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

[GaryHinshaw]

Hi Ed,

I like what you've got there.  The side slots and bottom flange are a nice touch, and the tabs on the rear of the bottom cover should be good enough to maintain position under load.  (Without some kind of tabs, there is very little to prevent the coupler post screw from torquing forward under load.)

I agree with DKS' posted inside dimensions.  (These FT boxes are really small!)  The center of the coupler post/screw hole is 0.110" back from the front face of the FT box, so I would stick with that here.  (By the way, I definitely vote for FT dimensions here.  There is no way I'm interested in going to this trouble for a beefy McHenry...)  I'd love to convince Will to just sell bare couplers - not that I would succeed, mind you.

A few other comments:

* I think .010 brass is likely to be quite strong, but trying a few thicknesses is probably warranted.  The little housings on the back of Traincat's signal heads are folded .010 boxes and they're really tough: (and not dissimilar to an FT box in size)

http://www.traincat2.com/images/models/1300903.jpg

* I would be inclined to drill the mounting hole(s) out with a Dremel.  For a 00-90 screw, the tap drill is a #60 and the clearance drill is a #55.  These are plenty beefy for a Dremel, and a starting dimple makes it very easy to get a good accurate hole.

* I'd be inclined to keep the sides full thickness, and to make sure the inside of the side walls are smooth, so the centering leaf springs can work smoothly.  I'm a bit unclear in your drawing what direction the fold should go, but if the sides come up, out of the page, the slot detail will be on the inside of the box.   

* I've been trying to come up with some kind of folding loop on the bottom cover to hold a cut lever, rather than just a hole.  I'll think about that still.

* I'd vote to chamfer the corners of the fold-up lip, like in MM's picture.

Cheers,
Gary

[GaryHinshaw]

Okay, I decided to update my sketch with more accurate relative dimensions for the FT box:



The scale is 1 Keynote pixel per mil (.001")    I have not yet included the side slots or the cut lever and air hose fixtures, but that's next.  Also, I'm not totally happy with the fold-up lip yet.

One small functional concern is the fact that the box cover tabs are only half-etched, so they might not mate as tightly to the slots as full etches would, but it's probably ok.  (I reverted to two sets of tabs to withstand both pushing and pulling loads on the coupler post screw.)

I'd love to try something like this out soon.  Do folks with experience think something like this is at all close to being functional for a contract etching shop, if an actual dimension is supplied?

Thanks,
Gary

[ednadolski]

Looking good Gary!   I’ll start playing around with the DraftSight this weekend, and see how it works out.   Looks like PPD recommends doing this as a layered drawing,  I’ll look into the details.

Sounds like the FT is the way to go.   I recall someone saying that the McHenry resembles a ‘boxing glove’, and the more I look at it the more I think I agree (tho it’s less noticeable when 2 cars are coupled, and I do like some of the other detailing on the McHenry). 

I think the 0.010” should be fine, as long as the fold lines don’t turn out to be a weak point.   Presuming then that the half-etch produces a 0.005” thick brass, I’m wondering what a good width for the fold lines would be. I would think that the thickness of the metal stock (0.010” in this case) should work.   Question: which side of the bend is best for the fold line to be on?

Going with four cover tabs should be fine.   Since the cover has the half-etch running the length of either side, the inside surface of the cover will actually extend into the inside pocket space by the depth of the half-etch (i.e., 0.005” in this case).  I think this extra overlap makes a stronger overall assembly, it’s just something to keep in mind when figuring on the size of the side panels.   One alternate idea:   Instead of a half-etch along each side, would it be any better to do this as tab-and-slot?

Do you know: what is the actual thickness of the FT coupler shank?  I’m just wondering how much vertical clearance it will have, if the interior height is the 0.034”.   I would think that just a few mils are all that is needed to allow free swing, but if the cover plate screw is put on tight, could that cause any binding?

Cosmetically, I agree on the chamfered strike plate (confession, I was just being a little lazy with the drawing).   I like how you’ve done it so that it projects a little bit wider than the pocket body.   We might want to consider doing it as an (optional) third detail piece that gets installed with a little CA, that could maybe also include a bit more face detail, a la the MM .jpg (not sure if that’s getting into overkill).

For the side slots, if we do the full 0.010” thickness of the sides, then the slots would have to be a simple full etch-thru, without details.  Again we could easily include a few optional detail parts for modelers thus inclined, however these would be pretty tiny, and again maybe it’s overkill?

Also I’m all for a fold-out loop on the bottom, I think it’s just a matter or working out the dimensions.  If it  works out OK for the bottom cover, then maybe we could also do it for the side, to hold the BLMA air hose.   What diameter holes do we need for these?

Cheers,
Ed

[ednadolski]

which side of the bend is best for the fold line to be on?

