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Headlight switch problem- 1978 280z


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I should get some acrylic rods to experiment with tomorrow to see if I can develop some techniques with what I have on hand.

I know that I encounter melted nubs when I help people with the switches.

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Posted (edited)

Acrylic will probably abrade and wear pretty quickly.  Nylon and polyacetal (Delrin) have what's known as "natural lubricity".  And acrylics are more difficult to machine, they tend to be brittle.

Since the part is plastic it will machine pretty easily compared to metal.  A lathe will offer accuracy and precision, but, for what it is, a drill press and some handiwork with sharp objects should get the job done easily.

I guess I'm saying don't make it overly complicated.  It's not an engine part.

Here's an in-depth article about plastics and friction.   If you want to test the original material you can stick a red hot wire in it, or touch it with a torch flame, and take a whiff of the vapors.  If it smells like burnt hair it's nylon.  If it smells like formaldehyde it's polyacetal.  The smell test is an actual test method from the past.  Probably not allowed anymore though.  Odds are it's nylon.

https://www.machinedesign.com/archive/article/21816534/plastics-that-dont-wear-out-their-welcome

"

The most important semicrystalline polymers for friction and wear include:

Acetal (POM) which is rigid and strong with good creep resistance. It has a low coefficient of friction, remains stable at high temperatures, and offers good resistance to hot water.

Nylon (PA) absorbs more moisture than most polymers, affecting processability, dimensional stability, and physical properties. However, nylon's impact strength and general energy absorbing qualities improve as it absorbs moisture. Nylons also have a low coefficient of friction, good electrical properties, and resist chemicals.

High-temperature nylon (HTN) and polyphthalamide (PPA) extend the nylon family through improved temperature resistance and lower moisture absorption. They ....

Edited by Zed Head
apostrophes, commas and periods
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5 minutes ago, Zed Head said:

Acrylic will probably abrade and wear pretty quickly.  Nylon and polyacetal (Delrin) have what's known as "natural lubricity".  And acrylics are more difficult to machine, they tend to be brittle.

Since the part is plastic it will machine pretty easily compared to metal.  A lathe will offer accuracy and precision, but, for what it is, a drill press and some handiwork with sharp objects should get the job done easily.

I guess I'm saying don't make it overly complicated.  It's not an engine part.

I have some ABS rod on order, too. The first materials are just to get my technique going, such as drilling out the rod for the spring.

As for the lathe, I was planning on using the drill press. LOL  It's the cutting tools that I need to figure out.

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9 hours ago, SteveJ said:

I have some ABS rod on order, too.

I would not consider either ABS or acrylic to be a good choice in the long term. Certainly usable for proof of concept and testing a procedure. Careful with the acrylic as it can be brittle and shatter if you push it too hard. Don't hurt yourself and wear eye protection!   :geek:

This could be done in a drill press, but it's really not the tool for the job. For the spring hole, you want the hole in the center and it probably has a flat bottom. The rounded tip is actually the easy part here... Just use a file while the part is spinning. Heck, since I don't consider it to be a high precision job, that's what I would do on the lathe. Use a file and eyeball the radius.

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I see a brass tube with a plastic knob inserted.  That is an injection molded part.  Those thin walls will be difficult to replicate.

The cost of machining is in the tolerances, not the dimensions.  

image.png

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I'd look into UHMW plastic for the button. It's tough, durable and abrasion resistant. Curbell Plastics sells 5' of 1/4 rod for $10.09. That small investment would build well over 200 buttons and put you in the button business.

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51 minutes ago, Zed Head said:

I see a brass tube with a plastic knob inserted.  That is an injection molded part.  Those thin walls will be difficult to replicate.

The cost of machining is in the tolerances, not the dimensions.  

image.png

That's what I was thinking when I looked at the 4mm rod I received today.

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6 hours ago, Zed Head said:

I see a brass tube with a plastic knob inserted.  That is an injection molded part.  Those thin walls will be difficult to replicate.

Yeah, the original part was injection molded. That's what you do when your making hundreds of thousands of them. Or you're @SteveJ

And I'm not sure what you meant about a brass tube with a plastic knob inserted... Are you suggesting the possibility of making the finished item out of two parts pressed together? If that's the case, I'd be wary of that. Remember, the bottom of the hole is the spring seat. And it's pressing in a direction to separate the two parts.

Yes, in theory, all the force would be on the spring seat (and not on the thin wall tube around it), but there's the transition positions when the spring extends and all that inertia. I don't know how many G's that part sees when it snaps from one position to another, but I bet it's not trivial.

Remember the same lubricity the plastic provides to the tip (to let it slide smooth across the switch contacts) will be allowing the two parts to come apart.

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23 minutes ago, Captain Obvious said:

Are you suggesting the possibility of making the finished item out of two parts pressed together? If that's the case, I'd be wary of that. Remember, the bottom of the hole is the spring seat. And it's pressing in a direction to separate the two parts.

Yes.  I consider the brass tube to be the locater of the spring, just holding it under the contact point.  The forces aren't really trying to separate the parts.  At worst they have to resist a side-load, mostly resulting from friction as the switch is actuated.  You can look at the pictures of the parts and see that there is little (no?) sign of distortion of the tube even though there was, apparently, enough heat to melt the tip. 

Actually, the flatness of that melted part in the picture is kind of surprising.  That takes a lot of heat to cause that.

 

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Well I'm no ME, but I have concerns about using two dissimilar parts for that assembly. It's really not a big deal and I'm not going to throw my body in front of anyone who wants to try it, but I've just got concerns. Things like this:

If you make the tip out of some slippy plastic and press it into a tube... How deep of an engagement do you get? The whole thing is 5mm long. With the spring seat being maybe 3mm deep? So you get .078 inches of some slippy plastic into the end of a brass tube?

