Gunner Asch wrote:
On Wed, 22 Jan 2014 15:40:25 -0800, wrote:

On Wed, 22 Jan 2014 21:26:06 +0000 (UTC), Cydrome Leader
wrote:

I've tried to look this up and found no real answers so far.

Is there any sort of standard for cutting the chamfer on a thread lead-in?

Say I'm just threading the end of a 1/2" Al rod. The start of the thread
at the end will be jagged and weak. Cutting a 45 (I found 60 does nothing
useful) degree chamfer helps and makes thing far prettier, and for
anything I've done you can just eye-ball this and it really doesn't matter
too much how you do it for my uses.

What's done in the production world for stuff like this where looking
pretty is key? Is there a special angle and distance to cut this chamfer?

Would it be measured as distance into the thread, or the diameter of the
end of the fastner once cut?

Last question- how does one really measure a chamfer anyways? There's no
real surfaces to measure off.
Typically on a 60 degree thread a 45 degree chamfer will be cut just
beyond the major or minor diameter. Major for internal threads, minor
for external. So, for example, a 1/4-20 tapped hole will be
countersunk 90 degrees included angle to .265 diameter. But on work
that has a large tolerance the countersink may be much larger. When
measuring a chamfer it is fairly easy measure the diameter where the
chamfered surface intersects either the O.D. or I.D. There several
ways. One is to use a magnifier and calipers. This method is good
enough for +or- .003 for someone competent at inspecting machined
parts. Then there are magnifiers with built in reticles with scales
for measuring angles and distances. An optical comparator can be used
as well and then measurements to .001 are easy. Gauges are also
available that have a plunger ground for the specific angle of a
countersink, 100, 90, and 82 degree being the most common ones, that
have a dial indicator that shows either the depth or the diameter of
the countersink. These gauges are used by pressing them into the
countersink until the flat surface that the plunger protrudes from
contacts the work. If you are doing work for yourself then do just
what looks good. I like to finish screws with a rounded end. The
radius used on the end of the screw is much larger than the radius of
the screw, so the end of the screw isn't quite flat. This type of
finishing of screws is common on screws used in high quality
inspection equipment.
ERic

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And most of those are indeed done on an optical comparator, sometimes
with additional magnification. Its the fastest and easiest way to
check. Yeah..you can use all manner of nifty indicators and gauges
and whatnot..but with an OC..you turn on the light, focus and turn the
screen to the angle section.

What about for cutting the parts?

I use a sherline, so the compound slide cuts from the "back" of the lathe
with upside down toolbits. I've just been touching the end of the work
with the cutter tip and then doing the math and making the cuts. I touch
off on the end of the work piece as if I prick it and mess up the surface,
it doesn't matter as that side gets cut off anyways. I can't think if any
tricks to make this easier, but I'm all ears if there are tips for this.