Test rig for FXD printed truck frames with metal axles.

[Lemosteam]

Myself and others have wondered here how the FXD material properties will hold up over time with FVM metal axles in place.  I had cleaned out the printed axle pockets as I always do with a Dremel 105 (0.8mm dia. sphere) engraving bit.

For fun, I devised a mechanism from an old oscillating tower heater to test this.

The "track" is mounted to a 1.3"+ diameter paint bottle with the bottle's lid mounted to the motor shaft.  The track is a 3D printed flat strip that has a 9" reversing radii through its center that once cleaned and warmed was wrapped around the bottle and glued in place.  Unfortunately I spaced the sides 10mm apart instead of 9mm... so I added 0.5mm styrene strips against the original track to correct the gauge.



Here is a video of the dynamic fixture in action.  The motor is a 120v that turns at 2.3-3 rpm.  As you can see the weight of the arm keeps the truck down against in the track, and the arm can move toward and away from the motor as the track radii moves the truck.  Also as i had hoped the track is not "perfect" so the truck jerks around a little bit as well. The truck has been running about 2.5 hours so far.

I'm planning on letting it run for a week or so.  The circumference is about 4.7" X 2.5rpm x 1440 minutes per day is 1410 feet of travel per day.

Some questions:

-When should I stop to inspect or should i run to failure?

-At what point to we say that there are no issue running the metal axles in the FXD truck frame?

@narrowminded , this is curvature what I was asking you to mill into a tube for me.

[prbharris]

John

Thanks very much for this - a great idea. You will know that the PRR Queen Mary heavy duty depressed well car that we produce http://www.nscalekits.co.uk/FD2.html runs on the T1 tender trucks that are Shapeways printed. So an evidential trial of the suitability of printed trucks is very useful.

It would help to know which truck you used - and allow me to consider whether the weight of the metal FD2 would have a different effect!

Best wishes

Peter

Peter Harris
N Scale Kits
www.nscalekits.com

[Chris333]

No hard concrete evidence, but just about all of my HOn30 equipment hads Shapeways FUD trucks with 36" n scale metal wheels. Haven't had one failure yet. Other 4 wheel cars are completely made of FUD with metal wheels.

Too seat the axles points in place I fan a nylon brush wheel in the Dremel against them running at high speeds. After that they roll smooth.

[narrowminded]

That looks like it should work over a truck pretty good.  

I'd run it and check it after a few hours initially and if all's going good, let it go eight or so.  If that goes good, go 24 hours.  Then a week, a few weeks, out to a few months or a failure, whichever comes first.  Anything after a month I'd call great and less might still be OK.  After three months I'd call the test done and a TOTAL success but might keep it running just out of curiosity.

A week of running 24 hours is about the same as somebody running it once a week for eight hours for nearly a half year.  If it goes a month that's a weekly running for eight hours over nearly two years.  I won't be surprised if it does that.  On the other hand, I wouldn't consider it a failure if it went at least a week.  Anything less than that, hmmm.   And if it doesn't go the duration make sure that your test rig wasn't a little too aggressive.  Good luck and let us know.    

@tom mann , you could be taking bets here, funding the Christmas party in Bermuda.

[djconway]

I like narrowinded's test scheam however, I would take closeup photos of the truck, axle pockets, and axle points.

[central.vermont]

I see you are giving it lateral forces just by simply giving it a curvy track to follow
 but I am wondering how you are monitoring the downward force?

Jon

[Lemosteam]

The arm and block above are close to a 1/2 oz. if there were no weight above it would not track. I may add a lead weight there anyway.

[Dirk Jan Blikkendaal]

Nice test John!
I dont expect failure of the truck/material but just good to know what happens.
Just let it run for a week or so... more than enough I would say.
Keep us posted!

[central.vermont]

The arm and block above are close to a 1/2 oz. if there were no weight above it would not track. I may add a lead weight there anyway.

John,
I'm wondering if there is a way you could build a platform off to one side of that rig so that you could have an actual car that was properly weighted per NMRA standards held in place but free standing. One end of it on your test rig and the other on the platform. This way you could get a real world test of  the longevity of the truck.

Just me thinking.
Jon

[Chris333]

I have a set of Photon trucks on the cooker right now     Mama said resin is as resin does.

[thomasjmdavis]

I hope I'm not going too far off topic here, but in the general area of Fox Valley wheels and shapeways truck frames...

I am about to mount my first set of wheels into shapeways truck frames.  My concern is that I have found FUD and FXD to be, well, brittle- and have lost my share of little details here and there- had horns pop off a diesel shell while rinsing it, for instance.  Clearly not as forgiving as Delrin and similar engineered plastics used in mass produced trucks.  Already following John's advice on the Dremel 105.  Any other tips on getting FV wheelsets into the journals of a shapeways truck with breaking or otherwise damaging said truck?

[tom mann]

I have a set of Photon trucks on the cooker right now     Mama said resin is as resin does.

He’s a madman ladies and gentlemen!

[narrowminded]

You know, after thinking about this a little, you probably will know all you need to know within a week if the test shows no discernable wear in that time.  Afterall, it won't be failing in the next five minutes if it just went a week.   It might still be fun to just keep running it but I suspect you'll have all you really need to know in a week.

[Lemosteam]

I hope I'm not going too far off topic here, but in the general area of Fox Valley wheels and shapeways truck frames...

I am about to mount my first set of wheels into shapeways truck frames.  My concern is that I have found FUD and FXD to be, well, brittle- and have lost my share of little details here and there- had horns pop off a diesel shell while rinsing it, for instance.  Clearly not as forgiving as Delrin and similar engineered plastics used in mass produced trucks.  Already following John's advice on the Dremel 105.  Any other tips on getting FV wheelsets into the journals of a shapeways truck with breaking or otherwise damaging said truck?

I have been designing all of my latest trucks with an axle point lead-in vee groove from the bottom angled toward the the center of the truck this helps spread the journals just enough for the axle to snap in, after cleaning the pocket of course.

This can be simulated with a triangular file if the groove is not there. Just don't file to the very bottom of the pocket point or the axle will fall out.

[Lemosteam]

Ok seven straight days of testing. The next video is after five days. There were no derailments during testing or interruptions whatsoever.

Here is a picture of a truck freshly assembled with new wheels on a flat, next to it on the same FXD truck printing is the test truck, just removed from the rig



Here is the closest I can get to the axle point, new left, tested, right, also note the tread wear. New axle left, tested axle right.



Here are the same axles, opposite ends.



Here are closeups of the FXD truck frame axle pockets.



Opposite side.



One side front axle pocket



Same side rear, opposite side was consistent with this.



My observations are as follows:

-More wear on the wheelsets in the form of polishing from the styrene "track"
-Minor wear and polish on the axle points
-Minor rub marks on the top-front of the axle pocket, consistent with the direction of the drum rotation
-No discernible failures after seven straight days
-No excess movement of the axle in the pocket
-No pocket ovaling or change in the shape of the pocket
-Light dust on the wheel face, I am thinking that the axle eventually completely burnished the axle pocket
-No failures in the truck
-MT pin and bolster hole and surface did not show unexpected wear

My conclusions:

-Metal wheelsets pose no threat to the FXD material in a long-term use situation
-Based on the time and distance calculations, the truck should last forever with respect to rolling
-The truck will not experience loosening of the axle over time from wear in the pockets

Other considerations:

-FXD is brittle and will break if dropped, unlike a molded Delrin casting
-Axle pockets pockets require initial cleaning/smoothing for good initial rolling characteristics

You really should have no fear of long term use of an FXD truck over any other truck, unless you are prone to dropping your models.