Would 3D couplers be strong enough?

[bbussey]

The Athearn TOFC thread and the lack of BLI coupler availability got me wondering: is there a black resin strong enough where it would be practical to 3D print the BLI coupler knuckle and thumb?  It could be designed to accept the MTL trip pins, which are available in bulk. Could they withstand the load of push/pull operation, and would the AccuMate-style springs be flexible enough to center the coupler and sturdy enough not to break?

[GaryHinshaw]

My guess is yes, but it definitely depends on the coupler design details.  I can report that the LEZ coupler boxes I print have been robust enough for the relatively demanding conditions on my layout.  The pulling force is transmitted via a .040" post that is printed directly into the box roof (image) and I've never had one of those fail.   I think @Lemosteam may have some useful input on this question.



Of course, I would be remiss if I did not recommend that you look at the LEZ coupler as an option for some of these cases.

[Missaberoad]

I wonder if the centering springs would be the sticking point?

Is there a resin robust enough to maintain its rigidity at that profile? Even if they don't break would they quickly loose their spring?

Very interested in this topic, I have a Mono x sitting in its box waiting to be set up and the 3d files for the original Sergent Engineering couplers.

[bbussey]

The two Accu-Mate style finger springs are my primary concern as well.  But having a 3D option would circumvent BLI's stinginess with their couplers.

[Lemosteam]

I have been investigating various reports of resin mixtures that may produce a more durable print. I have also developed a coupler pull block to measure force to failure to test any coupler in a 1015 box using a screw.

That testing for the Protomate using my printer to print the coupler with various resin mixtures is a ways off.

 If I can achieve similar pull forces to an MT coupler, that would be the target.

[timwatson]

The Athearn TOFC thread and the lack of BLI coupler availability got me wondering: is there a black resin strong enough where it would be practical to 3D print the BLI coupler knuckle and thumb?  It could be designed to accept the MTL trip pins, which are available in bulk. Could they withstand the load of push/pull operation, and would the AccuMate-style springs be flexible enough to center the coupler and sturdy enough not to break?

You can tint any resin with alcohol ink. So you can get it closer to black. You might have to play with the mix. Also using Siraya Blu would be strong enough for couplers.

[bbussey]

Color isn't the problem since there are black resins.  Would the resin coupler be strong enough to handle the load, would the fingers be flexible enough not to break, and would the fingers be springy enough to center the coupler when not under load?  If there is a resin that would support all of those, then it would work.

[peteski]

Color isn't the problem since there are black resins.  Would the resin coupler be strong enough to handle the load, would the fingers be flexible enough not to break, and would the fingers be springy enough to center the coupler when not under load?  If there is a resin that would support all of those, then it would work.

In my experience with the existing (injection molded) plastic couplers, plastic whisker springs are a non-starter. They are too stiff for magnetic uncoupling and many suffer from plastic fatigue where the do nto retain their original shape.  I suspect the UV-cured resins will not be any better. I guess that they will be acceptable if uncoupled manually.

[bbussey]

I haven't had any operational issues with the BLI coupler regarding magnetic functionality, or any of the other non-MTL magnetics.  But I use stronger magnets than the industry standard (K&J Magnetics) that are embedded 1/8" below the track, so I may not be the best witness.

That said, I removed a coupler from one of my N&W hoppers and reverse-engineered it.



I was wrong, they didn't copy the MTL knuckle verbatim.  But the functionality is the same.  If I can get this to work, I'll design the 2004-style offset shank as well as the 1016-style and 1019-style extended shanks.

[Chris333]

If you didn't already know the parts will grow a gair from light bleed around the pixels. I sure you can resize it easy to make up for it.

[peteski]

I haven't had any operational issues with the BLI coupler regarding magnetic functionality, or any of the other non-MTL magnetics.  But I use stronger magnets than the industry standard (K&J Magnetics) that are embedded 1/8" below the track, so I may not be the best witness.

That said, I removed a coupler from one of my N&W hoppers and reverse-engineered it.



I was wrong, they didn't copy the MTL knuckle verbatim.  But the functionality is the same.  If I can get this to work, I'll design the 2004-style offset shank as well as the 1016-style and 1019-style extended shanks.

Bryan,
as I understand BLI started using the RMR (Vlk) coupler head recently (similar to what Hornby/Arnold did on S1).  Yes, it seems to be compatible with other N scale knuckle couplers.  See https://www.therailwire.net/forum/index.php?topic=51455.0

With standard magnets I found couplers with plastic springs a bit too stiff to reliable uncouple magnetically.  Nothing beats the very soft springs of MTL couplers.

[garethashenden]

I think it should be fine. I've used printed 3 link couplings for some of my British trains and they work fine. No problem pulling heavy whitemetal wagons with them. Knuckle couplers are a better design anyway, the force gets applied to the body of the car more directly than with chain and there's less slack movement. I don't think 3D printed knuckle couplers would be too much of a risk.

[bbussey]

Bryan,
as I understand BLI started using the RMR (Vlk) coupler head recently (similar to what Hornby/Arnold did on S1).  Yes, it seems to be compatible with other N scale knuckle couplers.  See https://www.therailwire.net/forum/index.php?topic=51455.0

With standard magnets I found couplers with plastic springs a bit too stiff to reliable uncouple magnetically.  Nothing beats the very soft springs of MTL couplers.

Perhaps on the motive power.  But this is the coupler they have used and are using on the freight rolling stock.

I use stronger magnets so plastic spring stiffness isn't an issue for me.

[Rasputen]

I think that hole for the trip pin is going to have to be perfect.  Pressing a metal wire into resin that is brittle could be problematic.  Plus, you would want to inspect and perhaps debur every trip pin before attempting to press it in.

[timwatson]

Color isn't the problem since there are black resins.  Would the resin coupler be strong enough to handle the load, would the fingers be flexible enough not to break, and would the fingers be springy enough to center the coupler when not under load?  If there is a resin that would support all of those, then it would work.

Yes it is Siraya Blu v2 but it is clear and has a yellow tint. That’s why I suggested the alcohol ink. There are darker resins but most are really brittle. They would not be able to check off your first criteria. I hope that helps to clarify.