Help needed designing joint between 2 bars of plastic 1

[ship69]

Hello

I have a design challenge for you.

I need to design a joint between 2 round bars of plastic. It is part of a consumer product.
- Diameter of both bars: 10mm
- Material: injection moulded plastic (probably LDPE)
To keep costs down there should be no metal or other materials - just the injection moulded plastic.
Because they have been injection moulded the contours of the parts can be complex.

TWO MODES
The two bars need to snap together with a push fit, and once snapped together, the joint between the two bars should be able to operate in two different modes:

A) 'Stiff-to-Turn Mode'
In this mode, the bars need to be fairly stiff to turn and should also 'snap' to the nearest 30 degree angle.

B) 'Spin Mode'
1. Ideally this mode should be triggered by the a user action - e.g. the user pushing the two bars together. (Conversely the user should be able to return the joint to "Stiff-to-Turn" mode by for example pushing the bars together.)
2. In this mode the bars should be able to spin very easily (and would for example turn very easily by hand) BUT:
3. With the help of gravity they should *tend* to come to rest in one of two preferred directions 180 degrees away from each other.
(e.g. a given point on the lower bar might come to rest pointing either what happens to be north OR the exact opposite direction - south.)

4. In Spin Mode, the also user needs to be able to *change* which direction the 'preferred direction' will be.
How this change in the 'preferred directions' should be achieved is open to debate - possibly the user could move a collar around the higher rod in order to achieve this,

Any suggestions?

J

 

[TheTick]

No

 

[3DDave]

I enjoy the conflicting requirements that the spin mode should require the user to push the rods together and still be under the easy influence of gravity. It's unclear how plastic can be used to detect and react to the Earth's magnetic field.

 

[ship69]

3DDave - The point about the "Spin Mode" is simply that it needs to turn very easily but TEND to stop in at compass bearing (or 180 degrees from it)

To get clear, the device will not pay any attention whatsoever to *actual* compass bearings - I only used them as random examples and to avoid referring to too many numbers of angles.
I have edited the original post to simplify the requirement.

 

[MintJulep]

Take apart kayak paddles do this. Sort of. At least aspects of if.

 

[ship69]

> Take apart kayak paddles do this. Sort of. At least aspects of if.
Interesting. I have only ever seen fixed kayak paddles. Does this only apply to some variety of collapsible paddles?
Short of going to a canoe retailer can you say any more about this or where I could find out more?

 

[TheTick]

The list of things you won't do for your own project is pretty long, isn't it?

 

[dhengr]

Ship69:
That sound like a hell of a lot happening in a pretty small space. I think you should allow for a cubic volume about 3x3x3m btwn. the two 10mm bars, at their ends. Then, get in touch with Rube Goldberg and let him have at it.

 

[ship69]

> I think you should allow for a cubic volume about 3x3x3m btwn. the two 10mm bars, at their ends.
Confused. Do you mean 18 cubic meters of space at the ends of the two bars... ?

To try to simplify the original problem, I think part "A" (the Stiff to Turn" aspect) should be fairly simple to design on its own. We would simply need a male part going into a female part. There would then be three zones of the overlapping area.
1. Mating surfaces with slots/ridges at 30 degree intervals
2. Some sort of compression/spring zone (to maintain force between the slots & ridges)
3. Some sort of clipping zone (to put force onto the spring zone)

The Spin Mode could be a separate zone that is either locked or spinning very nearly freely.

Something like that?

 

[Pud]

Start with a Google search for "snap fits plastics".

Good luck with using LDPE for snap fits, and better luck with tooling costs (if even feasible)...

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[ship69]

Out of interest, ignoring the purple rubber bits, what materials do you think this hanger is made out of?

Link

The white plastic is extremely waxy to the touch.
The hook section at the top rotates very easily.

 

[Pud]

If you've got one: Burn Test

Just be cautious in case it's acetal. No big sniffs - (unless you need your sinuses removed!)

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[zeusfaber]

Anything helpful by way of recycling marks on it?

A.

 

[ship69]

> Anything helpful by way of recycling marks on it?
Nope absolutely none.