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Discussion Starter · #1 ·
Well, anything might be a little broad, but I will attempt share with you guys my experiences so far with the art of small one-off parts prototyping, an art I (obviously) have not mastered, but I'm working on. (A little encouragement, please, my wife thinks I'm nuts.)

Today I attempted to make a distributerless ignition system housing for the D16Y8.

DISCLAIMER: WHAT I AM ATTEMPTING IS VERY DANGEROUS. WHILE I CAN BE SEEN IN MANY PICTURES WEARING MINIMAL SAFETY EQUIPMENT, KEEP IN MIND THAT I AM DUMB AND LUCKY. FEEL FREE TO ATTEMPT AT YOUR OWN RISK, BUT DON'T COME WHINING TO ME IF YOU KILL YOURSELF.

Step 1) design something. I used Catia, since this is software I had available at work, but lots of people design some pretty cool stuff with cheap-to-free softwares... here's a pic of what I started out attempting to bring to life:


From there, I had to have some means of making a real-world pattern of this solid model. I looked at www.emachineshop.com, but decided that I could save money in the long run, and would have a lot more fun machining the part myself. I scored this SpectraLight (basically a Sherline mill in a box) on eBay for $600. I had to do a little reworking to the controller, and if the details of this are something you're really interested in, check out http://www.cnczone.com/forums/showthread.php?t=11221
A little plug here for cnczone- those guys rock when it comes to home machining and such. I finally ditched the idea of using a crappy old computer for now, and have it hooked up to my wife's laptop. (Which ain't exactly a powerhaus itself - a P2 500 with 64MB ram - but it's a beast running DOS) So far she's not missing it too much.

I machined out the blue part you see lying there from Freeman's machinable wax. (see this video, if interested)This is some really cool stuff. You can cut it with practically 0 tool wear about as fast as you want, within reason. I ran at about 15"/min at 1/8" deep using a wood router bit- not even a real end mill bit.

Of course, you don't want to go bolting up some wax part to your engine (although as tough as that machinable wax is, it might actually work!) I wanted to try my hand at casting an aluminum part, with dreams of making the part look like maybe it was part of the factory equipement to someone who doesn't know what it's supposed to look like. I got the idea that this COULD be done from this posting I got through www.hackaday.com (my second fav website, second, ofcourse, to this one!)

I knew I would need something to pour my molten aluminum into, so I started making a mold from plaster of paris in a dog-chewed tupperware dish:

Here is the homemade furnace after the test burn. I used about 1" of homemade refractory material (read pearlite mixed 4 parts to 1 by volume with furnace cement). As you can see, I drilled a hole in the side a tack welded a stainless tube which I had a roll of still lying around the garage from another project. Through this hole I pumped propane originally, but then decided that more heat could be made more economically by filling the furnace half full of charcoal and blowing air in the pipe. (read: I was out of propane).

This is my high tech, extremely well thought out and expert engineered crucible. Kinda looks like I just haphazardly welded a piece of steel tube to the side of an old paint can doesn't it... :)

I thought it would be best to cure my mold and heat it up before the pour to prevent freeze-off and thermal shock... here it is all assembled... if only there were some room left for some brots on there...

Meanwhile, the furnace is blazing away, and the aluminum has begun to melt. Liquid aluminum looks sooo cool. Look but don't touch. That's prolly close to 1000 deg F right now on the bottom.
 

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Discussion Starter · #2 ·
Git in yer hole!!!

OK, so maybe the first shot wasn't perfect... actually far from it. There are several voids, the finish has a lot to be desired, and I didn't even fill the whole mold... back to the drawing board, but at least I did get some cool looking run-off!

 

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d-series smartass
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i'm very impressed, far beyond some of the fiberglass molds i've attempted...

(i'll paypal you 5 bucks for the melted aluminum that looks like poop) ;)
 

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that's pretty cool... how do you get the wax model out of the mold?
 

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Discussion Starter · #6 ·
makku said:
that's pretty cool... how do you get the wax model out of the mold?
Made a core side and a cavity side to the mold, lined them up with the dowel pins in the pic- in the picture I had just made the cavity side. I then put seran wrap over the cavity side, cut out a hole around the inside of the part in the seran wrap for the plaster to flow into the cavity side and taped it down on the outside. so it would stay put, then just poured more plaster on top of it all. When it set up, I just tapped out the core from the bottom side until it got halfway out an then broke in three D'oh! Well good thing I had some of that furnace cement left over. Just glued it back together.

Without the core in there it wasn't terribly hard tapping the wax part out of the cavity... but if you look closely, you can see I did end up cracking my wax part getting it out of the mold (see the crack to the left side in the pic) oops.

Lule said:
I agree, that's cool! We should get together sometime and have a beer.
yer on! :beer:
 

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that is cool man...I mean what what you wanted but still cool and a starting point. Back to he drawing Board Wiley E. Coyote...hahaha Good luck w/ it
 

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the MAD scientist
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Thats cool!! I like seeing people do stuff like that.

Maybe the casting would work better if you pull a vacuum in the mold. It could help draw in the metal more evenly.
 

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the MAD scientist
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Oh I forgot to mention...
Whats the melting point of that wax you are using?
Because you can also use the "lost wax" method of casting. People have been using it for years. No large seams are created that the metal can ooze out of. It may work better.
 

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Discussion Starter · #13 ·
mikeD16Z6 said:
Oh I forgot to mention...
Whats the melting point of that wax you are using?
Because you can also use the "lost wax" method of casting. People have been using it for years. No large seams are created that the metal can ooze out of. It may work better.
The wax melts at about 250F, 500F ought cook it out of the mold real good, as any residual wax will be vaporized by 1200F Al causing a void. The only other downside here is that it takes a good bit of effort to machine just one wax pattern and if for whatever likely reason your aluminum pour doesn't go perfect, well, you're left with nothing to show for it. I used the method I did because I wanted to salvage my wax part in the likely event that it didn't go so well...

I'm thinking that for attempt 2 I'm going to melt all this back down into a very rough shape of what I'm making and then just machine the aluminum on the CNC.

Still lets me use free aluminum that way rather than turning $100 worth of billet 6061-T6 alloy into useless shavings.
 

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I wanna be just like Jimmy!!
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if you wanna cast it again, try making your mold a bit larger, than the actual piece, and have the mouth of it have a cone down into it. might help save on how much doesn't make it into the mold. big thumbs up on the handywork!
 
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I cannot see the mold very well so you may have already done this...

When you try again you might try to machine some small runners (enough to let any trapped air out) into the core that spread in a radial direction to the outside perimeter of the mold to allow the material to flow better since you are using a gravity feed system.

Then after it cools you can trim off your runners and have a part that filled more evenly.

Also the pervious post mentioned a good idea of casting a cone shape as your main gate to help in the loading of the mold...

BTW did you machine down the mating surfaces of the mold??

Overall very cool!!! Post up some more pics when you try again!!!
 

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you need a sprue bushing fo sho.
And i cannot remember what the vents in the mold are called, but they are nessicary for the proper filling of the mold.

Give er another go.
 

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Discussion Starter · #20 ·
Quick update - I've started plan B- and cast a big rectangle of aluminum to machine the final part out of. I've drilled and tapped the bottom of the part so that it can be bolted onto the CNC, so hopefully the casting is going to be void-free enough to machine nicely. I've got some titanium nitride plated end mill bits en route from littlemachineshop.com, supposed to arrive tomorrow, so we'll see how it works out. Meanwhile I'll cast a block for the other side of the housing and document with pics here.
 
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