Making New Twin Gears - Backlash Spec?

bradjacob · Dec 2, 2014

Calling anyone who's made their own shop-made twin-gears before...

I finally have a dividing head and am wanting to christen it by making some new twin gears for my reversing lever. I have most of the specs on them, but was wondering if anyone knows South Bend's exact spec for backlash. These gears needs some small amount, but I wanted to be dead-certain.

My *guess* would be somewhere around 3 thou?

Any info would be greatly appreciated.

johnoder · Dec 2, 2014

Any info would be greatly appreciated.

Manual of Gear Design Section Two by Buckingham says .030 for 1 DP in the 14 1/2 degree composite system

This equates to .0019" for 16 DP, your gears may be some other DP

iwananew10K · Dec 2, 2014

John O is right but no need to worry about backlash in this case - predetermined by the center to center distance on the reverser.
just make `em to the specs (DP,PA ,tooth count) and they`ll fit fine.

fun project, any specific material you`re going for?

bradjacob · Dec 2, 2014

iwananew10K said:
John O is right but no need to worry about backlash in this case - predetermined by the center to center distance on the reverser.
just make `em to the specs (DP,PA ,tooth count) and they`ll fit fine.

fun project, any specific material you`re going for?

Hey Chad! That too actually, not sure which steel SB used, but I'd love to know...
I believe that backlash is a required factor, no? DP, PA & teeth are all fixed but knowing how far "deep" to cut will be backlash factor, right? Since the gears are of pyramid shape, the deeper you cut them, the more space will be introduced and produce some space (backlash). I would figure that since these are high torque and low RPM, we would need (some) but not a lot of backlash in order for them to mesh freely, but also be as quiet as possible.

I dunno, I've never cut a single gear in my life, so this ought to be a real doozy, LOL

iwananew10K · Dec 2, 2014

pretty sure all the stock gearing were just cast iron.
wish I had my copy of MH and I could tell you the DOC for the cutter( assuming you`re going to use standard involute cutter?)
what DP are they? - I know the 10" used 16 on the reversers, but not sure about the 13"

Zahnrad Kopf · Dec 2, 2014

If you are looking for "quiet", then Hobbing is better than milling. And if that's the case, I was getting ready to Hob & Heat Treat some of those gears, shortly. ( actually my whole train, there. ) I might be talked or coerced into making more than one set... Maybe...

iwananew10K · Dec 4, 2014

is that a SB that you`re going to replace the train on Zahnrad? 8 gears, including the extra stud gear? (assuming a double lever gearbox)
that *would* be interesting, curious about the heat treating too.

Zahnrad Kopf · Dec 4, 2014

iwananew10K said:
is that a SB that you`re going to replace the train on Zahnrad? 8 gears, including the extra stud gear? (assuming a double lever gearbox)
that *would* be interesting, curious about the heat treating too.

Yes. It's my old Heavy10 that I've had for something like 25 years. The train is fairly noisy and worn by now so I thought to make replacements as I know someone that knows a little bit about making gears.

iwananew10K · Dec 4, 2014

wonder who that is?

that does sound great(no pun) - an entire train of gears with a true involute form on a SB... :smitten:

stephen thomas · Dec 4, 2014

[...quote]that *would* be interesting, curious about the heat treating too.[/quote]

Did SB _ever_ heat treat anything besides spindles? (& in the late days, beds)

One of the fascinating/aggravating things about SB's is how well they built the machines....with such crappy wear prone materials.
Reason they are so easy to work on/make new parts. Also the reason they need it.

Steel would not be my first preference for those gears, the CI will wear better. Especially since the spindle end is the gear you do not want to be the sacrificial member in the train. If the gears are to be hardened & ground, then maybe. But Zahnrad would be best advice for that. Also, if I was in a hurry and did use steel because it was on hand, would consider bronze bushed to run on the pins as that is another place steel might be an issue over time.

smt

bradjacob · Dec 4, 2014

iwananew10K said:
pretty sure all the stock gearing were just cast iron.
wish I had my copy of MH and I could tell you the DOC for the cutter( assuming you`re going to use standard involute cutter?)
what DP are they? - I know the 10" used 16 on the reversers, but not sure about the 13"

Yeah, I'll be using the involute cutter and referring to my Machinery's Handbook for sure.
I know the bigger, low-speed, side gears were cast, but all the twins on the machines I've had/restored (9a, 10 & 13) all are some grade of carbon steel. There's no grain.

bradjacob · Dec 4, 2014

Zahnrad Kopf said:
If you are looking for "quiet", then Hobbing is better than milling. And if that's the case, I was getting ready to Hob & Heat Treat some of those gears, shortly. ( actually my whole train, there. ) I might be talked or coerced into making more than one set... Maybe...

