On Jun 6, 8:02*pm, "Michael Koblic" wrote:
I have spent a very long and unproductive day trying to cut a 5/16-24 thread
on a cut-off piece of 5/16 bolt.
I knew things were not going to go well when I could not get the
*never-previously-used* die to even bite. I chamfered, then chamfered again,
nothing. eventually I made the tip almost conical. I got some purchase but
a) the effort to cut was disproportionate and b) the end result was a thread
which was skewed - and not subtly!
I tried again with another piece of 5/16 rod - same result.

I hit the books to see if I omitted something glaring. Most of the texts I
have are big on starting *taps* straight but they did not stress the dies so
much.

In the end I borrowed the tap technique: I gripped the rod in the chuck of
my drill press. I clamped the die in my drill press vise (there is a little
shoulder that allows it to rest flat). I raised the table and centered and
clamped the vise with the rod touching. I turned the rod with a pair of
vise-grips while simultaneously feeding the spindle (it would be really nice
to have three hands!). After the first turn the feed took care of itself.
This way I cut a reasonably straight thread but the effort was much harder
than I expected. Also, the vise-grips make a mess of the rod.

I tried it again with the cut-off bolt. This time I turned the spindle of
the drill press directly by a makeshift lever improvised from the same stock
and inserted into the chuck key holes. It was even harder to cut this time
(I checked the diameter etc. - all identical).

I should mention that the whole workshop was swimming in Rapid Tap at the
end - no dry cutting here.

I suspect that the die is crap and I will go and get another one but the
whole process brought up some interesting questions. The most important of
them is:
How does everyone manage to get a straight thread when die cutting?

I think the method I use is OK provided the workpiece *can* be held in a
chuck but if not, I am stumped.

BTW, if using a drill press to start a tap in a hole how do you turn the
tap? Do you grind flat spots on your taps to get a better wrench purchase?

--
Michael Koblic,
Campbell River, BC

dies
A lot of the dies out there are only suitable for rethreading,
particularly if you got them at a hardware store and they're hex in
shape. If it's Chinese, you've now got a nice paperweight. Round
split-button dies can be adjusted over- or undersize to fit the female
threads. About the only kind I have. You can order good ones from
MSC or the like.

5/16" bolt shanks aren't necessarily the right size for threading with
dies. They roll threads these days and cheap hardware store bolts
aren't necessarily precision stuff. Sure you didn't have a hardened
bolt?

Get a good die stock. The ones I use for freehand threading have an
"iris", a set of fingers that can be adjusted to the workpiece
diameter. I've seen these at True Value and Ace, the ones I use most
I bought at Sears decades back, before they peddled junk.

Most of my threading with a die is done in the lathe with a die
holder, ditto tapping.

Tap shanks are hard and will slip in a drill chuck, not recommended to
do it that way. You can buy/make a tap wrench with an extension that
can be chucked and slides up and down, a relatively cheap item, Enco
had them at one time. Another way is to get a decent T-handle tap
wrench with an accurately centered center hole, Starrett made the ones
I use, then put a center in the drill press to start the thing
straight. I do it this way in the lathe. Or you can make/buy a
tapping block to start things square. Get decent tap wrenches, the T-
handles with spring fingers made from the body should be junked, the
best sort have spring-loaded hardened jaws. Dog-bones are handy to
have on hand, too.

Stan