Scratch building trucks

[nkp174]

I've decided to save money by building my own trucks. On3 trucks cost $15-$40...so I can save some serious cash by building my own.

I first had to figure out how the trucks worked...which I did and then began my first effort using brass & styrene. The first effort is covered in this thread: http://forum.zealot.com/t153515/

After that, I then sat down and did a few calculations on where to drill holes & bend the side frame irons. I decided that I'm too lazy to drill through brass (I don't have a drill press...or even a vise), so I decided to use styrene instead. I started out by measuring out and then drilling holes in the bottom piece. I made a mistake with the length measurements...so I market those holes with red ink. I then cut a second piece to length and used the first as a jig to help me duplicate it. I used 0.020"x0.060" styrene with #77 holes.

Next I bent a piece of brass to match the contour of the top iron of the frame. I then followed the exact same procedure for the top as I did with the bottom...without making any mistakes. I then clamped a piece of styrene to the brass and let it hang out in some boiling water. Afterwards, I removed it from the brass.

Lastly, I formed a piece of brass to match the contour of the middle piece...and then repeated the procedure of the top piece...but without drilling the holes.

The results thus far were decent parts for the frame. I then formed the journal boxes from 0.125" x 0.156" styrene...filing the front to shape and drilling the axle holes. I then filed grooves into the sides to accept the "bolts" which keep the sides together. I then drilled the holes for one of the journal boxes at one end of the middle frame iron.

I next slid brass rods into those two holes, and glued that journal box to the bottom frame iron...and then to the middle and top irons.

[nkp174]

Next I glued the other journal box in place...and then figured out that when attempting to put the top of the frame into place...it distorted the frame. By checking the wheelbase...I accidentally used a bottom frame that was 4" too long...so I had to cut it free and then move it to the appropriate spot for a 4' wheelbase. This fixed the alignment issue and I drilled out the middle frame iron at that journal box and glued the rest of that end together with brass wires in place.

Next, I glued the center of the bottom frame to the middle frame and drilled out those holes too.

Since no one really knows exactly how the bolts were fastened on these trucks...I've decided to just leave the brass wires in place to act as headless bolts. I can always come back and add head later without any difficulty. I trimmed the "bolts" and glued them into position.

Currently, this master is sitting in an RTV mold which still has 6hrs left to cure.

This does not include the center assembly for the trucks as I intend to use these castings in three different varieties of trucks...and I intend to scratch build each of these different truck bolsters/beams for each truck I produce.

Next up is a 3'4" wheelbase Colorado Central truck...and then passenger car trucks...probably 5', 5'6", and 6' wheelbases.

[steamhead]

Ouch..!!! That looks harder than heart surgery...!! Great job..!! Did those trucks take some sort of springs...or did they just rely on the normal flexing of the truck..??

Keep posting progress pics...Very interesting how you're doing this..

[nkp174]

These had rigid sideframes which were mounted to a pair of 4x8s...these had a "spring sandwich" hanging in between them...which was how they were connected to the car.

I'll keep the updates coming (I generally work at a very rapid rate since I use styrene, I don't have a layout, and my day job is stressful). I didn't get to start the CC trucks tonight as I had a (church) small group leadership meeting tonight.

[60103]

nkp: glad to see you're willing to scrap your misteaks and redo.
Are you planning to enter any contests? making your own trucks is worth a smack of extra points.

[nkp174]

Originally Posted by 60103

nkp: glad to see you're willing to scrap your misteaks and redo.
Are you planning to enter any contests? making your own trucks is worth a smack of extra points.

Nope. Just wanted to save a bunch of money...and see if I could do it....and it allows me to actually have the third style of UP Swing Beam trucks which other south park modelers substitute a similar set of Carter Brothers trucks for.

I don't have money for an NMRA membership currently...but I might enter my passenger cars into something down the road. I should have quite a bit more money once I'm really working rather than a grad student . Plus I'll have more free time then .

