By Bob Winegard, Application Support and
Training
Thread milling surfaced approximately 25
years ago in response to NASA’s need to machine high-quality threaded holes in extremely
tough materials such as titanium, Hastelloy and Inconel – a feat not possible
with a tap. Over the years, thread milling has and continues to evolve, and
manufacturers are now using the process to produce strong, exceptional threads
in hardened materials up to 70 Rockwell.
Top six reasons thread milling is better than
tapping:
1. You’ll always achieve a better
thread quality with thread milling than tapping.
2. Depending on your hole size, you
can perform tapping either by hand or machine. With thread milling, however,
you must always use a machine, which ensures better overall thread consistency.
3. Thread milling is a lot easier on
your machine tool because it requires much lower cutting forces than tapping.
4. In thread milling, you don’t have
to have the hole right on size because the thread mill will cut the hole
larger. When people tap, they typically tap the hole larger than necessary
because it is easier. However, in doing so, they lose part of the thread and
reduce its overall strength.
5. It’s common for smaller taps to
break during the tapping process. Upon breaking, you can try to get the tap out
of the hole, which can be time consuming, but more often than not, you will need
to scrap your part.
6. With thread mills, you can create
right and left-handed threads using the same tooling.
Keep in mind, however, before you can thread
mill you must have a machine tool with three-axis capabilities. While most of
today’s machines have such abilities, a lot of older equipment does not. You
must also consider how deep you need to thread mill because you should not go
deeper than one and a half times the diameter of your hole. The reason being is
that the longer your milling tool, the more chance you have of experiencing
deflection, which can create inaccuracies in the thread.
With thread milling, you have a couple of
tooling options from which to choose. You can opt for either a solid carbide or
indexable tool. Solid carbide tools are ideal for smaller hole sizes because an
indexable tool typically won’t fit in holes that are ⅝” or less in diameter. In terms of cost, solid carbide thread
mills are more expensive than indexable designs. With an indexable tool, once
you've purchased the thread mill body, the cost of the inserts are more
affordable than solid tooling. Indexable tools also have shanks made of steel,
which makes them more forgiving than solid carbide tools.
Lastly, before you go to thread mill, be sure
to take advantage of Seco’s Thread Milling Wizard software, which is available
via our web site. The software will ask you a series of questions about the
type of thread you’re trying to achieve, and based on your responses, it will
create a highly effective, tailor-made CNC program for use with your machine
tool.
As an integral
member of Seco’s dedicated application support and training team, Bob works
closely with Seco customers to help them optimize their tool usage and find
ways to increase their productivity and reduce costs. Contact Bob at
bwinegard@secotools.com.
