Plastic Gas Cap Threads

[madmodifier]

Hi All,

I am looking for ideas on how I best go about reproducing the thread for this missing fuel cap. I would locate a factory part but due to the age of the weed whip this is not possible. So that leads me to making one.

Thanks,
Ben


https://goo.gl/photos/DtMGYEiG4gms8r4U9
https://goo.gl/photos/fpJtfej4sjdgkgto8

 

[Tony Wells]

Would have thought those are almost universal. Around here there are still lots of repair shops. If I couldn't get an aftermarket, I'd scrounge the junkyards for a replacement. Making one wouldn't be my first choice.

 

[John Hasler]

Mold it.

 

[Billh50]

As near as I can figure.
1) Measure the diameter just before the beginning of the thread. That should give you the minor diameter needed.
2) Measure The pitch as close as you can.
3) Measure the height of the thread by measuring from inside to top of thread. Then measure from inside to just before thread and deduct that from the first measurement.
4) Now with a radius gage see what the radius is on the top of the thread and put that on your threading tool.
5) Now make a part with the minor diameter and then thread to the depth you measured in step three. Maybe even a couple thousandths deeper.

 

[Billh50]

Unfortunately they are not universal. I have saved some from old weedwackers and such but it seems they never fit anything I need one for.

 

[jim18655]

+1 on John's suggestion. Cover the threads with plastic wrap and mold with 2 part epoxy putty. You could dress up the inside on a lathe and insert a gasket.

 

[TOOLMASTER]

same thread as a plastic gas can...

 

[francist]

I'm not sure molding is the answer. If you look closely at the pics the helix is not continuous around the neck of the piece. I think that might present a problem when one tried to take them apart after.

-frank

 

[Wreck™Wreck]

I'm not sure molding is the answer. If you look closely at the pics the helix is not continuous around the neck of the piece. I think that might present a problem when one tried to take them apart after.

-frank

If for some reason an opening mold is not desired, either unscrew the part from the mold or the mold from the part, this will add considerable cost to the mold itself and slow down the cycle time.

 

[francist]

If for some reason an opening mold is not desired, either unscrew the part from the mold or the mold from the part, this will add considerable cost to the mold itself and slow down the cycle time.

That's actually where I was foreseeing the problem -- in unscrewing the part from the mold. If the thread helix is interrupted as it winds around the neck I don't know that it could be unscrewed? Perhaps I'm looking at it wrong.

-frank