I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...Mill/specs.jpg

Thanks

On 12/29/2010 12:52 PM, Ignoramus18879 wrote:
I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

I still think this whole idea of measuring the input shaft rather than
measuring the actual spindle position is a mistake. I know it is harder
to do this, and it isn't easy to do on the 1J head, either.

You will need to tell what head you have for people to help. Most
Series-II machines have either a 3J or 4J head.

If nobody knows, you may have to open it up and count teeth on the gears
to be entirely precise.

Jon

In article ,
Ignoramus18879 wrote:

I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...CNC-Mill/specs
.jpg

The 8.3:1 is the decimal approximation to a rational number, and
probably isn't quite accurate enough. There is no real alternative to
counting teeth. Unless you have enough encoders to accurately measure
the ratio between input shaft and output shaft rotation, and have access
to both shafts. I bet counting is quicker.

Joe Gwinn

On Wed, 29 Dec 2010 12:52:56 -0600, Ignoramus18879
wrote:

I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...Mill/specs.jpg

Thanks

I had to do this on my excello. The trick is to get a very large
sample. Can you get encoder counts off your spindle encoder? You sure
should be able to. Then go a large number of turns on your bottom
spindle in back gear, say 100 revolutions. Then it only takes a second
in an excel spread sheet to find the exact ratio.

Karl

On 2010-12-29, Karl Townsend wrote:
On Wed, 29 Dec 2010 12:52:56 -0600, Ignoramus18879
wrote:

I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...Mill/specs.jpg

Thanks

I had to do this on my excello. The trick is to get a very large
sample. Can you get encoder counts off your spindle encoder? You sure
should be able to. Then go a large number of turns on your bottom
spindle in back gear, say 100 revolutions. Then it only takes a second
in an excel spread sheet to find the exact ratio.

Yes, I have a counting tachometer, I can do it to a good accuracy, say
10,000 turns (just five minutes at 2k RPM). That ought to be good
enough.

i

Ignoramus18879 fired this volley in
:

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

Wait! If it's _gear_ driven, and the "teeth ratio" is 8.3:1, then you can
be pretty comfortable that the ratio between the input shaft and the output
shaft will be 8.3:1, too (unless it skips teeth once in a while).

(or did you not mean to apply "teeth ratio" to the word "approximately"?)

LLoyd

Joseph Gwinn fired this volley in news:joegwinn-
:

The 8.3:1 is the decimal approximation to a rational number, and

Rational, or irrational, Joe? If it's rational, he can calculate the exact
value, with enough precision. If it's irrational, technically he cannot,
but still, within the few revolutions a tap makes, it would still be
accurate enough, with enough arithmetic precision.

LLoyd

On 2010-12-29, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Joseph Gwinn fired this volley in news:joegwinn-
:

The 8.3:1 is the decimal approximation to a rational number, and

Rational, or irrational, Joe? If it's rational, he can calculate the exact
value, with enough precision. If it's irrational, technically he cannot,
but still, within the few revolutions a tap makes, it would still be
accurate enough, with enough arithmetic precision.

All reductions done with gears, are rational.

i

In article ,
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

Joseph Gwinn fired this volley in news:joegwinn-
:

The 8.3:1 is the decimal approximation to a rational number, and

Rational, or irrational, Joe? If it's rational, he can calculate the exact
value, with enough precision. If it's irrational, technically he cannot,
but still, within the few revolutions a tap makes, it would still be
accurate enough, with enough arithmetic precision.

Rational. Although your point about required accuracy is probably
correct.

In mathematics, a "rational number" is defined as the ratio of two
integers (zero divisors being excluded). Such as counts of gear teeth.
It's mathematically impossible for an ordinary gear train to have an
irrational speed ratio.

By contrast, irrational numbers are those that cannot be expressed as
the ratio of integers. Standard examples are Pi and Sqrt[2]. In
mechanical terms, belt drives (excluding toothed timing belts) can
achieve any speed ratio, not being limited to rational ratios.


As a mathematical brain twister, there are infinitely more irrational
numbers than rational numbers, even though there are infinite numbers of
both kinds of number. It turns out that infinity comes in sizes, a
shock to all. When Georg Cantor published this in the late 1800s, there
were riots in the streets (of university towns anyway).
http://en.wikipedia.org/wiki/Georg_Cantor

Joe Gwinn

Ignoramus18879 fired this volley in
:

All reductions done with gears, are rational.


But you didn't clarify that it was _actually_ gears. You seemed to wonder
if the ratio wasn't somehow variable. We were still wondering how a "teeth
ratio" could be "approximately"...

LLoyd

Joseph Gwinn fired this volley in news:joegwinn-
:

In mathematics, a "rational number" is defined as the ratio of two
integers (zero divisors being excluded).

