N Scale Truck Reamers?

[narrowminded]

That is decidedly not aluminum!      Looks like my fear of rails coming off ties was unfounded too.  Did you test an NMRA gauge for the length of the track to see if the rails squeezed due to the vertical curvature?

I hadn't run the NMRA gauge on it due to no evidence of trouble while pre-curving (I threw this together) but due to the request and the ease of doing so, I just did.  It looks straight, is a touch wide if anything, but also fits the same on some unused, unbent new pieces from the bin.  While it may not be sufficiently accurate (nor would it be necessary for these purposes) for calculating to the fraction of the gram what the forces are generated or lost, the repeatability would be very accurate and useful through trial and error.

That truck in the video was a stock MT truck with plastic wheels that seemed to be very free running.  It will repeatedly complete 10.5 swings.  Changing to metal wheels or anything else changed could very accurately quantify the change as an improvement or not.  I'm sure it could be used to benefit by someone to develop their own standard for testing their own equipment's roll resistance and painlessly inspect each piece on the bench. 

The curve base is pretty good in radius and especially squareness due to the curve cutting fixture I used/ use.  It's an arm arrangement I fashioned for a router/ tile cutter attachment available for your Dremel tool (I've mentioned this before on this site).  Being an ABS base I was able to glue on a small dovetail piece ("I" beam) to the tool and fashion an arm from strip that slips into the grooves.  I can put it on or take it off at will.  It swings at various radii based on various holes drilled in the arm.  The center of the swinging radius pivot is accomplished with a tee pin pushed into the foam.  It rides on the surface of the foam, square to the surface as you would expect to see on any full sized router. 

I developed this concept for cutting pockets at a controlled accurate depth and curve radii for street car tracks but have found it very useful for the various pockets needed around a layout.  With the arm removed it can be run up against a straight edge for the straight runs or just free handed. For defined pockets like under switch, switch machine placements, a perimeter guide frame can be fashioned and just chased around.  For track related pockets the fixture placement can be based on track C/L and the end of the pocket so there's no measuring required to have a perfect placement.  Flip the guide over for right hand to left hand.  With the good depth control it can be a very quick way to do multiple pockets and with pretty amazing accuracy.  As good as the fixture, +/- the operator.

[DKS]

At the risk of taking the thread further afield, I'd always felt that there are two aspects to rolling resistance: that of rolling on its own, but also standing resistance (admittedly a misleading term, but I can't come up with anything better at the moment), which is the amount of resistance needed to overcome before something begins to roll. I'll perform a test to measure standing resistance by slowly raising one end of a flat piece of track until a car (or truck) begins to roll. It's then easy to observe the difference between the two factors by reducing the incline until the car or truck stops.

Given the two forms of resistance, I'm not sure what the "track bowl" test results reveal about them with respect to one another. Does the reverse move at each end involve overcoming the full standing resistance, or is this reduced because of factors not fully understood? Is it even possible to measure pure rolling resistance independently from standing resistance? Does standing resistance even have any significance in the grand scheme of things?

We must also take into account changes in rolling resistance as car weight changes. In theory it shouldn't matter, but that assumes a perfect (friction-free) system. I've found real-world tests produce results that are all over the place.

[ednadolski]

.... but also standing resistance (admittedly a misleading term, but I can't come up with anything better at the moment), which is the amount of resistance needed to overcome before something begins to roll.

Static Friction

Ed

[DKS]

Static Friction

Thank you, Ed!

[ednadolski]

While it may not be sufficiently accurate (nor would it be necessary for these purposes) for calculating to the fraction of the gram what the forces are generated or lost, the repeatability would be very accurate and useful through trial and error.

Agreed, it seems that the practical applications would be (a) the check the improvement of a given truck, and (b) to check if each truck meets a certain minimum.

Ed

[ednadolski]

Thank you, Ed!

Sure! 

