I need to make a 32t helical gear to mate with my 8TPI acme leadscrew. I have a couple of questions for those here who know way more than I do.

I need to mill slots into my 8TPI acme blank. It's just an old Sheldon leadscrew that fits nothing I have. I figure I'll cut 4 or 6 groves on my mill. My question is where should the leading edge be in relation to the center line of the blank. My gut tells me that the cutting edge should on the center line so the cutting edge is 90 degrees. If the center of the slot is centered instead the cutting edge will not be at a 90 degree angle. Does this matter?

Second, the diameter of the blank. The circumference of 32 teeth divided by Pi gives me a dia of 1.27. Following a different method, adding three teeth divided by DP of 25.13 gives me a diameter of 1.39

Color me confused. Can anyone here answer these questions please?

BTW the gear will be brass. I've made a jig to hold the blank in my tool post and hob will be in the lathe chuck. I intend to run the lathe as slow as I can and feed the gear blank into the hob slowly until I get enough teeth to operate my thread dial. I may do it in my mill, holding the blank in my vice and hob in my collet holder, depending on which one rotates the slowest. Thanks in advance for any feedback/suggestions

Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.

Gerry wrote:
I need to make a 32t helical gear to mate with my 8TPI acme
leadscrew. I have a couple of questions for those here who know way
more than I do.

I need to mill slots into my 8TPI acme blank. It's just an old
Sheldon leadscrew that fits nothing I have. I figure I'll cut 4 or 6
groves on my mill. My question is where should the leading edge be in
relation to the center line of the blank. My gut tells me that the
cutting edge should on the center line so the cutting edge is 90
degrees. If the center of the slot is centered instead the cutting
edge will not be at a 90 degree angle. Does this matter?

Second, the diameter of the blank. The circumference of 32 teeth
divided by Pi gives me a dia of 1.27. Following a different method,
adding three teeth divided by DP of 25.13 gives me a diameter of 1.39

Color me confused. Can anyone here answer these questions please?

BTW the gear will be brass. I've made a jig to hold the blank in my
tool post and hob will be in the lathe chuck. I intend to run the
lathe as slow as I can and feed the gear blank into the hob slowly
until I get enough teeth to operate my thread dial. I may do it in my
mill, holding the blank in my vice and hob in my collet holder,
depending on which one rotates the slowest. Thanks in advance for any
feedback/suggestions

It doesn't absolutely have to be cut helical . Since there is a very light
load , you can make the teeth a quarter inch wide and just cut them straight
..

--
Snag

Karl Townsend wrote:
Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.

I can second that . I bought the book and learned to cut gears for the
lathe QCGB . You want workshop series number 17 .

--
Snag

On Wed, 30 Mar 2016 18:19:21 -0500, Karl Townsend
wrote:

Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.
Karl is correct about Ivan Law's book. But if this gear is for a
threading dial than you don't really need a gear that has traditional
teeth. Just properly shaped pins would work because there is almost no
load on the gear. It is after all just an indicator. Unless you cut a
worm gear there will only be a line contact between the gear and the
worm. The proper hob for the worm gear will resemble the worm, in your
case the leadscrew. I have cut gears successfully using the info from
Mr. Law's book. The book isn't very long but is packed with easy to
understand information. It even has plans for making a tool for making
gear cutters. The tool has a couple eccentrics on it that enable a 12
tooth gear cutter to be cut in the lathe because each tooth is backed
off as the tool rotates. So there is constant relief for each tooth
while at the same time the tooth profile doesn't change and sharpening
only requires grinding the top of each tooth.
Eric

wrote:
On Wed, 30 Mar 2016 18:19:21 -0500, Karl Townsend
wrote:

Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.
Karl is correct about Ivan Law's book. But if this gear is for a
threading dial than you don't really need a gear that has traditional
teeth. Just properly shaped pins would work because there is almost no
load on the gear. It is after all just an indicator. Unless you cut a
worm gear there will only be a line contact between the gear and the
worm. The proper hob for the worm gear will resemble the worm, in your
case the leadscrew. I have cut gears successfully using the info from
Mr. Law's book. The book isn't very long but is packed with easy to
understand information. It even has plans for making a tool for making
gear cutters. The tool has a couple eccentrics on it that enable a 12
tooth gear cutter to be cut in the lathe because each tooth is backed
off as the tool rotates. So there is constant relief for each tooth
while at the same time the tooth profile doesn't change and sharpening
only requires grinding the top of each tooth.
Eric

Don't you mean to sharpen you just grind the FACE of each tooth ?

