"David Billington" wrote in message
news
On 24/07/18 02:39, Jim Wilkins wrote:
"David Billington" wrote in message
news
On 23/07/18 19:41, Jim Wilkins wrote:
I thought dies were split so they could be tightened back to size
after grinding inside the holes to resharpening them. I resharpen
old
taps by running a cylindrical stone in the flutes.
Most of my taps are small enough that if blunted for some reason
it's easier to replace but I'll bear in mind the sharpening for
some
larger ones that are losing their edge from cutting threads in
some
poor quality steel.
The small taps I used for electronics are new and high quality. The
1/2" ones that I bought for repairs and home projects like my
sawmill
came from a second hand store and were often dull from production
use.
The largest is 2" NPT for which I paid less than 10% of its retail
price. I have a surface grinder with a cylindrical/tapered tool
grinding attachment and make sure the used taps I buy have center
holes in the ends.


The tool grinding attachment sounds like another thing I'll have to
make when I get my surface grinder up and running soon, any images
of yours or similar available?


This shows the machine but I didn't find a photo of the center
grinding attachment
http://vintagemachinery.org/pubs/1141/1691.pdf

which looks like bench centers mounted on a swivel base.
http://www.penntoolco.com/spi-heavy-duty-bench-centers/

Notice that Chadwick copied the design of the head for the Quorn about
30 years later, except for the separate elevating screw.

This is the type of sharpening attachment I use the most:
http://www.shars.com/end-mill-grinding-fixture
It sharpens only the ends so when roughing a slot I minimize side wear
with plunge cuts.
-jsw