Pivot Friction Study

[Bob Tascione]

Hi all,
This is the study that I promised to put up here in Bernies thread about Junghans pivots at http://clockrepairtips.com/forum/viewtopic.php?f=2&t=1414

The study video link is https://www.youtube.com/watch?v=Wrg5b8U1zVM

Hope you enjoy it and please comment on it at youtube if you have a chance.

Bob

[bernie weishapl]

I did enjoy it Bob. Very interesting. Lots of food for thought.

[bernie weishapl]

I did enjoy it Bob. Very interesting. Lots of food for thought.

[bernie weishapl]

I did enjoy it Bob. Very interesting. Lots of food for thought.

[chris mabbott]

Excellent Bob, nice job and time consuming..

I haven’t used solidworks but I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

The other interesting point is that with the increased friction, due to dried up lubrication, the addition of dust etc, which, in turn, causes wear to the point of creating an elongated bushing. This also increases the contact point by a great percentage. Let’s say on a brand new bushing, and a newly polished pivot, that we have a point of contact on the bottom that is 10% of the circumference. Due to wear, we could see an increase of up to 30%+ of contact as the pivot gouges its way deeper into the bushing.

Which brought on my next thought 😮 The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of? 🙄

[chris mabbott]

Excellent Bob, nice job and time consuming..

I haven’t used solidworks but I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

The other interesting point is that with the increased friction, due to dried up lubrication, the addition of dust etc, which, in turn, causes wear to the point of creating an elongated bushing. This also increases the contact point by a great percentage. Let’s say on a brand new bushing, and a newly polished pivot, that we have a point of contact on the bottom that is 10% of the circumference. Due to wear, we could see an increase of up to 30%+ of contact as the pivot gouges its way deeper into the bushing.

Which brought on my next thought 😮 The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of? 🙄

[chris mabbott]

Excellent Bob, nice job and time consuming..

I haven’t used solidworks but I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

The other interesting point is that with the increased friction, due to dried up lubrication, the addition of dust etc, which, in turn, causes wear to the point of creating an elongated bushing. This also increases the contact point by a great percentage. Let’s say on a brand new bushing, and a newly polished pivot, that we have a point of contact on the bottom that is 10% of the circumference. Due to wear, we could see an increase of up to 30%+ of contact as the pivot gouges its way deeper into the bushing.

Which brought on my next thought 😮 The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of? 🙄

[Bob Tascione]

Hey glad you and Bernie liked it Chris.
SolidWorks is an incredible program.

I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

Either way Chris,
You can let Solidworks calculate the dimensional data and coefficient of friction which is determined by the material you choose (presets) or you can enter the coefficients yourself if you’re dealing with unusual alloys or materials that have been altered in some way. Entering your data also comes in real handy when setting up ‘what if’ scenarios such as what you mentioned about wear. It would spit out friction forces and other data as wear is introduced into the design. In fact it would not only calculate the torque losses from the additional contact area between pivot and plate hole but if you wanted would calculate the effects of power loss due to added frictional forces between teeth and leaf meshes introduced from the increasing center distances between wheels and pinions as the wear progresses! The torque from beginning to end of the train could then be determined under perfect and then less than perfect conditions. Cool stuff! You could then determine exactly how much impulse energy will be delivered to and throughout any escapement you were designing.
Solidworks uses both contact friction and mate friction. Mate friction being much more complicated since you’re not only dealing with joint friction but also contact friction between mating part surfaces. Solidworks will figure everything out for you once you have the design in place. When you design a part and choose the material then all properties such as mass, static and dynamic coefficients etc. are figured out and factored into any motion analysis study you can dream of doing.

It’s a very powerful and cool program that’s used a great deal in watch and other timepiece design.
Thanks for checking out the study!
Adios for now,
Bob

[Bob Tascione]

Hey glad you and Bernie liked it Chris.
SolidWorks is an incredible program.

