Understanding dangers of bull gear pin in wrong position when powering on lathe

twooldvolvos

twooldvolvos

Registered
Registered
Joined
Oct 19, 2020
Messages
160
As you can tell from these questions, I am entirely new to running a lathe. I am getting ready to turn my South Bend 10k on for the first time and would like some advice to avoid causing damage. Here are a few questions:

Q1: What would happen if I accidentally turned on the lathe with back gears engaged and bull gear pin engaged also?

Q2: What would happen if I accidentally turned on the lathe with my bull gear pin disengaged and back gears disengaged?

Q3: Is it proper to turn on the motor with the belts already tightened or is it better to turn on the motor and then tighten the belt?

Thanks for your advice.
 
Q1: Spindle is locked; hopefully a belt will slip- worst case break a gear
Q2: Spindle might rotate at a slow speed but will not transmit any force or do any damage
Q3: Most folks do the former, although the latter won't hurt anything
-Mark
ps this is all covered in the South Bend booklet "how to run a lathe" which I believe is still being printed-? Not sure
 
Last edited:
Q1: you will either break something or the belts will slip.

Q2: the motor will spin, but the spindle will not.

Q3: I always tighten the belts first. I have gotten in the habit of turning the chuck a fraction of a turn before cranking the motor just to be sure everything turns properly. Yes, I do this every time. Its a habit...

-Bear
 
I have a SB 9 and I've been running it for about 10 years. My understanding is that the 10k is essentially the same configuration.

1. nothing will move and the flat belt will slip off of the cone pulley in the direction of a smaller pulley. Engaging both back gears and pin is what you do to remove anything threaded on the spindle

2. Headstock won't spin, you engage the belt and nothing happens and you say "stupid" outloud

3. Always engage the flat belt last. The hand lever that engages/disengages the flat belt to the headstock is what you always use to start/stop turning. This plays into Q1 - as you engage the belt with the headstock locked it will start to slip and you realize that you forgot to unlock the spindle.

I've never had an "exciting" moment due to backgears and bull pin.
There have been other exciting moments.

-Dave
 
dbb-the-bruce said:
3. Always engage the flat belt last. The hand lever that engages/disengages the flat belt to the headstock is what you always use to start/stop turning. This plays into Q1 - as you engage the belt with the headstock locked it will start to slip and you realize that you forgot to unlock the spindle.

I've never had an "exciting" moment due to backgears and bull pin.
There have been other exciting moments.

-Dave
Click to expand...

OK, so two people disagree with me regarding using the flat belt tension handle as the main engage/disengage... Oh well.
I think that in the whole drive train, the flat belt slipping is generally the first thing happen when I screw up and lock up the lathe. It Seems to me that is somewhat intentional. When first leaning I ran the tension on my flat belt a LITTLE light for just this reason - incase I screwed up.

I am assuming that the 10K also has the handle to swing the cone pulleys into "engaged" like on the 9
 
Q1: The belt would slip. The pull on the belt isn't strong enough to break the pin. Been there, done that.

Q2: The cone pulley would turn and nothing else. Been there, done that.

Q3: Either way is fine. The only thing you should try to remember, is to disengage the belt tension at the end of your session. If not, it can stretch the belt a little (don't worry, it's just good practice to do this and I've done it more times than I would care to admit with nothing bad resulting from it).
 
dbb-the-bruce said:
OK, so two people disagree with me regarding using the flat belt tension handle as the main engage/disengage... Oh well.
I think that in the whole drive train, the flat belt slipping is generally the first thing happen when I screw up and lock up the lathe. It Seems to me that is somewhat intentional. When first leaning I ran the tension on my flat belt a LITTLE light for just this reason - incase I screwed up.

I am assuming that the 10K also has the handle to swing the cone pulleys into "engaged" like on the 9
Click to expand...
Add another person to the list of those who do not agree with you on the matter of having the belt tension released with the motor running. Also I quite agree that the belt tension should be released when the machine is not in use.
 
If you have replaced your leather drive belt with a serpentine belt, there is no need to release belt tension when the lathe is not in use. It will not stretch.
 
MrWhoopee said:
If you have replaced your leather drive belt with a serpentine belt, there is no need to release belt tension when the lathe is not in use. It will not stretch.
Click to expand...
Very true, I have a SB 9" lathe that has one, no stretch at all! I would like to sell the lathe, has quick change and 3 and 4 jaw chucks and a set of Armstrong tool holders, I am asking $1200, PM me for more info.
 
You must log in or register to reply here.
Back
Top