wrote:
On Tue, 8 Oct 2013 16:54:20 +0000 (UTC), Cydrome Leader
wrote:

F. George McDuffee wrote:
On Fri, 4 Oct 2013 22:34:36 +0000 (UTC), Cydrome Leader
wrote:

wrote:
On Fri, 4 Oct 2013 16:46:34 +0000 (UTC), Cydrome Leader
wrote:

Any wisdom here to share when it comes to hand tapping with roll taps?

I ordered some 1/4-20 and 10-32 ones to play with. I was having problems
with threads being stripped out of an aluminum pipe with a 1/4-20 bolt
with a knob that's used to clamp onto an inner cylinder.

Are a couple drops of cutting oil suitable as lubricant?

It seems some of these taps have flutes, some don't. Does it matter much?
You can use cutting oil for aluminum if tapping aluminum. The taps
that don't have flutes are not ground round. They are ground to have
high spots. If you grast the tap lightly and turn it you can feel the
eccentricity. A good hardware store will sell tapping fluid. The clear
works well for aluminum. For steel the dark sulfurized stuff is good.
You do know that hole size is critical for form taps? The hole will of
course be larger than for a cutting tap, but the size has less
tolerance than that for a cutting tap because the material is
displaced rather than cut.
Eric

I looked at some of the charts and other forums and the mention of using
larger and more specific hole sizes was mentioned.

Is it insanely hard to drive these things into metal, considering they
don't actually cut but form the threads with pressure?

I can't imagine their easier to drive than completely crossthreading a
fastener.
=========================

If you are "free" hand tapping, that is without a tapping
machine or using the drill spindle, it is very helpful to
fabricate a tap block which can be as simple as a piece of
scrap metal with a hole the OD of the tap drilled
perpendicular in it to insure the tap is straight when it
starts. Quickly pays for itself with avoidance of broken
taps and scrap parts. Much less time to fabricate than
remove a busted tap from a part.

Store bought ones generally sized for cut not rolled thds

For a fancier one see
http://www.littlemachineshop.com/pro...2571&category=
http://www.littlemachineshop.com/pro...3427&category=

If you are using the drill spindle/chuck see

high priced spread :-)
http://www.midwayusa.com/product/109...press-or-lathe

What I bought -- works a treat on both lathe, drill press,
and mill
http://www.wttool.com/index/page/cat...gory_id/22122/

For shop made (adj hole dia for roll form taps)
http://grabcad.com/library/tap-block
http://www.machinistblog.com/free-pl...rilling-block/

For some more advice see
http://www.practicalmachinist.com/vb...estion-212014/
http://www.emkaytools.com/threads_forming_tap.html
http://www.travers.com/100244-81-004-001

Let the group know how it goes.

The first taps arrived yesterday. They were some ebay special Brubaker HSS
10-32 H4 ones with a fairly shiny finish.

The test was pieces of 6061 and something else that was much softer and
gummier.

As with any tap chart, the more you look, the more answers you get for the
nominal drill to use.

The charts from a few makers seemed to suggest someting close to #17 drill
for about 75% thread, so that's what I used.

It worked fine. I used the wax stick for a bandsaw as lube and each and
every time the taps went straight into the aluminum with no problems. I
used a small tapping block for some holes, and did the rest with a lathe
to hold the tap straight. I did notice they started easier than cutting
taps and didn't try to wander on the first cut.

I didn't measure torque, but they felt much smoother than any cutting
taps I've used, even the good ones. No crunchines, no sticking, no need to
back out all the time. Backing out still required a wrench, but not much
effort. I did some bottom-out tests and it was easier to feel the bottom
of a hole with the roll tap.

The thread quality is clearly better too, fasteners go in smoother and
there's no fuss with cleaning crud out of the threads when you're done.

The one thing the databooks warn about is how the threads will make a
volcano shape if you thread straight into a flat surface. I actually
noticed the 6061 would split and flake more than in would make a nice
protrusion.

Countersinking before threading just resulted in the protrustion to occur
out of the way. Countersinking after threading solved this and gave the
prettiest results.

The 1/4-20 tap should arrive in the next few days. I'll try some brass and
steel with both next.

So far, two thumbs up. these things are pretty cool.

Though the brass will be easy to tap the results may not be so good.
When half hard free machining brass (the most common) is formed by the
tap it may flake. Tiny flakes may come off of the threads. You will be
able to see them easily with a magnifier. And the threads may be
weaker that cut threads. Gummy materials work the best for form
tapping, so mild steel and 5000 series aluminum work well. I have form
tapped many 10-32 holes in 304 SS, even though the torque required was
kinda scary.
Eric

you were right about the brass. The threads were pretty flakey and the
pieces I tested actually deformed quite a bit. The volcano shape around
the threads exceeded the diameter of the threads for the 10-32 thread in a
piece about 3/16" thick.

I tapped around an existing 1/2" hole and this hole which was about 1/4"
away actually changed shapes and no long press fit the mating part.

I guess the lesson is, just cut brass threads, which is no problem since
they're strong enough anyways.

Next test is to see what happens with copper.