Melted Axle Muffs

[Chinapig]

Hi,

I've just had another melted axle muff on a Backmann tender.  Two weeks ago the same but on a Kato axle.  The cause of the problem both times was a short that went unnoticed for too long.

Ok, so I should pay more attention .

Has anyone found a source for material that you can use to replace the muffs?  I appreciate that the Kato and Backmann have different axle diameters.

Cheers, Ted

[MK]

What is a muff?

Are you running DC or DCC?  If DCC, your command station should have tripped if a short occurred and power shut off.  If DC, your trip light should come on but I'm not sure if power would be cut (haven't run DC in years).

[Chinapig]

By muff, I mean the plastic cylinder that holds together the two axles of a pair of current collecting wheels.

I run DCC with PSX circuit breakers.  I know that once a short has been sensed and the PSX activated the circuit breakers test every second or so to see whether the short is still there.  If the cause of the short is not corrected quickly enough, I guess the metal causing the short can warm up.  If the cause is a wheel, I guess that the muff holding the wheel can melt.

Ted

[SkipGear]

Plastruct and evergreen both sell styrene tubing that can be used. They don't make one that is perfect so I usually get a size smaller and then drill it out to fit.

At one point I had some cotton swabs that had a plastic tube for a handle that was perfect but I have not been able to find them again.

[SkipGear]

As far as the cause....not enough feeders on the layout. There is too much resistance between your feeder and the point of the short. We went through this in our Ntrak club a few years ago. Feeders need to be on every leg of a turnout somewhere near it. I never rely on turnouts to pass current through them onto the next piece of track.

[thomasjmdavis]

I am not so much surprised that this could happen as I am surprised that the decoder doesn't toast itself long before the axles would heat up enough to melt those delrin (or whatever plastic it is) muffs/sleeves/cylinders that hold the axles together.  As this has become the preferred way to make loco and passenger car axles in recent years, and although I've never encountered this in my own fleet, it sounds like we need to get one of the electronics geniuses around here to come up with a "hotbox detector" that reports on wheels or axles that get above a certain temperature. 

[Chinapig]

The Plastruct/Evergreen tubing is a great idea and I'll get some at the next opportunity.

I totally agree regarding feeder wires and nowadays no single piece of newly laid track relies on just fishplates for transferring current.  If the fishplate joint isn't reinforced by soldering I'll add a dropper.  Having said that, there's no doubt that some of the track that's been there years hasn't been upgraded.

Yes, we need 'hotbox detectors'

[Lemosteam]

@Chinapig

These are designed to be lightly drilled out (1.5mm axles) but they are perpendicular on the ends and designed for perfect width.  I am not sure the axle diameter difference between Kato and Bachmann.

http://www.keystonedetails.com/keystone-customs/2016/9/12/n-scale-axle-muff-20pk-for-fvm-axles

[Chinapig]

John,

Kato axle diameters are about 1.0mm and Bachmann about 1.25mm, but what a brilliant idea.

Ted

[peteski]

The decoder doesn't get damaged because the current is only affecting the truck. Likely the short is between the front and rear wheel (on the same side of a single truck, or single side between trucks).  Even with enough track feeders it might not trip the breaker because all those very small contact points in the trucks (the pointy axle to the bearing cup, or the connection between the trucks) have high enough of resistance to heat up the metal part, and melt plastic without passing enough current to trip the breaker.  Being careful is the only good way to prevent this problem.

[Lemosteam]

John,

Kato axle diameters are about 1.0mm and Bachmann about 1.25mm, but what a brilliant idea.

Ted

I could quickly design some for both sizes.

Is that something that you would be interested in?

[nkalanaga]

Another way to get such a short, using only one wheel, is an old-fashioned "non-DCC friendly" turnout, with the point a little too close to the stock rail.  If the loco happens to be sitting on the turnout, it will do this.  A moving loco will usually either blow the breaker, or coast past the short, if it has a flywheel.

Yet another way is on a reversing section, loop, wye, or otherwise.  If the wheel is on the insulating gap, between opposite polarities, you have a short.

[Chinapig]

Lemostream,

I would certainly buy a set for each of the Kato and Bachmann, price being right.  One would need to check the axle diameter measurements though.

Thanks

[peteski]

Also measure the length of those muffs as different manufacturers use wheels that have different thickness (width of the tread and width of the flange), and that will determine the width of that muff.

[Chinapig]

I've just got my calipers to them and the results are:

Kato: Axle dia 0.97mm, muff length 7.51mm, muff length required to achieve NMRA back-to-back spacing 7.72mm.  It may be best to reduce the diameter of the inside of the muff by say 0.02mm and one could ream or drill to get a perfect fit - that's got to be better than finding 0.97mm is sloppy.

Bachmann: Axle dia 1.17mm, muff length 7.46mm, muff length required to achieve NMRA back-to-back spacing 7.85mm.  The axle has a knurled part which means it's going to end up being a push-fit.

I'm pretty sure these measurements will end up being ok, but if anyone cares to check them I won't be offended