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Author Topic: Advice please: shorting as loco reaches blades of curved point.  (Read 437 times)

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Offline Ricky B

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Advice please: shorting as loco reaches blades of curved point.
« on: January 24, 2020, 09:03:14 PM »
 :helpneededsign:

Hi all. I'm sure you knowledgeable folk will have advice (possibly including "you should've used point motors with polarity switch")!

So as a returnee to modelling I'm kind of building my first proper (DCC, electro frog points, code 55) layout but feeling my way. I've had a track plan (see pic 1)  temporarily pinned down and wired a wee while. In loft and not meant to be moveable I've shied away from using point motors (soldering not yet up to it though improving) instead, just relying on insulated joiners and power feed 'to toe'. And the layout works. But now ditching the idea of cassettes at either end in favour of fiddle yards off at right angles at either end, I've started laying the track (see pic 2), insulated joiners at the two inner rails of point 'heels' and track feeds from the bus wire to toe. I've only laid the curve leading from main layout into the curved point and have test run a loco (Dapol class 56) along it. The loco leaves the main layout and runs round the curve but, as soon as the wheels reach the curved point's blades with the point set to diverge i.e., turn right, there's a short and the old Prodigy Advance has to be turned off. Am assuming the 56's flange is in contact with the 'inner' point blade.

The main part of the layout runs fine and is just the same, small, medium and large radius Peco code 55 electrofrog points so I was a bit taken aback to find this issue. Incidentally if the curved point is set 'straight on' there is no shorting.

Maybe the 56 wheels aren't as fine as hoped? Is it my tracklaying?

I know some may say 'should be using polarity switching/frog juicer' etc but I'm surprised a new ish modern loco and the points seem 'incompatible' in this way.

Any advice or quick fixes gratefully accepted and well aware the subject is wel, trodden ground 😚

Offline ntpntpntp

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #1 on: January 24, 2020, 10:31:31 PM »
So if you're using unmodified Peco live frog pointwork that means that the open blade is the same polarity as the frog, ie. opposite polarity to the running rail it usually closes against.  There is a possibility of a wheel bridging the gap, it should normally be unlikely due to the width of that gap but perhaps as this is a curved point the wheels are tending to the outside of the curve and touching that open blade.

This is why there is such as thing as modifying a point to be "DCC friendly" which basically involves disconnecting the blades from the frog and bonding them to the nearby running rail.   You'll find the same arrangement with Peco's new Unifrog point design.  As noted above, the gap is so wide that many folk run their DCC layouts quite happily without ever making their points DCC friendly, but maybe your particular situation has hit that problem?

If this is indeed what's happening then frog polarity switching via a mechanical switch or a frog juicer won't cure the problem, it's the opposite polarity of the open blade that's the cause and the only cure would be to modify the point to be DCC friendly. If you do that then you WILL need to power and switch the frog itself.

Can I suggest that you take the troublesome loco, place it on the track just before the point with DCC power on but the loco stationary, and gently push/slide the loco's first bogie into the point whilst deliberately guiding the wheels on the inside of the curve (ie. away from the open blade). Does it short?  If you then wiggle the wheels to the outside does it then short?
« Last Edit: January 24, 2020, 10:39:03 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline jpendle

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #2 on: January 24, 2020, 10:33:35 PM »
First off you don't need polarity switching, and you definitely don't need a frog juicer.

You also don't need a point motor.

From your description you have wired everything correctly. I had two RH curved Electrofrog points and a CL56 on my last layout and didn't see any issues.

Have you tried any other locos?

One possibility is that the back to backs on the CL56 need adjusting.

Regards,

John P

Check out my layout thread.

Contemporary NW (Wigan Wallgate and North Western)

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=39501.msg476247#msg476247

Online chrism

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #3 on: January 25, 2020, 07:08:54 AM »
The loco leaves the main layout and runs round the curve but, as soon as the wheels reach the curved point's blades with the point set to diverge i.e., turn right, there's a short and the old Prodigy Advance has to be turned off. Am assuming the 56's flange is in contact with the 'inner' point blade.

The main part of the layout runs fine and is just the same, small, medium and large radius Peco code 55 electrofrog points so I was a bit taken aback to find this issue. Incidentally if the curved point is set 'straight on' there is no shorting.

Maybe the 56 wheels aren't as fine as hoped?

I occasionally get the same with my Union Mills 2F and 3F. I'm pretty sure the stall is a short because if I nudge the offending end of the loco/tender sideways it happily sets off again.
I keep meaning to bung some paint on the backs of the wheels to see if a) that stops it and b) if I can later see any scuffing on the paint to confirm that the wheel backs are touching but, like so many things, I haven't got around to it yet.

What I have found seems to help is squeezing the "offending" point blade very gently and very slightly away from the corresponding stock rail so that it's got a few thou more clearance.

Interestingly, I found another issue with my Peco points, code 80 streamline ones this week. My Dapol 2MT "Mickey Mouse" tank frequently chucks off the leading pony truck wheel on points and I'd assumed that either the truck was catching on the crossing nose or the driving wheels were dropping into the nose gap and "bouncing" enough to kick the truck off.
However, this week I've been assembling the track for Broughton and, because it has some gradient changes including an up followed by a down immediately after a point, I've been running everything very slowly and watching carefully for anything amiss. What I found was that, yes, the 2MT was bouncing but apparently NOT at the crossing nose.
Looking closely I found that the leading driving wheel was snagging at the hinge between the point blade and the closure rail. Rubbing a finger along revealed a distinct "step" in the horizontal plane because the closure rail is proper rolled rail whereas the blade appears to be pressed metal and the rail head isn't as thick as the closure rail. A gentle tickle with a fine file on the end of the closure rail to "taper" the inside edge has worked wonders and Mickey is now very happy, as am I - apart from the number of other points on which I now need to do the same :D

Offline Bealman

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #4 on: January 25, 2020, 07:17:14 AM »
Very interesting and informative.

