# Question for Electronics and Car Guys



## ShopShoe (Aug 13, 2014)

Question for Electronics and Car Guys

I'm rewinding a fuel-level sensor for a 1968 Saab and I need a form for the coil. the original appears to me to be phenolic common to that era. I tried PTFE (teflon), but it is not working out well. 

Can anyone suggest a material that might be better than the teflon. Nylon? Obviously, whatever I need, I need to buy only a small quantity. Source? I'm in the USA.

I know that I can replace the whole sensor, but I am trying to get closer to the original calibration and these units have both a level-indicator and a "low-fuel" warning light. The original maker was VDO.

--ShopShoe


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## mayhugh1 (Aug 13, 2014)

How about PVC? Go to the plumbing section in your local building supply and you might find some pipe that is close to your requirement. PVC turns nicely and the ID and OD can be finished to your requirements. - Terry


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## kf2qd (Aug 13, 2014)

Any plastic will be problematic. Gasoline likes to dissolve or soften them. Phenolic will handle the environmental factors.


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## aonemarine (Aug 13, 2014)

HDPE isnt that what new fuel tanks are made of?


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## obrian (Aug 13, 2014)

There are several epoxy sealers used to cover and protect electronic circuits that are impervious once they are cured.  I used to work for a electronic manufacturer and we had samples of some of these.  I still have some.  What are the dimentions of your part?  Perhaps I could make a part for you.  I have some ideas if you are interested.

Dennis


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## ShopShoe (Aug 14, 2014)

Thank you mayhugh1, kf2qd, aonemarine, and obrian.

To clarify things, the coil assembly is mounted on top of the tank, not inside, so it does not come in direct contact with the gasoline. The more usual design is a coil assembly that is inside the tank, a "universal" replacement sender unit is available and that is what I used as a source for the wire to wind my coil. 

I tried the teflon as the coil form has a profile the result of which is a non-linear change in resistance which in the end results in a good correlation between the float level in the tank and the relative position of the needle on the dashboard guage. I cut the profile on the piece of teflon sheet with a jewelers saw, then wound the coil. 

Somewhere my train of thought wandered away from the idea of turning a round form, then cutting the profile.

Perhaps PVC is the answer if I use the turning/cutting process. Are there other materials I should consider? The "universal" sending unit coil form appears to be nylon.

I know that all of this sounds like a lot of work for a small result, but I am in most of my hobbies for the problem-solving, rather than the production of large volumes of work.

Thanks again and I'll follow up this thread as things develop

--ShopShoe


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## Omnimill (Aug 14, 2014)

You can still buy Phenolic resin plastics so I'd use that. Over here in the UK it's normally called Tufnol after the company that makes it.


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## Swifty (Aug 14, 2014)

Omnimill said:


> You can still buy Phenolic resin plastics so I'd use that. Over here in the UK it's normally called Tufnol after the company that makes it.



We can still get it here as well, it is usually paper or fabric based.

Found a link to a local supplier. http://www.eplas.com.au/3129050/eplas-engineered-industrial-plastics-canvas-b.htm

Paul.


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## Noitoen (Aug 15, 2014)

You can make a little mould (round stick), wind some thin fibreglass cloth with high temperature epoxy, and then turn it to size in the lathe when dry.


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## Omnimill (Aug 15, 2014)

Shameless plug for Tufnol!

http://www.tufnol.com


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## ShopShoe (Aug 15, 2014)

Thank you Omnimill, Swifty, and Noitoen,

Yesterday after making my last post, I started a new search and found some sources for phenolic. When I started this little project my searches for phenolic had been fruitless, so I ordered the teflon and moved on to other projects. This summer I   got back to this car and came back to the fuel sender and here we are.

Next week I think I'll see if I can get a small quantity of phenolic sheet and try that as per the original design.

Plan B: I found some phenolic tubing from one source. Perhaps I could turn a circular coil form from some of that. Has anyone machined this material in such a delicate situation. Cutting the profile I need on the circular coil form would involve using the rotary table on the mill and making a ramped cut. Has anyone done this with phenolic. My guess would be 2-flute end mill and fast spindle speed with slow feed. ?????

Thanks again,

--ShopShoe


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## GailInNM (Aug 15, 2014)

One minor caution.  A lot of people have reactions to phenolic dust caused by machining and sanding.  I don't think there is any permanent damage but the_* r*_espiratory distress is quite uncomfortable for a couple of hours. Never bothered me but my son was affected and would have to leave the shop where he worked when it was being machined.  A dust mask might be a good idea.

By the way, it tends to dull HSS cutters rapidly but for what little you would be cutting I would not think it would be a concern.

Gail in NM


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## Omnimill (Aug 15, 2014)

Yes, it does smell a bit when machining! Nice sharp HSS will cut it nicely.


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