You make the press fit mild and there's less force to hold it together.

You make the press fit aggressive and that slippy plastic squeezes itself out of the hole just sitting static on the desk like toothpaste extruding out of the tube.

Change the temperature and who knows what's gonna happen.

And then you put that assy into an un-damped spring snapping application? When that thing changes position, what's the frequency of the bounce? That brass isn't going to change direction instantaneously. Newton's laws and all that say there will be forces trying to pull that thing apart.

Like I said, not a big deal... A lot of discussion and analysis of such a small simple part.  LOL

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The machine shop made me a sample.  Going to pick it up today!  Stupid question?  How do you keep the washer button from falling out?  I cant see how it connects in other than that little tab.

 

 

 

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Posted (edited)

 

Hello Folks:

I do appreciatively applaud the effort to provide the switching bits that time has forgetten; rest assured that I'll be in the line to obtain those parts that make the combo switches work at their peak again.

That being said, I hope I will be forgiven for taking a sharp left at Mr.Head's post #14, regarding the concept of Relay Options that minimize the high-amp effects on the stock combo switch configuration of the equipment (old or new).

I have studied the issue of electrical stress on the Combo switch, and while I make no claim to Electrical Engineering proficiency, I have come up with a diagram that would, in my ignorance, seem to be a workable integration of 30amp relays as a workaround for the effects of routing amp-heavy loads thru the two Combo switches.

Thus, I would humbly offer this potential solution that seeks to provide all the stock switch functions, without running big-amp loads thru the actual combos. I would note that with but a couple exceptions, the current version does not require substantial alterations to the stock harness (the exceptions are centered around connections to a couple plug bodies).

I proffer this proposal with the express purpose of soliciting critical feedback from any and all among this august body of readers, hoping they can show me the errors of my construction, thus enhancing a better solution for all.  

I whole-heartedly encourage corrections/alterations/thoughtful crits to the following diagram (which depends on my ability to insert a jpg (and no, I can make no promises here either}) ....

If you please, look this over and share your improvements for our mutual benefit.

I thank you for your attention.

P.S.: Wouldn't cha know it: I've just noted a connector graphic error at the interception of the incoming red/white hot line. Very embarrassing.

 

ComboSw relays_fnl.jpg

Edited by ensys
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Posted (edited)
5 hours ago, ensys said:

 

Hello Folks:

I do appreciatively applaud the effort to provide the switching bits that time has forgetten; rest assured that I'll be in the line to obtain those parts that make the combo switches work at their peak again.

That being said, I hope I will be forgiven for taking a sharp left at Mr.Head'st #14, regarding the concept of Relay Options that minimize the high-amp effects on the stock combo switch configuration of the equipment (old or new).

I have studied the issue of electrical stress on the Combo switch, and while I make no claim to Electrical Engineering proficiency, I have come up with a diagram that would, in my ignorance, seem to be a workable integration of 30amp relays as a workaround for the effects of routing amp-heavy loads thru the two Combo switches.

Thus, I would humbly offer this potential solution that seeks to provide all the stock switch functions, without running big-amp loads thru the actual combos. I would note that with but a couple exceptions, the current version does not require substantial alterations to the stock harness (the exceptions are centered around connections to a couple plug bodies).

I proffer this proposal with the express purpose of soliciting critical feedback from any and all among this august body of readers, hoping they can show me the errors of my construction, thus enhancing a better solution for all.  

I whole-heartedly encourage corrections/alterations/thoughtful crits to the following diagram (which depends on my ability to insert a jpg (and no, I can make no promises here either}) ....

If you please, look this over and share your improvements for our mutual benefit.

I thank you for your attention.

P.S.: Wouldn't cha know it: I've just noted a connector graphic error at the interception of the incoming red/white hot line. Very embarrassing.

 

ComboSw relays_fnl.jpg

And I have already demonstrated that your flawed design won't work and should be consigned to the trash heap.

But what would I know? I only work with these kinds of circuits for a living.

Edited by SteveJ
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Mr.J:

Well, then.

I wonder; when you were introduced to Calculus, did you ever diligently struggle with a difficult problem solution unsuccessfully several times, just to have your Teacher advise disrespectfully, that you should burn your math book? Somehow, I don't believe you would have quit, and nor will I.

However, I will continue my education on a new thread; I apologize to the Forum for the interruption of the original discussion focus of this thread.

 

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My post about the relay was meant only about taking the load off of the power supply switch, which has the plastic nubbin melting problem, and the solder joint breaking problem (which the new brass piece won't fix.  It will still get hot).  I haven't seen any overheating problems described at the dimmer switch, which is where high and low are separated.

Zs-ondabrains setup had relays on both ends, I thought.  Might be worthwhile to go back and look at his work.

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Mr.Head:

It was the hdlite rotary power sw. issue (that I began to appreciate when I had the combo sw. apart looking for lost "enlightenment") that got me started with relays. But it was what I found to be the cause for the sporadic issues with hi/low sw. operation that made the second relay look like a good idea too.

After that, it simply became the fetish for a minimally-invasive elegant solution that would not, even in unseen ways, compromise the fairly remarkable originally of the Trusty Z.

Text book Obsessive/Compulsive I suppose, but hey...

 

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9 hours ago, ensys said:

Mr.J:

Well, then.

I wonder; when you were introduced to Calculus, did you ever diligently struggle with a difficult problem solution unsuccessfully several times, just to have your Teacher advise disrespectfully, that you should burn your math book? Somehow, I don't believe you would have quit, and nor will I.

However, I will continue my education on a new thread; I apologize to the Forum for the interruption of the original discussion focus of this thread.

 

No, but then again, I didn't come across as an obtuse fool, and I'm willing to re-think things after I'm proven wrong.

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