N Scale Truck Reamers?

[DMetz]

I see a need for this type of reamer for 3D printed trucks, as found on Shapeways.  I have some Fox trucks that I wanted to use, but the journal pockets are too rough for smooth rolling.  I tried to clean up one, but I got mixed results.  I have also seen some warpage over time for other 3D printed trucks.  A journal reamer would clean this up easily.  I have not experienced a true need for a journal reamer for other trucks, like Micro-Trains, Atlas, and others.  On the rare occasion that there was a problem, I just swapped the truck.  But if a tool was available, I would definitely buy one.

[Lemosteam]

Since I have been designing FXD truck frames, I have developed a theory on the cone point.  Since the axle point can never reach the bottom of the truck cone, it would not make sense to have the point taper be the same as the truck taper or the design would risk too much friction. I suspect that the truck pocket is a larger included angle taper than the axle point to avoid this. Unfortunately, I cannot measure either accurately.

As a result, I have resorted to cleaning out the bottom of my truck journal pockets with a spherical 107 105 Dremel engraving bit instead (0.8mm sphere). Spun gently only by hand, this ensures that the axle point can only make a single point contact inside the pocket and the user can judge how deep to keep grinding.

[Lemosteam]

Cannot edit the post above.

@DMetz , seriously, try this on the FUD.  These are available at nearly every hardware store, lowes, home depot, graingers, etc.

https://www.dremel.com/en_US/products/-/show-product/tools/105-engraving-cutter

[VonRyan]

I'll see if I can find the spec sheet that a friend of mine drew up before I was even born.

I've used a tool he made, which was a reprofiled drill-bit of a specific size, and was specifically made for Kadee/MT trucks, and thus is optimized based on the specs of the MT axle points.
Makes a world of difference honestly.
Every car I used the tool on rolls far better and longer than a car that is stock.

The better rolling quality also eliminates the slinky effect.

[mmagliaro]

Cannot edit the post above.

@DMetz , seriously, try this on the FUD.  These are available at nearly every hardware store, lowes, home depot, graingers, etc.

https://www.dremel.com/en_US/products/-/show-product/tools/105-engraving-cutter

Yeah!  I have those, and I've used them to smooth and deepen cone pockets.  They work great.

[peteski]

Single flute countersinks leave a much better finish.  They cut at the single edge while the rest of the circumference aids in smoothly guiding the cutter through its rotation.  Around a machine shop you're unlikely to see anything else.  Various angles and diameters but always single flute.  Multi-flute are for woodworking, I believe.

That is exactly why that is what I chose for mine.  A burr mentioned recently is a totally wrong tool for the job!  We need t leave as smooth of a surface as possible.

[SandyEggoJake]

@Lemosteam

Since the axle point can never reach the bottom of the truck cone, it would not make sense to have the point taper be the same as the truck taper or the design would risk too much friction. I suspect that the truck pocket is a larger included angle taper than the axle point to avoid this.

Well, actually.... as designed the axle is to reach the bottom (and just the bottom) of the cone.  But you are correct that there would be too much friction... if the cone angle was the same.  But a close read of the NMRA specs shows your guess is correct... by design the cone angle of the side frame and of the axle are not the same.   60 degrees for the pocket.  max 50 degrees for the point.  Thus again a 5 degree of relief on all sides, with friction minimized as well as vibrations of a point rattling around in a spherical pocket. 

While a single ended spherical engraving burr might work of very tight POM trucks or developing a rudimentary pocket in FUD, it will not yield optimal geometry, nor give you much depth control or as smooth a result. 

But hey, if they work for you?  Smoke 'em if you've got 'em!   

[Lemosteam]

@Lemosteam

Well, actually.... as designed the axle is to reach the bottom (and just the bottom) of the cone.  But you are correct that there would be too much friction... if the cone angle was the same.  But a close read of the NMRA specs shows your guess is correct... by design the cone angle of the side frame and of the axle are not the same.   60 degrees for the pocket.  max 50 degrees for the point.  Thus again a 5 degree of relief on all sides, with friction minimized as well as vibrations of a point rattling around in a spherical pocket. 

