Spirals on a shaft.

[Duey C]

Is there a setup method for a math dumb dumb to cut spirals (AKA very coarse shallow threads) with an old SB 9C? The spirals are oil movers.
One is 15/16“ between the grooves. .938 tpi?
I have trouble just expressing these pitches.
The other is 1/4“ between grooves. 4 tpi?
In my writing this, did I actually figure out the pitches? Hehe, nah can’t be.
Your thoughts?

Swami sees the future of my start to experimenting with the gear train and a marker in a tool holder for testing. If wrong, wipe it off.
The factory did it in the 20‘s and 30‘s and I’m guessing with a lathe.
Alas, the fellow that made repro’s/repops isn’t anymore.
Five different diameters, two different spirals, two different keyways and one hole thru.

 

[EmGo]

Is there a setup method for a math dumb dumb to cut spirals (AKA very coarse shallow threads) with an old SB 9C? The spirals are oil movers.

Spirals are cone-shaped. That's a helix, just a normal thread with a long lead. Of course you can do it, just set the threading gears for a ridiculous lead, but it will be hard on the geartrain.

 

[johnoder]

For instance - if the lathe is set up to cut 8 TPI that is a .125" lead -and incidentally the spindle and lead screw will turn the exact same speed. Now if you wanted say a 2" lead on your part the lead screw would have to turn 16 times faster than the spindle.

This is because the screw lead is still .125 and 16 times .125 is 2.000".

Your gear train driving the lead screw has to put up with this torture

 

[guythatbrews]

Consider 4 TPI means 4 threads/inch. The reciprocal of 4 threads/inch is (one inch)/(4 threads) or a pitch of 1/4 ". So threads/inch is the reciprocal of inches/thread. Inches/thread is called pitch.

Your groove with a pitch of 15/16" is thus 16/15 TPI, or 1.067 TPI. Crazy I know. But it makes sense, just over one thread per inch.

If you can find room for a big enough gear train to cut a 15/16ths pitch, which is unlikely, you'll probably need to drive it by powering the leadscrew, not the spindle. Maybe you could do this with a hand drill at low speed.

Rather than interminable trial and error read up on setting change gears to cut threads.

For oil grooves this seems like quite a bit of work. Consider laying out a helix and filing the groove. You can do this with a triangular piece of paper and a prick punch. If you are interested i can describe that.

 

[kitno455]

list all the gears you have, including the compounds, and what is the biggest gear you can fit on the reverse tumbler stud.

allan

 

[EmGo]

I don't know how slow your lathe can go, but if you put a cutoff wheel on a 1/4" arbor (make one from a socket head cap screw) and lay out the helix on your shaft, you can do a pretty nice job with a dremel by hand. Similar to guy's method but less manual labor

 

[guythatbrews]

I don't know how slow your lathe can go, but if you put a cutoff wheel on a 1/4" arbor (make one from a socket head cap screw) and lay out the helix on your shaft, you can do a pretty nice job with a dremel by hand. Similar to guy's method but less manual labor

What about one of those dremel rubber-bonded cutoff wheels?

 

[EmGo]

What about one of those dremel rubber-bonded cutoff wheels?

If they're over a buck fifty I ain't goin' for it

 

[Duey C]

Thank you. Some info to chew on.
Spindle speed would be 55.

 

[animal12]

Like mentioned above , what gears do you have ? You may be able to get creative with the gears in your gear train to get what our after . You may need a new gear of 2 . You might want to look at cutting a worm gear , there may be something there that my help .
animal

 

[Duey C]

Thanks.
I have the set of gears that came with the lathe. I believe complete minus the 32 which I borrowed the extra from 926 the 12". Needed the extra many years ago for threading an 8 tpi... 32 & 32.
I have a gear change coming for the next step on a project in the lathe so a good time to take a few minutes to fiddle with the gears a bit.
Yes, I need to see how big of a gear I can cram on the "stud" for the intermediate gear.
Likely need to flip the intermediate.

 

[johnoder]

Here are TWO compound gears helping get things done - but you need such to be the "other way around" - to speed-up the lead screw

Added some scans in case you need to bone up on simple and compound gearing

 

[Duey C]

Thank you John! Good reminders or food for thought for the rest of us.
Thank you if you read this thru to the end.
.
Neat exercise! Before changing to 14 tpi for my parts, I fussed with gearing.
This lathe has a single neck banjo not the double so that’s as course as I can go.
The largest gear I can put on the spindle/stud is a 72T.
I could cut the end of the spindle off with a hacksaw for more room... I’m KIDDING!
The little 18T on the screw.

The intermediate double-gear idler cannot be reversed, no room.
72T to 18T yielded about .555-.560 carriage travel per revolution.
81T intermediate idler in between.
I can deal with that.

About twice as many grooves as the factory. Starting about 1925 for this particular style shaft, they used a mill (think of the spinning gear train and travel of the mill table), a lathe (like I’m trying) or a specialized machine at far higher speeds for production shaft helix’s.
Helix: The grooves are the same distance between each throughout.
Spiral: The grooves are going to change spacing distance at some point.
Courtesy of the content authority. All rights to them if any.
Differences Between Helix and Spiral
When a Helix is described it's like this "…a line called the axis from which every point on the curve is at equal distance." And the Spiral as "…a curve that originates from some point(origin) and moves away from it in a uniform fashion."
Now, if you read carefully you might say it is the same definition, but a Helix has the same radium and the Spiral has a reducing or expanding radius and is progressive.
There are sources that explain that Helix is associated with mathematics and spiral to geometry.

Hehe, I was a bit butt-hurt about splitting hairs concerning the difference between the two.
That went away. You were correct.

Not scary at all at 55 spindle rpm’s!
This old lathe is well oiled, the carriage has little sliding resistance (my choice), the lead screw is pretty darn clean and the half-nuts have been cleaned out fully.
I don’t care to ruin anything on a 95 year old small time money maker.
The gear train was completely quiet for non-cutting trials.

Thanks gang!