All understood and approved, Joe... I was just sort of needling Iggy
(ineffectively, apparently) about the fact that he seemed to think a "teeth
ratio" could also be "approximate".

It's one, or the other...

The joke failed...

LLoyd

On 2010-12-30, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Joseph Gwinn fired this volley in news:joegwinn-
:

In mathematics, a "rational number" is defined as the ratio of two
integers (zero divisors being excluded).

All understood and approved, Joe... I was just sort of needling Iggy
(ineffectively, apparently) about the fact that he seemed to think a "teeth
ratio" could also be "approximate".

It's one, or the other...

The joke failed...


That 8.3 ratio looks a little suspect to me. It could be a 83:10 pair
of gears, but maybe this is another gear ratio that just is close
enough to 8.3 to put that number into the spec sheet for for simplicity...

i

In article ,
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

Joseph Gwinn fired this volley in news:joegwinn-
:

In mathematics, a "rational number" is defined as the ratio of two
integers (zero divisors being excluded).

All understood and approved, Joe... I was just sort of needling Iggy
(ineffectively, apparently) about the fact that he seemed to think a "teeth
ratio" could also be "approximate".

It's one, or the other...

The joke failed...

I wondered, I must say, but decided that deadpan was safest, if more
annoying. And Iggy is still being serious.

Joe Gwinn

Ignoramus18879 fired this volley in
:

That 8.3 ratio looks a little suspect to me. It could be a 83:10 pair

Could be 106/20 or 212/40 (might be a more likely combo) or it could be two
steps (like in a conventional back-gear relationship).

I kind of like to think that Bridgeport engineers (back when that mill was
made) were _engineers_, and would've blanched at the thought of putting
something "approximate" in the specs when it was an integer ratio.

LLoyd

On 2010-12-30, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus18879 fired this volley in
:

That 8.3 ratio looks a little suspect to me. It could be a 83:10 pair

Could be 106/20 or 212/40 (might be a more likely combo) or it could be two
steps (like in a conventional back-gear relationship).

I kind of like to think that Bridgeport engineers (back when that mill was
made) were _engineers_, and would've blanched at the thought of putting
something "approximate" in the specs when it was an integer ratio.

Maybe they were engineers, but by now no one is left there.

i

"Lloyd E. Sponenburgh" wrote:

Ignoramus18879 fired this volley in
:

That 8.3 ratio looks a little suspect to me. It could be a 83:10 pair

Could be 106/20 or 212/40 (might be a more likely combo) or it could be two
steps (like in a conventional back-gear relationship).

If the head on his mill is the same basic design as the 1J, it is indeed
a double reduction with the first stage being a timing belt and the
second stage being gears.

On Wed, 29 Dec 2010 16:46:16 -0600, Ignoramus18879
wrote:

On 2010-12-29, Karl Townsend wrote:
On Wed, 29 Dec 2010 12:52:56 -0600, Ignoramus18879
wrote:

I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...Mill/specs.jpg

Thanks

I had to do this on my excello. The trick is to get a very large
sample. Can you get encoder counts off your spindle encoder? You sure
should be able to. Then go a large number of turns on your bottom
spindle in back gear, say 100 revolutions. Then it only takes a second
in an excel spread sheet to find the exact ratio.

Yes, I have a counting tachometer, I can do it to a good accuracy, say
10,000 turns (just five minutes at 2k RPM). That ought to be good
enough.

i

My backgear ratio was 92:15

What did yours come out?

Karl

On 2010-12-30, Karl Townsend wrote:
On Wed, 29 Dec 2010 16:46:16 -0600, Ignoramus18879
wrote:

On 2010-12-29, Karl Townsend wrote:
On Wed, 29 Dec 2010 12:52:56 -0600, Ignoramus18879
wrote:

I need to know the exact back gear ratio for Bridgeport Series II
Interact 2. I need to know it exactly, because I need it for rigid
tapping.

I know that it is between 8.2 and 8.42 from just looking at my dial,
but I need to know the exact value, not approximate.

The specs on my spec sheet say 8.3:1 ratio, but I am not totally sure
if this is this ratio exactly or approximately (as in teeth ratio).

http://igor.chudov.com/projects/Brid...Mill/specs.jpg

Thanks

I had to do this on my excello. The trick is to get a very large
sample. Can you get encoder counts off your spindle encoder? You sure
should be able to. Then go a large number of turns on your bottom
spindle in back gear, say 100 revolutions. Then it only takes a second
in an excel spread sheet to find the exact ratio.

Yes, I have a counting tachometer, I can do it to a good accuracy, say
10,000 turns (just five minutes at 2k RPM). That ought to be good
enough.

i

My backgear ratio was 92:15

What did yours come out?

Karl


Spec sheet says 8.3.

i