Thanks for that post!  :thumbsup:
Vision over visibility. Bono, U2.

Offline Izzy

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #5 on: January 25, 2020, 08:41:36 AM »

I feel certain @ntpntpntp has nailed the issue but how to solve it probably depends on whether it’s just the one loco, or the point. Do other locos act the same? Or does the 56 both ways around? If it only does it facing one direction then you would tend to suspect btb variance. If not, or other locos do it, then the point blade distance is the problem, and DCC friendly mods would be the long term answer.

Izzy

Offline Ricky B

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #6 on: January 25, 2020, 10:41:01 AM »
Thanks chaps for the input thus far. I discovered this issue late on Thursday and decided to leave it to mull over and no, I neither tried turning the 56 round or trying any other traction. Now I'm 200 miles away from it preparing to visit Pontefract model railway show. I won't be back 'aloft' until Tuesday night.

Chrismif I tried easing (bending) the blade away a touch from the stock rail, aren't I then compromising it's ability to keep the 'juice' flowing when the point is in the other position?

ntpntpntp-and jpendle. thanks- will run those checks in the week. Checking the loco by pushing it about with power on is a good idea . I understand the theory of disconnecting the blades from the frog and then bonding the blades to the nearby running rails but might come back for further guidance prior to that.

Off to Ponty show now.




Online chrism

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #7 on: January 25, 2020, 10:54:15 AM »
Chrism if I tried easing (bending) the blade away a touch from the stock rail, aren't I then compromising it's ability to keep the 'juice' flowing when the point is in the other position?

Sorry, I wasn't clear about that - I only eased the middle of the blade, leaving the hinge and tip end untouched, because on mine the issue appeared to be when a wheel was partway along the blade, not catching right at the tip.

Offline PLD

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #8 on: January 25, 2020, 12:32:58 PM »
As ever, if it is only the one loco that has issues, concentrate on the loco. If several/all locos have issues it's more likely to be a track issue.

From the OP, I'm not clear whether other locos have been tested through the point in question or not, so that is the first step to pinpoint where the fault lies i.e. loco or track...



Offline Ricky B

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #9 on: January 25, 2020, 01:14:22 PM »
No, as yet no other locos have been tested

Offline lil chris

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #10 on: January 25, 2020, 04:34:10 PM »
I had the same issue on my old layout “East Lancashire Lines”, I had several locos with the problem a Union Mills 3f and a class 47 was another. The Deltic I bought just before I disassembled the layout sailed through. By the way I even bought a back to back gauge and the loco’s involved were within the limits. One of the things I tried was painting the side of the switch rail with acrylic paint, It worked sometimes but not 100%. The new layout I am building has a curved point leading in a similar place, if after testing I have problems I will cut the ties to the frog this time and bond the switch rails before I do any ballasting. Others on here have these curved points and have no problems,I thought it was just me who was unlucky. I have bought a brand new curved point for the layout I might just bond the rails and be done with it.
« Last Edit: January 25, 2020, 04:35:26 PM by lil chris »
Lil Chris
My new layout here, Irwell Valley Railway. https://www.ngaugeforum.co.uk/SMFN/index.php?topic=47127.0

my old layout was East Lancashire Lines.

Offline lil chris

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #11 on: January 25, 2020, 09:34:47 PM »
Well I decided not to take the chance, I spent hours last time alighning the curve into the point fitting check rails etc, painting the side of the switch rails checking back to backs the list goes on.... So I have just modified a brand new curved point, hopefully I have done it correctly the test will be in the pudding so to speak, ie run trains round it and see what happens. See my layout post's if you fancy doing the same, you do need a steady hand with the soldering iron.
Lil Chris
My new layout here, Irwell Valley Railway. https://www.ngaugeforum.co.uk/SMFN/index.php?topic=47127.0

my old layout was East Lancashire Lines.

Offline Ricky B

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #12 on: February 16, 2020, 08:40:07 PM »
Hello all,

It's taken a while to report back but I wanted to say that my shorting at the curved points blades is now sorted and to tell you the reason.

It was nothing to do with back to back measurements- it was in fact the simplest of all reasons..because the track you see in my pictures (see first post above) was not fastened down properly, the natural inclination of the flexible track to spring back towards 'the straight' meant there was a definite sharp kink to the right at the point at which the flexible track was joined to the Peco point. So the approaching loco's front pair of wheels was thrown too far to the left as the loco entered the toe end of the point, thus, it connected with the inner blade of the point..
When I secured the flexible track more efficiently,so it was then meeting the point 'square on' with a smooth transition into the point, then no more shorting.
Thanks for your input guys n gals.

I've an Unifrog question for you next. I'll post that separately. :thankyousign:
« Last Edit: February 16, 2020, 08:41:33 PM by Ricky B »

Offline lil chris

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #13 on: February 16, 2020, 10:54:26 PM »
Well done, I spent ages alighning the curved track before the point trying to make a nice transition from curve to the point. I have not took the chance with my new layout, pleased that yours is fine though.
Lil Chris
My new layout here, Irwell Valley Railway. https://www.ngaugeforum.co.uk/SMFN/index.php?topic=47127.0

my old layout was East Lancashire Lines.

Offline Bealman

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Re: Advice please: shorting as loco reaches blades of curved point.
« Reply #14 on: February 16, 2020, 10:57:37 PM »
Good to hear you've got it sorted!  :thumbsup:
Vision over visibility. Bono, U2.

 

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