Attaching wires to pot metal frames.

[chadbag]

I am not sure what the typical frame is made of of a locomotive, for example, Tomix.  It appears to be some sort of "pot metal."    However, for those locomotives that use a metal frame as a power bus for the motor, is there a good way to directly attach my rail wires on a decoder to the frame?  Solder does not stick well.

 

Or should I figure something else out, like using a brass strip in between something somewhere and soldering to that strip?

 

 

[Martijn Meerts]

I've used several techniques for this. If at all possible, I try to solder the wires to the pickup strips that connect the bogie and the frames. This is in many cases possibly with no adjustments needed to the frame, or just minor adjustments like making a small channel in the frame for the wire to go through. More often than not though, the wires can go in between the 2 frame halves.

 

Another option I've used, is to take a brass strip, solder a wire to it, and gluing the brass strip to the frame using a minimal amount of super glue or epoxy, making sure to not accidentally create an isolating layer of glue between the strip and the frame.

 

In case of a Kato steamer, I actually had to drill some holes in the frame halves, tap some thread in them, and put some tiny screws in there. I soldered the wires to the screws.

 

[chadbag]

Thanks Martijn.

 

I have a plan on this one. It does not have any brass rails or obvious brass or non-pot-metal places but there are two light boards I need to insulate from the frame.  I will put some of my copper foil underneath the light boards and attach wires to that.  That will be pressed against the frame by the plastic that holds the lightboard down. I think that will work.

 

This is a Tomix locomotive (EF210 from the basic freight set 92491 that comes with two KoKi) and the bogies have little springs that swipe directly against the frame.

 

[Martijn Meerts]

Ah yeah, the light board is another option I've used before, but it was a bit fiddly in my specific case. Definitely a possibility though.

[chadbag]

4 minutes ago, Martijn Meerts said:

Ah yeah, the light board is another option I've used before, but it was a bit fiddly in my specific case. Definitely a possibility though.

 

Yeah we'll have to see how it goes.  Hopefully the extra layer of Kapton tape will allow the plastic holder that presses the light board against the frame to keep it in good contact.  I wish this one had brass rails for the bogies power pickups to swipe against.  Would make things easier.

 

Except for figuring out where the rail power wires go, this was surprisingly easy and the shell has plenty of space for the decoder to sit in above the frame.  I was supposed to go to bed last night as it was late but I took the body shell off to have a look so I could think about how to attack it and I just went ahead and did most of it.  Of course, I was hating life this morning when the alarm went off.

 

Thanks for the input.

[cteno4]

There is always the conductive glue (usually with silver in it). It does add a tiny bit of resistance though I think. You can get a ml of it on ebay for a buck.

 

cheers

 

jeff

[gavino200]

1 hour ago, cteno4 said:

There is always the conductive glue (usually with silver in it). It does add a tiny bit of resistance though I think. You can get a ml of it on ebay for a buck.

 

 

Have you had a good experience with CG? I've tried it and wasn't impressed. I may have just received a bad batch. But I did a search and found a lot of people with similar levels of disappointment with the product.

 

I've also used the screw technique. That works quite well but is a pain. (drill into the body/weight, and tap. Then solder wires to a screw and screw into the metal body). Instead of doing this I generally use the methods described above..

Edited February 25, 2019 by gavino200

[cteno4]

I had decent luck with the ebay stuff on magnets to hold wires to them. But was not carrying much current at all.

 

i have some very good stuff that’s expensive, but most likely shot now, it’s like 10 years old. I only did one test with it when I got it and it held very well and no measurable resistance really. It was good colloidal silver stuff that Adarsh of trainaidsa.com had and I got some from him as it is hard to get in small quantities. He was using it on some markin part he had fabricated and was selling and worked really well. 

 

Conductive glue aint solder but in some situations it’s all that will work well. For the magnet connectors I needed to use the glue as overheating the neodymium magnets makes them loose oriented magnetic field, so you easily ruin 1 in 4.

 

jeff

[The Next Station Is...]

I have a Kato M250 that I converted to DCC. The motor block has a plastic cap that help holds the two halves of the frame together. Soldering the decoder wires to copper strips and 'wedging' the the copper strips between the cap and block worked fine for me, although I infrequently run my models so haven't had a chance to come across any long-term issues that approach might have. 

[chadbag]

I am looking for very small (and small diameter) sheet metal screws (ie, ones I can drill a small hole into the frame and then screw the screw in to force the threads).  With a flat head.  Have not found anything small enough.  I want to screw a piece of brass strip down to the frame.  For now I soldered the wire to a scrap of brass strip and then "glued" that brass strip down to the frame using this black carbon based conductive paint I got to use with my guitar work to shield the electronics chambe. I painted it on the frame and on the strip and let it dry.  Then I used more to "glue" the two pieces then I liberally spread it around to make a "shell". so to speak.  It seems to have worked.  The EF210 drives over DCC now just fine.   Still working on adding in tail lights.

 

As an aside, now that I have the HN flux and solder, I tried to see if the Tin/Zinc (91% tin / 9% zinc) solder would stick to the frame, after fluxing it well.  No dice.  You cannot get the frame hot enough in any case and it just won't stick.  I did not think it would but had to try it.

[cteno4]

I’ve not seen many tiny flat head sheet metal screws. Pleanty of small flat head bolt screws that you would just need to tap a hole drilled in. Micro tap and die sets are pretty inexpensive and they will cut pot metal very easily.

 

https://www.amazon.com/Eurotool-Tap-Die-14Piece-TAP-135-00/dp/B005KLCXL8/ref=sr_1_5?keywords=Micro+tap+die&qid=1553410412&s=gateway&sr=8-5

 

jeff

[gavino200]

Chad, when I use this technique I use the Kadee tap and drill sets. They come in various sizes. https://kadee.com/htmbord/page247.htm

 

I buy them from my local train guy who just gives me matching screws which he refuses to take money for. What he usually gives me are phillips head (cross) screws that are slightly raised rather than completely flat. They work fine. 

 

If you have no space for even a millimeter or two of screw head, you could always counter-sink them with a larger drill bit, or grind them down after they've been tightened into place.