apparently meant for milling machine spindles and such.

       British Standard Tapers: mentioned in Machinery's Handbook
       but not really explained.  Sorry.