Best Of Notes on body-mount couplers (work-in-progress)

[ednadolski]

Isn't the elongated hole a bit wide? 

It's the 0.050" for the 00-90 clearance.   I think perhaps just looks wider because the other hole got smaller.

(BTW on this image I had the grid turned on. The white dots are on a 0.005" spacing, so that can be used as a guide for the dimensions on this one.)

Also, isn't the color of part which is to remain supposed to be black with white where everything will be etched through?  Or will the artwork colors be reversed later?

I think there are a variety of conventions & preferences, but not any one way to do it.  My understanding is that it's a matter of telling the etcher which colors you want for the full, half-front, and half-back layers.   Besides, this is what Gary used for the v1, so it must be good.  I'm just following his footsteps 

Also, what are the rectangular holes in the side walls for?  It was probably mentioned earlier and I just missed that (I'm a late arrival to this thread and I didn't read all of the previous posts).   

No worries, those are just cosmetic, to give a suggestion of some of the detail on a proto pocket like this one.   It does look kinda crude on the drawing, but on the pocket it will be pretty small, even in close-up pics of the finished model.

(BTW that reminds me -- I still gotta do the cut lever bracket for Gary....)

Thanks for looking

Ed

[GaryHinshaw]

Looks good Ed.  A couple more things:

- It seemed like the tab & slot arrangement worked very well before.  Do you think it needs to be enlarged?

- Re the little side slots - it would be good to check that they won't catch or interfere with the coupler centering spring whiskers. 

Did I send you the guidance from James about how to size the sheet to maximize roll efficiency?  I recall that the best width to use was ~285 mm (I'll double-check that).  Anything less than that is wasted (i.e. paid for).  The other dimension is flexible, since it just comes off the spool.

Let's roll!
-gfh

[peteski]

- Re the little side slots - it would be good to check that they won't catch or interfere with the coupler centering spring whiskers. 

That is exactly the reason I was curious about those slots. I guess I should have been more specific in my question. 
Even if they don't interfere with the whiskers, if the whiskers will rub against that area, then the sharp edge of those slots might wear grooves in the outside surfaces of the whiskers. Maybe those slots should be half-etched on the outside only?  That will still give a visual queue that there is some extra detail in that area.

[GaryHinshaw]

Like they were originally. 

[ednadolski]

Thanks guys for the excellent point about the whiskers (I didn't even think about that).  You're right, it should be a half-etch from the front (red) side, I'll add that change. (You're right about the original too...  if it ain't broke.... <sheepish>)

On the long slots, I thought it would be good to make them about 0.003" wider than nominal after looking thru some of those design guides.  Holes are easy to enlarge, slots are almost impossible.   I'd have to check the size on the v1 drawing, but I'm guessing one reason v1 came out OK here was because of the over-etch.  Since this one doesn't have the little holes I'm not sure that PPD would produce identical results.  Could very well be overkill, but it seems like a slightly safer hedge -- what do you think?

BTW Gary if you could forward a copy of that guide from James, I'd be very appreciative.

Thanks,
Ed

[ednadolski]

Here is revision 2C, updated as follows:



 - Adds the elongated pocket
 - Cover for the elongated pocket has the 'looped' kind of air hose like on this proto.   Since I could not draw it actually hanging under the cover, it will need a bit of gentle bending when installed.
 - The air hose for the 'standard' cover has been re-drawn and now includes a curve.
 - Added a folding 'hook' for installing a cut lever bent from wire.
 - Changed the side slots back to a half-etch.

Please let me know your comments.  I'm getting ready to put this into a fret and send it out for etching, so if anyone is interested in some sample parts, please send me a PM.

Thanks!
Ed

[peteski]

Shouldn't the hole in that elongated cover be etched through (not half-etched)?

I also don't understand that super-long curved up hose in the elongated coupler pocket's cover.  John Holmes of Z-scale couplers? 

[ednadolski]

Shouldn't the hole in that elongated cover be etched through (not half-etched)?

On the extended pocket, the pivot screw could end up in a visible location.  So rather than have it protrude thru the top, the idea with the half-etch is to use a shorter screw that would not be visible.  The half-etch just gives a little bit of recess to receive the end of the screw.  This does raise the question of how to hold the cover in place.  It would have to be glued or soldered (the latter probably being the sturdiest).   Alternately, I thought of maybe extending the tabs that go thru the cover and adding a half-etch so that they could be bent to hold the cover in place, but I'm not sure how sturdy that would be.

I also don't understand that super-long curved up hose in the elongated coupler pocket's cover.

It's a generic version of some of the proto air hoses, like these for example:

http://i218.photobucket.com/albums/cc97/notllr/centaout_zps70931a43.jpg
http://i218.photobucket.com/albums/cc97/notllr/nadxbend_zps272a25f8.jpg
http://i218.photobucket.com/albums/cc97/notllr/bnsfairlineholder_zpsbe77aa2f.jpg

The 'looped' hose doesn't always correspond to an extended pocket on the proto.  However, since the cover is the same, you could use either type with the standard or extended pocket as desired.

Ed

[peteski]

Thanks for the explanation Ed.  Only one thing I don't like is that on the extended pocket you depend on the threaded hole in the cover (which only has a depth of a single thread) to keep the pivot screw tight.  Also since the cover hole is the female thread, the screw will not be perpendicular to the cover but it will be tilted by the angle of the screw's thread. While that is not much, my anal personality doesn't like that. 

