JimK
Diamond
- Joined
- Apr 25, 2003
- Location
- Berkeley Springs, WV, USA
We of the South Bend set and thise who otherwise work with or restore old machinery must be acquainted with the flat belt drive for power transmission.
Many young people never see it until they are invoved with a South Bend lathe, so things that we older guys take for granted might not be apparant to thm.
The flat belt transmits power by friction alone, it doesn't have the advantage of the wedging action of the "V" belt.
Without the aid of the wedging action, how does it do so well?
For starters, flat belt drive is efficient. There is very little flexing friction as the belt goes from straight to the bend around the pulley. In a simple two pulley drive, that bend happens four times.
No, it is not like a spring, the belt takes up friction returning to straight, it doesn't give back part of the energy it took to flex it.
Any idler pulley adds two flexes.
From this we can see that the flat belt will be more efficient than the "V" belt because of it's lower flexing friction and the absence of the wedging friction of a "V" belt drive.
There are three ways of increasing friction of a flat belt.
First is increasing the width of the flat belt, that is obvious.
Second is incrasing the tension of the belts, while that is obvious, incrasing tension has serious limitations.
Third is increasing friction by the treatment of the friction surfaces of the belt and pulley.
The most common friction enhancment for drive pulleys is to make them as smooth as possible.
That seems counter intuitive, but in the long run, smooth pulleys are fundamentally correct because there is intimate contact between the belt and the surface of the pulley.
A rough pulley will wear smooth and if the belt depends on roughness, then the drive will fail.
A smooth pulley will wear smooth if it wears at all. A properly rigged belt drive with smooth pulleys will not fail until the belt does.
The flat belts of preference were always Leather. Leather as two sided, Flat and Scruggs.
Tanned belting leather has the smooth side because it is the Animal's skin. The scruggy side was inside of the Bovine.
Leather is a very durable and stong natural material, it still is one of the best materials for flat belts except that it is now expensive.
Since tanners can make smooth leather belts, the smooth pulley trick works very well. The skin side literally gabs clean, smooth cast iron. The friction is actually amazing. Leather will transmit significant power without undue tension.
Some of the thinner synthetic belts make a flat belt drive wonderfully efficient. There is less flexing friction beacuse they are so thin. The synthetic materials are smooth, many of them are smooth on both sides.
The material is thin compared with leather and glue joints, especially the heated ones are permanent.
Synthetic belts require more tension. The chemists on Earth haven't yet figured out what God put in Cow Skin that works the way it does.
One other advantage of the synthetics is that it doesn't stretch as much as leather, so the drives don't need to be taken up as often as leather ones.
Thin synthetic belts are usually hot glued in place, the material doesn't have the tenacity to accept allegator clasps, and if laced, there will be a"jump" as the laces come around into the pulleys.
Now for the other pulley tricks.
At least one of the flat belt drive pulleys must be crowned, otherwise the belt will slip off.
There are two types of crowning, taper and spherical.
South Bend and most other pulleys are taper crowned. That is, the surfaces of the pulley are tapered unifrmly from both ends with the largest diameter in the middle.
This sets up balanced stresses in the belt so it doesn't meander.
Belts always go to the big end of a taper when running, so if the big end of two tapers is in the middle of a pulley, the belt will naturally want to track in the middle of the pulley.
One complaint about taper crowning is that the middle of the pully gets tighter and starves the outside ends for tension.
Spehrical crowning tries to lessen that effect by making the dfifference in diameters less abrupt. The belt tends to cling tighter to the smoothly curved pulley surface more intimately across more of the width of the pulley surface.
Troubles wth flat belt drive.
Age and oil are enemies of leather. The oils used to make leather supple and smooth are not the oils used to lubricate machinery.
Leather will pick up oil, especially on the scruggy side. The oil will be absorbed and the belt will loose it's tensile strength. There will be no way to satifactorilly apply constant tension to such a belt. The drive will fail because the belt fails.
Being a natural material, leather obeys the Laws of God. From dust it was made, to dust it will return. Don't expect a really old leather belt to do well in service.
Synthetics last a bit longer than leather. they have been around only a historically short time and nobody has seen what a hundred years will do to one.
Synthetics don't like oil of any kind. They won't accept it into themselves and the will loose friction dramatically if oil gets between the pulley and the belt - more so than leather.
All of the above means that flat belt drives must be run DRY at ALL Costs.
South Bend drive mechanisms are not the best engineered of the flat belt systems, there are too many places that oil can find it's way into the flat belts.
