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| Metal fatigue http://fast-tracks.net/forums/viewtopic.php?f=4&t=880 |
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| Author: | jdm_com_au [ Sat Jun 07, 2008 8:03 am ] |
| Post subject: | Metal fatigue |
As one end of the points blades are fixed, is there an issue with metal fatigue due to the flexing when the point blades are moved? |
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| Author: | rdressel [ Sat Jun 07, 2008 11:39 am ] |
| Post subject: | Re: Metal fatigue |
Yes, thats why I use a brass or stainless steel wire soldered to the point rail. This wire is then routed to a hole in the throwbar, takes alot of stress off the solder joint. Rob |
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| Author: | jdm_com_au [ Sun Jun 08, 2008 6:38 am ] |
| Post subject: | Re: Metal fatigue |
As I am unable to visualise what you're describing, I would really appreciate a photo of this modification. |
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| Author: | rdressel [ Mon Jun 09, 2008 11:23 am ] |
| Post subject: | Re: Metal fatigue |
Cannot give you a pic at this time. but the techique is simple. Take some spring brass wire. Nickel silver will do to. Put a 90 degree bend in about 1/4 inch less in you in to N scale. Before you solder your point rail in mark the point rail with a pen on the foot of the rail towards the center of the turnout. The mark should be dead center where the throwbar goes, That way when you drill the hole for the throwbar points bearing hole they will be in the center of the throwbar, (width wise) Your going to cut with a file a notch in the rail foot as big as the wire. At thesame time mark the pc tie right at the rail foot notch. then Try to use as small a wire as you can but strong enough not to break. Too big a wire will interfere with flanges. Place the short end of the 90 degree bend on the foot of the rail, and place the wire into the groove in the foot of the rail so its pointing down. You want it to point straight down with no angles. Solder the wire to the rail foot. Place the wire in the PC throwbar hole, if you measured correctly the points, throwbar, and closure rails will all be in the correct position. Solder the closure rails to the pc ties. Flip the turnout over and bend the wire under the pc tie so the points dont ride up. Repeat the whole procedure for the other point rail. I predrilled some holes where the throwbar is on the jig so I can do this in one step during the turnout construction stage.. Rob |
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| Author: | emccamey [ Mon Jun 09, 2008 12:02 pm ] |
| Post subject: | Re: Metal fatigue |
The idea is much like the FastTracks instructions for hinged points in the double slip construction. (Also a newsletter topic on the same subject). Only with FastTracks - they use spikes in their documentation. What you are doing is using the brass rod and making a spike like hook on the top solder to the points end - only the rod is bigger than the spikes on the twisting through the throw rod part. Makes for a good solid and nicely near frictionless connection. There's several places in the forum threads where this is discussed and illustrated. -ed- |
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| Author: | jdm_com_au [ Mon Jun 09, 2008 10:12 pm ] |
| Post subject: | Re: Metal fatigue |
No worries, I'll have a search through the forums to see what I can dig up. |
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| Author: | jdm_com_au [ Tue Jun 10, 2008 11:03 pm ] |
| Post subject: | Re: Metal fatigue |
I suppose other ways to reduce the problem would be to use #10 instead of #4 turnouts. That way the blades are longer and will have less deflection ( in degrees ), so therefore less flexing at the soldered joint. The other suggestion would be to use the smallest code rail possible, as a code 40 rail would flex a lot easier than a code 100 rail. I realise these ideas may not be practicable for all users, but it may be beneficial for some. |
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| Author: | emccamey [ Wed Jun 11, 2008 8:10 am ] |
| Post subject: | Re: Metal fatigue |
The rails themselves don't get sufficient stress to actually incur metal fatigue. The problem area is the soldered joint of the PC throwbar and the rail base. Here a pivoting pin soldered to the rail base works well and reduces the stress of the throw bar. Nickel Silver has a tensile strength that will handle the slight twisting stress of the rails themselves practically indefinitely. They function much like the old torsion bar suspensions did - and those had tremendous amounts of stress. It's only the solder joint that has some question. The reason for using hinged joints on the point switch blades is not a concern of metal fatigue, but the degree of tensile stress induced to the throwbar movement. With double slips especially having four points moved in tandem, it takes a powerful throw mechanism unless freedom is provided with using hinge joints. I suspect you may have been chasing a red herring. -ed- |
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| Author: | jdm_com_au [ Thu Jun 12, 2008 5:29 am ] |
| Post subject: | Re: Metal fatigue |
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