DIY GDI --> DIY EDM
Posted: Fri Dec 19, 2008 8:42 pm
I've been dreaming of a DIY GDI, and I'm thinking of modifing a small engine by changing the spark plug for a plug with a hole down the middle. The fuel would be injected through the specail spark plug. So where do you find a spark plug with a hole in it, you ask. You don't you make it. This brings me to DIY EDM, and I'm wondering if anyone out there knows much about EDM.
A bit more background, I've been thinking of different ways to get a hole in a spark plug. Recently I found a spark plug with a funny prong for the other side of the electrode. This would allow fuel squirted down the middle of the plug to pass by the prong with out direct contact. Causing the fuel charge to be placed in the center of the cylinder, rather than swirled around and evenly distributed like normal. However, with out a hole down the center, it doesn't like to squirt fuel. The plug is about 1.5 inches (about 35mm) long so drilling a hole with a conventional drill really isn't an option. Drills like to wonder to much and you wouldn't come other the other end in the middle. I've been thinking of having someone drill it via laser, but lasers often want a focal point as well as then loose their strength the father away you get. It would likely be difficult and expensive to drill the hole this way. So far the best I've come up with is Electronic Discharge Machining EDM.
I'm picturing an electrode made from 3 or 4 mechanical pencil refills, with a mild varnish or something to bond them together. This would create a channel down the center making them into a reasonable long straw. Then with a little rubber hose clamped to one side, and a fuel pump, I can pump kerosene down the center. This should create the washing action desired for discarding removed material.
To me it sounds low enough cost to give it a try. I've got a couple power supplies, one does 30 amps at 12VDC, another can do an amp or so at up to 60VDC. I think both should work well for EDM. What I don't know is anything real about EDM. I don't know what voltages are required or preferred, or how fast they work. Is pecking a good approach. Should I stop penetration and let it burn, then once I see the current has dropped plunge some more. These are items I simply don't know.
If the power supplies at arms length will take a day or two to drill the hole, I'd want to build a robot to do the pecking / paused burning. However if it will only take half an hour, I'll simply put it on a drill press and have at it.
Does anyone know specific details for EDM, like what voltages are preferred / required, what current draw to expect, how to predict how long it will take to burn a hole with the power supplies I have, ect.
A bit more background, I've been thinking of different ways to get a hole in a spark plug. Recently I found a spark plug with a funny prong for the other side of the electrode. This would allow fuel squirted down the middle of the plug to pass by the prong with out direct contact. Causing the fuel charge to be placed in the center of the cylinder, rather than swirled around and evenly distributed like normal. However, with out a hole down the center, it doesn't like to squirt fuel. The plug is about 1.5 inches (about 35mm) long so drilling a hole with a conventional drill really isn't an option. Drills like to wonder to much and you wouldn't come other the other end in the middle. I've been thinking of having someone drill it via laser, but lasers often want a focal point as well as then loose their strength the father away you get. It would likely be difficult and expensive to drill the hole this way. So far the best I've come up with is Electronic Discharge Machining EDM.
I'm picturing an electrode made from 3 or 4 mechanical pencil refills, with a mild varnish or something to bond them together. This would create a channel down the center making them into a reasonable long straw. Then with a little rubber hose clamped to one side, and a fuel pump, I can pump kerosene down the center. This should create the washing action desired for discarding removed material.
To me it sounds low enough cost to give it a try. I've got a couple power supplies, one does 30 amps at 12VDC, another can do an amp or so at up to 60VDC. I think both should work well for EDM. What I don't know is anything real about EDM. I don't know what voltages are required or preferred, or how fast they work. Is pecking a good approach. Should I stop penetration and let it burn, then once I see the current has dropped plunge some more. These are items I simply don't know.
If the power supplies at arms length will take a day or two to drill the hole, I'd want to build a robot to do the pecking / paused burning. However if it will only take half an hour, I'll simply put it on a drill press and have at it.
Does anyone know specific details for EDM, like what voltages are preferred / required, what current draw to expect, how to predict how long it will take to burn a hole with the power supplies I have, ect.