My willingness to scrap mistakes depends on how far along I am....or what can be done. I slightly messed up my B&S boxcar's roof...the roof walk is 6" to wide...and the car body is also 2" too narrow...but those are small as long as I remember that "oh, the South Park shops rebuilt that or I don't have it next to a correct B&S car. I have a 27' boxcar that's justing sitting in my china cabinet with no plans...there were two problems with its plans: they showed an end door...and they didn't have the roof being adequately peaked...so I'll probably finish her as a Kansas Central car rather than the 800 series DSP&P car that she was going to be. I've already ripped the board by board roof off...and removed some extra weight as I incorrectly remembered the NRMA weighting standard for On3 when I glued the weights into her.

[myltlpny]

Wow, that's a lot of work. Thanks for the pictures and the excellent write-up. I don't build in O, nor do I use that type of truck, but I always enjoy seeing how people approach a modeling project. I look forward to your future installments.

[nkp174]

This looks like it's complete...but it isn't. It still needs journal box covers, the spring sandwich, the pins between the transoms & the sideframes, and paint. (the brakes were body mounted in the era that I'm modeling) I haven't decided if I'll add better detail to the pins on the sideframes...but I can always do that later. The wheels are from NWSL...Dave Grandt, on the On3 forum, stated that they are the best (mechanically) product on the market...so I won't think twice about using anything else...except maybe Grandt's old, beautiful steel tired wheels.

It takes around 5min per sideframe casting...with 30-60secs of working...3-4min of waiting...and then a minute or so to trim the flash. If I have the "lumber" already cut...it takes around two minutes to build the spacers/transom assemblies...and a couple minutes to drill the axle holes.

Edit: myltlpny...my little pony It would be amazing to see an n-scaler building bettendorf trucks...which would be useful to you!

[modelsof1900]

I'm surprised again, what for fine items are build from the modeler specialists! I'm interested also in different trucks for special cars, in all cases 6-wheel trucks for flat cars but I never have had the idea for scratch build. Congratulation und good success for finishing!

But can I made a small note for correction?
Can you give the upper bands sharp bends left and right of bolster beams? The arches in center of upper bands should be avoided if you can do it. The truck will look many time closer to original trucks after this correction.

Bernhard

[nkp174]

Bernard, I agree about the top of the truck! I want sharp bends...curves look bad! Originally, the pieces did sort of have the right shape, but not quite. I'm going to use super glue to prevent the irons from arching above the transoms like that...to get, hopefully, crisp bends.

Dr. Wayne also had a few questions for me...so I'll just share them here...good things to think about with such projects.

Not all resins are strong...some are weak & brittle. I'm using Alumilite which is very strong. This is important when you have tiny cross sections like here. The tensile strength of Alumilite is 6000psi....styrene is 8000psi...with 13,000psi in compression. Other resins can be half of Alumilite's tensile strength or even much less...the downside to alumilite is that it is expensive and not very good (imho) for small details...it is too air bubble prone in the tiny bottom corners of your molds...but it sets really quickly.

Curious, and armed with a piece of paper that declares me a Civil Engineer (I've never met one of those )...I decided to calculate the approx loading on each member of the truss. Note: this is not the sort of thing that meticulous structural engineer would approve of, but it is pretty close to accurate.

I'm ignoring the center 16" since it isn't a concern...I'm pretending that it is just a single member...so I don't have to perform a finite element analysis which wouldn't really matter much here. I'm also treating each journal box the same way...with these being at the pins. I'm also pretending that every connection is a pin connection...for elegance.

This truss is symmetric...so the loading is identical for each half. Since the corresponding member to "C" does not have resistance...we can see that neither it nor see carry any load...they are there only for stability if problems occur. So therefore we have "B" in tension car and "A" in compression, with their horizontal components (their push and pull horizontally) offsetting. (at the center of the truss...their corresponding members on the other side offset their lateral pull). So, we have two equations...at the point where A & B meet...
Sum X = 0 = 11/12A-11/14B
Sum Y = 0 = -1/6A-8/14B+1/2L
L is the weight applied to that sideframe...so it is 1/4 of the car weight when sitting on level track.

The fractions were determined based on the length horizontally and vertically of each member.

