On 2017-02-17, Bob La Londe wrote:
Overall I am pretty happy with my Chinese made Precision mathews PM1440LBE
lathe. However there are some little things that just make me go,
"Hmmmmm...."

The 1440 mostly gets used for quick and dirty single setup one off projects.

[ ... ]

Recently my success and happiness with the little 3C hand wheel closer on
the small 8.5x18 HF lathe got me thinking that there would be jobs that
would be handy to do with a 5C closer on the 1440.

I recently picked of a lever style collet closer. The price was cheap
enough I don't mind using it as a learning tool, or even scrapping it after
learning how to make one if necessary. Now to figure out how to setup a
spindle adapter. I've found MT5 to 5C adapters. The factory claims the
spindle bore is MT6, but it also came with a "MT6" to MT4 adapter so I can
turn between centers if I so choose. I figured a cheap import MT6 to MT5
adapter would atleast get me in the right ballpark to start figuring stuff
out.

I didn't even have to put the import adapter in the spindle to see it didn't
match up. Its a different taper angle than the adapter that came with the
lathe. So...

I dropped Precision Mathews an email and asked what the heck the spindle
bore really is. This is their reply.

************
"Hi Bob, They are listed from the factory as MT6. But our other machines
are listed the same way, and its actually an MT 5-1/2 So that might be
it."
************

Ok.... I had not heard of half sizes before and a cursory search doesn't
bring them up.

Interesting. In _Machinery's Handbook_ 29th edition, page 956,
table:

"American National Standard Ring and Plug Gauges for the
self-holding taper series ANSI/ASME B5.10-1994(R2008)"

I see what I always knew as the only half-size Morse taper, MT-1/2. The
table was made up of three earlier tapers, with the middle being the
Morse tapers -- 1 through 7. Before that are some decimal fraction
tapers (Brown & Sharpe tapers), and after are 200 through 1200. (1/4"
per foot tapers" with no other name showing. I found them identified
by name in a similar table a couple of pages earlier, but with less
detail about other maters.

.... grumble grumble grumble ....

Now for the fun part. The lever closer did come with a 5C adapter. I don't
know what the outside is, but... It doesn't fit in a MT4 or an MT5 sleeve.
Is it an MT4-1/2?

It likely is. That was made (I believe) from part of the MT-5
taper. It is the smallest which will accept a 5C collet, and I have
that taper in the spindle of my 12x24" Clausing, which came with a
lever style closer.

LOL.

A little more sarching and I discover Morse Tapers are all different angles?
What? Dang-it!

The reason for that is that the Morse tapers were developed
before it was easy to measure taper angles in degrees. So, they were
defined as a length, a small end diameter, and a big end diameter, which
worked out to weird tapers. The MT-4-1/2 is designed for that, and for
a 1-3/8" spindle bore to clear a 1-1/4" drawtube.

The other tapers are constant taper per foot .50200 for the
early ones in the table -- Brown & Sharpe, and 0.75000 for the later
ones, which are simply called "3/4 inch per foot taper".

Can you get a hardenable steel taper to fit your spindle? If
so, silver braze a ring to the front to aid in extracting it, then bore
it cylindrically and bore the closing taper, then drill from the side at
the right place and put in an index pin for the anti-rotation groove in
the collet. If you are working from a spindle which accepts MT-5-1/2
(no data on that size). Perhaps bore and taper slightly undersized, and
then use a toolpost grinder to get the finish good and to final
dimensions. (Of course, protect the ways from the grinding products.)

Good Luck,
DoN.

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