I believe your comment about R8 and 30 taper being the same is
incorrect. 30 taper is 3.5"/ft or 7 in 24 whereas R8is about 3.555"/ft.
I was helping my neighbour make an R8 spindle earlier and had to check
this. The info on the www seems incorrect or misleading, my bridgeport
manual shows the taper as 16 degrees 51 minutes, yet some web pages show
16.51 degrees. 16 degrees 51 minutes works out at a taper of 1 in 3.375
on diameter or 3.555"/ft or 16.85 degrees included. This was checked
against an R8 taper and verified.
DoN. Nichols wrote:
In article . net,
Karl Townsend remove .NOT to reply wrote:
"DeepDiver" wrote in message
...
Are there any differences between NT40 and CAT40 spindle tapers? I've also
seen reference to 40 National Taper, 40 National Taper with Drive Flange,
and 40 National Taper with "V" Flange. What are the differences (and why)?
Can anyone provide a reference to the actual design specs for the various
National Tapers?
I've got NMTB 40 taper on my mill. It uses a threaded draw bar to pull the
tool in tight. The CAT taper has a pull stud on the end. So, they are not
interchangable even though the taper part is identical. I have modified a
few rare CAT 40 holders over to NMTB40. More work than its worth but doable.
It depends on the particular taper you are adapting *to*.
I've got both NMTB 30 taper (Bridgeport Boss-3 CNC mill), and
generic 40 taper (Nichols horizontal mill, plus vertical head to use the
same tooling).
Converting a CAT-40 to the Nichols mill (which only needs the
threads for the drawbar and (optionally) the notches) involves:
1) Heating the ball-pull to debond the Loctite so you can unscrew
the ball pull.
2) Turning an adaptor which threads into the original threads for
the ball pull in the back of te taper, and which provides the
orientation collar and the female threads to match the drawbar.
(You could make an alternative drawbar which fits through the
spindle, is a bit longer, and threads directly into the CAT-40
threads for the ball pull.
3) Loctiting that adaptor into the CAT-40 to keep from
experiencing the adaptor unscrewing from the CAT-40 while stuck
on the drawbar, thus trapping the drawbar. (My really old
Nichols has too small a spindle bore to allow the alternative
design, and I *really* did not want to have to try cutting off
the drawbar to get the parts out.
However -- converting a CAT-30 (or similar) to fit into the
Erickson quick-change head for NMTB-30 tools) requires turning the
flange down to a precise thickness so the quick-change lock will work on
the flange. (The BOSS-3 has no drawbar.)
The drive flange and V flange are two different ways to keep the holder from
slipping. The V flange also has the drive flange collar so they will
interchange if you use drive flange.
You mean for a tool turret to automatically change tools on a
running machine? The 'V' is for the gripping part of the tool turret.
After using taper 40, I will never buy and R8 machine again. So much better.
And interesting thing is that the taper of an R8 and a 30-taper
is identical, as is the larger diameter end of the taper. An R8 taper
stops sooner, at a larger minimum diameter. But, with a drawbar, you
can hold a 30-taper into an R8 spindle. Unfortunately, you lack the
keys to prevent spinning -- both under cutting load and when trying to
unscrew the drawbar.
Finally, why are 40 National Taper spindles so rare in milling machines
sized for the small shop? It seems to be vastly superior (in strength,
concentricity, rigidity, and ability to accommodate larger-sized tooling)
to R8. Yet, even the 10"x54" class milling machines (costing $7,000+) are
fitted with wimpy R8 spindles. Not that I'm ready to buy such a machine...
But the Bridgeport BOSS-3 (and later) were often fitted with
NMTB-30 taper with an Erickson quick-change head in the spindle.
Enjoy,
DoN.
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