Ground clearance

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Geochurchi
Posts: 153
Joined: Mon Feb 22, 2021 7:49 am
Location: Concord ,NH / Naples, Fl

Ground clearance

Post by Geochurchi »

Hi All, new to this site, trying to figure out the best way to gain ground clearance using Tom Bee Trucks, I will post what we are attempting to to do, one question is wether or not these rollers are supposed to turn, they were originally sitting on the raised piece on the truck which is only may be 3/8” wide and some have grooves, we have washers between the car frame and the truck, I have seen mention of using a Teflon washer there.
Question is what should be pivoting on what?
69D9188E-0A2C-4FA6-835B-585B3E9C3AE5.jpeg
C69F67EA-38ED-44D6-A465-1966C6C54B8C.jpeg
If it ain’t broken keep working on it until it is .
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Greg_Lewis
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Location: Fresno, CA

Re: Ground clearance

Post by Greg_Lewis »

Welcome to the Chaski board.

What you want is to have the weight of the car riding on the center bearing. I use oil filled UHMW polyethylene
(https://www.mcmaster.com/plastic-oil-fi ... ne-sheets/)
for the center and side bearings. Teflon has a tendency to flow under pressure.

Set up your side bearings so one truck is almost touching on both sides — leave just a smidgen of clearance. Then on the second truck leave a gap of about 3/32 on both sides. Thus the car won't rock too much side to side as truck #1 will keep it steady, while truck #2 will rock with variations in the track. The RRSC engineering handbook describes it as like a three-legged stool. I've followed this protocol and the result is a stable car and almost no derailments.

I'd take a serious look at those outboard rollers and insure that they are free to turn. I wouldn't be comfortable with them pivoting on a possibly rusty bolt. If those were mine I'd replace the whole shebang with UHMW poly.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Geochurchi
Posts: 153
Joined: Mon Feb 22, 2021 7:49 am
Location: Concord ,NH / Naples, Fl

Re: Ground clearance

Post by Geochurchi »

Hi Greg, at the risk of sounding stupid, sounds like you are using that polyethylene between the car frame and truck, what are the side bearings? What is first truck and second truck?
We do have a few new rollers.
This whole thing is kind of dumped in my lap so it is a learning curve.
0E58F971-397C-427A-8193-5F21F737B4A5.jpeg
Geo 🇺🇸
If it ain’t broken keep working on it until it is .
Geo 🇺🇸
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Greg_Lewis
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Re: Ground clearance

Post by Greg_Lewis »

Geo:

Please forgive me if I tell you things you already know, but I'll try to use consistent terminology. You have a bolster on the car and a bolster on the truck, both of which are the cross members in question. When I referred to trucks 1 and 2, I meant the front and rear trucks on the car. One truck should have minimal clearance between the truck and car bolsters, while the other should have about 3/32 inch on each side. I like to have the front truck be the one with the larger clearance.

I make a thick poly washer to go where you've indicated in the photo with the black arrow, the center pivot bearing. Then I make poly blocks for the outboard side bearings, which in your case are just high spots on the truck bolsters. I put one on each side of the truck bolster. In my case the car bolsters are long enough that they ride on the poly blocks. In your case the car bolsters are shorter to allow for the rollers. If the rollers work, no need to replace them. What I'd do is replace those two pieces of strap metal with a thick center bearing washer (or two) from UHMW poly and put poly blocks on top of the bumps on the truck bolster, making those blocks the appropriate thickness to give the clearance needed.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Geochurchi
Posts: 153
Joined: Mon Feb 22, 2021 7:49 am
Location: Concord ,NH / Naples, Fl

Re: Ground clearance

Post by Geochurchi »

Hi, here are a couple of pics of our solution, we gained close to a 1/2” clearance, replaced rollers, your saying that there should be slight clearance between the roller and the added flat stock, others say the same thing, can you explain why?
Can’t ad pics
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If it ain’t broken keep working on it until it is .
Geo 🇺🇸
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Greg_Lewis
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Re: Ground clearance

Post by Greg_Lewis »

The clearance allows more freedom of movement. By having almost no clearance on one truck and about 3/32 on each side of the other truck, the car will be stable yet the trucks can move better with variations in the track. Since the springs in our trucks are required to operate over a far wider range of weights between an empty car and a loaded one, there is less flexibility between the truck bolster and the truck sideframes that the prototype and the extra clearance helps with that.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Geochurchi
Posts: 153
Joined: Mon Feb 22, 2021 7:49 am
Location: Concord ,NH / Naples, Fl

Re: Ground clearance

Post by Geochurchi »

Hi Greg, Got it, It just seems that there should be something else instead of rollers, to me the rollers should be able to roll on the bolster pads instead of something of something to prevent sway, my thinking is a a pad to be adjusted for 3/32” clearance, we have all rollers so that’s what we will use.
ALL LIVES MATTER!
Geo 🇺🇸
If it ain’t broken keep working on it until it is .
Geo 🇺🇸
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Greg_Lewis
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Re: Ground clearance

Post by Greg_Lewis »

Below are some images of the prototype. Here is a quote, in typically wordy form of the era, from one of my references, Locomotive Cyclopedia 1925:
------
"The importance of equipping the modern rigid underframe locomotive tender with efficient anti-friction side bearings is now generally recognized for the reason that it has been repeatedly demonstrated that excessive wheel flange and rail wear, also derailments, will surely result from the application of improperly designed side bearings.

[S]ide bearings provide an efficient medium for properly swiveling the the trucks under all conditions of track curvature. They are, therefore, effective not only in preventing derailments resulting from trucks binding when operating on curved track, but also in reducing wheel flange and rail wear to an absolute minimum."
------
First up is a shot of a truck bolster with plain side bearings below a car bolster:
Screen Shot 2021-03-02 at 4.26.01 PM.png

Here is a set of cutaway drawings showing the truck and car bolsters with side bearings:
Screen Shot 2021-03-02 at 4.42.01 PM.png

And here is a page from the Locomotive Cyclopedia 1925. The quote above was from the company selling the roller bearings:
IMG_8534.JPG
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Geochurchi
Posts: 153
Joined: Mon Feb 22, 2021 7:49 am
Location: Concord ,NH / Naples, Fl

Re: Ground clearance

Post by Geochurchi »

Thanks
If it ain’t broken keep working on it until it is .
Geo 🇺🇸
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