Since B is in tension, and compression strength is commonly higher...I've decided to base the load off of the tensile strength of B. The narrowest cross section is where it would fail...at the rod holes...0.020"x0.040" (0.020" lost to the hole)...which corresponds to 4.8lbs is the maximum load that B can carry. Solving the truss equations...we have A would be carrying 3.46lbs...and that sideframe could be carrying 6.64lbs. That means that a 26.5lb car could sit on those trucks...successfully...in theory. Due to concerns such as bouncing on track, grades, curves, etc...you'd never want to try that. I also don't know the shear strength...but there is 3x as much material that would need to be sheered than there is to be pulled...so it is fine. I could go on and on here...

The moral of the story is that my 5.8-7.1oz freight cars can ride on these trucks free of worries. I never would have guessed that the FoS would be 64 for my B&S boxcar's trucks! That's insane!

Doctor Wayne also brought up a wonderful question that I'd tossed back and forth...these trucks would have originally had extension from which the brake beams would hang. I ultimately decided that since I'm modeling a few years after these extensions were removed...I didn't want to have to cut a bunch of them off. Still, it was a difficult call since I could have just used the same master for all of the trucks...rather than building an additional one. If I made one with the extensions...I think my fellow DSP&P modelers would be demanding that I offer them commercially since I'm pretty sure that they've never been commercially.

[nachoman]

This truly is impressive work. Possibly worthy of the gauge e-mag?

Kevin

[nkp174]

Morning update.

Last night I spent two hours learning about the next steps.

First...I can't consistently drill a straight hole through the transoms & spacer as aesthetically pleasing as I'd like. Another time when I find myself wishing that I had a drill press. While it doesn't hamper operation...it does bother me aesthetically. So I'm going to try super gluing the sideframes in place first. Other types of trucks won't be this difficult.

Second, the spring sandwich was fun...it is always fun to deal with tiny springs It consists of two planks which are 1.020" long...one is a 2x8, the other a 6x8. These are essentially the same as what you would have on a more modern freight car truck, except that they don't also serve as the transoms...and that normal spring planks extend through the sideframes with the outer springs visible.

I cut the planks and then drilled a hole for the truck mounting screw. I then drilled a hole on each side where the springs will go. Next I inserted plastic rods into these holes to keep the springs from shooting out. I then experimented with Kadee knuckle springs and On3 coupler centering springs...which was the biggest headache.

I then filed a recess into the side of each plank...and formed a couple u-shaped pieces of brass wire to allow the load to be transfered prototypically from the car to the top of the spring sandwich...through the springs...through the spring plank and onto hangers which are connected to a rod above the assembly which connects to the transoms.



I found that I can't bend the brass wire accurately by hand.

I've also yet to decide how exactly to set up the mounting screw...I've tried both planks of the spring sandwich...it should be in the top member.

I now need to develop jigs in order to accurately and quickly produce them in the future.

Michael

[doctorwayne]

Originally Posted by nkp174

I've also yet to decide how exactly to set up the mounting screw...I've tried both planks of the spring sandwich...it should be in the top member.

You could drill a clearance hole for the screw in the top member, and a clearance hole for a screwdiver (suitably modified if necessary) in the lower member, and put the screw in place before assembling the spring sandwich. Alternatively, you could eschew screw mounting completely and use the "dress-snap" truck mounting system used for Central Valley passenger car trucks, although this may require a modification to either the top plank of the truck or the carbody bolster, in order to maintain proper car height.

Wayne

[MilesWestern]

It looks like your truck building project got a smidge larger, judging by your last photograph. Where was that photo taken? You're doing something very amazing, how about turning it into an Article for RMC or MR?

[nkp174]

Miles, that isn't me or my project in that picture. That's a picture a website I thought I'd linked to in this thread...but I guess that I only linked to it in my boxcar thread.
http://www.spcrr.org/NARFGrantWheels.html

I posted it because it illustrates what I mean by a spring sandwich hanging in between the transoms that run between the sideframes. Sorry for the confusion.

Doctor Wayne, I've toyed with both ideas...my smallest screw driver is MIA...so I don't know how much of a hole it would take...I've already enlarged the hole in the spring plank...but I could probably build (crudely) my own out of brass...If I needed something smaller. I don't know what that is that Central Valley uses...but I had been thinking about something like someone's trucks used...where there'd be a little pedestal extending down through the spring plank...allowing the screw to go through the spring plank with being attached.

I need to find a CV passenger car pick to examine what they've done!