13" South Bend lathe Quick Change Tumbler Lever Question

dwall174 · Apr 5, 2022

I'm currently working on rebuilding a 13" South Bend turret lathe & I've came across a possible issue with the tumbler levers. The castings are worn/elongated where the tumbler shaft runs through the casting.

I'm wondering if there may be an old print/drawing of these castings?

Knowing the center-to-center dimension of the tumbler shaft & the tumbler gear, I could always bore it out & install a bushing.

Pic. with gears meshed together gives me an educated guess, but a print or drawing with the dimensions would help out if there was one out there.

Doug

johnoder · Apr 6, 2022

I'd be counting teeth, coming up with a pitch dia for each gear and half of the two pitch dias added together and divided by two is the center distance

in the process you will also come up with Diametral pitch of those gears

Example...

32 teeth and 2.125 OD

Add TWO to the two count

Example:

32 plus 2 = 34

34 divided by 2.125 = 16 DP

32 teeth of 16 DP has a pitch dia of 32 divided by 16 = 2.000"

You could see if you are close that way as compared to your pictured way

dwall174 · Apr 8, 2022

johnoder said:
I'd be counting teeth, coming up with a pitch dia for each gear and half of the two pitch dias added together and divided by two is the center distance

Never really working with gears that much, all that gear terminology basically just confuses me!

Trying to follow your example given, I'm coming up with 12 for the Diametral pitch, which I don't think is correct? From other remarks about the change gears on a 13" South Bend I believe they are 16 DP with a 14.5 pressure angle?

The large gear has 32 teeth & a outside dia. of 2.840"(outer edge of teeth)
The small gear has 20 teeth & a outside dia. of 1.840"(outer edge of teeth)
The depth in-between each gear/tooth is approx. 0.200" deep.

Doug

johnoder · Apr 8, 2022

Good work - 12 DP it is ( 11.95 is close enough to say 12)

So,, PD for 32 would be 2.6666 and PD for 20 would be 1.666 (find PD by dividing tooth count by 12)

Add those together and you have 4.333 and half of 4.3333 is 2.166 - which is the center distance you would have for the pair

You can see in your first photo you are only ten thou different than my way - so a real good way to check

A thing to keep in mind is the gears are not metal to metal in assembly. If your first photo has them touching each other there is part of the ten thou

dwall174 · Apr 8, 2022

johnoder said:
A thing to keep in mind is the gears are not metal to metal in assembly. If your first photo has them touching each other there is part of the ten thou

I knew that they're not metal to metal in assembly, but I was trying to get a rough idea of the center-to-center dimension. In the casting's current elongated condition there's a lot of play on the tumbler shaft. Getting it back close to the original dimensions should help in the engagement of the change gears.

According to the serial # "https://www.practicalmachinist.com/...mbers-wanted-128483/index129.html#post3846990" it looks like this lathe was made in 1961~62. At 60 years old, I'm guessing there's also some wear to the original gears OD.

I plan to replace at least one of the tumbler gears, which looks to have been repaired! Probably do to the gears not engaging properly do to the elongation of the lever castings.

Doug

SBLatheman · Apr 8, 2022

dwall174 said:
I knew that they're not metal to metal in assembly, but I was trying to get a rough idea of the center-to-center dimension. In the casting's current elongated condition there's a lot of play on the tumbler shaft. Getting it back close to the original dimensions should help in the engagement of the change gears.

According to the serial # "https://www.practicalmachinist.com/...mbers-wanted-128483/index129.html#post3846990" it looks like this lathe was made in 1961~62. At 60 years old, I'm guessing there's also some wear to the original gears OD.

I plan to replace at least one of the tumbler gears, which looks to have been repaired! Probably do to the gears not engaging properly do to the elongation of the lever castings.

Doug

I have some new gears, and probably can get the correct center distance for you.
Send me an email
Ted
[email protected]

dwall174 · Tuesday at 10:46 PM

Bringing this old post of mine back up, still trying to find the correct C/L distance of the two holes!

If anyone happens to currently have a 13" double tumbler gearbox disassembled, it would be great to know the correct C/L distance!

SBLatheman said:
I have some new gears, and probably can get the correct center distance for you.
Send me an email
Ted
[email protected]

Ted sending you an email.

Doug

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