[modeleng] Re: Track circuiting & Loctite

Ron,

Here are the results of my resistance measurements:-
Where possible I've allowed for meter lead resistance. Locomotive brakes 
were wound well off. Coupling rods were left on!

5" Metro 2-4-0T - not built by myself so I can't comment on costruction 
methods. Measured on complete loco.
Leading wheelset 0.1 Ohm
Driving wheelset (crank axle, pinned) 0.1/0.2 Ohm
Trailing coupled wheelset 0.0 Ohm

5" Sweet Pea 0-4-2 - Measured on rolling chassis. Wheels are loctited and 
the driving and coupled wheels are also located by a 4BA socket grub screw 
tapped into the interface between the wheel and the axle.
Leading coupled wheelset 0.1/0.2 Ohm
Driving wheelset 0.0/0.1 Ohm
Trailing pony - this is where it gets interesting - 60 to 200 Ohms. This 
resistance is all in the interface between one wheel and the axle, and I 
couldn't get a steady reading. I wonder if I should investigate this a 
little closer?

4 wheel driving truck. Wheels are loctited to axles, no pins and there are 
no alternative paths for the current - ball races sit in tufnol housings and 
brakes are cycle blocks.
Leading wheelset 0.0 Ohm
Trailing wheelset 0.0 Ohm

Old wheelsets from Bromsgrove SME passenger cars - not fitted to anything at 
the moment. Wheels are loctited on but since I didn't make them I've no idea 
of the clearances involved.
Wheelset 13    0.2/0.3 Ohm
Wheelset 16    13.8 Ohms
1st unmarked wheelset 4.4 Ohms
2nd unmarked wheelset 4.65 k Ohms (Yup, 4650 Ohms)
3rd unmarked wheelset 160 Ohms

I suspect that what this tells us is that loctited wheels may be 
satisfactory for track circuiting ( and they work fine for us in practice ), 
but to be really certain may require care in fitting and pins on the 
interface.

Hope this helps (he said, muddying the waters!!)

Cheers,

JohnP 

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