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Alyn

Scratch Building - OMG, I lost my dizzy

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The first step in scratch building is usually to break down a complex shape into simple geometric shapes. Take for example a distributor. This is a fairly simple shape consisting of three progressively larger cylinders. The top and largest cylinder is surrounded with equally spaced 1/2 round cylinders.

Step two is to reduce the dimensions to something reasonably close in scale. In most of my modeling, this is 1:25 or 1:24 scale. The difference between these two scales is merely 1/2" in a foot, so I don't worry too much and generally will use the same scale conversion for either. After doing this exercise numerous times, you get to know some of the common measurements. For example, 1/8" rod is about 3" in scale, 1/16" is about half that, or 1 1/2". Another common measurement is 1" which is about .040" in scale. Therefore, .030" should equate to 3/4" These measurements should be about all we need to build the distributor.

Start with some 1/8" styrene rod for the cap and .030" half round styrene to surround it.

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The most difficult task in building a distributor is to keep the 1/2 round equally spaced around the cap. I start by drawing vertical and horizontal lines on the end of the rod as accurately as possible. Find a stable platform to hold the rod and glue some 1/2 round along the length of the rod in-line with one of the marks.Once this dries, roll the rod 180º and glue another strip on the opposite side.

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After the second strip dries, the rod can be rotated 90º. At this point, my first two strips help the rod sit nicely in my impromptu fixture with the guide line perfectly vertical. Glue another 1/2 round strip in this position and once dry, rotate another 180º and add the fourth strip. At this point, you should have four 1/2 round strips glued on the rod at 90º increments. Hopefully, they look equally spaced and run straight down the length of the 1/8" rod.

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Four additional 1/2 round strips are now glued between the first four. We no longer need the marks on the end as it is easier at this point to position each 1/2 round strip evenly spaced between two of the existing strips. Glue on all four and you should end up with something like this.

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I make a point of being generous with the liquid qlue. Correctly applied, the plastic will fuse together and eliminate any sign of a gap. A coat of primer should reveal the quality of you work so far. The folded edge of some 400 grit sand paper can be run up and down through the grooves to clean things up if necessary. At this stage, I liken the part to an extrusion. It's far longer than needed for one distributor. When you need to build one, just cut off a slice and continue with the final steps.

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Edited by Alyn

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Let the extrusion dry overnight before continuing with the next steps.

Before cutting off a piece for your distributor, trim down the end to form the base of the distributor. This is easily done by scoring the 1/2 round slightly more than 1/32" from the end; then use your Ex-acto knife to trim off the small bits of 1/2 round. Clean this area up with a small jewelers file or 400 grit sandpaper (or both).

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Now you can cut the end section off the extrusion. Around 1/8" or slightly longer (plus the trimmed area) is about right for the height of the cap. Clean up your saw marks with some 400 grit paper, and then follow up with something finer like 600 grit. Try to keep the top as flat and square as possible. For the shaft, drill a 1/16" hole in the base of the distributor and glue in a short section of aluminum rod or tube. I like to use tubing as it provides the excess glue a place to go which actually provides added glue surface. While the shaft doesn't need to be very long, I allow for enough to use it as a handle, or to chuck it in my Dremel (if I need to square the top). Clean off any glue that oozes out around the shaft while it's still wet.

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Your new distributor is almost done now and is actually starting to look like one. In the next view you can see that I've drilled eight equally spaced holes around the top and another directly in the center. Of course you want to align the holds with each 1/2 round segment. I position the drill bit very close to where the seam between the 1/8" rod and the 1/2 round. If you haven't let the glue dry for a sufficient amount of time, it is easy to accidentally split off the half round. Not cool. Make sure to allow plenty of drying time.

The holes in this picture are drilled with a .0175" bit. The size should be determined by the diameter of the plug wire used. It this case, my .015" wire slides right in and allows for a thin film of CA to hold it in place.

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Finally, a bit of silver on the base and your favorite color on the cap. Over spray can be easily scraped off the aluminum shaft with an Ex-acto blade. Here's one ready for wiring. I don't worry about creating the small nibs on the top of the cap as the wiring and boots will cover it up. For color, black, red, light blue and light brown are common colors for the cap plastic. Just make sure the color looks nice with your choice of wire. You may want to go further and add a vacuum advance diaphragm, but that's optional.

And don't forget, you've got plenty of extrusion to make more parts for your next build

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Edited by Alyn

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Awesome tutorial Alyn, thanks a million! Now I can make my own, and stop digging in the carpet for the ones I lost.... :lol:

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That's a great concept, Alyn!

But, it's a whole lot more work than opening up another Arrowhead Aluminum pre-wire distributor and gluing it on. I'm getting too lazy to fabricate what's already available, but I admire your ingenuity.

Great tutorial, too!

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These kinds of tips do keep you sharp and focused, but I agree with Dan, I am too old for that kind of patience . . .

Great job though.

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Thank you for sharing.

Each piece even the distributor is a kit in its self.

I normally hog out the kits distributor and insert 9 wires.

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I came back to this one because I really do think it deserves a Tip of the Month tip of the hat!

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I second that, Cranky. I went to the LHS yesterday to get the half round and it's all glued up waiting for me in the shop.

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Neat idea. I have not looked in on this post because I couldn't really figure out what was being done based on the post's title. Glad I looked. A nice clear title would probably increase visits.

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It's a great idea. I've cut & glued a couple already. AI find it easier to paint before drilling the holes. Later today I plan to wire one up.

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Great tuorial....I've been using this method for years. Instead of using smaller diameter rod for the lead fairings, I use wire insulation. That way I do not have to worry about drilling out those small holes ;)

Jimmy

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Excellent scratch build!

Heck, I do magnetos because I haven't figured these out yet.  Now I get it, thanks Alyn.

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Did plastruct even make 0.30" half round rod because I have asked around only 0.40" hope to get some answers thanks

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Check you messages, Ben. I sent the following;

"I use plastic from both Plastruct and Evergreen. The .030" half-round was from Plastruct. I buy both locally in Kansas City hobby shops. The Plastruct part number is 90879. catalog number MRH-30. I would assume you could find this online."

A quick google search on "Plastruct MRH-30" brought up numerous sources with product in stock.

Alyn

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