Ignition boot molding

[Ken I]

Great tutorial Gail definately worth a karma point.

I do something similar using polyurethane but using a vacuum pump and compressed air - when I have a suitable project I'll do a post.

Would polyurethane be suitable for these applications ??

Regards,
Ken

 

[T70MkIII]

Thanks so much, Gail - great tutorial with lots of detailed information.

 

[tel]

Brilliant Gail - I can see quite a few applications for that! Karma for you!
Thm:

 

[ozzie46]

Thanks Gail, Very informative. :bow: :bow:

Ron

 

[Groomengineering]

Thank you Gail for the excellent tutorial! Thm:

+1 K ;D

Cheers

Jeff

 

[danstir]

Thanks for the great tutorial. And thanks for the pointers to materials for doing it.

 

[GailInNM]

Thanks to all who commented on the process.

Post #2 of this thread has been edited.
In it I made a recommendation for a pigment that I thought would work, but it does not.

stevehuckss396 tried it and the silicon would not set up. Details in his Small V8 thread at:
http://www.homemodelenginemachinist.com/index.php?topic=9609.msg159224#msg159224

Sorry for any inconvenience. I don't have another recommendation at this time.

Another apology is also in order. In reviewing this thread I see that I missed Ken'[s question about using polyurethane instead of silicon. Sorry Ken. I was not ignoring you on purpose.

I have not used any urethane rubber for at least 15 years so my knowledge is limited. Rigid urethane would not work as it has no stretch.

I see no reason why urethane rubber would not work with a few reservations. If trying it, I would use some that sets up to about a Shore 30 hardness. Shore 40 might work, but I think it would be harder than I would want. Other possible problems:
1. What I have used cures slowly so it would be several hours before it could be demolded.
2. The resins have a low viscosity so the mold would have to be machined carefully to prevent leakage.
This could probably be overcome with a thickening agent also.
3. Some of the urethane rubbers want to stick to metals. Most do not, but a mold release may be necessary.

Gail in NM

 

[Ken I]

Gail, Thanks for the comments.

Urethanes do stick to metals but release agents work fine.

You get some pretty quick curing urethanes these days and I have managed with some pretty "leaky" moulds - although this is not desirable. Because of the low viscosity gravity poured moulds work well.

Like I said - as soon as I have something, I'll do a post.

As regards pigments - try the "Smooth On" range of products - their "so strong" pigments seem to work on just about anything - although I have not tried them with silicone.

http://www.smooth-on.com/

Thanks,
Ken

 

[stevehuckss396]

If you don't care about color do this exactly as Mr. Graham described using the micro mark materials he suggested. It worked just as easy as he said it would and the boots are perfect. This thread couldn't have come at a better time.

Thanks again for showing us!!!!!!!

 

[mu38&Bg#]

Are there any casting compounds like this that would hold up to gasoline fuels? I'm thinking about making some fuel system components.

Greg

 

[lazylathe]

What about vacuum forming the boot over a mold?

I have small vacuum forming machines at work and a variety of rubber sheets that we use to make mouth guards out of.
Anything from thinner than 1mm to about 6mm in thickness and pretty much any colour you want.

Just an idea!

Andrew

 

[Swede]

This is outstanding! I've never been happy with commercially-made boots for these tiny plugs. I can see using a hydraulic press, if one is available, to press in the silicone material. With high pressures, you can drill some very tiny vent holes, and when you see the material exit all of the vent holes, you can be assured of a good fill.

For ignition cables, I've always liked the type of wire used for test leads. This wire is a bit more expensive, but it has some advantages...

- It's extremely limp. Handle the test lead wires from your digital volt meter to get a feel. The wire behaves in a "scale" manner. It's not all stiff like a typical #16 stranded hookup wire might be.

- The sheathing is usually durable and resistant silicone rubber, not like PVC or some other cheap sheathing. And the sheathing is DESIGNED for extreme voltages. It has to, for user safety reasons.

- The internal strands are usually super-fine and very numerous, which is necessary so the wires are limp.

Remember, these cables carry extreme voltages but very low currents. You don't need a lot of copper in them.

Digi-Key, among others, carries test lead wire in differing colors.

Digi-Key: http://www.digikey.com/

 

[GailInNM]

Greg:
The only two component elastomeric compounds that I know of are the polyurethanes. Most of them are very resistant to gasoline, some more than others. Some are used as liners for gasoline tanks. I am not very current on them so can not recommend any particular one.

Swede:
A hydraulic press is way overkill. With a 1/4 inch diameter plunger a 50 pound pressure on the plunger will generate over 1000 psi on the compound. At this pressure no vent holes will be necessary as it will flash around the cores and the machined surfaces of the mold. A mechanical press gives you some feel as to when the mold is filled and you can back off the pressure to prevent too much material flash in the mold. The reduced flash makes it easier to clean up the part. One could always make a high precision mold that would take the higher pressure with out flash, but for me it is hardly worth while to spend the time to do so for only a dozen or two parts.

I sure agree about the test lead wire. That is all that I have used for a long time and is what is in photos.

Gail in NM

 

[mu38&Bg#]

Thanks Gail. My search lead me to the same conclusion. I'm waiting on a reply from a supplier about chemical compatibility.

 

[canadianhorsepower]

. About two fly specks is enough and you can add a little more if it is not dark enough.

great post, what is the colorant you are using ??

 

[stevehuckss396]

Hey Luc!

The colorant was a flop. I tried it and the material wouldn't set up. It was messy as hell and not worth the trouble. On a positive note the MSD wires as well as a few other performance wire makers do put a gray end on. If you are considering using this method, it works as easy as described.