Zahnrad - tell me about that, I never heard of Hob & Treat? Sounds interesting and Chad is drooling, so it's gotta be good!

Zahnrad Kopf · Dec 4, 2014

bradjacob said:
Zahnrad - tell me about that, I never heard of Hob & Treat? Sounds interesting and Chad is drooling, so it's gotta be good!

Nothing special. I do it almost every single day. I would estimate that we do 95% of our Gear making in this way. Most of the time I make them of 4140, so it's Turning, Milling if needed, Hobbing, Heat Treat, & Temper. Then, any Grinding and/or Honing, as needed. I'm thinking Turn, Hob, install keyway, Heat Treat, & Temper. This should ensure that they last forever and maintain a good Involute.

iwananew10K said:
that does sound great(no pun) - an entire train of gears with a true involute form on a SB...

You raise a question and curiosity for me -

I assumed that SB Hobbed their Gears. Did they? From your post it seems to imply otherwise. Did they Mill them? Either way, I'm betting that with hardly any effort I can drastically improve the smoothness and running quality as well as the sound of this old girl. And I plan to do so!

iwananew10K · Dec 4, 2014

I`m sure they did hob them,but I have seen a few originals that were not done particularly well(especially the banjo idlers)
was more referring to my own shop made ones.

Ted may correct me on this but I *think* aside from the spindle and hard beds that most of the hardware was heat treated.
(fasteners, gear studs and such)

SBLatheman · Dec 4, 2014

stephen thomas said:
[...quote]that *would* be interesting, curious about the heat treating too.

Did SB _ever_ heat treat anything besides spindles? (& in the late days, beds)

smt

Heat treat is any treatment using heat. Stress relieving, annealing, normalizing, carburizing, hardening, drawing, etc.
South bend did all those things.
Have any blue or black parts on you lathe? They even did "heat treat blue"

Zahnrad Kopf said:
You raise a question and curiosity for me -

I assumed that SB Hobbed their Gears. Did they? From your post it seems to imply otherwise. Did they Mill them? !

Of course they hobbed gears. They also shaved some of them.

iwananew10K said:
Ted may correct me on this but I *think* aside from the spindle and hard beds that most of the hardware was heat treated.
(fasteners, gear studs and such)

They used a cyanide treatment on screws to make them screw driver resistant. Some bolts and washers too
They also hardened twin gear studs, collet sleeves, cross feed and compound screws(optional), tailstock spindles(optional), and a lot more.

Ted

bradjacob · Dec 4, 2014

SBLatheman said:
Heat treat is any treatment using heat. Stress relieving, annealing, normalizing, carburizing, hardening, drawing, etc.
South bend did all those things.
Have any blue or black parts on you lathe? They even did "heat treat blue"

Of course they hobbed gears. They also shaved some of them.

They used a cyanide treatment on screws to make them screw driver resistant. Some bolts and washers too
They also hardened twin gear studs, collet sleeves, cross feed and compound screws(optional), tailstock spindles(optional), and a lot more.

Ted

Uhhhh' can someone please tell me what hobbing is?

bradjacob · Dec 4, 2014

Zahnrad Kopf said:
I assumed that SB Hobbed their Gears. Did they? From your post it seems to imply otherwise. Did they Mill them? Either way, I'm betting that with hardly any effort I can drastically improve the smoothness and running quality as well as the sound of this old girl. And I plan to do so!

You ask if they milled their gears. How else do gears get cut if not milled? You "gear guys" are confusing me right now, LOL

Zahnrad Kopf · Dec 4, 2014

bradjacob said:
Uhhhh' can someone please tell me what hobbing is?

LOL. Here, Let Me Google That For You.

tgolden · Dec 4, 2014

You should build your own small gear hobber. Then you can make all the gears you'll ever need.

Martin Model & Pattern - your online source for fine quality patterns and castings

bradjacob · Dec 5, 2014

** Not knowing the pressure angle, I took a chance and bought a Brown & Sharpe involute gear cutter (NOS) on eBay yesterday for $35 bucks.

It's a No. 4, 16-DP, 26-34 teeth. Other markings are: D"+F .1348"

What does all this mean - and can anyone tell what it's PA (pressure angle) is?

Here's the eBay item:
New Old Stock No 4 B s Involute Gear Cutter 16DP 26 to 34 T | eBay

Making New Twin Gears - Backlash Spec?

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