The countershaft bearings many times are just pain bearings with cup oilers. any excess will be slung outward and eventually get on the belt. That entire mechanism must be kept clean and not over oiled.
It is extremely important that the headstock pulley have oil inside it in order to lubricate the pulley bearings when the lathe is in back gears.
The oil screw cap is right in the middle of one of the pulley surfaces. Oil will dribble when it is put into such a samll hole, and if the screw isn't sealed, oil will also dribble when the pulley stops in the screw-down position.
If you are having trouble with a South Bend flat belt drive, look at those two places first.
First, stop the oil intrusion, then clean the pulleys with something like alochol. Don't forget to clean the belt thoroughly. The belt and pulleys must be Clean and Dry!
Running the lathe.
Power is the product of speed and torque. If a lathe motor has a given power, then it will produce more torque when the spindle speed is slow ad less torque when the spidle speed is high.
To transmit increased torque, you need more friction on the slower speed shaft. That is a natural consequence of the larger pulley.
Theoretically, a South Bend Lathe should be able to stall it's motor driving through any step of it's cone pulleys. Don't bet on it.
If you are having slippage problems and your pulleys are clean and dry, you must go to a bigger pulley step on the headstock.
It is easy to overload a South Bend Lathe with dull or low rake cutting tools. "How to Run a Lathe" rccomends using a lot of rake on tools for most materals. This eases the cut and puts less strain on the drive.
If you want to remove a lot of metal in a hurry, then put the lathe in Back Gears and FEED the tool. The slow cutting speed won't hurt a heavily raked tool bit and the machine will take a very deep cut in back gears without making too high a demand on the flat belt drive.
TNMG carbide negative rake inserts just won't cut it on the South Bend. Don't Use Carbide Lathe Tools Unless Absolutely Necessary.
If you want to use Carbide, then get a Series 60 Monarch.
If you are putting an old South Bend back in action it is best to start with a new belt. Use the kind you want, but make sure that those pulleys are free from any oil and that the belt stays free from any oil.
If you haven't run a South Bend Lathe much, then by all means read "How to Run a Lathe" and pay attention to the parts of the book concerning cutting tool angles.
The Flat Belt Drive is the Essence of the South Bend Lathe. Work with it and you will be more than satisfied, work against it and you will have no end of trouble.
[This message has been edited by JimK (edited 02-14-2004).]
Many young people never see it until they are invoved with a South Bend lathe, so things that we older guys take for granted might not be apparant to thm.
The flat belt transmits power by friction alone, it doesn't have the advantage of the wedging action of the "V" belt.
Without the aid of the wedging action, how does it do so well?
For starters, flat belt drive is efficient. There is very little flexing friction as the belt goes from straight to the bend around the pulley. In a simple two pulley drive, that bend happens four times.
No, it is not like a spring, the belt takes up friction returning to straight, it doesn't give back part of the energy it took to flex it.
Any idler pulley adds two flexes.
From this we can see that the flat belt will be more efficient than the "V" belt because of it's lower flexing friction and the absence of the wedging friction of a "V" belt drive.
There are three ways of increasing friction of a flat belt.
First is increasing the width of the flat belt, that is obvious.
Second is incrasing the tension of the belts, while that is obvious, incrasing tension has serious limitations.
Third is increasing friction by the treatment of the friction surfaces of the belt and pulley.
The most common friction enhancment for drive pulleys is to make them as smooth as possible.
That seems counter intuitive, but in the long run, smooth pulleys are fundamentally correct because there is intimate contact between the belt and the surface of the pulley.
A rough pulley will wear smooth and if the belt depends on roughness, then the drive will fail.
A smooth pulley will wear smooth if it wears at all. A properly rigged belt drive with smooth pulleys will not fail until the belt does.
The flat belts of preference were always Leather. Leather as two sided, Flat and Scruggs.
Tanned belting leather has the smooth side because it is the Animal's skin. The scruggy side was inside of the Bovine.
Leather is a very durable and stong natural material, it still is one of the best materials for flat belts except that it is now expensive.
Since tanners can make smooth leather belts, the smooth pulley trick works very well. The skin side literally gabs clean, smooth cast iron. The friction is actually amazing. Leather will transmit significant power without undue tension.
Some of the thinner synthetic belts make a flat belt drive wonderfully efficient. There is less flexing friction beacuse they are so thin. The synthetic materials are smooth, many of them are smooth on both sides.
The material is thin compared with leather and glue joints, especially the heated ones are permanent.
