Wooden bearings

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marinesteam
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Re: Wooden bearings

Post by marinesteam » Sat Oct 23, 2021 10:00 pm

No need to guess

https://www.qbcbearings.com/TechInfo/PD ... arings.pdf

Many factors go into selecting a bearing. Pressure and RPM are part of it, service conditions are important as well. Agricultural bearings run in dirty conditions often with little lubrication or chance of being service properly. One would never use a ball bearing meant for agricultural service in a dental instrument , it couldn't handle the speeds and the shaft would wander around like a drunken sailor due to the large clearances. Likewise, the tiniest bit of dirt will destroy a high-quality bearing that you would find in a medical instrument.

Same apples to plain bearings, wood was used because it can handle large loads at low speeds with little lubrication and are is sensitive to dirty conditions. They also work well when flooded with water as the lubrication. There's a reason that wood isn't used as journal bearings for engines, there's far better materials that can candle the pressures, speed and that can conduct heat away from the journal.

Cheers

Ken
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Re: Wooden bearings

Post by Lopez Mike » Mon Oct 25, 2021 2:42 pm

Thanks Ken,

As to things like acetal resins getting hot, heat is caused by friction. The coeffient of friction with materials like Delrin and Teflon is so startlingly low that hardly any heat is generated.

A pumped oil bearing is the gold standard of low friction and zero starting force. The extreme example that comes to mind is that of very large telescopes such as the ones on Hawaiian mountains. The Keck series have a moving mass of 5000 tons (4,000,000 kG.) That mass is supported on a ring perhaps 20 feet in diameter and a foot or so wide by four bronze pads with fairly ordinary oil pumped into the center of each pad. The resulting oil film where the oil escapes around the edge of the pad is about the thickness of a sheet of paper and has the modulus of elasticity of metal. Totally non-intuitive to me!

This incredible lump of machinery is moved with such little force that if the driving machinery is uncoupled, the wind blowing over the telescope causes it to follow the wind.

All rather distant from our small engines but reminder that this is a mature technology and, in the case of our applications, sorted out around a 150 years ago. I feel like such a radical using sealed ball bearings on my main bearings and eccentrics!

Mike
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Re: Wooden bearings

Post by DetroiTug » Tue Oct 26, 2021 3:06 am

Lopez Mike wrote:
Mon Oct 25, 2021 2:42 pm
I feel like such a radical using sealed ball bearings on my main bearings and eccentrics!

Mike
For clean, quiet trouble free operation, it's the only way. On the tug and the car, which both have ball bearing lower ends, I never even think about them. One less thing to deal with.

Ron
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Re: Wooden bearings

Post by Kelly Anderson » Tue Oct 26, 2021 9:38 pm

DetroiTug wrote:
Tue Oct 26, 2021 3:06 am
For clean, quiet trouble free operation, it's the only way.
Provided that one doesn't fail. I recall coming up on Mike Condax rafted to another launch in the middle of Lake Winnipesaukee, several miles from Lee's Mills. I pulled up to find them trying to engineer a way to limp the other launch back to Lees Mills after a needle bearing failed. Mike came up with a piece of single strand copper wire of the right diameter, that he wrapped around and around the journal like a coil spring, to take up the space left by the missing needle bearing.

The beauty of plain bearings is that you can virtually always get home with them in the event of a failure (reduced speed and extra oil are your friends). When an anti friction bearing fails, you aren't going anywhere.
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Re: Wooden bearings

Post by DetroiTug » Wed Oct 27, 2021 12:43 am

DetroiTug wrote: ↑
Mon Oct 25, 2021 10:06 pm
For clean, quiet trouble free operation, it's the only way.

Provided that one doesn't fail. "'

Sealed ball bearing are extremely unlikely to fail in steam engine service. Low RPM and virtually no side loads. The size bearings we use are rated many times higher than the forces or speeds we subject them to.
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Re: Wooden bearings

Post by lostintime » Wed Oct 27, 2021 4:14 am

marinesteam wrote:
Sat Oct 23, 2021 10:00 pm
No need to guess

https://www.qbcbearings.com/TechInfo/PD ... arings.pdf
I find the numbers in graph 3-2 of the link rather interesting, I'm a bit old fastioned and I like babbit bearings with removable shims to take up clearance on rods and mains but the engine I have now has roller bearings in that place and I would not consider replacing them with babbit, I am concerned about my roller crosshead arrangement though. The reason for my original post was because I am considering replacing it with slides and guide blocks. I have a good stock of canvas reinforced phenolic as well as Derlin on hand, I would like to convert it to the slides with adjustable jack screws and lock nuts to set clearances but I think it will look out of place and in the service of crosshead sliders on a low speed engine I thought/think that wood would work. My engine also is a centeral sprocket pto so must be connected to a line shaft, then chained again to the paddle wheel. My primary thoughts were on the "transmission" and alignment side.
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Re: Wooden bearings

Post by DetroiTug » Thu Oct 28, 2021 7:25 pm

Adding to what I wrote above regarding ball bearing service.

On the tug I use a DC brushed servo as a generator belted to the engine. After many hours of service, the bronze sleeve bearing in the case wore out. Opting to fix instead of replace, I machined a pocket and installed a ball bearing, never any trouble since.

Never really understood why the bronze bushing failed, the belt tension was reasonable and these servos endure daily service for many years without failure with belted transmission, although usually as driver, not driven. Anyways, it's held up since the repair.

Ron
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Re: Wooden bearings

Post by marinesteam » Sat Oct 30, 2021 3:32 am

DetroiTug wrote:
Thu Oct 28, 2021 7:25 pm
<snip>
Never really understood why the bronze bushing failed, the belt tension was reasonable and these servos endure daily service for many years without failure with belted transmission, although usually as driver, not driven. Anyways, it's held up since the repair.

Ron
Servos and Steppers aren't designed for side (overhung) load. Most general duty motors have surprisingly small overhung load capability.

Ken
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Re: Wooden bearings

Post by DetroiTug » Sat Oct 30, 2021 8:35 pm

marinesteam wrote:
Sat Oct 30, 2021 3:32 am
Servos and Steppers aren't designed for side (overhung) load. Most general duty motors have surprisingly small overhung load capability.

Ken
There are literally millions of CNC machines that run steppers and servos with timing pulleys and belts. It has to do with available, pitchleads of ballscrews, desired resolution and the torque characteristics of each type of motor, they are different as daylight and dark.

Ron
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Re: Wooden bearings

Post by marinesteam » Sun Oct 31, 2021 5:30 pm

DetroiTug wrote:
Sat Oct 30, 2021 8:35 pm
marinesteam wrote:
Sat Oct 30, 2021 3:32 am
Servos and Steppers aren't designed for side (overhung) load. Most general duty motors have surprisingly small overhung load capability.

Yes, but loads are within the design parameters of the motors used. Over-tightening belts or overloading the screws will quickly kill motor bearings. The screws act as gear reduction, reducing belt load at the shaft. It's not uncommon for high load situations to use a gear reducer or use an overhung load adapter to absorb the overhung load instead of using the motor shaft to take that load. Belt load (power and sheave size) and distance from the bearing are the main variables.

Ken
There are literally millions of CNC machines that run steppers and servos with timing pulleys and belts. It has to do with available, pitchleads of ballscrews, desired resolution and the torque characteristics of each type of motor, they are different as daylight and dark.

Ron
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