Aha, answered my own question:  the same side as the fold:

http://www.tech-etch.com/photoetch/formedguide.html

[GaryHinshaw]

Looking good Gary!   I’ll start playing around with the DraftSight this weekend, and see how it works out.   Looks like PPD recommends doing this as a layered drawing,  I’ll look into the details.

That would be great!

Sounds like the FT is the way to go.   I recall someone saying that the McHenry resembles a ‘boxing glove’, and the more I look at it the more I think I agree (tho it’s less noticeable when 2 cars are coupled, and I do like some of the other detailing on the McHenry).

I agree.  There is some nice detail on the McH, and this could be readily adapted, but I'm more bullish on the FTs for now.

I think the 0.010” should be fine, as long as the fold lines don’t turn out to be a weak point.   Presuming then that the half-etch produces a 0.005” thick brass, I’m wondering what a good width for the fold lines would be. I would think that the thickness of the metal stock (0.010” in this case) should work.   Question: which side of the bend is best for the fold line to be on?

I'm basing .010" on my experience with the Traincat signal housing boxes.  It's a comparable size to an FT coupler box and plenty rugged when folded.  As you noted, the half-etch fold lines should be inside the fold, and they should be roughly one metal thickness wide.  That is how I have drawn it now.

Going with four cover tabs should be fine.   Since the cover has the half-etch running the length of either side, the inside surface of the cover will actually extend into the inside pocket space by the depth of the half-etch (i.e., 0.005” in this case).  I think this extra overlap makes a stronger overall assembly, it’s just something to keep in mind when figuring on the size of the side panels.   One alternate idea:   Instead of a half-etch along each side, would it be any better to do this as tab-and-slot?

The way I've drawn it, the inside of the bottom cover would be flush with the inner surface of the indents on the side face.  [Clear? ]  I'll add dimensions to the drawing.  I think it might be worth running a few variant designs at the same time.

Do you know: what is the actual thickness of the FT coupler shank?  I’m just wondering how much vertical clearance it will have, if the interior height is the 0.034”.   I would think that just a few mils are all that is needed to allow free swing, but if the cover plate screw is put on tight, could that cause any binding?

The ring that sits around the center post is the thickest part of the shank.  It's about .030 thick, but I can measure it more carefully.  Binding could be an issue, but if we size the vertical dimensions well, I doubt the cover plate could flex enough to bind.  Only one way to find out...

Cosmetically, I agree on the chamfered strike plate (confession, I was just being a little lazy with the drawing).   I like how you’ve done it so that it projects a little bit wider than the pocket body.   We might want to consider doing it as an (optional) third detail piece that gets installed with a little CA, that could maybe also include a bit more face detail, a la the MM .jpg (not sure if that’s getting into overkill). For the side slots, if we do the full 0.010” thickness of the sides, then the slots would have to be a simple full etch-thru, without details.  Again we could easily include a few optional detail parts for modelers thus inclined, however these would be pretty tiny, and again maybe it’s overkill?

These boxes are really small.  Most of the detail will be completely lost, especially the side slots, because the box is relatively short and squat compared to the proto box.

Also I’m all for a fold-out loop on the bottom, I think it’s just a matter or working out the dimensions.  If it  works out OK for the bottom cover, then maybe we could also do it for the side, to hold the BLMA air hose.   What diameter holes do we need for these?

I'm playing around with some ideas.  Stand by.   

Cheers,
Gary

[GaryHinshaw]

Okay, here's another iteration of the sketch:



Notes:

* I added some extra side material to the extension tab behind the pocket.  This folds along with the sides to make a shallow channel for additional stiffness.  I think this will be a very beefy, but simple, structure.

* I added half-etch slots to the outside of the side panels to suggest pocket detail.  I think anything more would be overkill on these small pockets.  And by leaving the inner surface smooth, there is no chance for the centering leaf spring to hang on something.

* I added two foldable loops: one for an air hose and one for a cut lever.  I'm not sure if the fold lines are in the best position here, but this would make the front face of each loop flush with the front plane of the pocket. 

* I tweaked the shape of the fold-up lip.  I like it better this way.

Any comments or suggestions for improvement?

Thanks,
Gary

P.S. In this drawing, the red folds would be out of the page, the blue folds into the page.

[ednadolski]

Looks pretty good Gary, I just make a few minor tweaks:

- Make the slots for the cover as a thru-etch, and extended the sides.   This should make the assembled unit a little stiffer/stronger.

- Rotated the tab for the cut lever by 90 degrees, so it could take a cut lever from the side without requiring any bending (not sure it's facing the right way).


Thoughts?   Seems to me we're getting close!   

[GaryHinshaw]

Brilliant!  That's a much better tab & slot layout.  Now I see what you had in mind there.

