Re: R8 Taper socket dimensions and an update

On Fri, 10 Feb 2006 08:14:58 +1300, Tom <tmartin@xxxxxxxxxx> wrote:

John Stevenson wrote:

Ok we need to look at a bit of history here to get the full picture.
The R8 collet was devised by Bridgeport back around WW2, before that
they were using the B&S collets or sometimes the Morse.
All this is rather hazy due to licensing agreements.

Because the R8 was classed as a proprietary taper it was never listed
in places like Machinery Handbook, to my knowledge unless it's in V27
it still isn't.

Many people have listed various drawings for the R8 some very crude
and some with a few major dimensions on them as a guide.
many of the collet manufacturers have them on line.

The first recorded entry I can find on the FULL specs is in a 1952
edition of the National Machine Tool Builders manual.
This was a professional body of interested people who went about
setting various standards, machine noses and tapers being one.

Incidentally the initials NMTB is still prevalent today as a standard
taper although it has also been superceded by the term INT

Here's a copy of that drawing hosted by Scott Logan of Logan lathe

So now we had a standard and all was fine - until.............

Sometime with the last three of four years with the import of tools
from the far east a certain American manufacturer who was building his
version of a machine with an R8 taper sent a sample to China for
collets to be made.
Unfortunately due to a lack of published standards his spindle wasn't
standard so the Chinese working with what they had made collets up to
fit this spindle.
The Yank was pleased as he now had a supply of collets but in the
process had pissed up the whole shooting match.

So what has now happened is that in certain provinces they are making
collets to the Twonk spec and in other provinces they are making
collets to the correct spec.

The importers know this problem but it depends on where they are
buying from whether they admit to knowing about this.


John Stevenson
Nottingham, England.

Missed this for some reason. It sounds like the orientals could
have ended up grinding the collets to 30 NMBT taper of 3-1/2" per
foot, it only has a few minutes difference in taper to R8. In
actual fact, people have been known to use 30 Int in R8 machines.
Requires a longer drawbolt and the some of the more "fussy" even
fit an extension to lengthen it to fit the R8 upper register..:-)


They could have made this mistake, it's hard to measure a couple of
minutes of a degree by hand but the biggest difference is in the
0.9490 / 5 diameter.
They have probably rounded off this to 0.950 /5 and if the collet has
been made to suit, and on the plus side it's a whack in fit into a
correct spindle.

John Stevenson
Nottingham, England.

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