Synthetic belts require more tension. The chemists on Earth haven't yet figured out what God put in Cow Skin that works the way it does.
One other advantage of the synthetics is that it doesn't stretch as much as leather, so the drives don't need to be taken up as often as leather ones.
Thin synthetic belts are usually hot glued in place, the material doesn't have the tenacity to accept allegator clasps, and if laced, there will be a"jump" as the laces come around into the pulleys.
Now for the other pulley tricks.
At least one of the flat belt drive pulleys must be crowned, otherwise the belt will slip off.
There are two types of crowning, taper and spherical.
South Bend and most other pulleys are taper crowned. That is, the surfaces of the pulley are tapered unifrmly from both ends with the largest diameter in the middle.
This sets up balanced stresses in the belt so it doesn't meander.
Belts always go to the big end of a taper when running, so if the big end of two tapers is in the middle of a pulley, the belt will naturally want to track in the middle of the pulley.
One complaint about taper crowning is that the middle of the pully gets tighter and starves the outside ends for tension.
Spehrical crowning tries to lessen that effect by making the dfifference in diameters less abrupt. The belt tends to cling tighter to the smoothly curved pulley surface more intimately across more of the width of the pulley surface.
Troubles wth flat belt drive.
Age and oil are enemies of leather. The oils used to make leather supple and smooth are not the oils used to lubricate machinery.
Leather will pick up oil, especially on the scruggy side. The oil will be absorbed and the belt will loose it's tensile strength. There will be no way to satifactorilly apply constant tension to such a belt. The drive will fail because the belt fails.
Being a natural material, leather obeys the Laws of God. From dust it was made, to dust it will return. Don't expect a really old leather belt to do well in service.
Synthetics last a bit longer than leather. they have been around only a historically short time and nobody has seen what a hundred years will do to one.
Synthetics don't like oil of any kind. They won't accept it into themselves and the will loose friction dramatically if oil gets between the pulley and the belt - more so than leather.
All of the above means that flat belt drives must be run DRY at ALL Costs.
South Bend drive mechanisms are not the best engineered of the flat belt systems, there are too many places that oil can find it's way into the flat belts.
The countershaft bearings many times are just pain bearings with cup oilers. any excess will be slung outward and eventually get on the belt. That entire mechanism must be kept clean and not over oiled.
It is extremely important that the headstock pulley have oil inside it in order to lubricate the pulley bearings when the lathe is in back gears.
The oil screw cap is right in the middle of one of the pulley surfaces. Oil will dribble when it is put into such a samll hole, and if the screw isn't sealed, oil will also dribble when the pulley stops in the screw-down position.
If you are having trouble with a South Bend flat belt drive, look at those two places first.
First, stop the oil intrusion, then clean the pulleys with something like alochol. Don't forget to clean the belt thoroughly. The belt and pulleys must be Clean and Dry!
Running the lathe.
Power is the product of speed and torque. If a lathe motor has a given power, then it will produce more torque when the spindle speed is slow ad less torque when the spidle speed is high.
To transmit increased torque, you need more friction on the slower speed shaft. That is a natural consequence of the larger pulley.
Theoretically, a South Bend Lathe should be able to stall it's motor driving through any step of it's cone pulleys. Don't bet on it.
If you are having slippage problems and your pulleys are clean and dry, you must go to a bigger pulley step on the headstock.
It is easy to overload a South Bend Lathe with dull or low rake cutting tools. "How to Run a Lathe" rccomends using a lot of rake on tools for most materals. This eases the cut and puts less strain on the drive.
If you want to remove a lot of metal in a hurry, then put the lathe in Back Gears and FEED the tool. The slow cutting speed won't hurt a heavily raked tool bit and the machine will take a very deep cut in back gears without making too high a demand on the flat belt drive.
TNMG carbide negative rake inserts just won't cut it on the South Bend. Don't Use Carbide Lathe Tools Unless Absolutely Necessary.
If you want to use Carbide, then get a Series 60 Monarch.
If you are putting an old South Bend back in action it is best to start with a new belt. Use the kind you want, but make sure that those pulleys are free from any oil and that the belt stays free from any oil.
If you haven't run a South Bend Lathe much, then by all means read "How to Run a Lathe" and pay attention to the parts of the book concerning cutting tool angles.
The Flat Belt Drive is the Essence of the South Bend Lathe. Work with it and you will be more than satisfied, work against it and you will have no end of trouble.
[This message has been edited by JimK (edited 02-14-2004).]