I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

Either way Chris,
You can let Solidworks calculate the dimensional data and coefficient of friction which is determined by the material you choose (presets) or you can enter the coefficients yourself if you’re dealing with unusual alloys or materials that have been altered in some way. Entering your data also comes in real handy when setting up ‘what if’ scenarios such as what you mentioned about wear. It would spit out friction forces and other data as wear is introduced into the design. In fact it would not only calculate the torque losses from the additional contact area between pivot and plate hole but if you wanted would calculate the effects of power loss due to added frictional forces between teeth and leaf meshes introduced from the increasing center distances between wheels and pinions as the wear progresses! The torque from beginning to end of the train could then be determined under perfect and then less than perfect conditions. Cool stuff! You could then determine exactly how much impulse energy will be delivered to and throughout any escapement you were designing.
Solidworks uses both contact friction and mate friction. Mate friction being much more complicated since you’re not only dealing with joint friction but also contact friction between mating part surfaces. Solidworks will figure everything out for you once you have the design in place. When you design a part and choose the material then all properties such as mass, static and dynamic coefficients etc. are figured out and factored into any motion analysis study you can dream of doing.

It’s a very powerful and cool program that’s used a great deal in watch and other timepiece design.
Thanks for checking out the study!
Adios for now,
Bob

[Bob Tascione]

Hey glad you and Bernie liked it Chris.
SolidWorks is an incredible program.

I’m wondering how it determines the frictional values COF of various materials, are there presets for the COF relationship between different metals, alloys etc or is that something that has to be entered manually into the program? i.e. between hardened pivot steel and brass or teflon.

Either way Chris,
You can let Solidworks calculate the dimensional data and coefficient of friction which is determined by the material you choose (presets) or you can enter the coefficients yourself if you’re dealing with unusual alloys or materials that have been altered in some way. Entering your data also comes in real handy when setting up ‘what if’ scenarios such as what you mentioned about wear. It would spit out friction forces and other data as wear is introduced into the design. In fact it would not only calculate the torque losses from the additional contact area between pivot and plate hole but if you wanted would calculate the effects of power loss due to added frictional forces between teeth and leaf meshes introduced from the increasing center distances between wheels and pinions as the wear progresses! The torque from beginning to end of the train could then be determined under perfect and then less than perfect conditions. Cool stuff! You could then determine exactly how much impulse energy will be delivered to and throughout any escapement you were designing.
Solidworks uses both contact friction and mate friction. Mate friction being much more complicated since you’re not only dealing with joint friction but also contact friction between mating part surfaces. Solidworks will figure everything out for you once you have the design in place. When you design a part and choose the material then all properties such as mass, static and dynamic coefficients etc. are figured out and factored into any motion analysis study you can dream of doing.

It’s a very powerful and cool program that’s used a great deal in watch and other timepiece design.
Thanks for checking out the study!
Adios for now,
Bob

[Bob Tascione]

Chris, I got carried away blabbing about SolidWorks and forgot about what you said here:

The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of?

Yeah I would think that tunneling would eventually occur. Making these pivots shorter wasn’t necessarily a good thing to do for the clock and actually seems more like a botch job. May have just bought the factory or repair person (whoever did the pivot shortening) some time between cleaning and oiling. Good for them but not for the clock.

[Bob Tascione]

Chris, I got carried away blabbing about SolidWorks and forgot about what you said here:

The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of?

Yeah I would think that tunneling would eventually occur. Making these pivots shorter wasn’t necessarily a good thing to do for the clock and actually seems more like a botch job. May have just bought the factory or repair person (whoever did the pivot shortening) some time between cleaning and oiling. Good for them but not for the clock.

[Bob Tascione]

Chris, I got carried away blabbing about SolidWorks and forgot about what you said here:

The demonstrative gear is at the top of the train, so it has more rotation, but less power, and can be easily halted in its journey. I’m just wondering if the bushings for these gears also wear, or tunnel, and if so, I wonder why, with less power available to drive them, that they wouldn’t tend to seize before gouging the bushing or at least in the very early stages of?

Yeah I would think that tunneling would eventually occur. Making these pivots shorter wasn’t necessarily a good thing to do for the clock and actually seems more like a botch job. May have just bought the factory or repair person (whoever did the pivot shortening) some time between cleaning and oiling. Good for them but not for the clock.

[chris mabbott]

@Bob Tascione wrote:

Chris, I got carried away blabbing about SolidWorks and forgot about what you said here:

This gift can be a little misunderstood by those that don’t possess it, fortunately, it was passed on to me genetically 😆

Thanks for the info Bob.. I may have to look in to getting the program…

[chris mabbott]

@Bob Tascione wrote:

Chris, I got carried away blabbing about SolidWorks and forgot about what you said here:

This gift can be a little misunderstood by those that don’t possess it, fortunately, it was passed on to me genetically 😆

Thanks for the info Bob.. I may have to look in to getting the program…

[Author]

Posts