--
Snag

Thanks for the comments, All. Problem is I do not have the equipment to cut gears of any type. I am trying to cut one or two helical gears from brass or plastic. I don't intend on making other gears so I do not want to spend a bunch of money on an indexing table. I have tried to contact two gear manufacturers but thus far they have not responded to my inquiries. Also, I have been unable to locate another lathe that uses a 7/8"X8TPI leadscrew and a 32 tooth thread dial gear. This is why I asked two specific questions which so far I have been unable to find the answers for. I feel certain that someone here, perhaps a lot of people here can provide the answers. Thanks again, Gerry

On Wed, 30 Mar 2016 17:01:40 -0700 (PDT), Gerry
wrote:

Thanks for the comments, All. Problem is I do not have the equipment to cut gears of any type. I am trying to cut one or two helical gears from brass or plastic. I don't intend on making other gears so I do not want to spend a bunch of money on an indexing table. I have tried to contact two gear manufacturers but thus far they have not responded to my inquiries. Also, I have been unable to locate another lathe that uses a 7/8"X8TPI leadscrew and a 32 tooth thread dial gear. This is why I asked two specific questions which so far I have been unable to find the answers for. I feel certain that someone here, perhaps a lot of people here can provide the answers. Thanks again, Gerry

Gerry, as many of us have pointed out, this job doesn't require
anything more than the crudest "gear." How adventerous are you about
doing some experimenting? Especially if you make it out of plastic,
you can produce a fine gear on your lathe with an 8 tpi bottoming tap
and a jury-rigged "spindle" on your compound. I've made them out of
steel, in much finer pitches, but this one should be no problem.

The hard part is getting the right number of teeth. g That's because
the method, which many here could explain, is based on letting the tap
(which is held in a collet in your lathe, if you have the right size,
or which you can even hold in a chuck if you have to) free-feed itself
into the gear blank, and the number of teeth depends on how it feeds
into the blank. But you can get really nice teeth.

That means you might have to make a few tries before you get it right.
But, hey, you'r cutting plastic. If you like, after getting it right
in plastic, turn a brass blank to the same dimensions and try it in
that.

This is about the easiest kind of gear you could make. Give it a try.
You may amaze yourself. d8-)

--
Ed Huntress

On Wed, 30 Mar 2016 18:19:21 -0500, Karl Townsend
wrote:

Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.

I second the suggestion
Gunner

On Wednesday, March 30, 2016 at 3:26:51 PM UTC-4, Gerry wrote:
I need to make a 32t helical gear to mate with my 8TPI acme leadscrew. I have a couple of questions for those here who know way more than I do.

I need to mill slots into my 8TPI acme blank. It's just an old Sheldon leadscrew that fits nothing I have. I figure I'll cut 4 or 6 groves on my mill. My question is where should the leading edge be in relation to the center line of the blank. My gut tells me that the cutting edge should on the center line so the cutting edge is 90 degrees. If the center of the slot is centered instead the cutting edge will not be at a 90 degree angle. Does this matter?

Probably makes no difference. If the cutting edge is on the centerline , that would be good. If the cutting edge is a little off , it should be so the tooth are a bit sharper.

Second, the diameter of the blank. The circumference of 32 teeth divided by Pi gives me a dia of 1.27. Following a different method, adding three teeth divided by DP of 25.13 gives me a diameter of 1.39

Is the larger diameter for the OD and the smaller diameter is based on the diameter being half way up the tooth? That is the 1.39 is the diameter of the blank. And the 1.27 being the diameter of the contact with the worm.

