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Metric threading "close enough" chart


brettn048 <Brett3ww@...>
 

Setting up to cut metric threads on a 9 or 10K Model-A can be
expensive. So what do you do if you need to cut a metric thread for
a quick repair job where accuracy is not the main issue? Even
without the 100/127 metric transposing gear pair, if you just have a
good set of change-gears handy you may be able to cut a pretty good
approximation to most metric threads.

The Excel chart, which can be downloaded at
<http://bnordgren.org/files/metappr.xls> shows QC setups to cut
metric threads accurate to +/-0.1%, hopefully "close enough" for many
purposes. The chart also has an accuracy computer which lets you
test how accurate a thread is going to be for a particular setup.
You can get the same information from Guy Cadrin's spreadsheets, but
this chart is just arranged a little differently.

In all the combinations, using stud gears from 20 to 56T and output
gears from 42 to 60T, there are quite a few QC settings which produce
metric threads accurate to +/-0.1%. On average, there are more than
five gear combinations which can approximate each of the threads on
SBL's metric threading chart, though some threads have only two.

Hope this is useful.

Brett


albieguy
 

Thanks for the chart, it looks exactly
what I am looking for.

Where are the stud and output gears located?
I am referencing off the How to Run a Lathe
manual. I believe the stud gear is above the
idler #612k24 on page 122. But they list two
stud gears
Not sure where the output gear is, not shown in
this manual.
If I understand all this correctly I need
to obtain a set of change gear and use
as per your chart. Very nice.

Thanks
Dan




--- In southbendlathe@yahoogroups.com, "brettn048" <Brett3ww@b...>
wrote:

Setting up to cut metric threads on a 9 or 10K Model-A can be
expensive. So what do you do if you need to cut a metric thread
for
a quick repair job where accuracy is not the main issue? Even
without the 100/127 metric transposing gear pair, if you just have
a
good set of change-gears handy you may be able to cut a pretty
good
approximation to most metric threads.

The Excel chart, which can be downloaded at
<http://bnordgren.org/files/metappr.xls> shows QC setups to cut
metric threads accurate to +/-0.1%, hopefully "close enough" for
many
purposes. The chart also has an accuracy computer which lets you
test how accurate a thread is going to be for a particular setup.
You can get the same information from Guy Cadrin's spreadsheets,
but
this chart is just arranged a little differently.

In all the combinations, using stud gears from 20 to 56T and
output
gears from 42 to 60T, there are quite a few QC settings which
produce
metric threads accurate to +/-0.1%. On average, there are more
than
five gear combinations which can approximate each of the threads
on
SBL's metric threading chart, though some threads have only two.

Hope this is useful.

Brett


brettn048 <Brett3ww@...>
 

Dan,

On my 10K Model-A the stud gear is the top/outermost 20T gear of the
pair that mates with the reverser gears. That's why HTRAL is listing
two. Then the Stud gear mates with an 80T idler which goes on to the
56T Output gear, connected to the QC box. In mine the Output gear
sits behind/under a 40T spare gear that is to be used as a stud gear
for coarse threads.

In HTRAL page 74, Fig 211A, The Stud Gear is shown as the "Small Stud
Gear" and the Output gear is located behind/under the "Large Stud
Gear.

Also, if the book isn't handy, it might help to look at the image of
SBL's Metric Threading Chart, located here in
Files > Techinfo > Gears & Gearing > metricgearchart.jpg

Their 56T gear is the Ouput, and you will be using the regular (80T)
idler gear in place of the 100/127 transposer pair shown on the
Metric Chart.


Hope this all helps,

Brett


--- In southbendlathe@yahoogroups.com, "albieguy" <albieguy@y...>
wrote:

Thanks for the chart, it looks exactly
what I am looking for.

Where are the stud and output gears located?
I am referencing off the How to Run a Lathe
manual. I believe the stud gear is above the
idler #612k24 on page 122. But they list two
stud gears
Not sure where the output gear is, not shown in
this manual.
If I understand all this correctly I need
to obtain a set of change gear and use
as per your chart. Very nice.

Thanks
Dan


albieguy
 

Brett, Thanks for the info, I guess the only
remaining question is in using the threading dial.
I'm guessing to be safe just use the same mark
each time.

The generous sharing of information
on the board is only surpassed by the
quality of the information, amazing.
Regards
Dan


gorvil
 

--- In southbendlathe@yahoogroups.com, "brettn048" <Brett3ww@b...>
wrote:

Dan,

On my 10K Model-A the stud gear is the top/outermost 20T gear of the
pair that mates with the reverser gears. That's why HTRAL is listing
two. Then the Stud gear mates with an 80T idler which goes on to the
56T Output gear, connected to the QC box. In mine the Output gear
sits behind/under a 40T spare gear that is to be used as a stud gear
for coarse threads.
Dan,

The 40, 56 and 80 toot gears are pretty common as they are part of the
normal complement of change gears used on model "C" lathes. The 20
tooth gear is not. I made a some a few months ago basically to test my
gear cutting skills. I bought the gear cutters from Grand Tool when
they had them on close out. I still have a few 20 tooth stud gears
left. If you want one for $20.00, let me know.

Glen Reeser
gorvil(at)aol.com


brettn048 <Brett3ww@...>
 

Dan,

Unfortunately, when you're cutting metric threads with an English lead-
screw, the same mark doesn't get you to the same thread. You pretty
much have to forget the threading dial.

The advice I've seen posted before around here (search on "metric") is
to leave the half-nuts or the clutch knob locked in and just stop and
reverse the motor to power the carriage back to the start of each cut.
And you can do the last turn by hand if you have to, to set it exactly
where you want to start.

I know it doesn't sound all that easy, but after a few cuts you start
getting a feel for how it goes.

Regards,
Brett

--- In southbendlathe@yahoogroups.com, "albieguy" <albieguy@y...> wrote:




Brett, Thanks for the info, I guess the only
remaining question is in using the threading dial.
I'm guessing to be safe just use the same mark
each time.

The generous sharing of information
on the board is only surpassed by the
quality of the information, amazing.
Regards
Dan


albieguy
 

Glen, What material did you use for these?
Do these need to heat treated?
20 bucks sounds reasonable, I machine
for the satisfaction of creation, and would
enjoy making some gears just for the sake of it.
Dan



,

** I still have a few 20 tooth stud gears
left. If you want one for $20.00, let me know.**

Glen Reeser
gorvil(at)aol.com


gorvil
 

I made them out of brass.

Glen Reeser



--- In southbendlathe@yahoogroups.com, "albieguy" <albieguy@y...>
wrote:




Glen, What material did you use for these?
Do these need to heat treated?
20 bucks sounds reasonable, I machine
for the satisfaction of creation, and would
enjoy making some gears just for the sake of it.
Dan



,
** I still have a few 20 tooth stud gears
left. If you want one for $20.00, let me know.**

Glen Reeser
gorvil(at)aol.com