While a single ended spherical engraving burr might work of very tight POM trucks or developing a rudimentary pocket in FUD, it will not yield optimal geometry, nor give you much depth control or as smooth a result. 

But hey, if they work for you?  Smoke 'em if you've got 'em!   

Just because there is a proven standard that works for mass produced designs (which FUD is not), it really does not matter how you achieve a single point contact inside the pocket.

Mass production would require a spherical point in the pocket anyway- it cannot be sharp- the plastic requires a radius in the bottom of the cone, likely a very small one, to be manufactured.

In a dynamic condition the axle point will make contact in multiple areas of the cone due to car rocking, slowing, starting and track irregularities, etc, but none more so than the TOP, due to the weight of the car.

The Dremel bit produces a very smooth surface inside the FUD pocket and accuracy to the axle axis is not an issue because I can still clean up the bottom of the cone with the bit at an angle to the sideframe.  With FUD, opening and closing a truck frame can be perilous so I like to leave that to the final operation of inserting the axle.

When used, the bit makes my sideframe designs roll as smoothly as a Kato passenger car truck on electrical pickup stampings.

I have not tried it inside a Mass produced truck as yet.

[mmagliaro]

Right.  If you look inside a Kato truck with the contact strips in it, the bronze cups are rounded.  The axle point isn't riding in a "pointy-bottomed" cup.   I think for the sizes and tolerances we really need here, the axle point riding in a rounded cup works out just fine.  The wheelset and point find a happy spot and just spin along.  It's not like we see those wheelsets wobbling and bobbing around.

[peteski]

Actually if you think about this the pointy axles are always a bit loose in the bearing cups. So they never ride in the cup. Instead, the cone part of the axle (Or even the tip) contacts the cone surface of the cup.  The shape of the end of the axle or the bottom of the cup is irrelevant under most operating conditions.

[Lemosteam]

Note that the NMRA standard does not dictate the distance between the pocket bottom across the truck.

Below is a link to comparison on a 1.67 degree incline. I tested a brand new Kato Broadway Limited replacement truck, one of my FXD 2DP5 passenger trucks with FVM axles and an MT passenger truck with its center axle removed.

https://photos.app.goo.gl/cVnYX20VYIFbHcGH3

[chicken45]

So the trucks on my queen mary flat car...the wheels roll like squares, but they still roll. There's just a lot of resistance. I cleaned them out with those drill bits @Lemosteam suggested and they roll a lot better.
There's a lot of wheels on that sucker. Thirty two, in fact.

[wm3798]

I ave never run a train of more than 30 cars or So, and have been running N scale trains for more than 40 years.  I think you might be over thinking tbis...

[ednadolski]

Any interest in such a tool?

Yes -- esp. if it could help improve some of those Exactrail trucks that are disappointingly tight OOTB (and I don't want to replace the wheelsets).

Has there never been such a tool in N?  That seems kinda surprising.

The better rolling quality also eliminates the slinky effect.

Possibly a YMMV thing, considering MT sells those 'restraining springs' which work by increasing the rolling resistance to stretch out the slinky.

... I ave never run a train of more than 30 cars or So ...

FWIW, I've run 60 car trains and I am planning for longer ones on my new layout.  So it pays to get rid of every last bit of rolling resistance (or at minimum fix the 'tight' ones e.g. those Exactrails). 


Ed

[mmagliaro]

I ave never run a train of more than 30 cars or So, and have been running N scale trains for more than 40 years.  I think you might be over thinking tbis...

I don't know, Lee.  I don't run long trains either (unless I'm doing a stress test just to see what an engine can pull).
And one bum car with a draggy wheelset can really cut down on the pulling power of an engine, not to mention causing
trouble getting up hills.