Taper for points in changeable point Z Live Center?

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mcdanlj

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When I bought my lathe, it came with a changeable point center that sure looks like one of these: https://zlivecenter.com/index.php?_route_=interchangeable-live-centers/07012MT3

Does anyone know whether the tips it comes with follow a standard taper?

It occurred to me that set in a MT3 BXA #53 toolholder, this would basically be a rotary broach tool, if a broach were made with the matching taper and installed like one of the tips. I expect that if I did that I'd be copying the taper anyway as the best way to get a close match, but I'm still curious about formal dimensions.
 
well, a rotary broach needs to have the tip out of the center line. That way it cuts on one side. So that won't work unless you take it off center.
The exampled today tilts the plane, some tilt the plane and have an adjustment back to a center location by sliding.
 
That's the entire point of using the MT3 BXA #53 toolholder: to set at a 1° angle. (Otherwise I'd just put it in the tailstock, which is of course possible with an offset / wobble style which would also work in the mill.)

I had been thinking of adding a BXA #53 to my set anyway, and I just had the insight that brings me almost to the point of already having a broach.

But I'm curious whether anyone knows whether the tip taper is a standard taper.
 
Taper should be 60 degrees. Same as the angle created by a center bit.
 
I'm talking about the taper where the changeable tips engage with the bearing, not the "business end" which is of course a standard workholding taper.

There are three tapers here.
  1. MT3 taper on the back to mount to the tailstock, or in my case to get the 1° offset, a QCTP block
  2. Some unknown-to-me taper that mates the bearings to the changeable tips
  3. The normal 60° included angle workholding taper on the end of the tip, or a bull nose.
Obviously, if I'm cutting a new broach to use in place of one of the changeable tips, there will not be a 60° included angle on the working end; it will be, say, a hex broach end. But the end that engages with the body of the tool is a self-holding taper. Anyway, I was just wondering whether anyone just knew the answer; if it was one of those things that a neophyte like me wouldn't necessarily know but someone more experienced would say "of course it's such-and-such". I can measure the taper and start looking for matching tapers in MH. Maybe it's a jacobs taper?
 
I wonder if you scale it off the drawing? Just doing some very rough approximation using your screen shot link the smaller taper for the tip does not match the taper for the spindle (MT-3) with respect to the angle. Suggests to me the drawing may actually be accurate enough to be referenced as opposed to just a representative illustration. Wouldn’t take much to lay it out and see.

-frank
 
I don't see anything about the taper angle in that image for the second taper on my list. I can copy a taper using a DTI to get the angle right, and cut to a close measurement, and test fit to be sure. However, the drawing doesn't dimension the taper angle nor call it out by specification. Trying to hold a protractor to a fuzzy, poorly-scaled graphic is a bad substitute to actually measuring the parts I have.
 
I agree, I would not have chosen a protractor for such a task. I would have compared the drawing of smaller taper against drawings of known tapers to see if one matched. You clearly have a better understanding of what you want though.
 
Let me try again.

I am curious about whether this is a form of standard taper. Alternatively, it may be peculiar to Z Live Center's changeable point centers. I'm just curious!

I marked the point where one of the points exits the tapered socket, and measured there 15mm (0.59 ") across the wide end. At the narrow end, I got 12.6 mm (.496"). These were about 25mm (about 1") apart Then I tried to use a normal 320° machinists protractor to measure the angle. both holding it up to the light and feeling for engagement. The best I did was about 6° included; I have low confidence in the precision of that measurement.

Of course, cross-checking, those measurements don't quite square with each other, but it's somewhere between these two pictures:

1647906027652.png
1647906489855.png

It looks vaguely similar to a JT#2 but the angle is definitely larger than 5° and closer to 6°, whereas a JT#2 is ~4.67° included angle (~2.33° side angle) like so:

1647907025665.png

It's reasonable for it not to be a Jacobs taper because the JT should hold very tight (lower angle) whereas changing the points in the center should be relatively easy though still self-holding (closer to the magic 3° borderline between self-holding and self-releasing).

I can't find any other self-holding tapers in this size, but I'm a neophyte.

Anyone know of a taper about an inch long, with an included angle between about 2.75° and 3°, with a large diameter of 15mm / .59"?
 
The Z Live Center sales folks said that it's the same angle as MT3. That's 1.4377° from center or 2.8754 included, less than half what I measured. This seems unlikely to be accurate.
 
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