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Manufacture Distributor Cap?

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Manufacture Distributor Cap?

Postby TigWelder » Thu Mar 24, 2011 10:09 pm

Hi SpeedTalk Gurus,

Does anyone know how a simple distributor cap is manufactured (6 cylinder engine)? I've completed 2 CAD certifications at my community college and I want to design and manufacture a different shaped dizzy cap for fun :D . But, if I can understand how they're manufactured (injection molding , etc?), i.e. how they combine the metal and plastic into one unit, I would be able to design something that is more friendly to a small volume manufacturer. I would greatly appreciate any pointers to tutorials or any help at all..couldn't find much on the net.
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Re: Manufacture Distributor Cap?

Postby Kevin Johnson » Sun Apr 10, 2011 11:48 am

TigWelder wrote:Hi SpeedTalk Gurus,

Does anyone know how a simple distributor cap is manufactured (6 cylinder engine)? I've completed 2 CAD certifications at my community college and I want to design and manufacture a different shaped dizzy cap for fun :D . But, if I can understand how they're manufactured (injection molding , etc?), i.e. how they combine the metal and plastic into one unit, I would be able to design something that is more friendly to a small volume manufacturer. I would greatly appreciate any pointers to tutorials or any help at all..couldn't find much on the net.



Start reading patents, new and old. Quite often they will give detailed instructions on how to make the item of interest and also explain why it is made that way rather than another way. This will also help keep you from possibly infringing on a design or method that is still under protection.

http://patft.uspto.gov/netahtml/PTO/search-adv.htm

Good luck.
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Re: Manufacture Distributor Cap?

Postby TigWelder » Tue Sep 27, 2011 8:50 pm

Kevin,

thanks for your helpful response. The CAD model is looking decent but I don't know how to measure the bolt-hole pattern for the base of the distributor cap that bolts down to the rest of the motor. Are there any drafting tools I can buy to find the exact center of the distributor cap's holes and their displaced angles?
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Re: Manufacture Distributor Cap?

Postby Barbapapa » Tue Sep 27, 2011 9:20 pm

To machine a low quantity and install metal inserts is practical but the material to use is a dilema.
Commonly available plastics in bar form such as Delrin have significant thermal growth. Using something impregnated with fibers helpd that. Maybe a Nylon 66 perhaps?

BTW, how can you not figure out a way to measure a bolt pattern without some kind of software? C'mon man! Use all the Pythagorem theorums and pie are square stuff from grade school.
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Re: Manufacture Distributor Cap?

Postby Kevin Johnson » Wed Sep 28, 2011 8:32 am

TigWelder wrote:Kevin,

thanks for your helpful response. The CAD model is looking decent but I don't know how to measure the bolt-hole pattern for the base of the distributor cap that bolts down to the rest of the motor. Are there any drafting tools I can buy to find the exact center of the distributor cap's holes and their displaced angles?


Try measuring the ID of the plug holes and then take a pair of calipers and measure the OD of some bolts. If you are lucky you will find some with a snug fit. Chop off a longish section of the bolt and chuck it up in a drill press. Run the press and take an angle grinder and create a conical point. Remember that three points determine a plane so take three of these tools you have made and install them at the same relative height in the cap every 120 degrees.

Print out a diagram of the six plug holes with their centers marked and an array of evenly spaced lines bisecting the center of the major circle on whose perimeter the centers of the six holes lie. Add another major circle that tangentially contacts the outer rims of the plug circles and a third major circle that if you cut it out with scissors will allow the outer pattern to fit over the distributor cap without interference. Unless you have printed to very heavy stock paper you may want to transfer/glue the design to flat cardboard stock. Do not trim away the outer edges yet. Prick through the centers of the plug circles with a pin.

Before doing the above you should print some circles of known diameter on the printer and check the x and y dimensions because often there are correction factors needed.

Ensure that the distributor cap will sit down evenly on a planar surface (a very flat table or a granite countertop). You may have to sacrifice a cap by carefully grinding the bottom so that it will seat flat/evenly on this surface.

Obtain a machinists square. Carefully seat your printout so that the pricked pinhole centers align with the conical tips of the ground bolt tools. Slide the upright machinists square so that you approach the outermost tangent point of the mounting holes in the cap. Now you may find that you will need to trim the printout to allow the square to approach the cap but still allow the upright portion of the square to become a "pointer" of sorts at the array of lines bisecting the major circle. This is like using a degree wheel to check your timing.

From these measurements you should be able to determine the approximate offset of the mounting bolts to the plug holes. You will have gained experience in making your own tools and learned of myriad sources of possible error which you can and should write up.

With a laser scan of the cap you could also do this but save that for later projects. If you do it manually you will remember, probably for the rest of your life, all the issues and possible inaccuracies.

Good luck.
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Re: Manufacture Distributor Cap?

Postby Warpspeed » Wed Sep 28, 2011 7:51 pm

TigWelder wrote:Kevin,

thanks for your helpful response. The CAD model is looking decent but I don't know how to measure the bolt-hole pattern for the base of the distributor cap that bolts down to the rest of the motor. Are there any drafting tools I can buy to find the exact center of the distributor cap's holes and their displaced angles?


Best way to measure coordinates of an odd bunch of holes is on a milling machine with X and Y digital readout.

Then trial drill a plate to the measured figures, and see if the threaded holes all exactly line up with the holes in the plate.
If you want angles, a rotary table might help, but for drafting and most manufacture, precise X and Y coordinates are usually far more useful than angles.
Cheers, Tony.
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Re: Manufacture Distributor Cap?

Postby Kevin Johnson » Wed Sep 28, 2011 10:48 pm

Which is another form of CMM -- I have a vintage Mitutoyu one that is manual. There are a lot of ways to do it.

I am hopeful that some geometry classes still allow the use of a dividing compass and unmarked straightedge so that students can try their hand at geometric proofs. Maybe even ponder a few days about trisecting an angle. http://en.wikipedia.org/wiki/Angle_trisection

Just don't hold and point that straightedge like the barrel of a gun -- or (shudder) launch a rubber band off it -- you might get locked up.
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