Yet another 3D printed coupler design

[RFGuy]

If you do start making them I could use a couple of ends to try some things.

It might be impractical for you to keep printing the central tube if it could be replaced by a piece of stock tubing glued to the ends.

That could be a good option. Thanks for the idea.

It is a good idea, but just wondering if glue will work for this application. I have had good luck (strength and holding power) using wood with wood glue or epoxy for most things, but...I have had very mixed results whenever I attempt to glue different types of plastics in the past (not counting PVC). Using CA glues, even the ones specially formulated for plastics, have always failed eventually for anything more than a decorative item, i.e. not strong enough to hold for a joint that sees stresss. Maybe just a function of the kinds of items I tried to glue. Perhaps if you print the ends with an interior mortise to accept the tubing/pipe it may last (more glue surface area). Not trying to discourage trying it, but just wondering if it will hold.

[edma194]

For same type of plastic there is often a very good glue available. Different plastics not always so much.

I think this application of one tube concentrically glued to another shouldn't be a problem for the proper glue. I don't think ordinary CA is well suited for this though. It would not take much of a small shear piece to prevent the joint from rotating loose.

I don't know much about the plastics used in printing, sounds like Paul knows what he's doing though.

[paulrussell]

I had intended this to be a one-and-done project, but it appears there is considerable interest. To that end I've been doing my homework regarding making the best possible part.
i suspect a high-grade nylon would be better than the carbon fiber nylon. The carbon fiber makes the part stiffer, which probably doesn't gain much for this application. At the moment, Zytel is almost impossible to source, and is very expensive
So I am looking at Taulman 645 nylon. It is not cheap, but is much less than Zytel.

• Taulman 645 Uses per Manufacturer:
  Gears - Med/Heavy load
  Propeller blades
  General Industrial needs
  Large Flanges, Housings, positioning
  Wide Chemical resistance of petrol's
  Sand blasting
  Masking
  Spacers/Interconnect

This sound a lot like what we'd want.
In addition, printing with a larger nozzle should increase strength by about 25%.
If there is enough interest I'll go ahead and purchase both.

As far as making ends only -- right now I'm going forward with a one-piece design and will consider that if all goes well. Gluing dissimilar non-solvent reactive plastics is tough. Probably the only way to go is a good epoxy. Nylon is especially slippery. The carbon-fiber nylon probably has more grip.

Updated design mockup with bevel at headstock end and an indicator aligning with a keyways.

[paulrussell]

For same type of plastic there is often a very good glue available. Different plastics not always so much.

I think this application of one tube concentrically glued to another shouldn't be a problem for the proper glue. I don't think ordinary CA is well suited for this though. It would not take much of a small shear piece to prevent the joint from rotating loose.

I don't know much about the plastics used in printing, sounds like Paul knows what he's doing though.

This is a mockup to fit in a 3/4" pvc pipe. I would rough up both interior of pipe and shaft of this part and use a good epoxy. Notch at the end for a bit of extra rotational grip and/or mechanical link.

Just brainstorming at the moment as I have a few mins of downtime.

Shopsmith Single End v1.png (80.23 KiB) Viewed 2484 times

[edma194]

I'll buy one from you if it helps. But you should keep in mind the limited size of the market before you invest in new equipment, unless this is just the excuse you needed to spend the money on that new equipment

[dusty]

I too would be interested. Just let me know via PM when you are ready to take on a production run.

[paulrussell]

I'll let folks know by PM when it is ready to roll.

[lahola1]

A couple of observations from a plastic guy.
-Dupont makes several different types of Zytel nylon ; type6, type 66, type 612, etc. each with different properties.
Type 66 natural color is yellowish and is one of the toughest nylons; but can be dyed many different colors as can most plastics.
The newer ones may or may not be made out of nylon or some other material; may be made out of regrind instead of virgin mat'l where strength is also lost.
-I would think that glued on ends wouldn't be near as tough as the injection molded original parts because of how the plastic's crystaline molecules bond together.
I would think the 3D molded parts would be weaker also for the same reason ; they may be strong enough for this application, just somewhat weaker; don't know how much.
-I saw a couple years ago on this forum or on youtube a break test comparision of SS couplers; can't remember where.
-I would think PET would be a pretty tough mat'l for this application if it works ok in 3D printing.
-If you are going to make them in sections, I would put a large radius at the bottom of the notch instead of the sharp corners for strength.

[paulrussell]

Addressing the previous post.
Full disclaimer: I'm not a plastics guy and much appreciate your feedback.
Right now Zytel, of any type, is a no-go for me due to cost and availability.
Regarding injection molding vs 3d printing. Indeed 3d printed parts are weaker -- most notably along layer lines -- than their injection-molded equivalents. I have increased wall thicknesses to (hopefully) address this. I may need to increase further if prototypes don't meet expectations.
I have printed couplers in PET and in CF-nylon. The PET was substantially less resistant to breakage from lateral forces, such as when wiggling a snug coupler to free it.
(As a side note I suspect the current white couplers are PET -- injection molded of course, with its inherent adventages.)
Regarding rounding the sharp edges (stress points) in a glue-in version... that makes great sense. Thank you for pointing it out.

[RFGuy]

-I saw a couple years ago on this forum or on youtube a break test comparision of SS couplers; can't remember where.

I think this is the video of torque testing power coupler potential replacements:



Also, a couple of other coupler threads of interest:
viewtopic.php?f=10&t=22834&hilit=coupler+test
viewtopic.php?f=7&t=23589&p=269890&hili ... er#p269890
https://www.shapeways.com/marketplace/t ... er+coupler