[GaryHinshaw]

* I tend to agree that the half-etch top hole might be problematic.  In addition to Peteski's worry (which hadn't really occurred to me), I have a hard time picturing cutting a 00-90 screw to the precise length needed to sit in the dimple, while threading tightly to the cover.  Perhaps it doesn't need to if the cover is soldered on, but it would be desirable.  (I also have a hard time imagining holding such a short screw.)   The dimple can always be drilled through if it turns out to be a problem, then the screw can be cut & ground from above.  Unsightly perhaps, but probably functional.

* Another thought is that it might be desirable to make the the cover an integral part of the box.  This could be achieved by having it joined with a fold on the opposite side to the air hose.  There is really no need for the cover to be removable since coupler maintenance can be achieved by removing the screw and pulling the coupler out.  What we really want is a rectangular box with screw holes.  The downside of that approach is that you lose the lower flap extension, but that is not really a key feature of the prototype, and the left-right symmetry is already broken by the air hose detail on the one side, so it wouldn't really be that noticeable.  Another downside is that it might be tricky to fold, but the functional advantages are potentially significant.

* The looped air hose looks interesting - I'm curious to see how it does with bending.

* I'm afraid I don't understand the bends in the cut lever bracket...    If the blue etch were red it would make more sense to me.  What am I missing?

Cheers,
Gary

P.S. I'll see what I can dig up from James' correspondence.

[ednadolski]

I'm scratching my head about the screw for the extended pocket.   So far it seems to me that the best approach is what you suggest, Gary: go thru the top and then cut off the protruding portion with a Dremel cut-off wheel.  Perhaps the unsightly top could then be covered with a strip of brass or styrene, kind of like the top plate in this image:

http://www.mellowmike.com/Prototypes/Coupler.jpg

I have a slight concern that it might not be so easy to remove & replace the screw, if trimming it leaves any burrs on the threads.   But I'm not sure if that's worth worrying about.

Regarding a shorter screw, Gary I looked back and noted this pic that you had posted a while back on the first page of this thread (hope you don't mind me re-posting here):



My main question is, how well did this hold, when only threaded from one side?   I'm guessing this is 0.014" wall tubing... our pocket cover is only 0.010, but OTOH the 00-90 is a finer thread, with a pan head that should add strength.  Maybe it would hold well enough, if the cover hole were etched smaller and then properly tapped?  Also re: length, the coupler box screw on the Athearn 2-bay hopper is a 00-90 and only 0.075" long including the head.  Tiny, yes, but perhaps workable -- what do you guys think?

I like the idea of a folding cover.   Do you think it makes sense to do that too for the standard length?   Here is a thought:  what about two bottom flaps, one that folds over the other?   That would give us a 0.020" thick bottom cover; more than the 0.014" tubing so it should be plenty of metal to securely anchor a 00-90 screw from one side without protruding through the top.  No glue or soldering either.   (Might have to re-work the hose attachment, but that seems doable.)

On the cut lever bracket, the rightmost tab folds up, and is meant to go into a #80 hole in the floor of the car.  The next segment lies flat against the bottom of the car. The segment with the angled side then folds down, perpendicular to the floor of the car.   (Hope that's clearer, it's one of those things a picture shows right away, but words take some effort.)

Thanks again guys for all the great feedback.   Thanks too Gary for sending those notes from James, I'll be poring  over them in detail

Ed

[peteski]

My main question is, how well did this hold, when only threaded from one side?   I'm guessing this is 0.014" wall tubing... our pocket cover is only 0.010, but OTOH the 00-90 is a finer thread, with a pan head that should add strength.  Maybe it would hold well enough, if the cover hole were etched smaller and then properly tapped?  Also re: length, the coupler box screw on the Athearn 2-bay hopper is a 00-90 and only 0.075" long including the head.  Tiny, yes, but perhaps workable -- what do you guys think?

Ed,
keep in mind that none of the hobby screws have full thread which extends all the way to the base of the head. So, you cannot tighten the head all the way against the surface of the coupler pocket.  There might be fully threaded screws available but if they are, they'll be quite pricey (in 00-90 size).

Also, that photo made me think about another possible issue. The coupler will pivot on the sharp threads fo that 00-90 screw.  How durable will that be in a long run?  It might be ok on short trains with not much stress on the couplers but what if you run 100-car trains going through curves for hours at a time, year after year?  Will the screw's sharp thread wear out the coupler shaft's hole?

[Sokramiketes]

Use brass rod, glue/solder it in, and be done.  If you really had to get in there, you still could. But does it really need to be serviceable to the point of using a 00-90 screw?

[ednadolski]

I've been working on some attempts to drill and tap 0.010" and 0.015" brass for a 00-90 screw, and it has turned out to be rather unsatisfactory.  The brass is simply too thin to hold a screw with such fine threads.

An alternate approach for the extended pocket might be to lightly solder the 00-90 screw onto the cover, then trim it with a Dremel to about 0.030" (the thickness of the coupler shank) from the inside face of the cover.  Then install the coupler and cover in place on the body, and use solder or CA to hold the cover into place.

Another option to that last solder/glue step would be to make longer tabs where they go thru the cover -- these could be folded over with a pliers to hold the cover in place.

I agree that a 3/64 brass rod could work instead of a screw (perhaps with a bit more trimming), tho I wouldn't be too worried about excessive wear from the coupler rubbing against the screw threads.  Before things get to that point I'll hopefully be replacing these with the NZT Protomates anyway ... 

One other thing I did was to try the FT couplers out in the ExactRail body-mounted coupler boxes.  It was pretty straighforward, all I had to do was remove the center post with an X-acto blade, and add a 00-90 washer to take up the extra space in the pocket when installing the coupler.  Here are a few pics:




Cheers,
Ed

[Philip H]

Wow Ed, that's slick . . . makes me really wish FT had their couplers sold separately.