The cut lever loop is definitely better in that orientation (and that was roughly what I was originally thinking).  The only minor concern is that there could be a tendency for the coupler to snag on the gap while negotiating a turn.  That was why I put the loop off the end; but then you have to hook the end of the cut lever to thread this loop.

By the way, I think it should be rotated 180 deg.  We're looking at the inside of the bottom cover, so as drawn, the loop is closer to the air hose side of the pocket.   I think it's better to have it closer to the other side.

Let's try a test run!  Can you try to draw it up in CAD?   

-gfh

[James Costello]

Looks like I need to get my hands on some FTs then.

No thoughts on the MTL Z coupler or even (gasp) the N?

[GaryHinshaw]

Hi James,

I think this basic design would port well to an Accumate or McHenry style with some simple dimension changes.  We could look into that if there's interest.

The MT design is slightly more problematic because of the centering spring which pushes against the center post in the standard box.  I think it would be tricky to assemble these when the center post is also the screw that holds the cover on.  You'd have to somehow keep the spring compressed while placing the cover on, then get the screw through, then release the spring tension.  Lord knows, the MT couplers are hard enough to assemble as is!  If you have any suggestions, I'm all ears.

Cheers,
Gary

[James Costello]

I think I'd rather play with the FTs.... I went back through the thread and had another look at the photos.

[ednadolski]

Let's try a test run!  Can you try to draw it up in CAD?   

Sure thing!   I've got DraftSight fired up, now it's a matter of going thru the learning curve.   I've also located a few design guides to digest, tho at this point I don't anticipate any drastic changes.  I expect to be a bit tied up over the next few days but I'll post updates as available.

BTW are you still thinking PPD, or are there any other places to consider?


Ed

[GaryHinshaw]

Sure thing!   I've got DraftSight fired up, now it's a matter of going thru the learning curve.   I've also located a few design guides to digest, tho at this point I don't anticipate any drastic changes.  I expect to be a bit tied up over the next few days but I'll post updates as available.

Great!  If you want to shoot me any draft files I can have a look and maybe learn along with you.  (That would help me reboot my hand rail project too...)

BTW are you still thinking PPD, or are there any other places to consider?

If they're good enough for Chris333 they're good enough for me.    I didn't have anyone else in mind at this point.

-Gary

[Chris333]

I just sent another order to PPD yesterday.

[bbussey]

Ed clued me in that this thread had been revived.  Some observations come to mind after reviewing the recent postings:

• Brass fold-up draft gear - This is roughly the initial design I had for the X58, and I decided to go away from it for a number of reasons.  How are you going to anchor the pivot post without it being visible, especially on the extended draft gear of a cushioned underframe?  What material will be pivot post be?  How are you going to firmly secure the pivot post to brass stock so thin so that the load of pulling a long freight consist (if the cars are up front near the motive power) will not compromise the integrity of the post and or draft gear?  How do you fold up the three sides and attach the lid so that it looks like a complete rectangular housing, with no gaps between the folded sides and the lid?  With an etched draft box, I would look at stainless steel rather than brass.  Slightly more expensive, but no integrity problems with the housing itself.  The pivot post is another issue.
  
  
• FT couplers - aren't these difficult to come by, and aren't they pricey as well?  Designing draft gear that fits only the FT coupler and not common N scale couplers is a mistake in my opinion.  The de-facto standard is the MTL coupler, and any new coupler box should take that under consideration.  All other N scale couplers work in an MTL coupler box, but the reverse is not true.  The inside of any draft gear box should be equivalent to an MTL 1015 box, regardless of what the wall thickness or outer dimensions are.  If getting the spring into the box is an issue, then the design should be re-thought.  The redesigned X58 draft gear is a prime example.
  
  
• Etching artwork - you guys are overthinking how you represent half-etches and full etches.  Keep it simple - use red/black or magenta/black to represent back/front (I use magenta because then the artwork can be split easily into CMYK plates).  Wherever there is no etching on the top half, that artwork is black.  Whenever there is no etching on the bottom half, that artwork is magenta.  Any white areas represent full etch.  You also should have two layers to your artwork (top and bottom) - all detail on the top layer is black and all detail on the bottom layer is magenta.  So, if you have a "fold line" where the metal bends up, then there would be no black and the line would appear to be magenta.  If you have a "fold line" where the metal bends down, then there would be no magenta and the line would appear to be black (if you could see the artwork from behind).  Also, the thickness of your fold lines (and your relief detail) is determined by the thickness of the metal to be etched.  They must be at least half the thickness of the metal.  If the brass is .30mm for example, then your lines can be no thinner than .15mm.  And finally, you should measure by millimeters instead of inches.  Aside from being a "less messy" measuring system, the units are much smaller than inches and therefore you have greater precision to work with.  I do all of my solid modeling and etching design in mm.