What is a thrust washer?

[cedarwoodron]

I am powering the rotor on an Athearn BB Rotary Snow Plow and just behind the plastic retention tube piece that sits at the end of the rotor shaft is a "thrust washer", as per the original diagram. When I researched it online, it just looks like a plain old metal washer. Is this something special, or can I just assume it is something I can pull from my small parts inventory? Cedarwoodron

[riogrande5761]

When I think thrust washer, I think of the washer that fits on next to the worm gear which spins off the end of the shaft on either side of the motor in the Athearn BB diesels.  The worm gear drives the gears down in the gear tower that drives the 2 or 3 axle power trucks.  There may be nothing special about the thrust washer other than it is sized for the job and it's function.  People who have problems with say, a diesel bucking going down hill, are usually advised to put in a thrust washer sized as to remove the slop from the worm gear so it doesn't wiggle back and forth too much.

[MonkeyBucket]

Just an opinion...

I'm sure it stops the worm gearing moving back and forth freely. Like said above.

Makes me think of the "thrust bearing" in my truck. It sits against the clutch and takes forces from two areas stopping it from moving freely up and down the drive shaft while its spinning .  

[farrellaa]

A thrust washer is normally just a flat washer but  with very smooth or machined surfaces so it will provide a smooth rotating surface for another component to run against, like a worm gear or motor end bearing surface. They are sometimes made in various thicknesses (like shims) to take up 'slop' or end movement in a drive system. A worm gear will produce end or lateral movement when pushing against its mating gear and when direction is reversed, the thrust is transfered to the other end. By limiting this amount of lateral movement, you get a smoother operating system.

    -Bob

[ndbprr]

In other words without something to stop your rotor driveshaft from moving in and out it will go roundy round while moving in and out.

[Medina1128]

As has aleady been mentioned, the thrust washer takes up end play in the worm gear shaft. To see a perfect example of that, run your locomotive slowly downhill. If there is too much play, you'll see the locomotive bucking and lurching.

[richg1998]

I have used thrust washers from NWSL so the below is from a search for NWSL thrust washers.

I have cut one side of a 2.4 mm thick thrust washer with a small wire cutter and slipped them into a place to reduce end play on a motor shaft.

http://tinyurl.com/6nz3ctr

Rich

[ndbprr]

While the discussion regarding worm gears is factual it has.no bearing on motorizing a rotary snow plow since the rotor wil be an extension of the motor shaft.

[maxman]

cedarwoodron

I am powering the rotor on an Athearn BB Rotary Snow Plow and just behind the plastic retention tube piece that sits at the end of the rotor shaft is a "thrust washer", as per the original diagram. When I researched it online, it just looks like a plain old metal washer. Is this something special, or can I just assume it is something I can pull from my small parts inventory? Cedarwoodron

Does the unit you have look like this: http://www.hoseeker.org/athearninstructionscars1970/rotarysnowplow.jpg?

What they are calling a thrust washer basically acts like a space filler/locating washer to position the rotor shaft in what I believe they are calling the sub frame.  The thickness of the washer is what's important.  Too thick and the rotor shaft will bind in the sub frame.  Too loose and the shaft will have too much axial movement.  I can't tell from the diagram how the rotor fits in the rotor housing, but I suppose that it would be conceivable that too much axial movement could result in the rotor face rubbing on the rotor housing.

How are you intending to position the motor?  Will it be placed in the back of the unit with a direct connection to the rotor shaft?  If so you will need to make sure that the coupling between the motor and rotor shafts has some axial play so that the rotor shaft thrust washer and the motor thrust bearing don't fight each other.

[ef3 yellowjacket]

Re:  Bob's post: 

This is as accurate a description as there can be.  I have a PFM HOn3 K-28, and this is what was needed to keep the worm gear from binding in forward direction.  Worked like  gangbusters!

Rich

[Boise Nampa & Owyhee]

For modeling purposes a flat washer, either steel, brass or engineering plastic will work with nearly no lubrication.  In heavier load applications, like inside of a transmission, Torrington patented years ago a radial roller thrust washer.  The pin sizes can be amazingly small, .040" to .050" and then up from there depending on space and load.

Someone above mentioned locating a worm gear with thrust washers and yes, NWSL is the premier place for selection of sizes for our purposes.  In locating a worm on a spur gear try and space it so the last turn of the worm is not engaged.  Sometimes the thread pattern (pitch) is altered in the pressing of the worm onto the shaft.  A little space is necessary so that the motor can move without a load and get moving when changing directions.  It should not, however, have over a quarter turn of slack.  The slack comes from the worming having to "walk" to the other end of the gear case to then apply force to the spur.

see ya

Bob

[maxman]

ndbprr

While the discussion regarding worm gears is factual it has.no bearing on motorizing a rotary snow plow since the rotor wil be an extension of the motor shaft.

ndbprr:

If you ever wondered if some did not read all the posts................

[Train Modeler]

I have made some from tube stock, plastic sheet, steel sheet and modified washers to fit.    Sometimes a high impact plastic is better than steel.

Richard

[richg1998]

ndbprr

While the discussion regarding worm gears is factual it has.no bearing on motorizing a rotary snow plow since the rotor wil be an extension of the motor shaft.

I never saw anything about motorizing the snow plow. Just reducing end play on the motor shaft.

I did see a couple examples of how thrust bearings can reduce end play.

Rich

[cedarwoodron]

Fortunately, after your (plural) informative responses, I was able to locate a suitable very small metal washer. #2 steel washer, at a Hobbytown in their RC parts area. It fit over the rotor shaft and I then replaced the flexible plastic retention tube piece. I can't see how it (the washer) made any difference when the original rubber band drives were the "motive power" for the rotor shaft, as their rpm could not have been very high, even when the plow car was pushed at full speed, due to the limiting nature of those rubber bands and ungainly wide axles. Cedarwoodron

[ndbprr]

I don't believe the rotor turned very fast on the prototype on the order of 60 rpm. It was more brute force that moved the snow.

[Lake]

Not to pick nits, but the screw gear on the motor shaft is called a worm or worm screw.

The round gear that the worm contacts is the worm gear.

And now back to the thrust of the post.

[hon30critter]

cedarwoodron

My understanding of the purpose behind a thrust washer is to reduce the friction between a rotating part and a stationary part. In the example of a rotary snow plow, the rotary blade has to run up against a surface which is not rotating. Without a thrust washer you will have a lot of friction and wear where the rotating and stationary surfaces come together. The thrust washer theoretically rotates at half the speed of the rotating shaft so the wear is reduced on both sides of the thrust washer. The thrust washer also provides two additional surfaces for lubricant to relieve friction and reduces by half the difference in speed between rotating surfaces. They also serve the purpose of eliminating excessive end play in the drive train. Somebody please correct me if I am wrong on this. I ain't no mechanical engineer!

In your case, with the relatively low speeds involved with the snow plow blade, it might not be a big deal. It might be more important to find the right plastic compatible lubricant in order to get good performance out of your snowplow, but thrust washers certainly can't hurt.

Dave