Color me confused. Can anyone here answer these questions please?

BTW the gear will be brass.

I like UHMW poly. It wears well and is easy to cut.

I've made a jig to hold the blank in my tool post and hob will be in the lathe chuck. I intend to run the lathe as slow as I can and feed the gear blank into the hob slowly until I get enough teeth to operate my thread dial. I may do it in my mill, holding the blank in my vice and hob in my collet holder, depending on which one rotates the slowest. Thanks in advance for any feedback/suggestions

If you wrap a piece of paper around the black and cut it so it makes exactly one wrap. You can then mark it so you have 32 divisions, and use that to gash the blank so you do not have the problem of having one tooth too many or too few. See Ed's comment on self feeding.

Dan

On 2016-03-30, Terry Coombs wrote:
Gerry wrote:
I need to make a 32t helical gear to mate with my 8TPI acme
leadscrew. I have a couple of questions for those here who know way
more than I do.

I need to mill slots into my 8TPI acme blank. It's just an old
Sheldon leadscrew that fits nothing I have. I figure I'll cut 4 or 6
groves on my mill. My question is where should the leading edge be in
relation to the center line of the blank. My gut tells me that the
cutting edge should on the center line so the cutting edge is 90
degrees. If the center of the slot is centered instead the cutting
edge will not be at a 90 degree angle. Does this matter?

Second, the diameter of the blank. The circumference of 32 teeth
divided by Pi gives me a dia of 1.27. Following a different method,
adding three teeth divided by DP of 25.13 gives me a diameter of 1.39

Color me confused. Can anyone here answer these questions please?

BTW the gear will be brass. I've made a jig to hold the blank in my
tool post and hob will be in the lathe chuck. I intend to run the
lathe as slow as I can and feed the gear blank into the hob slowly
until I get enough teeth to operate my thread dial. I may do it in my
mill, holding the blank in my vice and hob in my collet holder,
depending on which one rotates the slowest. Thanks in advance for any
feedback/suggestions

It doesn't absolutely have to be cut helical . Since there is a very light
load , you can make the teeth a quarter inch wide and just cut them straight

Or -- you can cut them straight and wider, and mount the gear's
arbor at an angle matching the angle of the thread on the leadscrew. A
lot easier to do than cutting helical teeth -- especially without a
universal lathe (one whose table can be set to angles other than 90
degrees to the Y-axis.)

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Wed, 30 Mar 2016 18:46:54 -0500, "Terry Coombs"
wrote:

wrote:
On Wed, 30 Mar 2016 18:19:21 -0500, Karl Townsend
wrote:

Complicated subject. You've got more questions you don't even know to
ask yet.

Get the bible on gear cutting:

"Gears and Gear Cutting" by Ivan Law

I've seen a couple good You tube videos also.
Karl is correct about Ivan Law's book. But if this gear is for a
threading dial than you don't really need a gear that has traditional
teeth. Just properly shaped pins would work because there is almost no
load on the gear. It is after all just an indicator. Unless you cut a
worm gear there will only be a line contact between the gear and the
worm. The proper hob for the worm gear will resemble the worm, in your
case the leadscrew. I have cut gears successfully using the info from
Mr. Law's book. The book isn't very long but is packed with easy to
understand information. It even has plans for making a tool for making
gear cutters. The tool has a couple eccentrics on it that enable a 12
tooth gear cutter to be cut in the lathe because each tooth is backed
off as the tool rotates. So there is constant relief for each tooth
while at the same time the tooth profile doesn't change and sharpening
only requires grinding the top of each tooth.
Eric

Don't you mean to sharpen you just grind the FACE of each tooth ?
It depends on how you look at it. The top or face being the same
surface, which is essentially flat, as opposed to the rest of the
cutter which has a gear tooth contour. However, you are technically
correct and I should use the correct terminology.
Eric