Repairing stripped thread in brass loco

[Sharky_McSharknose]

I recently purchased a Key NYC H10B steam loco and I noticed the front-most drivers have a bad wobble to them. The front two drive axles are crank-driven. When I took the bottom plate off to investigate, I found that the front screw was barely tight. This is probably the cause of, or a major contributor to, the wobble. When I tried to tighten the screw, I could feel that the threads in the loco were stripped. There's enough to hold the screw in place when its running, but not much more.

How can I go about repairing the threads on a brass loco such as the H10B?

[narrowminded]

How can I go about repairing the threads on a brass loco such as the H10B?

Well, it depends.   No, really.   I'm not specifically familiar with this loco or this detail  but in a way, threads is threads. 

Do you have a photo showing the hole and vicinity?  Depending on the vicinity there could be many options.  Also, how much thread engagement is there.  Especially, the ratio of the screw diameter to the length of thread engagement.  Is it 1 diameter? 2 diameters?  Could it be that deep?  Your options could be dependent on things like this.

[Sharky_McSharknose]

I'll get pictures and measurements tonight. Right now I'm Railwiring from work like a lazy

[learmoia]

Maybe drill and tap the next size up?.. is it a machine screw or self taping kinda thing...

For the same issue in wood, I have started the wood glue and toothpick solution..

~Ian

[rray]

Super easy... I had the same problem a couple weeks ago. Just use a pointy tip soldering iron and fine solder, and solder a tiny patch to the inside of the threads. Then the screw will have something to bite. Solder is soft, so it is a one or two time fix, meaning you will have to re-melt that solder if you unscrew and re-screw in the screw a couple times, but if you do it correctly, one time is all you need.

[woodone]

I would be real careful with solder idea. If this happens to be a left rail driver. There is an insulating ring between the tread and the hub
You could melt that insulation and have a short.
I think that I would try som J-B Weld, fill the hole and let cure for 24 hours ,then drill and tap..

[Angus Shops]

Is the hole stripped, or the screw, or both? If you’re lucky it’s just the screw, which can be replaced. Maybe,if it’s both, a new screw will be sufficient...
Geoff

[Steveruger45]

That’s what I was thinking too.  I have had success on soft materials such as brass by using a different thread form than the original but of closely similar size such as a BA threaded machine screw in a metric threaded hole such that the new screw re-taps the hole.

https://britishfasteners.com/threads/

[mmagliaro]

This is the hole in the frame, right?  And the cover plate goes on the bottom, keeping the drivers in, and then screws go through to hold the plate on.  And one of those screw holes is stripped out?

Assuming I understand the problem correctly:

I would not try to solder anything.  Unless you have a resistance soldering iron, soldering anything to a brass loco frame is an exercise in futility.  By the time you heat everything up enough for solder to flow, the frame will come apart in pieces when all the solder joints let go.

If there is enough metal around the hole, I vote for retapping the hole 1 size larger than it is.  It is probably a metric thread, something like M2.  But since you are retapping, you can make it anything you wish that you have a convenient screw for.  I'd guess since it's a retaining plate, you're looking at 2-56, something relatively big like that, as opposed to 00-90 or 0-80.

Idea 2:
If there isn't room to tap larger, is there anywhere else near there that you can just drill and tap one or two little 00-90 screws?
You can do that and forget the screw that won't tighten.

Like the others, I eagerly await your photos!

[Sharky_McSharknose]

Here are a couple of pictures of the bottom of the H10B. I was wrong in that the two outer axles are crank-driven, not the front two (I may have been thinking of another one of my 8-coupled locos). The front is to the left in these pictures.





The diameter of the threads on the front plate screw is 1.37mm/0.054in and the shaft length is 2mm/0.08in (queue Beavis & Butt-head snickering).

[PaulP]

I just bought some 1.4mm screws from McMaster Carr which sounds like that size.
 They have 1.6mm which is about .063 which you could tap that hole out to.
They are SS flat head slotted 8-18. Just a thought.

[narrowminded]

It looks like plenty of room for a larger screw.  Probably the best way to go.

Take the time to get the proper screw length, head style, etc.

[Maletrain]

Larger screw size will probably mean lower thread count per inch/millimeter of engagement.  Because the shaft length of the current screw is not much more than its diameter, I am thinking more about getting good thread engagement for the available length.  My choice would be to clean/degrease the hole thoroughly and then fill it with enough JB Weld to allow you to redrill and retap for the current screw size.  If the threads on the current screw look at all buggered, I would replace it with a new one.

[learmoia]

Looking at the first photo.. It appears that one screw was already replaced.. or when previously reassembled, the correct screw was used else ware.

Edit: It looks like the front pilot screw matches the cab side gear plate screw?..

~Ian

[peteski]

The diameter of the threads on the front plate screw is 1.37mm/0.054in and the shaft length is 2mm/0.08in (queue Beavis & Butt-head snickering).

Many brass locos have the frame (and the crossmembers where the screw holes are) are made from etched and soldered sheet brass plates.   However, this model seems to have the frames cast from brass, so the screw hole is in  much thicker piece of brass.  Still, the most feasible solution is likely to tap the hole for a larger screw.  Too bad there are no Helicoils are available for such small application.

I did not realize that Helicoil was now an Indian company - thus whole world is going to hell in a handbasket!