3/4" scale riding car are needle roller bearings worth it?

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apm
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3/4" scale riding car are needle roller bearings worth it?

Post by apm »

I need a sanity check here I have some of the old Don Ritchie castings that Jim Abrams currently sells for trucks for 3-1/2" gauge 3/4" scale riding cars based on the old Van Brocklin design. I was thinking of taking the lazy way out and using plain bearings but now I am having second thoughts. I am wondering does consensus agree with me that I really should go with needle roller bearings on the trucks?

A quick googling shows that bronze bushings should have a coefficient of friction of .12-.18. Estimating that out to be about .15ish on a 200lb load I am getting 30lb friction does that sound about right? Vs Google says needle roller bearings are around 0.0025-.0035 which I get to be about 0.7lb of friction on the same car. Does this seem about right? What is the tractive effort of a 3/4" scale 0-8-0 locomotive such as say a Caribou (not to be too specific). I am thinking that the locomotive only being about 50-60lbs can't be all that much. So are my napkin calculations here correct to say that needle roller bearings are the way to go or am I missing something? Anyone have experience with both plain vs needle roller bearings care to comment?

I never really liked doing heat treating of steels. It has been years since I did it on some pins and they wound up changing shape/diameter quite a bit after heat treat and I really hated doing it What's the recommended material here? Is W1 water hardening going to work. It has been years since I last worked with drill rod and I seem to recall it all changing shape on me quite a bit. I suppose maybe it will also be time to get the tool post grinder up and running.

Thanks,

Adam
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Bill Shields
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Bill Shields »

Been riding on those designs using cheap roller blade ball bearings for decades....set loose in the frame, free to float and rock, some semblance of a seal . And when they go bad ..just throw them away. Cheap axles, no heat treating or grinding....is a win win..

Why try to reinvent the wheel?
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apm
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by apm »

Bill whats the bearing you use? I only have a 5/8" bore to work with on these trucks.
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Bill Shields
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Bill Shields »

Literally...they are bearings for roller blade skates...maybe $15 for a set of 8...or used to be $15 😀

Do not remember the size...Google them .

Is something metric...

Why 5/8 od ..some casting limit I would guess?

Cheap (loose) which means low abec grade but sealed.

Charlie purinton first started with this design in the late 60"s ...or early 70's. I have a riding car built to his design prior to 1972 that is somewhat the bases for Jim Abraham's design.

Don't look like much but track nicely, do not float on springs (that they do not have) and easy to maintain.

I even have 1.5" scale riding cars with these trucks on them ..but not with the same size bearings.

If you go to the ibls www site, they have pictures of these larger trucks. I used some cheap pressed steel flange bearings for the axles and 1/2" hex head bolts for the pivots.
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Dick_Morris
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Dick_Morris »

Another option is to use non-rotating axles and mount a couple of bearings in each wheel. This has the advantages that on curves the wheels can each turn at their own rate rather than one or both always slipping a little bit and you aren't locked into the small space available in the journal boxes.

If you look hard, there are bearings that have a lot of small balls instead of fewer big ones so the ID is closer in size to the OD than the typical bearing. I have a set of them, but my recollection is that they are somewhat specialized and not cheap like the roller blade bearings. They are probably also more delicate in how much they will hold. That wasn't important to me as I was going to use them on a caboose.

I've seen it suggested to drill the ends of the axles and Loctite in hardened dowel pins for needle bearings to ride on.

Divide the weight of the locomotive on the drivers multiply it by .4 to .5 and you can approximate the tractive effort. Most model locomotives have more power than they can use without slipping the wheels to tractive effort is determined by the traction between the drivers and track.
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LVRR2095
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by LVRR2095 »

Adam, I have several 3/4” scale riding cars and all of them use plain bronze bushes for journal bearings.
They work just fine and as you probably won’t be pulling trains of ten or more cars loaded with kids….that is all you need.
The only thing I would recommend is to not use sintered bearings.

Keith
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cbrew
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by cbrew »

Morning,
Look into cam follower or track bearings
not cheap, but they will last a life time with these loads
https://www.mcmaster.com/cam-followers/ ... ter~0-625/
If it is not live steam. its not worth it.
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Bill Shields
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Bill Shields »

several members at our club have free wheel riding cars (most are 1" scale) and they work just fine.

I have used the - dowel pin in the end of the axle trick - in the past -> and is a viable alternative (forgot about that since it has been a long time since I used it).

Keith is correct -> plain bronze works just fine and amen on the sintered...bad choice...
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jscarmozza
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by jscarmozza »

Hi Keith, what's the problem with sintered bearings? Just curious.
John
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Bill Shields
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Bill Shields »

they tend to crack and fall apart
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apm
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by apm »

Bill I looked up roller bearings earlier in the day they're 22mm I think from memory on the OD I don't think the castings have enough metal there to go that size. Maybe they do s I will take a closer look tomorrow when I am back in the shop to be sure. Are you sure that you used the same patterns that Jim Abrams or Don Ritchie used to sell?

Keith, my current riding car is plain bearings and the drivers can spin quite a bit starting just me. If my numbers are right that 200lb me creates 20lb friction I think that explains a lot. I am thinking I will have to try roller bearings at this point and maybe report back on the difference between cars. I was surprised when I tossed the numbers in and saw just how much higher the friction loads should be in theory of plain bearings vs ball/roller.

Lastly I really like the idea of inserting hardened pins to an axle that will make life easy! I will have to take a closer look tomorrow before deciding whether to go with roller bearings or see if there is room for roller skate bearings after all.
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Bill Shields
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Re: 3/4" scale riding car are needle roller bearings worth it?

Post by Bill Shields »

A properly designed plain bearing (with a groove - wedge - to entrain oil) and the correct oil -> will roll along quite nicely, even with you on board (not like I weigh a lot less).

have you ever actually looked at some of the standard mechanical engineering concepts for plain bearing / oil wedge design?

it's more than the common bushing with a hole in the top to take a bit of oil when we remember to dribbled it in....

in some cases it is not much more than oil up from the bottom and an axial groove to ensure that the ENTIRE BEARING LENGTH of the axle can be lubricated....WHAT OIL UP FROM THE BOTTOM -> BUT THE LOAD IS FROM THE TOP DOWN!!!! (exactly....)

Once you figure out how to do it -> is like falling off a log...almost...

then there is the 'wick'....but we don't get into that now...

take a look here and see how it is taught to beginners: You are looking at Hydrodynamic lubrication

https://uni.edu/~rao/Md-19%20Plain%20su ... arings.pdf

this is also quite good:

http://edge.rit.edu/edge/P14453/public/ ... arings.pdf
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