On Tue, 4 Apr 2017 14:35:28 -0700 (PDT), Daniel Koller
wrote:



Hi folks,

I have a machining question for the group. I have acquired a nice boring head for a lathe tail stock. It has a smooth adjustment motion with a big dial calibrated in mils and it would be a really nice accessory for my 1952 Montgomery Ward / Logan 200 10" lathe.

However, the integral shaft of the head is 3/4" in diameter and will not fit the Morse #2 taper of my tail stock. So, what can I do about it?

I was thinking I should cut a Morse taper into the shaft. There is plenty of diameter and length to do that, and it would allow for quick swap-outs when I need it. I read through "How to Run a Lathe" and browsed the various ways to cut a taper:
A) turn the compound to the desired angle and cut at an angle.
B) Offset the tail stock and hold the part between centers. Cut straight.
C) Use a taper attachment.

I don't have a taper attachment, so C) is out. B) seems a little iffy and I'd need to grind down a center to clear parts of the dovetail integrated into the head. Also I don't trust how securely the part can be held at the necessary offset to get the taper.

So, A) seems to be the best option. I can set the angle to better than a degree by putting a micrometer on my compound and running it along the side of a known good MT2 taper held in the lathe chuck. ...actually, I just calculated, if I get the compound parallel to the desired taper by 0.5 mils over a 2" length, that's within 0.15 degrees of the correct angle.

QUESTION 1: How accurate does this angle have to be to have a good Morse taper? How smooth does the cut have to be? What are the pitfalls to cutting a taper by rotating the compound?

And it appears that my boring head shaft is soft enough to scratch with a hard steel cutting tool, so...

QUESTION 2: Do I have to grind the taper or can I cut it with a carbide tipped turning tool?

I've never cut a taper before, and I need to get this one right to make sure I don't screw up my boring head, so advice would be appreciated!

Thanks,

Dan
Greetings Dan,
Since you are only doing one part turning with the compound should
work OK. You will need a Morse #2 socket to use as a gauge as well as
some prussian blue. Keep in mind that the finished shank must be long
enough for you to be able to eject it from the tailstock quill. If the
existing shank isn't long enough you will need to add some length. To
do this the end of the shank can just be tapped for a screw that
sticks out enough. The screw does not need to be machined with a
taper, it's just there to add enough length so that the shank can be
ejected. Now, about turning that taper. Start gauging the taper well
before you get to the finished diameter. To get a good enough finish
will probably require polishing the the taper with sandpaper and/or a
stone. So, turn the shank until you have a taper about 2 inches long.
Wrap some good wet or dry sandpaper around something flat, like a 123
block, so that the sandpaper is backed up by a flat surface. Sand the
taper carefully making sure that the surface is sanded evenly. Then
try a test fit with a known good #2 socket. If the taper is pretty far
off you will feel it rocking. You should be able to tell if the taper
is more or less than the proper angle by observing where the socket is
pivoting from, either the front or the back. Once you are very close
apply a very thin layer of the prussian blue on the taper. Now try the
socket on the taper, pushing it on and then twisting slightly.
Removing the socket will reveal where the bluing has been rubbed off.
You want to remove material from wherever the bluing has been rubbed
off. The bluing can be bought at a good auto parts store. Ask for
"bearing blue" or "high spot blue". If they don't know what that is
tell them you need the marking compound used for setting the pinion
distance in a rear differential. When you get the compound set
correctly start removing enough material to get the taper to the
proper length. When you are close and only a tiny amount of material
needs to be removed for the taper to go deep enough into the socket
don't move the tool in the X axis. Instead move the tool in the Z
axis. This will make it much easier to get the shank to go in the
proper amount.
Good luck,
Eric