[narrowminded]

At the risk of taking the thread further afield, I'd always felt that there are two aspects to rolling resistance: that of rolling on its own, but also standing resistance (admittedly a misleading term, but I can't come up with anything better at the moment), which is the amount of resistance needed to overcome before something begins to roll. I'll perform a test to measure standing resistance by slowly raising one end of a flat piece of track until a car (or truck) begins to roll.

In the valve industry that I spent a lot of time in we called that "Break away torque" vs: "Running torque".   I learned it that way and never gave much thought to the idea that there might be more specific terms.  That was satisfactory to me.

Given the two forms of resistance, I'm not sure what the "track bowl" test results reveal about them with respect to one another. Does the reverse move at each end involve overcoming the full standing resistance, or is this reduced because of factors not fully understood? Is it even possible to measure pure rolling resistance independently from standing resistance? Does standing resistance even have any significance?

Standing or breakaway resistance at the fundamental level will be higher but due to the basic design will be hard to measure and even harder to modify as they are likely material issues and the design is pretty efficient as is if executed well.  What we can do something about with the repeatability of a fixture like this will afford a very accurate measure in units of "more than" or "less than" which, in my way of seeing it, is a very practical standard for this work.  Much more precise than "it felt pretty good" or "these don't roll as good" when I changed... whatever.

We must also take into account changes in rolling resistance as car weight changes. In theory it shouldn't matter, but that assumes a perfect (friction-free) system. I've found real-world tests produce results that are all over the place.

That could potentially be true and a few experiments performed by adding a known amount of weight (half of NMRA standard?) to the truck could measure that as well, proving howw much of an issue it actually is.  A screw with washers added and assembled through the bolster hole might accomplish that adequately and again, would be totally repeatable with an honest "better" or " worse" answer. 

Bottom line, this wasn't my baby although I have cars that are clearly freer running than other cars as determined by the fingertip and bump test.   As I've fooled with this rig I think I will do a few experiments with changes.  It's simple enough and with the rig that affords a very repeatable test I expect to find meaningful results, all at little to no expense.   For someone trying to pull long trains it might be very useful and save some disappointment after setting up a whole train only to find it won't pull what they thought it should or what it did last week... but with different cars.   This whole venture was not in my current needs nor my idea but as I've messed with it I think it has the potential to be the answer for those who need a practical way to measure this.  I may do a few measured changes later, like metal wheelsets  vs: plastic in the same truck.  It will be interesting at least.

[narrowminded]

OK, I couldn't stand it and did a simple test, plastic wheels to metal wheels.  The truck seemed quite good to the eye and the observed cycles suggest it is good.  10 full cycles with standard plastic wheels.  Changed to metal wheels, 14 full cycles.  With one metal and one plastic, guess.  You're right!  12 full cycles.  It's a meaningful and repeatable measurement. 

Now, with metal to plastic, what portion of that is weight?  I don't know yet but fiddling with weights could answer that, too.  If you need to know rolling resistance I think it's a useful, practical tool, very simple to use and very simple to build.

[peteski]

Don't forget to include air resistance (aka. drag coefficient) in the test. You should construct a streamlined shroud over the truck 

[MK]

Build a vacuum chamber and put the test rig in it. 

[MK]

To remove the mass factor when comparing plastic vs. metal wheels, add weight to the plastic wheeled truck to be equal of the weight of the metal wheeled truck.

[narrowminded]

Don't forget to include air resistance (aka. drag coefficient) in the test. You should construct a streamlined shroud over the truck 

As was already suggested and I would have known if I had bothered to read, maybe build a chamber and connect it up to the vacuum pump?    If you thought the whole idea sucked this far, just you wait Henry Higgins!

[wm3798]

With my curvy little layout I probably need to worry more about scale flange oilers...

[up1950s]

How about attaching a weight of about a half a car ( whatever that is , but something easy ) to the bolster hole to mimic gravatational friction .

[SandyEggoJake]

@narrowminded

Love the test rig... though expected a duel gauge rig from you to test both N & Z trucks on the same set up!